Process Unit 73 O2 -2 - Knick

Instruction Manual 

Process Unit 73 O 2 -2 

SO05E7xxxx


Knick 

Elektronische Meßgeräte 

GmbH & Co. 

P.O. Box 37 04 15 

D-14134 Berlin 

Germany 

Tel: +49 (0)30 - 80191 - 0 

Fax: +49 (0)30 - 80191 - 200 

www.knick.de 

knick@knick.de 

Warranty 

Defects occurring within 3 years from delivery date 

shall be remedied free of charge at our works 

(carriage and insurance paid by sender). 

Accessories and display backlighting: 1 year 

TA–168.500–KNE02 220101 

Software release: 7.x

Changes for Software Release 7 

No logbook recording of error messages during maintenance, calibration, and 

parameter setting 

During maintenance work, such as cleaning the sensor or during calibration, often a 

great number of error messages is generated. These messages are completely 

meaningless for the measurement because the unit is in functional check mode and 

the current is frozen. Therefore, they are not recorded in the logbook any more. 

“Temperature Detection” menu 

The “Temperature Detection” menu is integrated as submenu in the “Sensor Data”. 

Manual selection of temperature probe 

Automatic Pt 100/Pt 1000 recognition and selection is omitted.

Safety Information 

Be sure to read and observe the following requirements! 

Before connecting the apparatus to mains, make sure that the mains voltage corresponds 

to the voltage rating given on the rating plate. 

Opening the apparatus exposes live parts. Therefore, the apparatus shall not be 

opened. If repair should be required, return the apparatus to our factory. 

If opening the apparatus is inevitable, it shall first be disconnected from all voltage 

sources. 

Make sure that the mains supply has been disconnected. 

Repair or adjustment of an opened apparatus under voltage shall be carried out only 

by a skilled person who is aware of the hazard involved. 

Remember that the voltage across accessible parts of the open apparatus may be 

dangerous to life. 

Whenever it is likely that the protection has been impaired, the apparatus shall be 

made inoperative and secured against any unintended operation. 

The protection is likely to be impaired if, for example: 

the apparatus shows visible damage 

the apparatus fails to perform the intended measurements 

after prolonged storage at temperatures above 70 C 

after severe transport stresses 

Before recommissioning the apparatus, a professional routine test according to 

EN 61 010-1 shall be performed. This test should be carried out at our factory. 

Information 

I


Installation and Start-Up 

Installation of the Process Unit 73 O 2 -2 must be 

carried out only by specially trained personnel in 

accordance with this instruction manual and per 

applicable local and national codes. Make sure 

that the technical specifications and input ratings 

are observed. 

For information on installation, refer to chapter 10. 

Start-up of the Process Unit 73 O 2 -2 must be carried 

out only by specially trained personnel in accordance 

with this instruction manual and per applicable 

local and national codes. 

Before first start-up, a complete parameter setting 

procedure must be performed by a system specialist. 

At ambient temperatures below 0 C display readability 

might be restricted. This does not affect 

instrument function. 

Real-time clock, logbook, cal record and sensor 

statistics are battery backed for approx. 1 year. 

After longer power outages these data can be lost. 

In that case the Process Unit displays ”Warn Time/ 

Date” and the date is reset to 01–01–1990. Time 

and date must be updated. 

II 

Information

Information on Electromagnetic Compatibility 

Compliance with Interference Immunity 

Requirements 

The Process Unit 73 O 2 -2 is designed for tough 

industrial use and fulfills the demanding EMC 

requirements of the NAMUR recommendations 

and the EN basic specifications for industry. 

However, should problems result in spite of this, 

the following measures may be taken: 

 

 

 

Install power supply separately from other consumers 

Route measuring and control lines separately 

from high-voltage lines 

Route related cable cores together and twist 

whenever possible 

If the limits for immunity to ESD are exceeded at 

the site due to interference sources, either the 

interference level must be reduced or additional 

measures must be taken to increase the immunity 

to ESD, e.g. 

 

 

 

 

Shielding of individual measuring or signal lines 

Installation of mains filter in supply line 

Spatial separation of interference sources and 

unit 

Shielding of entire unit 

All inputs and outputs of the Process Unit 73 O 2 -2 

are isolated from each other. The isolation voltages 

are limited to approx. 50 V with Usags (gasfilled 

surge voltage protectors for adherence to the 

EMC as per NAMUR). 

Information 

III


Option 351 (Interface) 

Shielded cable is to be used for connecting the 

RS 485 interface. 

To meet the radio interference limits at the RS 485 

interface, terminal 15 (shield) must be grounded. 

Do not use the protective conductor for grounding! 

The Process Unit 73 O 2 -2 meets the following generic 

standards: 

 

 

Electromagnetic Emission 

EN 50081-1 Domestic, Commercial and Light 

Industry 

Immunity to Interference 

EN 50082-2 Industry 

and can therefore be used on residential, commercial 

and light industrial premises and in industry. 

IV 

Information

Package Contents and Unpacking 

Unpack the instrument carefully. 

Check the shipment for transport damages and for 

completeness. 

The package should contain: 

the Process Unit 73 O 2 -2 

 

 

this instruction manual 

the accessories you have ordered 

(for available accessories, see chapter 13) 

Description of this Manual 

This manual describes 

what you can do with the Model 73 O 2 -2 

how to operate the Model 73 O 2 -2 

 

what you have to know for installation and 

mounting 

Warning 

Warning means that ignoring the given instructions 

may lead to malfunction or damage of the 

instrument or other equipment and to personal 

injury. 

Note 

Notes call your attention to important information. 

Remarks on Representation 

The keys of the Model 73 O 2- 2 are represented as 

follows: 

, , , , 

, , , , 

A term printed in bold-faced text is explained in 

chapter 16: “Technical Terms”. 

Italics are used to emphasize certain information. 

Information 

V


The representation of a menu in this manual can 

slightly differ from the display of your Process 

Unit. This depends on the options your Process 

Unit is equipped with. 

Example: 

Diagnostics menu ”Measurement Data” 

for a standard instrument. 

Example: 

Diagnostics menu ”Measurement Data” 

for an instrument with option 352 (probe rinsing). 

Structure of this Manual 

Like the Model 73 O 2 -2, this manual is divided into 

three levels: 

Viewing Level: 

You can view all information on instrument state 

and sensor as well as the settings. 

Refer to chapters 1, 2, 4 and 6. 

Operator Level: 

You can edit selected parameters and calibrate 

the O 2 sensor. 

Refer to chapters 1 through 7. 

Administrator Level 

You can set all parameters of the Model 73 O 2 -2 

and make use of special functions (such as passcode 

editing). 

Refer to chapters 1 through 10. 

If you are looking for information on a topic that is 

not listed in the table of contents, the index at the 

end of this manual will help you. 

If the behavior of your Process Unit differs from 

the description in this manual, check if the manual 

corresponds to the software version of your instrument: 

see page 4–6. 

VI 

Information

Overview of the Process Unit 73 O 2 -2 

Operating the Process Unit 73 O 2 -2 

Calibration 

Diagnostics Menu 

Maintenance Menu 

Display of Settings 

Parameter Setting on the Operator Level 

Parameter Setting on the Administrator 

Level 

Capabilities of the Process Unit 73 O 2 -2 

Information on Mounting, Installation and 

Maintenance 

Error Messages 

Interface Commands 

Product Line and Accessories 

Specifications 

Appendix 

Technical Terms 

Index 

Chapter 1 gives you an overview of the performance 

of the Model 73 O 2 -2. 

Chapter 2 introduces you to the user interface and 

describes the keypad assignments. Selection of 

menu items and input of numerals is explained. 

Chapter 3 shows how to select the calibration sequence 

and how to perform a calibration. 

Chapter 4 describes how the Diagnostics menu 

provides you with information on the state of sensor 

and instrument. 

Chapter 5 explains how the installation can be 

maintained. 

Chapter 6 explains how to read out instrument settings. 

Chapter 7 explains how to set instrument parameters 

on the Operator level. 

Chapter 8 describes complete instrument parameter 

setting. 

Chapter 9 gives a detailed description of the 

instrument’s capabilities and applications and provides 

useful information on operation. 

Chapter 10 contains all required terminal assignments, 

dimension drawings and installation 

instructions, as well as information on instrument 

maintenance and cleaning. 

Chapter 11 lists all error messages that might appear 

during operation. 

Chapter 12 provides a summary of all commands 

for controlling the Process Unit 73 O 2 -2 via 

RS 485 interface. 

Chapter 13 lists the accessories and options available 

for expanding the instrument functions. 

Chapter 14 contains the complete technical specifications. 

Chapter 15 shows you how to replace the 

EPROM. 

Chapter 16 explains technical terms. 

Chapter 17 helps you find information in this 

manual. 

Information 

VII


VIII 

Information

Contents 

Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

I 

Installation and Start-Up 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

II 

Information on Electromagnetic Compatibility 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

III 

Compliance with Interference Immunity Requirements 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 

III 

Package Contents and Unpacking 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

V 

Description of this Manual 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

V 

Remarks on Representation 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

V 

Structure of this Manual 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

VI 

1 Overview of the Process Unit 73 O 2 -2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–1 

Instrument Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–1 

User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–1 

System Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–2 

Menu Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–3 

The Individual Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–3 

2 Operating the Process Unit 73 O 2 -2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2–1 

The Instrument in Measuring Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2–1 

Control Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2–3 

Menu Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2–4 

3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–1 

Why do you have to calibrate? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–1 

Monitoring Functions for Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–2 

How to access the Calibration menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–3 

What does “First Calibration” mean? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–4 

Single- or Dual-Point Calibration? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–5 

Automatic Calibration in Water or Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–6 

Calibration with Manual Input of Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–9 

Calibration by Data Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–10 

Contents 

IX


4 Diagnostics Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–1 

What you can do in the Diagnostics menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–1 

How to access the Diagnostics menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–2 

Message List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–2 

Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–2 

Calibration Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–3 

Sensor Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–3 

Logbook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–5 

Device Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–6 

Device Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–7 

5 Maintenance Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5–1 

What you can do in the Maintenance menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5–1 

How to access the Maintenance menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5–2 

Measurement Point Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5–2 

Current Source Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5–3 

Temperature Probe Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5–4 

6 Display of Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6–1 

What you can do on the Viewing level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6–1 

How to access the Viewing level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6–1 

7 Parameter Setting on the Operator Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7–1 

What you can do on the Operator level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7–1 

How to access the Operator level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7–1 

8 Parameter Setting on the Administrator Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8–1 

What you can do on the Administrator level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8–1 

How to access the Administrator level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8–1 

Marker Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8–2 

Passcode Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8–4 

Factory Set Passcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8–5 

X 

Contents

9 Capabilities of the Process Unit 73 O 2 -2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–1 

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–1 

Power Supply for the Process Unit 73 O 2 -2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–1 

Simple Oxygen Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–2 

Measurement Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–3 

Input Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–4 

Cal Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–5 

Pressure Correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–5 

Sensor Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–8 

Temperature Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–10 

Current Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–13 

Output Curves of the Current Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–14 

Complete Installation using all Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–21 

Presetting the Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–21 

Power Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–22 

Current Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–22 

Alarm Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–24 

NAMUR Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–26 

Limit Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–27 

Probe Rinsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–29 

Remote Interface Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–33 


10 Information on Mounting, Installation and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . 10–1 

Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10–1 

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10–5 

Maintenance and Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10–8 

11 Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11–1 

Alphabetical Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11–1 

According to Interface Error Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11–4 

Contents 

XI


12 Interface Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–1 

Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–1 

Transmission behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–4 

VALUE Commands: Query measured values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–5 

STATUS Commands: Query messages and states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–5 

PARAMETER Commands: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–9 

DEVICE Commands: Device Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–25 

COMMAND Commands: Control Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–26 

Interface Point-to-Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–28 

Interface Bus Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–29 

13 Product Line and Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13–1 

Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13–1 

Mounting Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13–1 

Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13–2 

Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13–2 

14 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14–1 

Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14–4 

15 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15–1 

EPROM Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15–2 

16 Technical Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16–1 

17 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17–1 

XII 

Contents

1 Overview of the Process Unit 73 O 2 -2 




applicable local and national codes. 


procedure must be performed. 

Instrument Concept 

Since we have largely followed NAMUR recommendations 

and customer demands – especially 

concerning safety, reliability and functional variety 

– this instrument provides state of the art technology 

showing a new standard for process instruments. 

User Interface 

The display interface consists of a backlit high-resolution 

graphical display (240 x 64 pixels) and a 

keypad. 

Each key has only one function and is definitely 

assigned to a menu or an input function. 

In measuring mode the graphical display allows 

simultaneous readout of the currently measured 

value via large numerals (25 mm) and of two further 

values on secondary displays, as well as display 

of status messages (to NAMUR) such as 

warning (maintenance required) and failure, and 

limit messages. 

Depending on your application, the displays can 

be assigned to different variables and output values: 

saturation index, concentration, partial pressure, 

ambient pressure, temperature, time, date, 

output current values 1 and 2 and input current. 

Operator guidance is supported by a 7-line plaintext 

display with information texts. During operation, 

the currently measured value and active status 

messages remain visible. 

The keypad includes the keys (measurement), 

(calibration), (maintenance), 

(parameter setting), (diagnostics), a 

cursor pad for selecting menu items or entering 

alphanumeric characters and for confirming 

your entry. 

Overview 1–1


System Functions 

10 11 

1 

O 2 

temp 

P 

air 

pressure 

sensor 

cleaning 

contacts 

24 V 

= 

power 

output 

limit 

contacts 

 

= 

power 

supply 


NAMUR 

contacts 

RS485 

mA 

9 

8 

3 

mA 

mA 

mA 

7 

4 5 6 

Fig. 1–1 System Functions Model 73 O 2 -2 

Fig. 1–1 shows the versatile system functions. 

Instead of Models SE 704 and SE 705 you can 

connect practically any membrane covered amperometric 

or galvanic sensor (1). When using sensors 

without temperature probe or with unsuitable 

NTC temperature probe you can connect a 

Pt 100/Pt 1000 probe for temperature detection. 

Instead of the integrated air pressure sensor you 

can also use an external pressure sensor. 

Saturation index, concentration and oxygen partial 

pressure can be determined and output. 

Sensor standardization can be done by calibration 

in water, air, by direct input of sensor data or 

by entering a saturation value. 

By adjusting the temperature probe, you can decisively 

increase accuracy of temperature measurement 

and therefore also of oxygen measurement. 

The instrument provides two galvanically isolated 

standard current outputs (0(4) to 20 mA) (7 and 8), 

which can each be assigned to saturation index, 

concentration, oxygen partial pressure or temperature. 

1–2 Overview

A standard current input (0(4) to 20 mA) (3) (galvanic 

isolation optional) allows detection of an external 

pressure sensor signal, for example. In 

addition, the power output (10) can be used to 

create complete 2-wire loops, e.g. for flow or level 

meters. The determined values can be read out or 

assigned to limit contacts and messages. 

Via a serial RS 485 interface (9) the Process Unit 

73 O 2 -2 can be completely remote controlled and 

all measurement data and status messages can 

be read out – even over long distances. In addition 

to ”point-to-point” connection, up to 31 devices 

can be connected by bus. 

The NAMUR contacts (6) allow direct on-site control 

of signalling units for functional check, warning 

(maintenance required) and failure. The limit contacts 

(5) alert to out-of-limit conditions. The cleaning 

contacts (4) allow actuation of suitable probes 

for rinsing and cleaning the sensor. 

Menu Structure 

From the menu structure (Fig. 2–1, page 2–4) you 

see how operation is strictly organized according 

to the different menu groups, providing outstanding 

ease of use in spite of the great functional variety. 

A menu is activated by pressing the corresponding 

key. At any time, also from a lower menu level, 

you can return to measuring mode by pressing 

. 

Operation is self-explaining by operator prompting 

in plaintext dialog. Even for the Administrator 

level, you neither require the instruction manual 

nor an additional device (terminal, laptop). 

The Individual Menus 

The Calibration menu offers you four different 

calibration sequences to choose from. 

Access can be blocked by a passcode (can also 

be disabled). 

During the calibration sequence you get instructions 

for each step. At the end, the determined 

sensor data are displayed and stored. 

Overview 1–3


The Parameter Setting menu is divided into 

Viewing, Operator and Administrator level according 

to the operator’s specialization. 

On the Viewing level, the parameters can only be 

displayed but not edited. 

On the Operator level, only marked menu items 

are enabled for parameter setting. 

On the Administrator level, all parameter setting 

functions are accessible. In addition, each item 

can be marked to configure an optimum menu for 

the Operator level. 

Operator and Administrator level are protected 

against unauthorized access by passcodes. For 

the Operator level, the passcodes can also be disabled, 

if required. 

The Maintenance menu contains functions for 

measurement point maintenance (rinsing and 

cleaning) and for temperature probe adjustment. It 

also provides a current source function for manual 

adjustment of the output currents, for example in 

order to set controller parameters or test external 

devices (recorder, indicator). 

Access can also be passcode protected if required. 

The Diagnostics menu provides information on 

sensor and Process Unit. 

Activated warning and failure messages are listed 

in plaintext in the message list. Furthermore, you 

can retrieve the latest sensor data and compare 

them with the data of the previous or the First Calibration 

(statistics). 

Messages and function activations are automatically 

stored with date and time in a logbook with a 

storage capacity of 200 entries. This allows tracing 

back and QM documentation of events according 

to ISO 9000. Comprehensive instrument testing 

(memory, display and keypad) can be performed 

on site using the diagnostics function. 

1–4 Overview

2 Operating the Process Unit 73 O 2 -2 



with this instruction manual. 



The Instrument in Measuring 

Mode 

In measuring mode, the main display reads the 

measured value. 

Below the main display there are two secondary 

displays. 

The symbol indicates that the secondary display 

can be edited using the scrolling 

 

keys. 

Pressing the scrolling keys and selects the 

process variable read on the left secondary display. 

Press cursor key to access the right secondary 

display. 

Then use the scrolling keys and to select 

the displayed variable. 

Pressing cursor key returns you to the left secondary 

display. 

At ambient temperatures below 0 C, display readability 

can be restricted. This does not affect 

instrument functions. 

The following variables can be read out on the 

secondary displays: 

SAT saturation 

cO 2 concentration 

pO 2 oxygen partial pressure 

NTC measured temperature (C) 

Operation 2–1


MAN manually entered 

temperature (only with corres– 

ponding parameter setting) 

p air pressure, manual, 

ext. pressure sensor 

I– IN input current 

OUTP1 output current 1 

OUTP2 output current 2 

(only with option 350) 

 

sensor current in nA/A 

CTIME calibration timer 

TIME time 

DATE date 

Alarm Messages 

If the user defined limits (e.g. of the oxygen value) 

are exceeded for warning message (”maintenance 

required”) or failure message, ”WARN” or 

”FAIL” will appear in the lower left corner of the 

display. 

The measurement display flashes. 

The corresponding NAMUR contacts are active. 

Active messages are listed in the message list of 

the Diagnostics menu. (See page 4–2.) 

For setting the warning and failure message limits, 

refer to chapter 9, page 9–24. 

Limit Contacts Active 

If the defined limit values are exceeded, e.g. for 

the oxygen value, ”L1” and/or ”L2” will appear in 

the upper right corner of the display. 

Limit contacts L1 and/or L2 are active. 

The limit value settings are listed under ”Measurement 

Data” in the Diagnostics menu. (See page 

4–2.) 

For setting the limit values, refer to chapter 9, 

page 9–27. 

2–2 Operation

Control Elements 

Pressing menu key , , or accesses 

the corresponding menu. 

Pressing cursor keys or selects the entry 

position on the display. 

Pressing scrolling keys or selects a display 

line. When entering numeric parameters, they are 

used to scroll the numerals 0 through 9 and 

change the sign. The keys provide a repeat function. 

All entries are accepted by pressing . 

Pressing returns you to measuring mode, 

regardless of which menu or submenu you are in. 

Pressing , , or activates 

the corresponding menu. 

In the upper left corner you read the menu (e.g. 

”adm”) and the menu level (e.g. ”Alarm Settings”) 

where you are at the moment. 

In the upper right corner you read the measured 

value (as on the large measurement display). 

Active warning or failure messages are indicated 

by ” W ” and/or ” F ” at the left of the measured value. 

To exit the menu and return to measuring mode, 

 

 

press the menu key once more (repeatedly, if 

required) or 

press . 

Information on operation is indicated by i. 

Operation 2–3



Measuring Mode 

Pressing a menu key accesses the corresponding function menu. 

Pressing meas returns you to measuring mode. 

cal diag maint par 

meas 

meas meas meas 

Calibration 

Diagnostics Maintenance Parameter Setting 

In the Calibration 

menu you select 

the calibration 

sequence and 

perform a calibration. 

In the Diagnostics 

menu you obtain 

information on 

active messages, 

sensor state and 

the instrument 

itself. 

In the Maintenance 

menu you can 

manually adjust 

the output current 

or clean the 

sensor. 

Parameter setting 

is divided into 

three levels. 

meas meas meas 

Administrator 

Level (adm) 

You can set all 

parameters, 

enable the selection 

menu for the 

Operator level and 

set the passcodes. 

Operator Level 

(opl) 

You can set the 

parameters enabled 

on the 

Administrator 

level. 

Viewing 

Level (view) 

You can view all 

parameters but 

not edit them. 

Fig. 2–1 


2–4 Operation

How to select a menu item 

Press scrolling key or to select a display 

line. The selected line is marked by a dark bar (reverse 

video). 

The scrolling keys provide a repeat function: 

When the key is held down, the lines are scrolled 

through. 

The arrows ”” and ”” indicate that more lines can 

be accessed by scrolling. 

The symbols and at the beginning of the display 

line indicate that you can access another 

menu level by pressing cursor key or : 

Pressing or accesses the next 

(lower) menu level. 

Pressing or the corresponding menu 

key accesses the previous (higher) menu 

level. 

How to change a setting 

Pressing or changes the parameter setting. 

The selected position is marked by a dark bar 

and flashes. 

A flashing entry position means: 

The setting has been changed but not yet accepted. 

How to store the edited value 

How to keep the old setting 

Pressing stores the new parameter (e.g. 

”On”). Flashing stops. 

Pressing the menu key (e.g. ) instead of 

restores the old setting (”undo” function). 

How to enter numeric values 

Press to access the number you want to edit. 

The flashing cursor is on the first digit. 

Select the entry position using cursor keys 

or . 

Press the scrolling keys or to scroll 

from 0 through 9 and change the sign. 

How to change a sign 

If the entry value has a sign, the flashing cursor 

can be placed on it using . 

Pressing or switches between ”+” and 

”–”. 

 

Operation 2–5


An Example 

In this example we want to change the temperature 

alarm ”Warning Limit Hi” from 50 to 67 C. 

Press three times until the flashing cursor is 

on digit ”5”. 

Press once (”6”). 

Press once: The flashing cursor is on digit ”0”. 

Press three times (”7”). 


Pressing menu key restores the old setting. 

Pressing stores the new value. 

2–6 Operation

3 Calibration 

Why do you have to calibrate? 

Every oxygen sensor has its individual zero 

point and its individual slope. Both values are altered, 

for example, by electrolyte consumption. 

For sufficiently high accuracy of oxygen measurement, 

the instrument must be regularly adjusted 

for the sensor data (calibration). 

For calibration, the sensor is immersed in a medium 

whose oxygen saturation is exactly known. 

The Process Unit 73 O 2 -2 measures sensor current 

and medium temperature and automatically 

calculates sensor zero and slope. 

Without calibration every oxygen meter delivers an 

imprecise or wrong output value! 

Especially after replacing sensor, electrolyte or 

sensor membrane, you must perform a calibration! 

Calibration 3–1


Monitoring Functions for Calibration 

The Process Unit 73 O 2 -2 provides comprehensive 

functions for monitoring correct calibration 

performance and sensor state. This allows documentation 

for quality management to ISO 9000 

and Good Manufacturing Practice (GMP). 

 

 

 

 

 

 

Sensocheck recognizes mechanical stress of 

the membrane that might modify the calibration 

data. 

Regular calibration can be monitored by a cal 

timer. (See page 9–5.) 

The calibration record (GMP) provides all 

relevant data of the last calibration. (See page 

4–3.) 

The sensor statistics show the behavior of the 

sensor parameters during the last three calibrations 

compared to the First Calibration. (See 

page 4–3.) 

The logbook provides time and date stamped 

records of calibrations performed within the last 

200 events. (See page 4–5.) 

For sensor slope, zero point and impedance, 

you can define limits for a warning and a failure 

message each. (See page 9–24.) This permits 

automatic monitoring of the sensor state 

using the calibration data. 

3–2 Calibration

How to access the Calibration 

menu 

Pressing activates the Calibration menu. 

Pressing exits the Calibration menu. 

When you are prompted for passcode entry, you 

must know the calibration passcode: 

Enter the calibration passcode using scrolling keys 

/ and cursor keys / and confirm your 

entry with . 

On the Administrator level you can set a new calibration 

passcode or disable it. (See page 8–4). 

When you select a calibration sequence, NAMUR 

contact ”functional check” and contact ”probe” 

(only with option 352 probe rinsing, see page 

9–29) will be active for the duration of the calibration. 

During , probe rinsing is locked, a rinsing cycle 

is not started. Calibration is locked as long as a 

timer controlled rinsing cycle is running. 

If you press before the first calibration step, 

you are prompted to confirm your decision to abort 

calibration. If you really want to, press to select 

”Yes” and confirm with . 

The old calibration data remain valid. 

If you press after the first calibration step, 

you are prompted again to confirm your decision 

to abort calibration. If you really want to, press 

to select ”Yes” and confirm with . 

The new slope is stored, but the old zero point 

value remains valid. 

 

How to select a calibration sequence 

Four different calibration sequences are provided 

for water/air calibration: 

 

 

 

 

automatic calibration in water 

automatic calibration in air 

manual entry of saturation 

calibration by data entry 

Calibration 3–3


When you press , the Process Unit automatically 

suggests the previous calibration sequence. 

If you do not want to calibrate, press or press 

to select ”Return to measurement” and confirm 

with . 

To start a calibration: 

Press or to select a calibration sequence 

and confirm with . 

Information displays provide information on the 

state of the Process Unit 73 O 2 -2 during calibration 

and guide you through operation. 

What does “First Calibration” 

mean? 

During a ”First Calibration”, the sensor data are 

stored as reference values for sensor statistics. 

The Diagnostics menu ”Sensor Statistics” shows 

the deviations of slope and zero, as well as the 

corresponding values for calibration temperature, 

calibration pressure and response time of the last 

three calibrations with date and time with respect 

to the reference values of the First Calibration. 

This allows to evaluate drift behavior and aging of 

the sensor. 

When do you have to perform a First 

Calibration? 

Each time you replace sensor, electrolyte or membrane 

you must perform a First Calibration! 

How do you perform a First Calibration? 

Select a calibration sequence. Then select “First 

Calibration Yes” using and and confirm 

with . 

If you do not want to perform a First Calibration, 

press to proceed to the next step of the 

calibration sequence. 

3–4 Calibration

Single- or Dual-Point Calibration? 

For the calibration sequences 

 

 

automatic calibration in water 

automatic calibration in air 

you can choose between single-point calibration 

and dual-point calibration. 

Single-Point Calibration 

The sensor is only calibrated using 100 % medium. 

This determines the present slope of the sensor. 

The old zero point remains unchanged. 

For the ”zero current free” sensors used here, 

single-point calibration should be completely sufficient 

in the most cases. 

Dual-Point Calibration 

The sensor is calibrated using two media with different 

oxygen saturation referred to air (100 % and 

0 %) . 

This determines the slope and zero of the sensor. 

Dual-point calibration is only necessary if the measured 

oxygen value is low or near the sensor zero. 

Calibration 3–5


Automatic Calibration in Water or 

Air 

Calibration can be performed as single or dual 

point calibration either in water or air. 

Calibration value is always the oxygen saturation 

referred to air. 

First, slope is corrected using the 100 % value. 

Then you can also correct the zero point using the 

0 % value. 

During calibration, output currents (1 and 2) are 

frozen at their last values; limit contacts are disabled, 

contact ”probe” is enabled (only with option 

352). 

What you have to know for calibration 

For calibration in water: 

 

 

Make sure that medium flow to the sensor is 

sufficient (see Specifications for sensors page 

14–4). 

The calibration medium must be in equilibrium 

with air. Oxygen exchange between water and 

air is only very slow. Therefore it takes quite a 

long time until water is saturated with atmospheric 

oxygen. 

For calibration in air: 

 

The sensor membrane must be dry, since adhering 

water drops influence the measured oxygen 

value. 

Make sure that the oxygen saturation index of the 

calibration medium is correct and remains 

constant during calibration. 

Make sure that all other parameters such as temperature 

and pressure are constant. 

When there is a temperature difference between 

calibration medium and measured medium, the 

sensor must be kept in the respective medium for 

several minutes before and after calibration in order 

to deliver stable measured values. 

Calibration pressure detection is preset on the Parameter 

Setting level (see page 9–7). 

3–6 Calibration

How to perform an automatic calibration 

in air 

Place sensor in air 

Select submenu “Automatic – Air” 

Press 

Press , or (if required) and to 

open the “Air” submenu . 

Here you can correct the calibration pressure 

manually preset during parameter setting (see 

page 9–7). 

In addition you can specify the relative air humidity. 

If you do not know exactly the relative humidity 

value for the air in use, you can take the following 

standard values for a sufficiently precise calibration: 

normal ambient air: 50 % 

bottled gas: 0 % 

If you do not want to perform a First Calibration 

(see above), press to proceed to the information 

text. 

The information text shows you again the calibration 

medium in use and the corresponding oxygen 

saturation referred to air. 

To start calibration, select ”Calibration Start” using 

. 

The oxygen saturation index indicated for air calibration 

is a hypothetical value. If water and air are 

in equilibrium, it corresponds, however, to the oxygen 

saturation index for water. 

The Process Unit automatically recognizes when 

the sensor potential is stable. From the response 

time you see how long it takes for the sensor potential 

to stabilize. After a minimum response time 

of 1 min the sensor drift is checked and calibration 

is stopped if appropriate. 

If you are sure that sensor potential has stabilized 

earlier, you can already stop calibration after 10 s 

by pressing . 

With unstable sensor potential, this reduces accuracy 

of the calibration values! 

Calibration 3–7


If the sensor current strongly fluctuates or drifts, 

calibration is stopped after 10 min. 

This may be caused by; 

 

 

 

insufficient polarization of the sensor (see operating 

instructions for sensor) 

unstable measured values 

insufficient temperature equalization between 

sensor and environment (observe equalization 

time, see page 3–6). 

For single-point calibration, press to select 

”Calibration End”. 

For dual-point calibration, place the sensor in oxygen-free 

medium (e.g. nitrogen), press to select 

”Calibration Start” and confirm with . 

After a successful calibration, the data calculated 

for slope and zero point are displayed. 

Place sensor in measured medium 

Press to stop calibration 

Press to return to measuring mode 

Press or to return to the Calibration 

menu, or 

press to activate measuring mode. 

If you want to repeat calibration, press to select 

”Repeat” and confirm with . 

If an error message is displayed, you have to repeat 

calibration (maintain sensor, if required). 

How to perform an automatic calibration 

in water 

The calibration sequence in water is identical with 

the calibration sequence in air. Only adjustment of 

relative humidity is omitted. 

Calibration media are 100% air-saturated water 

and O 2 -free water (water flown through by inert 

gas such as N 2 , Ar etc.). 

3–8 Calibration

Calibration with Manual Input of 

Saturation 

For calibration with manual input of saturation, you 

can correct the measured value by directly entering 

the actual process value. 

This permits a fast correction of slope without 

starting a complete calibration sequence. 

With manual input of saturation, slope is corrected 

without checking the drift. Therefore you should 

only make use of this method for corrections between 

two calibrations. 

It cannot replace regular calibrations! 

During calibration, the output currents (1 and 2) 

are frozen at their last values, limit contacts are 

disabled, the ”probe” contact is enabled (only with 

option 352). 

What you have to know for calibration 

Make sure that the oxygen saturation index of the 

solution is correct and remains constant during 

calibration. 

Make sure that all other parameters such as temperature 

and pressure are constant. 

How to perform a manual calibration 

Place sensor in a medium with known 

oxygen saturation 

Select submenu ”Manual Entry” 

Press 

Press and to open the “Manual” submenu. 

The currently measured value for oxygen saturation 

referred to air is displayed. 

Enter process value 

Press and to move the cursor to the 

entry position for the process value. 

Enter the actual process value using scrolling and 

cursor keys and confirm your entry with . 

For single-point calibration, press to select 

”Abort” and confirm with . 

Calibration 3–9



menu, or 


Press 

Place sensor in measured medium 

Calibration by Data Entry 

When you know the current values for slope and 

zero point of a sensor, you can directly enter them. 

During calibration, the output currents (1 and 2) 

are frozen, limit contacts are disabled, contact 

”probe” is enabled (only with option 352). 

How to enter the data 

Press and to open the “Data Entry” 

submenu. 

Enter the data using scrolling and cursor keys and 

confirm your entries with . 


menu, or 


3–10 Calibration

4 Diagnostics Menu 

What you can do in the Diagnostics 

menu 

The Diagnostics menu provides all relevant information 

on instrument status. 

 

 

 

 

 

 

 

The message list 

shows the number of currently activated messages 

and the individual warning or failure 

messages in plain text. 

The measurement data 

show the point of measurement (to DIN 19 227/ 

ISO 3511), the limit values, and whether probe 

rinsing is activated. 

The calibration record 

shows all relevant data of the last calibration for 

documentation according to GMP. 

The sensor statistics 

show the sensor data of the last three calibrations 

and of First Calibration. 

The logbook 

shows the last 200 events with date and time, 

such as calibrations, warning and failure messages, 

power failure etc. 

This allows quality management documentation 

to ISO 9000. 

The device description 

contains information on model designation, serial 

number and options of the Process Unit 73 

O 2 -2 

The device diagnostics 

allows comprehensive tests to check the function 

of the Process Unit 73 O 2 -2. 

This allows quality management documentation 

to ISO 9000. 

Instrument settings and parameters are not affected. 

Diagnostics 4–1


How to access the Diagnostics 

menu 

Pressing opens the Diagnostics menu. 

Pressing or exits the Diagnostics 

menu. 

Message List 

Press or to access the ”Message List”. 

All currently active failure and warning messages 

are displayed. 

For description of messages, refer to chapter 11. 

Press to return to the Diagnostics menu. 

Measurement Data 

Press and to access the 

”Measurement Data”. 

The point of measurement (to DIN 19227/ 

ISO 3511) is displayed. 

Below, you can read which limit values are set. 

If the Process Unit is equipped with option 352 

(probe rinsing), you can see if probe rinsing is activated. 


How to enter the point of measurement 

On the Administrator or Operator level you select 

menu item ”Point of Measurement”. 

You can enter . 0...9 A...Z – + / using the scrolling 

keys. 

Enter the point of measurement using scrolling 

and cursor keys (see page 2–5) and confirm your 

entry with . 

4–2 Diagnostics

Calibration Record 

Select ”Cal Record” using and . 


What you can do with the calibration 

record 

The calibration record contains all relevant data of 

the last calibration required for documentation according 

to ISO 9000 and GMP. 

 

 

 

 

 

date and time of last calibration 

calibration sequence (e.g. automatic in water) 

sensor zero point 

sensor slope 

relative humidity (for calibration in air) 

For the 1st and 2nd calibration step: 

 

 

 

sensor current 

calibration temperature 

sensor response time until stabilization of measured 

current 

For some calibration sequences, such as Data 

Entry, not all measured values are available. The 

relevant positions are covered by a gray bar. 

Sensor Statistics 

What is the sensor statistics? 

When you perform a First Calibration (see page 

3–4), the following values are stored as reference 

values: 

 

 

 

 

 

 

date and time of First Calibration 

sensor slope 

sensor zero point 


calibration pressure 

response time 

Diagnostics 4–3


When you then perform ordinary calibrations, the 

following data will be listed in the sensor statistics 

for the last three calibrations: 

 

 

 

 

 

 

date and time of calibration 

deviation of sensor zero point 

deviation of sensor slope 



response time 

This provides you with important information on 

sensor state, aging and the time for the next due 

calibration. 

If the time between two calibrations is less than 6 

minutes, the Process Unit interprets the second 

calibration as repetition of the first one (e.g. when 

an error has occurred). It does not store a new 

record. The last calibration record is overwritten. 

How to read out sensor statistics 

Select ”Sensor Statistics” using and 

. 

Press the scrolling keys to read out the statistics 

data of the First Calibration and the last three calibrations, 

respectively: 

 

 

 

 

 

zero point 

slope 



response time 


4–4 Diagnostics

Logbook 

You can only make use of the logbook if your Process 

Unit is equipped with option 354. 

Without this option, the menu reads ”Logbook (Optional)”, 

and this item cannot be selected. 

What is the logbook? 

The logbook contains the last 200 events with 

date and time and displays them. Error messages 

occurring during parameter setting, calibration or 

maintenance are not recorded. 

The following events are recorded: 

 

 

 

 

 

 

 

instrument in measuring mode 

instrument turned on/off 

: start of warning and failure messages 

: end of warning and failure messages 

calibration messages 

parameter setting, calibration, maintenance or 

diagnostics activated 

entry of wrong passcodes 

What you can do with the logbook 

The logbook entries can be used for quality management 

documentation to ISO 9000 and GMP. 

Logbook entries cannot be edited! 


remote interface (refer to page 9–34), the logbook 

contents can be read out and automatically documented. 

How to read out the logbook entries 

Select ”Logbook” using and . 

Press the scrolling keys to read out all entries. The 

latest event is always at the top of the display. 


Diagnostics 4–5


How to set time, date and date format 

Select menu item ”Set Clock” on the Operator or 

Administrator level. 

Select date format, time or date using and 

. 

Enter time and date using scrolling and cursor 

keys and confirm your entry with . 

On pressing , the clock starts running at the 

entered value. 

You can read out time and date on the secondary 

display, time also on the measurement display. 

(see page 2–1). 

Device Description 

Select ”Device Description” using and 

. 

You read: 

 

 

 

model designation and program module code, 

serial number, 

hardware and software version and 

instrument options. 


The software version must correspond to the version 

indicated at the bottom right of the second 

page of this manual. 

The options for power supply are not displayed. 

They are indicated on the rating plate (between 

the Pg cable glands). 

4–6 Diagnostics

Device Diagnostics 

What you can do with the device diagnostics 

The device diagnostics allows you to perform comprehensive 

tests to check the function of the 

Model 73 O 2 -2. 

This permits quality management documentation 

to ISO 9000. 

Instrument settings and parameters are not affected. 

How to perform device diagnostics 

Select ”Device Diagnostics” using and 

. 

You see when each test was performed and what 

the result was. 

Memory Test 

Select ”RAM Test”, ”EPROM Test” or ”EEPROM 

Test” using and . 

Press to start testing. 

Test progress is indicated by a bargraph. 

If ”Failure” is read in the menu after testing has 

been terminated, the Process Unit must be returned 

to the manufacturer for repair. 

The memory test can also be automatically performed 

by the Process Unit. To do so, activate the 

self test during parameter setting on the menu 

level ”Device Diagnostics” and specify the desired 

interval. In the case of memory failure the instrument 

sends a warning message. 

Display Test 

Select ”Display Test” using . 


Several test patterns will be displayed allowing 

you to check if all pixels, lines and columns function 

perfectly. 

If there are disturbances in the test patterns, you 

should return the instrument to the manufacturer 

for repair. 

Diagnostics 4–7


Keypad Test 

Select ”Keypad Test” using . 


You must press each key once. Keys that have 

been pressed are highlighted. 

If ”Keypad Test Failure” is read on the display after 

you have pressed all keys, you must return the 

Porcess Unit to the manufacturer for repair. 


4–8 Diagnostics

5 Maintenance Menu 

What you can do in the Maintenance 

menu 

The Maintenance menu provides all functions for 

sensor maintenance and adjustment of connected 

measuring instruments. 

Access to the Maintenance menu can be protected 

by a passcode. 

 

 

 

 

Measurement point maintenance allows to dismount 

the sensor. 

Probe rinsing function (option 352) permits automatic 

rinsing and cleaning of the sensor: see 

page 9–29. 

The current source allows to manually adjust 

the output currents (1 and 2) for adjusting and 

checking connected peripheral devices (such 

as indicator or recorder). 

Temperature probe adjustment allows individual 

calibration of the NTC temperature probe. 

Only with option 352: In the “Measurement Point 

Maintenance” submenu the “probe” contact is active. 

A timer controlled rinsing cycle will not be 

started. (see page 9–29). 

Maintenance 5–1


How to access the Maintenance 

menu 

Press to open the Maintenance menu. 

If you are prompted for a passcode, you must 

know the maintenance passcode: 

Enter the maintenance passcode using scrolling 

and cursor keys and confirm your entry with 

. 

The maintenance passcode can be edited or disabled 

on the Administrator level (see page 8–4). 

Measurement Point Maintenance 

Press or to select 

”Meas. Point Maint.”. 

Now you can remove the sensor for cleaning or 

replacement. 

The output currents (1 and 2) are frozen at their 

last values, limit contacts are disabled, NAMUR 

contact ”Functional Check” is active. 

Instrument with probe rinsing function 

(option 352) 

If your instrument is equipped with option 352 

(probe rinsing), you will see one of the following 

two displays. 

Probe rinsing has been disabled during parameter 

setting. 

For further information refer to page 9–29. 

Probe rinsing is enabled. 

You can start a rinsing cycle: 

Press to select ”Start probe rinsing” and confirm 

with . When the rinsing cycle is terminated, 

the Process Unit will go to measuring 

mode. 

Press to return to the Maintenance menu, 

or press to return to measuring mode. In 

this case, you will be prompted to confirm your 

decision to exit the function. If you really want to, 

press to select ”Yes” and confirm with . 

5–2 Maintenance

Current Source Function 

During current source function, the output currents 

do not follow the measured value! 

The values can be entered manually. 

NAMUR contact ”Functional Check” is active. 

Therefore, you must be sure that the connected 

peripherals (control room, controller, indicator) will 

not interpret the current value as measured value! 

Press and to select ”Current Source”. 

Now you can manually set the values for output 

current 1 (and 2) to check the connected peripheral 

devices. 

Enter the desired current value using scrolling and 



or press to return to measuring mode. In 

this case, you will be prompted to confirm your 

decision to exit the function. If you really want to, 

press to select ”Yes” and confirm with . 

Maintenance 5–3


Temperature Probe Adjustment 

This function allows you to compensate for the 

individual temperature probe tolerance and the 

influence of the lead resistances to increase accuracy 

of temperature measurement. 

This adjustment may only be performed after process 

temperature has been precisely measured 

using a calibrated reference thermometer! 

The reference thermometer must have an accuracy 

better than 0.1 C. 

Mind the response time of the temperature probe! 

To make adjustment easier, set 

”Measurement Display: Variable C” 


Open the Maintenance menu and select 

”Adjust Temp Probe” using and . 

If measurement display has been set correspondingly, 

the temperature measured by the temperature 

probe is now read in the upper right corner of 

the display. 

To start adjustment, press to select 

”Installation Adjustment On” and confirm with 

. 

Enter the process temperature measured by the 

reference thermometer using scrolling and cursor 

keys and confirm your entry with . 

Now the adjusted temperature measured by the 

temperature probe will be read in the upper right 

corner of the display. 

Permissible adjustment range is5 K from the 

value measured by the temperature probe. 


or press to return to measuring mode. 

5–4 Maintenance

6 Display of Settings 

What you can do on the Viewing 

level 

On the Viewing level you can display all instrument 

settings. 

Settings cannot be edited! 

How to access the Viewing level 

Press to open the Parameter Setting menu. 

Pressing exits the Parameter Setting 

menu. 


”Viewing Level (All Data)”. 

Pressing returns you to the Parameter Setting 

menu. 

Now you can read out all settings. 




video). 



through. 



The symbols and at the beginning of the display 

line indicate that you can access another 




Pressing or accesses the previous 

(higher) menu level. 

Viewing Level 6–1


An Example 

You want to read out the settings for temperature 

alarm. 



”Viewing level (All Data)”. 

Select ”Alarm Settings” using scrolling key . 

The selected line is marked by a dark bar (reverse 

video). 



through. 

Press or to access the next 


Select ”Temperature Alarm” using scrolling key 

. The selected line is marked by a dark bar (reverse 

video). 

Here you can already see if alarm is enabled. 

Press or to access the lowest 

menu level. 

The settings for temperature alarm will be displayed. 

Press or to return to the previous 

(higher) level. 

Press to exit the Parameter Setting menu. 

6–2 Viewing Level

7 Parameter Setting on the Operator Level 

What you can do on the Operator 

level 

On the Operator level you can edit certain parameters 

(menu items) of the Process Unit. 

Access to the Operator level can be protected by 

a passcode. 

How to access the Operator level 



menu. 

Press and to select ”Operator Level”. 

If prompted for passcode entry, enter the operator 

passcode using scrolling and cursor keys and 

confirm your entry with . 

The operator passcode can be edited or disabled 

on the Administrator level (see page 8–4). 


menu. 

You can edit the marked menu items: 

 

 

This menu item has been enabled on the 

Administrator level: It can be edited. 

This menu item has been locked on the 

Administrator level: It cannot be edited. 

The menu item is skipped during scrolling. 

However, it can be read out on the Viewing 

level. 




video). 

Operator Level 7–1




The symbols and at the beginning of the 

display line indicate that you can access another 






An Example 

You want to change the settings for the input filter. 


Press and to select 

”Operator Level (Operation Data)”. 

Enter the operator passcode using scrolling and 


Press to select menu item ”Input Filter”. 



To activate the input filter, press to select 

”Pulse Suppression On” and confirm with . 


Pressing menu key instead of restores 

the old setting (”undo” function). 

Pressing or returns you to the 

previous (higher) menu level. 


menu. 

7–2 Operator Level

8 Parameter Setting on the Administrator Level 

Before first start-up of the Process Unit 73 O 2 -2, a 

complete parameter setting procedure must be 

performed. 

What you can do on the Administrator 

level 

On the Administrator level you can edit all instrument 

settings including the passcodes. In addition, 

the marker function allows to lock individual menu 

items to prevent access from the Operator level. 

As delivered, all menu items are enabled. 

Access to the Administrator level is protected by a 

passcode. 

How to access the Administrator 

level 



menu. 

Select ”Administrator Level (All Data)” using 

and . 

 

Enter the administrator passcode using scrolling 


entry with . 


menu. 

Administrator Level 8–1


Marker Setting 

On the Administrator level, marker setting is explained 

by an information text. 

What you can do with marker setting 

Marker setting allows you to enable or lock each 

menu item on the highest level of the Parameter 

Setting menu (except ”Passcode Entry”) for the 

Operator level: 

 

 

This menu item has been enabled on the 

Administrator level: It can be edited on the 

Operator level. 

This menu item is locked: It cannot be 

edited on the Operator level. However, it 

can be read out on the Viewing level. 

As delivered, all menu items are enabled. 

How to set a marker 

Press to select the marker. 

Press or to enable () or lock () the 

menu item. 

Confirm the setting with . 




vieo). 



The symbols and at the beginning of the 

display line indicate that you can access another 






8–2 Administrator Level

An Example 

You want to change the settings for the input filter. 


Press and to select 

”Administrator Level”. 



entry with . 

Press to confirm the information text. 

Press to select menu item ”Input Filter”. 



To activate the input filter, press to select 

”Pulse Suppression On” and confirm with . 


Pressing instead of restores the old 

setting (”undo” function). 

Pressing or returns you to the 

previous (higher) menu level. 


menu. 



Passcode Protection 

Access to the Calibration menu, Maintenance 

menu, Parameter Setting on Operator level and 

Administrator level can be protected by passcodes. 

You can set or disable each passcode individually. 

(Administrator passcode cannot be disabled.) 

When a passcode is disabled, there is no protection 

against unauthorized access to the corresponding 

menu! 

The factory set passcodes are the same for all 

instruments. 

Therefore, you should define your own passcodes. 

How to set the passcodes 

Select ”Administrator Level” using and . 



. 

Select ”Passcode Entry” using and . 

Select ”cal”, ”maint” or ”opl” using . 

You can individually enable or disable the calibration 

passcode, maintenance passcode and operator 

passcode. 

Only if a passcode is enabled, the line 

”Change passcode” is displayed. 

The passcode remains stored even if it has been 

disabled. 

Edit the passcodes using scrolling and cursor keys 

and confirm your entry with . 

How to keep the old passcode 

Pressing instead of restores the old 

passcode (”undo” function). 


How to set the administrator passcode 

If you have lost the administrator passcode, system 

access is locked! The Administrator level cannot 

be accessed for parameter setting. All menu 

items locked for the Operator level () cannot be 

edited any more. 

Contact in this case: 

Knick Elektronische Meßgeräte GmbH & Co. 

Sales Department 

Beuckestr. 22 

D–14163 Berlin 

Germany 

Phone +49–30–80191–210 

Fax +49–30–80191–200 

Press and to select ”adm”. 

Edit the administrator passcode using scrolling 


. 

For reasons of safety, you have to enter the administrator 

passcode for a second time. 

If the second entry does not correspond to the first 

entry or if you abort by pressing , the administrator 

passcode will not be changed. 

If you set the administrator passcode to ”0000”, 

Administrator level can be accessed without passcode 

entry, by pressing at the passcode 

prompt. 

If you set the administrator passcode to ”0000”, 

menus and instrument settings will not be protected 

against unauthorized access! 

Unauthorized change of parameter settings can 

lead to instrument malfunction and wrong measured 

value outputs! 

Factory Set Passcodes 

The Process Unit is shipped with the following 

passcode settings: 

Calibration Passcode: 1 1 4 7 

Maintenance Passcode: 2 9 5 8 

Operator Passcode: 1 2 4 6 

Administrator Passcode: 1 9 8 9 




9 Capabilities of the Process Unit 73 O 2 -2 




applicable local and national codes. 



Overview 

The Process Unit 73 O 2 -2 provides a great variety 

of features and capabilities. 

This chapter describes: 

 

 

 

the instrument’s measurement capabilities 

how to connect the instrument 

how to set the parameters 

Power Supply for the Process 

Unit 73 O 2 -2 

Read chapter 10 ”Information on Installation” before 

connecting the power supply! 

Check if your mains voltage corresponds to the 

ratings given on the instrument’s rating plate: 

 

230 Vac 

115 Vac (option 363) 

24 Vac/dc (option 298) 

For approx. 10 s after connection of power supply, 

the current outputs and contacts are frozen at the 

levels before power supply failure. This ensures 

that no invalid messages are activated after power-on. 

Capabilities 9–1


Simple Oxygen Measurement 

Fig. 9–1, page 9–2 shows how the Process Unit 

73 O 2 -2 is configured for simple oxygen measurement 

with automatic temperature detection and 

oxygen signal evaluation by a connected recorder. 

You can connect SE 704, SE 705 oxygen sensors 

or other amperometric or galvanic sensors to the 

Process Unit 73 O 2 -2. 

yw/gn 

wt 

rd 

bk 

bk 

Fig. 9–1 

Oxygen measurement with recorder evaluation 

9–2 Capabilities

Measurement Display 

During parameter setting, you can define which of 

the values measured will be read out on the large 

display. The following variables can be displayed: 

 

 

 

 

 

 

oxygen saturation referred to air (%AIR) 

oxygen saturation referred to pure oxygen 

(%O 2 ) 

oxygen concentration (mg/l or ppm) 

oxygen partial pressure (mbar) 

temperature (C) 

time 

How to set the measurement display 

parameters 

Open the Parameter Setting menu (adm or opl 

level resp.), select ”Measurement Display” and 

confirm with . 

Menu item ”Unit of Concentration” allows to select 

unit ”mg/l” or ”ppm” for concentration displays using 

and . Confirm your choice with . 

The selected unit is valid for all concentration displays, 

on main and secondary displays. 

Menu item “Range Concentration” allows you to 

choose between the fixed measuring ranges “mg/l” 

and “µg/l” or “ppm” and “ppb”, or to select “auto”. 

In the “auto” mode the measuring range is 

automatically adapted to the measured value. For 

a fixed measuring range, all parameters with 

concentration values can only be selected within 

this range. 

Menu item ”Variable” allows to select the process 

variable you want to have displayed during measuring 

mode using and . Confirm your 

choice with . 

The process variable is read in the upper right corner 

of the display. 

Capabilities 9–3


Menu item ”Viewing Angle” allows you to adjust 

the viewing angle of the display. 

When the instrument is mounted at a very high or 

very low position, you can adjust the viewing angle 

for optimum display readability. 

Select the desired viewing angle using and 

(+ means viewing angle upwards and – means 

viewing angle downwards) and confirm your 

choice with . 

The angle is changed immediately. 

Input Filter 

For oxygen measurement with increased immunity 

to interference, you can activate input filters. 

 

 

The pulse filter suppresses fast pulses such as 

occur during line interferences. 

The low-pass filter steadies the measured 

value in noisy measurement environment. Response 

time is approx. 30 s. 

How to set the input filter parameters 


level resp.), press to select ”Input Filter”, and 


Press / to select the desired filter. 

Turn the filter on or off using and and 


9–4 Capabilities

Cal Timer 

The cal timer allows you to monitor if the sensor is 

regularly calibrated. 

The cal timer counts the time passed since the 

last calibration. When the preset time is reached, 

a message will be activated. 

In the ”Alarm Settings” menu you can preset one 

interval each for a warning and a failure message. 

The cal timer count can be read out on the secondary 

display (see page 2–1). 

How to set the cal timer 


level resp.), select ”Alarm Settings” using , and 


Select ”Cal Timer Alarm” using and confirm 

with . 

You can enable or disable alarm and set an interval 

for a warning and a failure message each. 

Pressure Correction 

Why Pressure Correction? 

The signal delivered by the oxygen sensor is directly 

proportional to the oxygen partial pressure. 

Since the partial pressure changes with the total 

pressure (air pressure), the Process Unit 73 O 2 -2 

must detect and take account of the total pressure 

to obtain a pressure-independent output signal. 

Pressure Detection Procedures 

The Process Unit 73 O 2 -2 provides different procedures 

for pressure detection: 

 

 

 

pressure detection using integrated air pressure 

sensor 

manual input of pressure 

pressure detection using an external pressure 

sensor (absolute-value or differential-value sensor) 

Capabilities 9–5


oxygen 

sensor 

p amb 

open container 

The integrated pressure sensor detects the ambient 

air pressure (p amb ). 

In closed containers the pressure must be measured 

directly in the gas-filled space of the container. 

To do so, you can detect the output signal 

of a pressure sensor (p sensor ) via the current input 

of the Process Unit 73 O 2 -2. You can either use an 

absolute-value or a differential-value sensor with 

0(4) – 20 mA output. 

For measurements under constant pressure, continuous 

pressure detection is not necessary. You 

can key in the pressure value at the instrument. 

Measurement in an open container: 

p tank 

pressure 

sensor 

p = p amb 

p amb is automatically detected by the integrated 

pressure sensor. 

Measurement in a closed container: 

p = p tank = p sensor 

oxygen 

sensor 

p amb 

p tank 

closed container 

ambient air pressure 

pressure within container 

When measuring with a differential-value sensor, 

the ambient pressure p amb must be added to the 

signal p sensor measured by the sensor. If you have 

selected the differential-value sensor during parameter 

setting (see page 9–7), the ambient 

pressure is detected by the sensor integrated in 

the Process Unit 73 O 2 -2 and automatically calculated 

with the sensor signal. 

9–6 Capabilities

How to set the pressure correction parameters 

Open a Parameter Setting menu and select menu 

item ”Pressure Correction” using . Confirm with 

. 

You can independently select a pressure detection 

method for measurement and calibration. Selection 

is using and . Confirm with . 

Press or to select if you want to detect 

the air pressure directly using the integrated pressure 

sensor (AirPressure) or if you want to enter 

the pressure value manually (man) or connect an 

external pressure sensor to the current input 

(I-Inp). Confirm your choice with . 

If you have selected ”manual“, you can now enter 

the pressure value using , and . Confirm 

with . 

If you have selected pressure detection via an external 

sensor at the current input (”I-Inp”), a new 

menu item ”Sensor at I-Inp” appears in the 

”Pressure Correction” menu. Select this menu item 

to enter the data for the external pressure sensor: 

Press or to specify if the sensor measures 

an absolute or a differential value. Confirm 

with . 

Enter the pressure delivered by the sensor at 

0(4) mA and at 20 mA using , and . 

Confirm each entry with . 

Selection between 0 to 20 mA or 4 to 20 mA is in 

the ”Current Input” menu (see page 9–23). 

If you use an external sensor for pressure detection, 

the ”Pressure Correction” menu assigns the 

current input to detect this sensor signal. If at the 

same time the current input is set as control input 

for probe rinsing (see page 9–23), the warning 

message ”Warn Application I-Inp” is activated. 

Capabilities 9–7


Sensor Data 

The data for the SE 704 and SE 705 are factory 

set in the Process Unit 73 O 2 -2. When you use 

another sensor, you must change the sensor data 

in the Sensor Data menu of the Process Unit 73 

O 2 -2. 

The following data must be edited: 

 

 

Polarization Voltage 

(Factory setting: -675 mV) 

During amperometric oxygen measurement the 

oxygen is cathodically reduced. Therefore, the 

required polarization voltage is negative. 

For the polarization voltage required, refer to 

the data sheet of the sensor in use. 

Set the polarization voltage to 0 mV for oxygen 

measurement with galvanic cells. 

TC Factor 

(Factory setting: 1.000) 

To determine the TC factor, you must measure 

the sensor current at two temperatures. Be 

sure that the water is air saturated at both temperatures! 

Make also sure that there is sufficient 

flow around the sensor. Temperature difference 

should be approx. 10 to 30 °C. Then 

you can calculate the TC factor according to 

the following equation: 

TC Factor 

ln I (t1) 

I (t2) 

p L 

–p W(t2) 

p –p L W(t1) 

 

2220 K 1 

T 2 

– 1 

T 1 

 

I sensor current [A, nA] 

p L air pressure [mbar] 

p W water vapor pressure [mbar] 

(see chart) 

t 1 temperature 1 [°C] 

t 2 temperature 2 [°C] 

T 1 absolute temperature 1 [K] 

T 1 = 273.15 + t 1 

T 2 absolute temperature 2 [K] 

T 2 = 273.15 + t 2 

9–8 Capabilities

(CRC Handbook of Chemistry and Physics 

56 TH Edition 1975 – 1976) 

Vapor Pressure of Water as a Function of Temperature 

Temperature 

[°C] 

Water 

Vapor 

Pressure 

[mbar] 

Temperature 

[°C] 

Water 

Vapor 

Pressure 

[mbar] 

Temperature 

[°C] 

Water 

Vapor 

Pressure 

[mbar] 

–10 2.9 21 24.9 51 129.6 

–9 3.1 22 26.4 52 136.1 

–8 3.4 23 28.1 53 142.9 

–7 3.6 24 29.8 54 150.0 

–6 3.9 25 31.7 55 157.4 

–5 4.2 26 33.6 56 165.1 

–4 4.5 27 35.6 57 173.1 

–3 4.9 28 37.8 58 181.4 

–2 5.3 29 40.1 59 190.1 

–1 5.7 30 42.4 60 199.2 

0 6.1 31 44.9 61 208.6 

1 6.6 32 47.5 62 218.3 

2 7.1 33 50.3 63 228.5 

3 7.6 34 53.2 64 239.1 

4 8.1 35 56.2 65 250.0 

5 8.7 36 59.4 66 261.4 

6 9.3 37 62.8 67 273.3 

7 10.0 38 66.3 68 285.5 

8 10.7 39 69.9 69 298.3 

9 11.5 40 73.8 70 311.6 

10 12.3 41 77.8 71 325.2 

11 13.1 42 82.0 72 339.4 

12 14.0 43 86.4 73 354.2 

13 15.0 44 91.0 74 369.6 

14 16.0 45 95.8 75 385.4 

15 17.0 46 100.9 76 401.8 

16 18.2 47 106.1 77 418.8 

17 19.4 48 111.6 78 436.4 

18 20.6 49 117.4 79 454.6 

19 22.0 50 123.3 80 473.4 

20 23.4 

 

 

Current Range 

(Factory setting: Auto) 

Usually the current range is automatically adjusted 

by the Process Unit (Auto). For special 

measurements, however, you can also select a 

fixed range. 

Temp Detection 

(See the following comments in section “Temperature 

Detection” on the following pages.) 

Capabilities 9–9


Sensocheck ® 

(Factory setting: Off) 

Sensocheck ® sensor monitoring has been optimized 

for the SE 704 or SE 705 sensors. 

When you use another sensor, Sensocheck ® 

function might be restricted. 

With Sensocheck ® enabled the impedance 

across anode and cathode is monitored. Fast 

impedance changes, e.g. due to mechanical 

stress at the membrane, activate the message 

”Warn Sensocheck“. In order to continue, this 

message can be acknowledged (reset) in the 

maintenance menu, or carry out a new 

calibration (and possibly also maintenance) of 

the cell. The message is recorded in the 

logbook both upon being output and when 

cancelled. Slow impedance changes are without 

effect. 

Temperature Detection 

Why Temperature Compensation? 

Temperature is automatically detected using a 

temperature probe integrated in the sensor 

(SE 704 and SE 705: NTC; other sensors: Pt 100/ 

Pt 1000) and is taken into account for calculating 

the measured value. 

When process temperature remains constant, you 

do not require a temperature probe. In that case 

you enter the temperature value manually. Temperature 

values for measurement and calibration 

can be entered separately. 

There are two important reasons for determining 

the process temperature: 

 

 

Compensating the temperature dependence of 

the sensor membrane: 

The membrane’s permeability for oxygen increases 

with rising temperatures. Therefore 

temperature is detected and the measured 

value compensated. 

Temperature-corrected display of oxygen concentration: 

Oxygen solubility in water as well as partial 

pressure of water vapor are temperature dependent. 

9–10 Capabilities

Automatic Temperature Compensation 

With automatic temperature compensation the 

Process Unit 73 O 2 -2 measures the process temperature 

using a temperature probe (with SE 704 

and SE 705: NTC; other sensors: Pt 100/Pt 1000). 

 

 

 

 

 

 

 

 

 

 

If you work with automatic temperature compensation, 

a temperature probe connected with the Process 

Unit 73 O 2 -2 must be in the process medium! 

If you have no temperature probe connected to 

the Process Unit 73 O 2 -2, you must select manual 

input of measuring temperature. 

To eliminate the temperature measurement error 

caused by the lead resistance, connect the temperature 

probe to the Process Unit 73 O 2 -2 in 

3-wire connection. 

The lines to terminals 6 and 7 must have the same 

cross section. 

For 2-wire configuration, connect the temperature 

probe to terminals 6 and 7. Make sure to place a 

jumper across terminals 7 and 8, no matter which 

temperature probe you use (NTC or Pt 100/ 

Pt 1000). 

 

Temperature Probe 

(Factory setting: 22 k NTC) 

The SE 704 and SE 705 sensors provide a 

22 k NTC. If you want to use another sensor, 

you can also use a Pt 100 or Pt 1000 temperature 

probe for temperature compensation. The 

respective temperature probe must be defined 

in the “Temp Probe” submenu. Select the temperature 

probe using and and confirm 

with . 

 

 

Measuring Temp 


You can choose between automatically or 

manually measured temperature. 

CalTemp 


You can choose between automatically or 

manually measured calibration temperature. 

Capabilities 9–11


How to set the temperature detection 

parameters 

Open a Parameter Setting menu and select menu 

item “Sensor Data” using . Confirm with . 

Press repeatedly to select “Temp Detection” 


Select the connected temperature probe using 

and and confirm with enter. 

 

Press to select “Measuring Temp” and choose 

between automatically or manually measured temperature 

using or . 

Confirm with . 

Manual Temperature Compensation 

You should only select manual temperature compensation 

if the process is running at constant 

temperature! 

With “Measuring Temp Manual” selected, 

“MAN.TEMP” is read in the bottom right corner of 

the main display during measurement. 

“MAN.TEMP” is not displayed when the display 

shows the measured temperature as measured 

value. The manually entered temperature can be 

read out in the secondary display (see page 2–1). 

With manual temperature compensation you must 

enter the process temperature: 

Measure the temperature of the process medium, 

e.g. using a glass thermometer, 

or 

make sure that the process medium is at a 

constant temperature, e.g. using a thermostat. 

Enter the measured temperature using scrolling 

and cursor keys and confirm your entry with 

. 

9–12 Capabilities

How to set the parameters for calibration 

temperature detection 

You should select manual detection of the calibration 

temperature if the sensor is calibrated outside 

the process medium while the temperature probe 

is kept in the medium. 

Select ”Cal Temp” using . 

Press or to choose between automatically 

or manually measured calibration temperature 


For input of calibration temperature, proceed as 

described above for input of measuring temperature. 

Current Output 

The current output provides an impressed standard 

current of 0 to 20 mA or 4 to 20 mA. The output 

current can be read out on an secondary display 


You can assign the output current to any of the 

following variables: 

 

 

 

 

 

oxygen saturation referred to air (%AIR) 

oxygen saturation referred to pure oxygen 

(%O 2 ) 

oxygen concentration (mg/l or ppm) 

oxygen partial pressure (mbar) 


Output current will be frozen at its last value: 

 

 

 

 

 

during calibration 

during current source function (manual entry) 

in the menu “Meas. Point Maint.” 

after the corresponding interface command 

during probe rinsing 

Capabilities 9–13


Output Curves of the Current 

Output 

You can choose between three output curves for 

the current output: 

 

 

 

linear 

trilinear (or bilinear) 

function 

If the initial value is lower than the end value, a 

rising output curve will result. 

To define a falling output curve, set the lower 

value as end value and the higher value as initial 

value. 

Linear Output Curve 

100 

0 (4) mA output current 20 mA 

beginning 0 % 50 % end 100 % 

90 

80 measured variable, 100 %AIR 

e.g. oxygen saturation 

To determine the span corresponding to current 

range 0 (4) to 20 mA, set an initial and an end 

value for the process variable. 

For permissible spans, refer to Specifications, 

chapter 14. 

80 

60 

output current [%] 

40 

20 

0 

80 85 90 95 100 

oxygen saturation [%AIR] 

9–14 Capabilities

Trilinear Output Curve 


100 

80 

60 

40 

20 

0 

80 85 90 95 100 


To determine the span corresponding to a current 

range of 0 (4) to 20 mA, set an initial and an end 


In addition, you can define two corner points. They 

divide the output curve into three regions of different 

slopes. 

Example: 

beginning: 

80 %AIR 

1st corner X: 

85 %AIR 

1st corner Y: 40 % 

2nd corner X: 

95 %AIR 

2nd corner Y: 60 % 

end: 

100 %AIR 

Bilinear Output Curve 


100 

80 

60 

40 

20 

0 

80 85 90 95 100 


To define a bilinear output curve, set the same X 

and Y values for the two corner points of a trilinear 

curve. 




In addition, you can define a corner point. It divides 

the output curve into two regions of different 

slopes. 

Example: 

beginning: 

80 %AIR 

1st corner X: 

85 %AIR 

1st corner Y: 40 % 

2nd corner X: 

85 %AIR 

2nd corner Y: 40 % 

end: 

100 %AIR 

Capabilities 9–15


Output Curve ”Function” 


100 

80 

60 

40 

20 

0 

0 20 40 60 80 100 


Especially when measuring low values, it is useful 

to measure over several decades while at the 

same time maintaining a high resolution for the 

low values. 

The output curve ”function” allows for a nonlinear 

output current characteristic. By defining a 50 % 

point, you can spread the beginning and compress 

the end of the range as required. 

This allows you to create a good approximation of 

a logarithmic output curve. 



value for the process variable. In addition, you can 

define a 50 % point (at 10 or 12 mA, resp.). 

Between initial and end value the output current is 

calculated from the following equations: 

output current (0 to 20 mA) = 

(1 + C) * x * 20 mA 

1 + C * x 

output current (4 to 20 mA) = 

(1 + C) * x * 16 mA + 4 mA 

1 + C * x 

C = E + I – 2 * X50% 

X50% – I 

x = M – I 

E – I 

I: initial value at 0 (4) mA 

X50%: 50% value at 10 (12) mA 

E: end value at 20 mA 

M: measured value 

Example: 

logarithmic output curve over one decade 

Example: 

logarithmic output curve over two decades 

Approximation of a logarithmic output curve in the 

range 10 to 100 %AIR (one decade): 

beginning: 10.0 %AIR 

50 % point: 31.6 %AIR 

end: 

100.0 %AIR 

Approximation of a logarithmic output curve in the 

range 1 to 100 %AIR (two decades): 

beginning: 1.0 %AIR 

50 % point: 10.0 %AIR 

end: 

100.0 %AIR 

9–16 Capabilities

2nd Current Output 

If your Process Unit is equipped with option 350, 

you can simultaneously output a second process 

variable via the second current output (Fig. 9–2, 

page 9–20). 

If the Process Unit does not provide a 2nd current 

output, the Parameter Setting menu reads 

”Output Current 2 (Optional)”. 

How to set the current output 

Open the Parameter Setting menu (opl or adm 

level, resp.), select ”Output Current 1” (or ”Output 

Current 2”) using , and confirm with . 

Select the process variable you want to assign to 

the output current using and , and confirm 

with . 

Press to select ”Output”. 

Press or to set the current output to 

0 to 20 mA or 4 to 20 mA (live zero) and confirm 

with . 

Press to select ”Curve”. 

Press or to determine if the curve shall 

be linear, trilinear or a function and confirm with 

. 

Press to select ”Curve Parameters” and confirm 

with . 

linear 

Enter the initial value (corresponding to 0/4 mA) 

and the end value (corresponding to 20 mA) for 

the process variable using scrolling and cursor 

keys and confirm your entries with . 

trilinear 



the process variable, as well as the corner points 

using scrolling and cursor keys and confirm your 

entries with . 

bilinear 



the process variable, as well as the corner points 

using scrolling and cursor keys (see page 2–5) 

and confirm your entries with . 

Enter the same values for 1st and 2nd corner X 

and for 1st and 2nd corner Y. 

Capabilities 9–17


”function” 



the process variable, as well as the 50 % point 

using scrolling and cursor keys and confirm your 


Error Messages for Current Output Settings 

The output current is linearly output (only determined 

by initial and end value). The alarm message 

”Warn Current Param” is generated if the 

settings fulfil one of the following conditions: 

100 

Trilinear (Bilinear) Curve 

(rising, beginning < end): 


Y 1 

0 

0 X 1 X 2 

beginning 

end 

Y 2 

0 

 

 

 

1st corner X beginning 

2nd corner X end 

1st corner X > 2nd corner X 

1st corner Y 0 % 

2nd corner Y 100 % 

 

 

1st corner Y > 2nd corner Y 

1st corner X = 2nd corner X and 

1st corner Y 2nd corner Y 

100 

Y 2 

Trilinear (Bilinear) Curve 

(falling, beginning > end): 

(Beginning always at 0 % 

End always at 100 % 

1st corner X always at beginning 

2nd corner X always at end) 

 

1st corner X beginning 


Y 1 

2nd corner X end 

1st corner X < 2nd corner X 

1st corner Y 0 % 

0 

end 

X 2 

X 1 

beginning 

2nd corner Y 100 % 

 

1st corner Y < 2nd corner Y 

9–18 Capabilities

Bilinear Curve (falling, beginning > end): 

 

1st corner X = 2nd corner X and 

1st corner Y 2nd corner Y 

Curve ”Function” (rising, beginning < end): 

 

 

50% point beginning 

50% point end 

Curve ”Function” (falling, beginning > end): 

 

 

50% point beginning 

50% point end 

Capabilities 9–19


yw/gn 

wt 

rd 

bk 

bk 

Fig. 9–2 Installation with Process Pressure Detection, Sensor Cleaning, Computer Connection, Recorder 

Evaluation of Oxygen and Temperature and Monitoring via NAMUR Contacts 

9–20 Capabilities

Complete Installation using all 

Functions 

Fig. 9–2, page 9–20 shows how to connect the 

Process Unit 73 O 2 -2 if you want to make use of 

all measurement and control capabilities. 

Presetting the Salinity 

Why presetting the salinity? 

Membrane covered oxygen sensors supply a current 


Henry’s Law allows to calculate the oxygen concentration 

from the oxygen partial pressure using 

a solubility coefficient. This solubility coefficient 

depends on the medium in which the oxygen is 

dissolved as well as on salt content and temperature 

of the medium. 

With the Model 73 O 2 -2 you can take account of 

the influence of the medium’s salt content on solubility 

(salinity to EN 25814 1992). 

The salt content can either be entered directly as 

salinity or chlorinity or you specify values for conductivity 

and temperature of the medium. Calculation 

of salinity from conductivity and temperature 

is according to: International Oceanographic 

Tables, Unesco / National Institute of Oceanography 

of Great Britain Volume 2, Wormley/Godalming/Surrey. 

How to enter the salt content 

Open the Parameter Setting menu and select 

menu item ”Salt Content” using . Confirm with 

. 

Press or to specify whether you want to 

enter salinity directly or chlorinity or conductivity 

(Cond). Confirm your choice with . 

Now enter the selected value using scrolling and 

cursor keys and confirm your choice with . 

Then the corresponding salinity value will be calculated 

and displayed from the chlorinity or conductivity 

value. 

Capabilities 9–21


Power Output 

The Process Unit 73 O 2 -2 provides a floating, 

short-circuit-proof power output (as standard). 

With this power output, you can supply sensors or 

switching contacts, for example, with 24 Vdc, 

30 mA (see Fig. 9–2, page 9–20). 

How to use the power output together with the current 

input to form a ”2-wire transmitter supply” is 

described below. 

Current Input 

The Process Unit 73 O 2 -2 provides a current input 

(as standard). The current input processes standard 

signals of 0 to 20 mA or 4 to 20 mA. 

The input current can be read out on the secondary 

display as % value (see page 2–1). 

In addition, the input current can be monitored by 

alarm limits (see page 9–24). Warning and failure 

limits can be set in the ”Alarm Settings” menu. 

The alarm limits are entered as percentage of input 

current range. 

With 

0 % corresponding to 0 or 4 mA, 

100 % corresponding to 20 mA. 

With current input setting ”Input 0...100% 

4...20mA”, you can enter negative percentage values. 

–25 % correspond to 0 mA. 

The currently active alarm messages can be read 

out in the Diagnostics menu ”Message List” (see 

page 4–2). 

Typical Application 

A typical application would be the connection of a 

2-wire pressure transmitter. The pressure transmitter 

is used for measured value correction, e.g. in 

closed containers (see page 9–5), and for pressure 

monitoring via alarm limits. The pressure 

transmitter is supplied through the power output. 

Its output current is measured via the current input. 

9–22 Capabilities

How to set the current input parameters 

If your Process Unit is equipped with option 352 

and probe rinsing has been enabled during parameter 

setting, the current input can be set to control 

probe rinsing (see below). 

If you use an external sensor for pressure detection, 

the ”Pressure Correction” menu assigns the 

current input to detect this sensor signal. If at the 

same time the current input is set as control input 

for probe rinsing (see page 9–7), the warning 

message ”Warn Application I-Inp” is activated. 

Open the Parameter Setting menu (opl or adm, 

resp.), select ”Current Input” using , and confirm 

with . 

Press or to select ”Input 0...100% 

0...20mA” or ”Input 0...100% 4...20mA” and confirm 

your choice with . 

To monitor the current input via alarm limits, open 

a Parameter Setting menu and select ”Alarm Settings”, 

submenu ”Current Input Alarm”. 

Enter the alarm limits using scrolling and cursor 

keys and confirm your entries with . 

Input current can also be controlled via the limit 

contacts. For setting procedure, refer to page 

9–28. 

Current input as control input for probe 

rinsing 

If your Process Unit is equipped with option 352 

probe rinsing, the current input can be used for 

remote control of probe rinsing (see page 9–31). 

When current input is used as control input, the 

menu item ”Current Input Alarm” does not appear 

in the ”Alarm Settings” menu. 

To set the current input as control input, open the 

Parameter Setting menu, select ”Current Input” 

using , and confirm with . 

Select menu item ”Application”. 

Press or to select ”Control Input”, and 

confirm your choice with (if current input 

has been set to live zero, this only applies for current 

display, current input alarm is disabled). 

Capabilities 9–23


Alarm Settings 

You can define alarm limits for each of the following 

process variables: 

 

 

 

 

 

 

 

 

 

 

oxygen saturation (referred to air) 

oxygen partial pressure 

oxygen concentration 

temperature 

pressure 

cal timer 

sensor zero 

sensor slope 

sensor impedance 

input current at current input 

(only when used as signal input) 

You can define four independent alarm limits for 

each of these variables: 

 

 

 

 

Failure Limit Lo 

If the measured value falls below this limit, NA- 

MUR contact ”Failure” will be activated, the display 

will read ”FAIL”. 

Warning Limit Lo 

If the measured value falls below this limit, NA- 

MUR contact ”Warning” will be activated, the 

display will read ”WARN”. 

Warning Limit Hi 

If the measured value exceeds this limit, NA- 

MUR contact ”Warning” will be activated, the 

display will read ”WARN”. 

Failure Limit Hi 

If the measured value exceeds this limit, NA- 

MUR contact ”Failure” will be activated, the display 

will read ”FAIL”. 

The activated alarm messages can be read in the 

Diagnostics menu ”Message List” (see page 4–2). 

Furthermore, you can enable or disable the alarm 

messages for each process variable. The alarm 

limits remain stored even if the message is disabled. 

9–24 Capabilities

Example: Settings for Saturation Alarm 

Meas. Value [%AIR] Message 

80.00 Fail Lo Saturation 

and 

Warn Lo Saturation 

80.1 – 85.0 Warn Lo Saturation 

85.1 – 94.9 

95.0 – 99.9 Warn Hi Saturation 

100.0 Fail Hi Saturation 

and 

Warn Hi Saturation 

How to set the alarm parameters 


level), select ”Alarm Settings” using , and confirm 

with . 

On this menu level, you can see which alarms are 

enabled. 

Press to select the alarm you want to set (e.g. 

”Saturation Alarm”) and confirm with . 

Enter the warning and failure limits using scrolling 

and cursor keys and confirm your entries with 

. 

Press to return to menu level ”Alarm Settings”. 

Repeat the procedure for setting further 

alarms. 

Impedance Alarm 

To recognize cable breakage or short circuit, you 

can enter warning and failure limits for sensor impedance. 

To do so, read out the impedance of the 

polarized sensor (on the secondary display). As 

suitable Hi limit you should enter at least twice this 

value and as Lo limit not more than half this value. 

Example: 

displayed impedance value 

Fail Lo 

Warn Lo 

Warn Hi 

Fail Hi 

600 k 

198 k 

300 k 

1.200 M 

1.800 M 

Capabilities 9–25


NAMUR Contacts 

The three NAMUR contacts functional check, 

warning (maintenance required) and failure are 

provided as standard. 

 

 

 

Functional check is activated: 

during calibration (), 

during maintenance (): current source, 

meas. point maint., 

during parameter setting () on the 

Operator level (opl) and the Administrator level 

(adm), and 

during an automatic rinsing cycle. 

Warning (maintenance required) is activated 

if a value has exceeded (or fallen below, resp.) 

a preset ”Warning Limit Hi” or ”Warning Limit 

Lo”, or if other warning messages have been 

activated. 

That means that the measuring installation is 

still functioning properly but should be maintained, 

or that certain process parameters have 

reached a value that requires intervention. 

Warning is disabled during ”Functional Check”. 

Failure is activated 

if a value has exceeded (or fallen below, resp.) 

a preset ”Failure Limit Hi” or ”Failure Limit Lo”, 

if the range limits of the Process Unit 73 O 2 -2 

have been exceeded, or if other failure messages 

have been activated. 

That means that the measuring installation is 

not properly functioning any more, or that certain 

process parameters have reached a critical 

value. 

Failure is disabled during ”Functional Check”. 

You can set the three NAMUR contacts as normally 

open contacts (active: closed) or as normally 

closed contacts (active: open). 

For safe operation, the NAMUR contacts must be 

set as normally closed contacts. 

Only this ensures that power failure will activate 

an alarm message! 

You can define a delay time for both the warning 

and the failure contact. If an alarm message is released, 

the contact will only be activated after this 

preset delay time. 

As delivered, the relay contacts are suitable for 

low signal currents (down to approx. 1 mA). 

If currents above approx. 100 mA are switched, 

the gold plating is destroyed during the switching 

process. After that, the contacts will not reliably 

switch low currents. 

9–26 Capabilities

How to set the NAMUR contacts 


level, resp.), select ”NAMUR Contacts” using , 



”NAMUR Contacts N/O” (normally open) or 

”NAMUR Contacts N/C” (normally closed) and 


Enter failure delay time and warning delay time 

using scrolling and cursor keys (see page 2–5) 

and confirm your entries with . 

Limit Contacts 

Two limit contacts are provided as standard. 

The limit contacts can be controlled by the following 

process variables: 

 

 

 

 

 

 

oxygen saturation (referred to air) 

oxygen saturation (referred to pure oxygen) 




input current at current input 

Limit Values and Hysteresis 

hysteresis 

Each of the two contacts can be set separately: 

 

The process variable 

controls the limit contact. 

active 

contact 

inactive 

setpoint min 

L1 

hysteresis 

measuring 

variable 

 

The effective direction 

indicates if the contact will be activated when 

the measured value 

falls below (min) or exceeds (max) 

the limit value. 

Limit values 1 and 2 (L1, L2) 

define the switching thresholds. 

active 

contact 

inactive 

 

The hysteresis 

defines how far the measured value must exceed 

(min) or fall below (max) the limit value 

until the contact returns to its rest position. 

measuring 

variable 

setpoint max 

L2 

 

Normally open or normally closed contact 

defines if the active contact is closed (N/O) or 

open (N/C). 

Capabilities 9–27


If the measured value exceeds the preset limits, 

”L1” and/or ”L2” will appear in the upper right corner 

of the display. 

Contact 1 and/or contact 2 are active. 

When the instrument is in remote status during 

interface operation, the ”L1”/”L2” display is covered 

by ”Remote”! 







How to set the limit contacts 


level’, resp.), select ”Limits” using , and confirm 

with . 

Press or to select ”Limit 1” or ”Limit 2” 


Select the variable to be measured, direction and 

N/O or N/C contact, respectively using scrolling 

and cursor keys and confirm your choice with 

. 

Enter limit value and hysteresis each using scrolling 

and cursor keys (see page 2–5) and confirm 

your entries with . 

Press to return to menu level ”Limits”. Repeat 

the procedure for the other limit value. 

9–28 Capabilities

Probe Rinsing 

You can only make use of the probe rinsing function 

if your Process Unit is equipped with option 

352. Without this option, the menu reads ”Probe 

Rinsing (Optional)”. This menu item cannot be selected. 

Probe rinsing is used, for example, for automatic 

rinsing and cleaning of the oxygen sensor. 

To do so, a rinsing cycle is started. 

A rinsing cycle can be started: 

 

 

 

 

timer controlled after expiration of the user defined 

interval, 

manually in the menu, 

by a current pulse (see page 9–31) at the current 

input (if current input has been set as control 

input, see page 9–23), 

remote-controlled via interface (see page 

9–34). 

You can define an interval in the range 0.1 to 

999.9 h. The interval extends from the start of one 

rinsing cycle to the start of the next rinsing cycle. 

To turn off the automatic rinsing cycle, set the interval 

to ”000.0 h”. 

Before starting a rinsing cycle, you must enter the 

individual step durations on the Parameter Setting 

level, menu item ”Probe Rinsing” (see page 9–31)! 

A rinsing cycle comprises the following steps: 

 

 

Start of Rinsing Cycle: 

NAMUR contact ”functional check” and contact 

”probe” are activated, output current 1 (and 2) 

is frozen, limits are disabled, and 

menus are locked, the interval timer is reset. 

Rinsing Lead Time: 

User defined waiting time until contact ”rinsing” 

closes. This allows you to monitor response 

times of the valve ”probe”, for example . 

 

First Rinsing: 

The contact ”rinsing” is closed for the (user defined) 

duration of first rinsing. 

Capabilities 9–29


 

Cleaning: 

The contact ”cleaning” is closed for the (user 

defined) duration of cleaning. 

 

Second Rinsing: 

The contact ”rinsing” is closed for the (user defined) 

duration of second rinsing. 

 

Wait Position: 

If current input has been set as control input, 

the probe remains in wait position as long as 

the start current of 10 to 20 mA is applied to the 

current input. 

Wait position can only be controlled via the current 

input. If current input has been set as signal input, 

wait position is omitted. 

 

Measurement Lead Time: 

The contact ”probe” is deactivated. 

Now, the user defined waiting time until rinsing 

cycle is terminated starts running. 

After expiration, ”functional check” will be 

turned off. 

If you have set one of these steps to 0000 s, it is 

omitted completely. 

Pressing during the rinsing cycle displays 

the measured value for approx. 5 s. 

9–30 Capabilities

How does probe rinsing operate? 

The rinsing equipment is controlled via three contacts: 

 

 

 

“Probe” contact: 

This contact can be set as normally open or 

normally closed. It controls a process valve in a 

flow-through cell, for example. In measuring 

mode the contact is deactivated. During rinsing 

cycle it is active to close the process valve, for 

example. 

“Rinsing” contact: 

can control the valve for the rinsing medium. 

The contact is closed during first and second 

rinsing. 

“Cleaning” contact: 

can control a valve for the cleaning liquid. The 

contact is closed during cleaning. 

The three contacts are electrically connected on 

one side. 


probe rinsing, the current input is used for remote 

control of the rinsing cycle (see page 9–23): 

 

 

 

0 – 10 mA (normal operation): 

A current in this range permits start of rinsing 

cycle by user defined interval or manually in the 

menu. 

10 – 20 mA (start): 

A current in this range starts a rinsing cycle. 

The current must be applied for at least 2 s. 

As long as this current is applied, the probe remains 

in wait position. That means: rinsing lead 

time, first rinsing, cleaning, and second rinsing 

are executed. Then the probe remains in wait 

position. When the current is removed, the 

cycle will be continued with measurement lead 

time. 

> 20 mA (lock): 

A current in this range locks start of a rinsing 

cycle independent of the user defined interval. 

Capabilities 9–31


How to set the rinsing cycle parameters 

Open the Parameter Setting menu (opl or adm, 

resp.), select ”Probe Rinsing” and confirm with 

. 

Press to select ”Probe Rinsing On” and confirm 

with . 

Enter interval and step durations using scrolling 



If you have set one of these steps to 0000 s, it is 

omitted completely. 

When probe rinsing is enabled in the Parameter 

Setting menu, the next automatic start of the rinsing 

cycle is only performed after a complete interval 

has been expired. 

Tips for Application 

While the rinsing steps are performed, you can 

change the step durations. This allows you to 

shorten or terminate step times that are too long. 

Timer Controlled Rinsing Cycle 

Set the current input as control input and enter an 

interval time. 

After expiration of this interval a rinsing cycle will 

be started automatically. 

If you want to lock automatic rinsing cycle (e.g. 

because you do not want to interrupt an important 

measurement), apply a current > 20 mA to the current 

input (e.g. by directly connecting the power 

output to current input). 

After a power failure the interval timer is reset. 

Then the next automatic start is only performed 

after a complete interval has been expired. 

Remote Controlled Rinsing Cycle 

Manual Start of Rinsing Cycle 

Set the current input as control input and enter the 

interval time ”0000”. 

Apply a current of 10 to 20 mA to the current input 

for at least 2 s (e.g. by connecting the power output 

via a resistor of 1.5 k). This starts a rinsing 

cycle. (Interval timer will be reset.) If the current is 

applied for a longer period of time, the probe remains 

in wait position until the current is removed. 

Open the menu and press or 

to select ”Meas. Point Maint.”. 

9–32 Capabilities

To start a rinsing cycle: 

Press to select ”Start probe rinsing” and confirm 

with . 

This starts a rinsing cycle. (The interval timer will 

be reset.) After termination of the rinsing cycle, the 

instrument will return to measuring mode. 

Manual Switching of ”Rinsing” and 

”Cleaning” 

Press to select ”Manual Control”. 

Press or to select ”Rinse” or ”Clean” and 

confirm with . The corresponding contact 

will remain closed until you enter ”Manual Control 

Off” or press or to exit the menu. 

You can never close two contacts at the same 

time! 

When a rinsing cycle is running, manual control is 

locked. 







If a rinsing cycle is interrupted by a power failure, 

probe rinsing is blocked. The error message ”Fail 

Rinsing Cycle” is released. All automatic starts are 

blocked! 

The cycle can be reactivated by: 

 

 

 

a manual start in the menu 

disabling and re-enabling probe rinsing in the 

Parameter Setting menu 

an interface command 

Remote Interface Operation 

You can only make use of the interface if your Process 

Unit is equipped with option 351. 

Without this option, the menu reads ”Interface 

(Optional)”. This menu item cannot be selected. 

When the RS 485 interface is used, terminal 15 

(RS 485 shield) must be grounded to meet the radio 

interference limits (according to German decree 

243/91). Do not use the protective conductor 

for grounding! 

To operate the Model 73 O 2 -2 at a PC, a commercial 

RS 232 C/RS 485 interface converter can be 

used. 

Capabilities 9–33


What you can do with the interface 

The serial RS 485 interface allows you to: 

 

 

 

 

read out all measured values 

query instrument status including limit and 

alarm messages, instrument diagnostics and 

logbook 

perform complete parameter setting 

start a rinsing cycle via remote control 

For description of the complete command set and 

the transmission protocol, refer to chapter 12. 

If the instrument is in remote status during interface 

operation, the reading ”Remote” appears in 

the upper right corner of the display in measuring 

mode. 

The keypad is locked for all entries! 

When the instrument is in measuring mode, you 

can press to return to ”local” status. (You 

are prompted for confirmation.) The keypad will be 

enabled. 

The interface can be defined for: 

 

 

point-to-point operation 

(Process Unit 73 O 2 -2 connected with a controller, 

e.g. PC) or 

bus operation with up to 31 instruments (73 pH, 

73 LF, 73 O 2 -1, 73 O 2 -2) and a controller (e.g. 

PC) at a bus. 

Interface Parameters 

Baud rate (transmission speed): 

The baud rate is indicated in bits/second. When 

selecting the baud rate the transmission time (high 

baud rates) or the transmission quality (low baud 

rate) may be decisive. Baud rates between 300 

and 9,600 baud can be set on the Process Unit 73 

O 2 -2. 

Parity (transmission error recognition): 

The parity is an additional bit that supplements the 

data bits in such a way that an even number (parity 

even) or an odd number (parity odd) of logical 

“ones” is transmitted. In the case of a parity error, 

the error message “Warn Interface” appears. 

Data bit (data width): 

The Process Unit 73 O 2 -2 transmits a data width 

of either 7 bits or 8 bits. The Process Unit 73 O 2 -2 

exclusively uses characters that can be transmitted 

in both the 7-bit and the 8-bit mode. The 

setting serves solely for adjustment to the controlling 

computer. 

9–34 Capabilities

The baud rate can be defined as 

300, 600, 1,200 or 9,600 baud, 

and the transmission formats as 

“7 Bit/Parity Even”, 

“7 Bit/Parity Odd” or 

“8 Bit/No Parity“ 

The interface is permanently set to 1 stop bit. 

To protect the instrument against unauthorized access 

also in interface mode, you can set a write 

protection. 

With write protection enabled, parameter or control 

commands can only be released after the write 

protection has been disabled via an interface command 

together with the administrator passcode 

(see page 12–28). Reading of measured values, 

parameters and status information is possible 

even with write protection enabled. 

After having sent the last control command, write 

protection can be reactivated by an interface command 

or by pressing the key. 

With write protection enabled, all attempts to write 

without previous disabling of write protection or by 

using a wrong passcode will be recorded in the 

logbook. 

As supplied, write protection is disabled. 

How to set the interface parameters 


level, resp.), select ”Interface” using , and confirm 

with . 

Select the type of bus connection, baud rate and 

number of data/parity bits, and enabled or disabled 

write protection using and respectively, 


Tips for Application 

If you connect the Process Unit 73 O 2 -2 to the RS 

232 interface of a PC or compatible via an 

RS 232 C/RS 485 interface adapter, you must observe 

the following: 

The connection lead between Process Unit 73 

O 2 -2 and PC is bidirectional. Therefore the converter 

must know the direction of transmission. If 

no data are sent, the converter must disable its 

transmission driver. With commercial converters, 

this changeover is usually done via a handshake 

line (e.g. DTR or RTS). 

Capabilities 9–35


The changeover must be controlled by the driver 

program of the PC. Commercial PC terminal programs 

do not automatically perform this changeover. 

Some converters (e.g. W&T Type 86000) can operate 

in ”Automatic Mode”. Here, the driver will be 

automatically disabled after a short period. However, 

this can cause bus timing errors if the automatic 

turn-off time does not correspond to the 

baud rate used. The W&T converter has automatic 

turn-off times for the baud rate 115200 bauds. 

According to our experience, operating the Process 

Unit 73 O 2 -2 in this case at the highest possible 

baud rate (9600 Baud) will offer the best results. 


The Process Unit 73 O 2 -2 can perform an automatic 

self test at regular intervals (memory test). 

In the case of memory errors the instrument sends 

a warning message. Self test is only executed 

when the instrument is in measurement mode. 

During the test, measurement continues in the 

background. All outputs remain in use. 

How to set the device diagnostics parameters 

Open the Parameter Setting menu, select menu 

item ”Device Diagnostics” using and confirm 

with . 

Press or and to enable or disable 

automatic device diagnostics. 

Enter the interval time using scrolling and cursor 

keys. Confirm your entry with . 

9–36 Capabilities

10 Information on Mounting, Installation and Maintenance 

Mounting 

 

The weatherproof enclosure allows direct wall 

mounting. For dimension drawing, see Fig. 

10–1. 

With ZU 0126 mounting plate and ZU 0125 

bracket kit, the instrument can also be post or 

pipe mounted. For dimension drawing, see Fig. 

10–2. 

 

ZU 0123 protective hood provides additional 

protection against direct weather exposure and 

mechanical damage. For dimension drawing, 

see Fig. 10–2. 

For mounting the protective hood, you require 

ZU 0126 mounting plate. 

 

ZU 0124 protective case provides optimum 

protection against dust, moisture and mechanical 

damage. For dimension drawing, see Fig. 

10–3. 

With ZU 0128 bracket kit, the protective case 

can also be post or pipe mounted. 

Installation 10–1


14,2 [0.56 

304 [11.97] 

293 [11.54] 

5 [0.2] 

87 [3.43] 

223 [8.78] 

124,5 [4.9] 

6,3 

[0.25] 

control panel 

138 [5.43] 

rating plate 

terminal 

compartment 

unit symbol 

26 [1.02] 

Pg 13,5 (10 pces) 

281 [11.06] 

72 [2.84] 

Note: All dimensions in millimeters [inches] 

Fig. 10–1 Dimension Drawing Model 73 O 2 -2 

309 [12.17] 

245 [9.65] 

holes for wall mounting 

85 [3.35] 139 [5.47] 

∅32...65 [1.26-2.56] 

245 [9.65] 

123 [4.84] 

54 [2.13] 

60 [2.36] 

7 [0.28] 

175 [6.89] 36 [1.42] 

for vertical or horizontal 

posts or pipes 

ZU 0125 bracket 

ZU 0126 mounting plate 

ZU 0123 protective hood 

Note: All dimensions in millimetres [inches]. 

Fig. 10–2 

Dimension Drawing ZU 0126 Mounting Plate and ZU 0123 Protective Hood 

10–2 Installation

front removable for 

instrument installation 

85,5 [3.37] 18 [0.71] 

175 [6.89] 

352 [13.86] 

polycarbonate 

protective panel 

transparent 

372 [14.65] 

∅ 5 [0.2] 

19 [0.75] 

302 [11.89] 

282 [11.1] 

Pg 13,5 

Note: All dimensions in millimetres [inches]. 

Fig. 10–3 

Dimension Drawing ZU 0124 Protective Case 

Installation 10–3


90 [3.55] 175 [6.9] 

∅ 32 ... 65 

[1.26-2.56] 

240 [9.42] 

31 [1.22] 

ZU 0124 protective case 

Note: All dimensions in millimeters [inches] 

for vertical or horizontal 

posts or pipes 

Fig. 10–4 

ZU 0128 Bracket Kit for ZU 0124 Protective Case 

82 [3.2] 

70 [2.73] 

Pg 13.5 

Ø 4,2 

[0.16] 

50 [1.95] 

80 [3.12] 

20 [0.78] 

55 [2.15] 

approx. 137 [5.34] 

Fig. 10–5 

ZU 0307 Terminal Box 

10–4 Installation

Installation 



accordance this instruction manual and per applicable 

local and national codes. Make sure that the 

technical specifications and input ratings are observed. 



with this instruction manual and per applicable 

local and national codes. 


procedure must be performed (see chapter 9). 

Before connecting power supply, make sure that 

your mains supply corresponds to the ratings on 

the instrument’s rating plate: 

 

230 Vac 

115 Vac (option 363) 

24 Vac/dc (option 298) 

To connect the Model 73 O 2 -2, open the cover of 

the terminal compartment (lower part of the instrument) 

by removing the three screws. 

Refer to Fig. 10–6 for terminal assignments. 

The terminals are suitable for solid wires and 

stranded wires up to 2.5 mm 2 . 

At the left side of terminal 1 there are two clamping 

screws for connecting the sensor cable shield. 

These clamping screws are electrically connected 

to terminal 5! 

As delivered, all terminals are open in order to allow 

easy insertion of the connecting wires. 

If the terminals are only half open, it may occur 

that the wire is pushed below the contacting element 

and thus does not contact when the terminal 

is closed. 

Should your Process Unit be supplied with a German 

assignment label, simply pull it out and turn it 

over to read the English text. 

Installation 10–5


Terminal Assignments 

0 electrode shield 

Jumper if required 

Jumper if required 

1 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 

18 19 20 21 22 23 24 25 

26 27 

28 29 

– 

+ 

– 

+ 

– 

+ 

cathode 

guard 

Pt/NTC 

sense line 

input 

0/4 - 20 mA 

output 1 

0/4 - 20 mA 

output 2 

0/4 - 20 mA 

shield 

(A) 

(B) 

– 

+ 

reference 

electrode 

anode 

 

power output 

24V / 30 mA 

functional 

check 

warning 

(mainten. 

required) 

failure 

limit 1 

limit 2 

– or + RS 485 250 V ac/dc to ground 

grounding possible 

30 31 32 33 34 35 36 

rinsing 

cleaning 

probe 

n.c. 

power supply 

ac/dc ac/dc 

230 V 

115 V 

24 V 

ac 

ac 

ac/dc 

50 mA T 

100 mA T 

500 mA T 

For fuse replacement 

remove this label 

Fig. 10–6 Terminal Assignments Model 73 O 2 -2 

10–6 Installation

Connection of Available Sensors 

SE 704, SE 705 Sensors 

Terminal Connection Color 

0 electrode shield yellow/green 

1 cathode white 

3 guard 

4 ref. electrode 

5 anode red 

6 NTC/Pt 100/Pt 1000 black 

7 NTC/Pt 100/Pt 1000 black 

8 sense line 

Jumpers 4–5 and 7–8 

To extend the connection from sensor and temperature 

probe to Process Unit 73 O 2 -2, you can use 

ZU 0307 terminal box and ZU 0075 cable. 

Connect the outer cable shield to terminal 0 (see 

Fig. 10–6). Terminal 0 may only be grounded 

when measuring in ground-free media. 

After connection of the oxygen sensor it must be 

polarized for at least 6 hours before first measurement. 

Connection of amperometric sensors 

2-electrode sensors 

Terminal Connection 

Electrode screen 

1 Cathode (working electrode) 

5 Anode (counter-electrode) 

Jumper 4–5 

3-electrode sensors 




4 Reference electrode 


If the sensor contains a protective cathode, this 

cathode is connected to terminal 3 (guard). 

The Pt 100/Pt 1000 temperature probe (internal or 

external) is connected to terminal 6 and 7. In the 

case of a 2-wire connection, the terminals 7 and 8 

are jumpered. For a 3-wire connection, the probe 

wire is connected to terminal 8. 

Installation 10–7


Connection of galvanic sensors 





Jumper 4–5 

To ensure proper operation, do not equip galvanic 

sensors with an internal working resistor. 

The Pt 100/Pt 1000 temperature probe (internal or 

external) is connected to terminal 6 and 7. In the 

case of a 2-wire connection, the terminals 7 and 8 

are jumpered. For a 3-wire connection, the probe 

wire is connected to terminal 8. 

Maintenance and Cleaning 

The Process Unit 73 O 2 -2 is maintenance free. 

To remove dust, dirt and stains, the outer surfaces 

of the instrument may be wiped using a soft, lintfree 

cloth moistened with water. If required, you 

may also use a mild detergent or 2-propanol (isopropyl 

alcohol). 

10–8 Installation

11 Error Messages 

Alphabetical Order 

Error Message 

(Display in Diagnostics Menu 

“Message List”) 

Fail CRC Error par 

Fail Current1 Load 

Fail Current2 Load 

Fail Hi Cal Time 

Fail Hi Conc Value 

Fail Hi Current Inp 

Fail Hi Impedance 

Fail Hi Part. Press. 

Fail Hi Press. Signal 

Fail Hi Saturation 

Fail Hi Slope 

Fail Hi Temp 

Fail Hi Zero 

Fail Input Range 

Fail Lo Conc Value 

Fail Lo Current Inp 

Fail Lo Impedance 

Fail Lo Part. Press. 

Fail Lo Press. Signal 

Fail Lo Saturation 

Fail Lo Slope 

Fail Lo Temp 

Fail Lo Zero 

Possible Error Causes and Remedies 

CRC data error during parameter setting: Check complete settings 

on the Administrator level! 

Current output 1: Load too high or circuit interrupted 

Current output 2: Load too high or circuit interrupted 

Cal timer above failure limit 

Concentration > 90 mg/l (ppm) or above failure limit 

Input current above failure limit 

Impedance above failure limit 

Partial pressure > 2000 mbar or above failure limit 

Air pressure > 110 mbar, 

with man / I–Inp setting: pressure > 9999 mbar 

or above failure limit 

Saturation > 600 %AIR or above failure limit 

Sensor slope > –2 mV/mbar or above failure limit 

Temperature > 80 C or above failure limit 

Sensor zero point > +10 mV or above failure limit 

Input current not corresponding to selected measurement range 

(see page 9–9) or input current too high 

Concentration below failure limit 

Input current below failure limit 

Impedance below failure limit 

Partial pressure < 0 mbar or below failure limit 

Air pressure < 700 mbar, 

with man / I–Inp setting: pressure < 0 mbar 

or below failure limit 

Saturation < 0 %AIR or below failure limit 

Sensor slope < –25 mV/mbar or below failure limit 

Temperature < –10 C or below failure limit 

Sensor zero point < –10 mV or below failure limit 

Error Messages 11–1


Error Message 



Fail Rinsing Cycle 

Fail Sensocheck 

Fail System Failure 

Warn Application I–Inp 

Warn Cal Temp 

Warn Current1 Span 

Warn Current1 20 mA 

Warn Current2 Span 

Warn Current2 20 mA 

Warn Hi Cal Time 

Warn Hi Conc Value 

Warn Hi Current Inp 

Warn Device Diagnostics 

Warn Hi Impedance 

Warn Hi Part. Press. 

Warn Hi Press. Signal 

Warn Hi Saturation 

Warn Hi Slope 

Warn Hi Zero 

Warn Hi Temp 

Warn Identical Media 

Warn Interface 

Warn Lo Conc Value 

Warn Lo Current Inp 

Warn Lo Impedance 

Warn Lo mV Value 

Warn Lo Part. Press. 


Rinsing cycle interrupted; must be restarted 

Sensocheck message active for more than 24 h 

Clock failure or CRC error in factory settings memory: 

Have Process Unit checked by manufacturer! 

Current input has been assigned for control of probe rinsing 

and as pressure measuring input 

Calibration temperature < –5 C or > +55 C 

Current output 1: Initial and end value too close 

Current output 1: Output current below defined initial value 

Current output 1: Output current above defined end value 

Current output 2: Initial and end value too close 

Current output 2: Output current below defined initial value 

Current output 2: Output current above defined end value 

Cal timer above warning limit 

Concentration above warning limit 

Input current above warning limit 

Error during automatic device diagnostics 

Impedance above warning limit 

Partial pressure above warning limit 

Air pressure above warning limit 

Saturation above warning limit 

Sensor slope above warning limit 

Sensor zero point above warning limit 

Temperature above warning limit 

Calibration with identical media 

Interface error: Parity or framing error 

Concentration below warning limit 

Input current below warning limit 

Impedance below warning limit 

Measured mV value below warning limit 

Partial pressure below warning limit 

11–2 Error Messages

Error Message 



Warn Lo Press. Signal 

Warn Lo Saturation 

Warn Lo Slope 

Warn Lo Temp 

Warn Lo Zero 

Warn Media Interchged 

Warn Range Pol Voltage 


Air pressure below warning limit 

Saturation below warning limit 

Sensor slope below warning limit 

Temperature below warning limit 

Sensor zero point below warning limit 

Sequence of media interchanged during calibration 

Entered polarization voltage < –1500 mV or > +0000 mV (see 

page 9–8) 

Warn RS485 Bus Address Interface error: Invalid device address entered (0 or >31) 

Warn RS485 Parameter 

Warn RS485 Overflow 

Warn RS485 Syntax 

Warn Sensocheck 

Warn Sensor Unstable 

Warn Temp O 2 –Conc/Sat 

Warn Time/Date 

Warn Write Protection 

Interface error: Command parameter error 

Interface error: Buffer overflow, too many characters received 

without message terminator 

Interface error: Command syntax error or 

command not available 

Sensocheck message active 

No stable end value for calibration after 2 min 

Temperature not within stored chart for water vapor pressure 

(see page 16–1) 

Clock had to be automatically initialized: Time must be set 

again! 

Interface error: Attempt to write without previous disabling of 

write protection 



According to Interface Error Code 

Error 

Code 

Error Message 




017 Fail Hi Zero Sensor zero point > +10 mV or above failure limit 

018 Warn Hi Zero Sensor zero point above warning limit 

019 Warn Lo Zero Sensor zero point below warning limit 

020 Fail Lo Zero Sensor zero point < –10 mV or below failure limit 

021 Fail Hi Slope Sensor slope > –2 mV/mbar or above failure limit 

022 Warn Hi Slope Sensor slope above warning limit 

023 Warn Lo Slope Sensor slope below failure limit 

024 Fail Lo Slope Sensor slope < –25 mV/mbar or below failure limit 

038 Warn Identical Media Calibration with identical media 

039 Warn Media Interchged Sequence of media interchanged during calibration 

054 Fail Hi Conc Value Concentration > 90 mg/l (ppm) or above failure limit 

055 Warn Hi Conc Value Concentration above warning limit 

056 Warn Lo Conc Value Concentration below warning limit 

057 Fail Lo Conc Value Concentration below failure limit 

080 Fail Hi Temp Temperature > 80 C or above failure limit 

081 Warn Hi Temp Temperature above warning limit 

082 Warn Lo Temp Temperature below warning limit 

083 Fail Lo Temp Temperature < –10 C or below failure limit 

084 Fail Hi Current Inp Input current above failure limit 

085 Warn Hi Current Inp Input current above warning limit 

086 Warn Lo Current Inp Input current below warning limit 

087 Fail Lo Current Inp Input current below failure limit 

088 Fail Hi Cal Time Cal timer above failure limit 

089 Warn Hi Cal Time Cal timer above warning limit 

092 Warn RS485 Overflow Interface error: Buffer overflow, too many characters received 

without message terminator 

093 Warn Interface Interface error: Parity or framing error 

094 Warn RS485 Syntax Interface error: Command syntax error or command not 

available 


Error 

Code 

Error Message 




095 Warn RS485 Parameter Interface error: Command parameter error 

096 Warn RS485 Bus Address Interface error: Invalid device address entered (0 or > 31) 

097 Warn Current1 Span Current output 1: Initial and end value too close 

098 Warn Current1 20 mA Current output 1: Output current above defined end value 

100 Fail Current1 Load Current output 1: Load too high or circuit interrupted 

101 Warn Current2 Span Current output 2: Initial and end value too close 

102 Warn Current2 20 mA Current output 2: Output current above defined end value 

104 Fail Current2 Load Current output 2: Load too high or circuit interrupted 

105 Warn Cal Temp Calibration temperature < –5 C or > +55 C 

106 Warn Sensor Unstable No stable end value for calibration after 10 min 

108 Warn Time/Date Clock had to be automatically initialized: Time must be set 

again! 

110 Fail CRC Error par CRC data error during parameter setting: Check complete 

settings on the Administrator level! 

115 Fail Rinsing Cycle Rinsing cycle interrupted; must be restarted 

116 Warn Write Protection Interface error: Attempt to write without previous disabling 

of write protection 

123 Warn Device Diagnostics Error during automatic device diagnostics 

130 Fail Hi Saturation Saturation > 600 %AIR or above failure limit 

131 Warn Hi Saturation Saturation above warning limit 

132 Warn Lo Saturation Saturation below warning limit 

133 Fail Lo Saturation Saturation < 0 %AIR or below failure limit 

134 Fail Hi Part. Press. Partial pressure > 2000 mbar or above failure limit 

135 Warn Hi Part. Press. Partial pressure above warning limit 

136 Warn Lo Part. Press. Partial pressure below warning limit 

137 Fail Lo Part. Press. Partial pressure < 0 mbar or below failure limit 

138 Fail Hi Press. Signal Air pressure > 1100 mbar 

with man / I–Inp setting: pressure > 9999 mbar 

or above failure limit 



Error 

Code 

Error Message 




139 Warn Hi Press. Signal Air pressure above warning limit 

140 Warn Lo Press. Signal Air pressure below warning limit 

141 Fail Lo Press. Signal Air pressure < 700 mbar, 

with man / I–Inp setting: pressure < 0 mbar 

or below failure limit 

143 Warn Sensocheck Sensocheck message active 

144 Warn Application I–Inp Current input has been assigned for control of probe rinsing 

and as pressure measuring input 

148 Fail Hi Impedance Impedance above failure limit 

149 Warn Hi Impedance Impedance above warning limit 

150 Warn Lo Impedance Impedance below warning limit 

151 Fail Lo Impedance Impedance below failure limit 

152 Fail Input Range Input current not corresponding to selected measurement 

range (see page 9–9) or input current too high 

153 Warn Temp O 2 –Conc/Sat Temperature not within stored chart for water vapor pressure 


154 Warn Range Pol Voltage Entered polarization voltage < –1500 mV or > +0000 mV 


255 Fail System Failure Clock failure or CRC error in factory settings memory: 

Have Process Unit checked by manufacturer! 


12 Interface Commands 

Contents 

Transmission behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–4 

Read/Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–4 

Parameter-setting strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–4 

Numerical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–5 

VALUE Commands: Query measured values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–5 

STATUS Commands: Query messages and states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–5 

Query sensor statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–7 

Query calibration record of last calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–7 

Logbook: Query entries (only with option 354) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–8 

Device Diagnostics: Query status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–8 

PARAMETER Commands: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–9 

Query settings and set parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–9 

Point of Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–9 

Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–10 

Manual Calibration – Entry of Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–10 

Calibration by Data Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–10 


Measurement Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–11 

Parameter Setting of Left Secondary Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–11 

Parameter Setting of Right Secondary Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–12 

Input Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–13 

Pressure Correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–13 

Sensor Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–14 

Temperature Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–14 

Salt Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–15 

Interface Commands 12–1


Temperature Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–15 

Saturation Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–16 

Partial Pressure Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–16 

Concentration Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–16 

Pressure Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–17 

Zero Point Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–17 

Slope Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–18 

Cal Timer Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–18 

Impedance Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–18 

Current Output 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–19 

Current Output 2 (only with Option 350) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–20 

Alarm Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–21 

NAMUR Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–21 

Limit Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–22 

Limit Contact 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–22 

Limit Contact 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–22 

Current Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–23 

Current Input Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–23 

Probe Rinsing (Option 352) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–24 

RS 485 Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–25 

Automatic Device Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–25 

DEVICE Commands: Device Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–25 

COMMAND Commands: Control Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–26 

First Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–26 

Automatic Calibration in Water or Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–26 

Manual Calibration – Entry of Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–26 


Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–27 

Measurement Point Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–27 

Probe Rinsing (Option 352) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–27 

Current Source Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–27 


Parameter Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–27 

RS 485 Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–28 

12–2 Interface Commands

Interface Point-to-Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–28 

Interface Bus Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–29 

Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–29 

Structure of a Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–29 

1st Field: Slave Address, Status Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–30 

2nd Field: Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–30 

3rd Field: ASCII Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–30 

4th Field: CRC16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–31 

Interface Bus Protocol of Slave (Model 73) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–32 

Interface Bus Protocol of Master . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–33 



Transmission behavior 

For fault-free data exchange between the connected 

computer and the Process Unit 73 O 2 -2 the 

parameter settings of both devices must match 

(also see pg. 9–35). 

Read/Write 

 

Read commands: 

Read commands (requests) always supply an 

answer. 

 

Write commands: 

For write commands, the answer depends on 

the parameter setting. 

The “WPMSR1” command switches on the 

check-back signal after write commands on. 

The check-back signal is output as an empty 

string (only message terminators). 

The check-back signal acknowledges the entire 

processing of the received command and the 

receiving buffer is released again. A checkback 

signal does not mean that the command 

has been transmitted fault-free! 

When the check-back signal is switched off, it is 

necessary to wait until the processing time of 

the Process Unit 73 O 2 -2 runs out. This may 

vary greatly. To prevent transmission errors, the 

waiting time should not drop below a minimum 

of one second. 

Parameter-setting strings 

The standard ASCII character set (numbers 0 ... 9, 

lower and upper-case letters, special characters 

such as +, –, ...) serve as transmission characters. 

Spaces (blanks) in the parameter-setting string 

are ignored. As a result, they can be used for formatting 

wherever desired. However, no spaces 

may be used in numerical parameters. 

Answers of the Process Unit 73 O 2 -2 contain only 

upper-case letters. 

Each parameter-setting string must be completed 

with a message terminator. A (carriage return), 

(line feed) or a combination of the two 

can be transmitted as message terminator. The 

Process Unit 73 O 2 -2 does not begin processing 

the received command until the message terminator 

has been received. 

Without message terminators the receiving buffer 

fills up. When the receiving buffer is full, the error 

message “Warn RS 485 overflow” appears. 


Numerical parameters 

Numerical parameters can be entered either with 

or without an exponent. Additional places to the 

right of the decimal point are ignored. Parameters 

can only be transmitted in their basic unit, e.g. 

“124 mV” is represented as “124E–3” in volts. 

The Process-Unit 73 O 2 -2 always selects the 

shortest possible form of representation, i.e. 

“87.0 % AIR” is transmitted as “87”. 

VALUE Commands: Query measured values 

With the value commands, all measured values of the Process Unit 73 O 2 -2 can be queried. Value 

commands are read commands. As a result, the device status of the Process Unit 73 O 2 -2 is not 

changed. 

Command 

RV2 

RV5 

Meaning 

Query measured C value (NTC) 

Query input current 

RVI1 Query output current 1 

RVI2 Query output current 2 (only with option 350) 

RVTRT 

RVDRT 

RV7A 

Query time ”hhmmss” 

Query date ”ddmmyy” (sequence depending on setting) 

Query saturation index %AIR 

RV7O Query saturation index %O 2 

RV4 

RVPO 

RVPA 

RVTCA 

RVIPO 

RVRS 

Query concentration [mg/l, g/l] 

Query oxygen partial pressure 

Query pressure 

Query cal timer count 

Query input current measuring input 

Query sensor impedance 

STATUS Commands: Query messages and states 

With the status commands, the device messages, such as the NAMUR messages Functional check, 

Warning (maintenance required) and Failure can be read out, device states monitored and the logs 

interrogated. With the status commands, data can be accessed which can be used for QM documentation 

to ISO 9000. Status commands are read commands. As a result, the device status of the Process 

Unit 73 O 2 -2 is not changed. 



Command Function Response Meaning 

RSF1 Query first failure message xxx 

RSFA Query all failure messages xxx;xxx ... 

RSW1 Query first warning message xxx 

RSWA Query all warning messages xxx;xxx ... 

RSP Query device status (”menu”) 00 measuring mode 

01 parameter setting opl, adm 

02 calibration cal 

08 maintenance maint 

10 measuring mode, probe rinsing 

running, started by timer 

11 parameter setting opl, adm & 

probe rinsing running, started 

by timer 

18 maintenance, probe rinsing 

running, started manually 

RSL Query limit messages 0 no limit message 

1 limit 1 enabled 

2 limit 2 enabled 

3 both limits enabled 

RSU 

Query device status (messages, 

limits, SRQS) 

1st bit 

”1” if one or more failure messages 

are active 

2nd bit 

”1” if one or more warning 

messages are active 

3rd bit 

”1” if functional check is active 

4th bit 

”1” if limit 1 and/or limit 2 are 

active 

5th bit 

”1” if outputs are frozen (e.g. 

during calibration) 

6th bit always ”1” 

7th bit 

”1” if there has been a status 

change since last query 

8th bit always ”0” 


Query sensor statistics 

Command Function Parameter 

RSSTTm Query time of calibration m = 0...3 

RSSTDm Query date of calibration m = 0...3 (format depending on setting) 

RSSTZ0 

RSSTS0 

Query sensor zero point 

Query sensor slope 

RSST2m Query calibration temperature m = 0...3 

RSSTPm Query calibration pressure m = 0...3 

RSSTTRm Query sensor response time m = 0...3 

RSSTZDm Query deviation of zero point m = 1...3 

RSSTSDm Query deviation of slope m = 1...3 

Query calibration record of last calibration 

Command 

RSCPT 

RSCPD 

RSCPH 

RSCPRS 

RSCP1IPO 

RSCP12 

RSCP1P 

RSCP1TR 

RSCP2IPO 

RSCP22 

RSCP2P 

RSCP2TR 

Function 

Query calibration time 

Query calibration date (format depending on setting) 

Query relative humidity (only for calibration in air) 

Query sensor impedance 

Query 1st sensor current 

Query 1st calibration temperature 

Query 1st calibration pressure 

Query 1st response time 

Query 2nd sensor current 

Query 2nd calibration temperature 

Query 2nd calibration pressure 

Query 2nd response time 


RSCPA Query calibration mode ”0” automatic in water 

”1” automatic in air 

”2” manual input of saturation 

”3” data entry 



Logbook: Query entries (only with option 354) 

For complete interrogation of the logbook, first use the “RSLOO” command to read the oldest entry. 

Then use the “RSLOOC” command until an empty string (message terminators only) is received as 

an answer. The empty string means that there are no more entries. 

If only new logbook entries are to be read which have not yet been read out via the interface, use the 

“RSLOOC” command immediately. 

Command 

RSLON 

RSLONC 

RSLOO 

RSLOOC 

Function 

Query latest entry 

Query previous entry (starts with entry previous to latest entry) 

Query first entry 

Query following entry (starts with entry following the first entry) 

Device Diagnostics: Query status 


RSTETR Query RAM test time hhmmss 

RSTEDR Query RAM test date ddmmyy* ) 

RSTERR Query RAM test result ”0” ok 

”2” failure 

RSTETP Query EPROM test time hhmmss 

RSTEDP Query EPROM test date ddmmyy* ) 

RSTERP Query EPROM test result ”0” ok 


RSTETE Query EEPROM test time hhmmss 

RSTEDE Query EEPROM test date ddmmyy* ) 

RSTERE Query EEPROM test result ”0” ok 


RSTETDI Query display test time hhmmss 

RSTEDDI Query display test date ddmmyy* ) 

RSTERDI Query display test result ”0” test executed 


RSTETKY Query keypad test time hhmmss 

RSTEDKY Query keypad test date ddmmyy* ) 

RSTERKY Query keypad test result ”0” ok 

*) format depending on setting 



PARAMETER Commands: 

Query settings and set parameters 

With the parameter commands, all functions of the Process Unit 73 O 2 -2 can be defined via the computer 

interface (with the exception of the interface transmission parameters). 

With the parameter commands, all instrument parameters can be read and written! 

Therefore, the correctness of the transmitted commands is particularly important. 

Transmission in the point-to-point mode is not secured with checksums. To avoid incorrect 

settings, it is therefore advisable to read back important parameters for a comparison. 

With the first write command, the controlling computer (PC, SPS, ...) assumes control 

of the Process Unit 73 O 2 -2. Security prompts must then be implemented in the computer! 

With the “WCOMIN0” command (go to local) the computer returns control to the 

Process Unit 73 O 2 -2. The Process Unit 73 O 2 -2 restarts in the measuring mode. 

Read commands cause no status changes and do not influence the system functions. 

The Process Unit 73 O 2 -2 continues to be in control. 

When the write protection is switched on, any write attempts without switching off the 

write protection beforehand or with an invalid passcode are entered in the logbook. 

As delivered, write protection is switched off. 

If parameter setting is called up with the device keypad, the NAMUR message Functional check is 

set. Warning and failure contacts are deactivated until parameter setting is completed. 

If device parameters are changed via the RS 485 interface, all messages are released. As a result, 

temporary messages may occur when changing parameters which would have been suppressed had 

the keypad been used. 

WCOM01 

WCOU1 

With the “WCOM01” interface command the device can be switched to the parameter 

setting mode. The NAMUR message Functional check is then set and with it the 

warning and failure contact also deactivated in the interface mode. 

Return to the measuring mode with “WCOM00”. 

If all device functions are to be frozen during parameter setting, use the “WCOU1” 

command. The functional check is set, and the warning and failure contact deactivated. 

The output current and controller are also frozen and the limit-contacts are inactive. 

Unfreeze the device functions with “WCOU0”. 

The command sequence corresponds to the description given in chapters 3, 4, 5 and 9. 

Point of Measurement 

RPUAM 

WPUAM0 

WPUAM1 

RPUAW 

Query marker 

Set marker ”Off” 

Set marker ”On” 

Query entered point of measurement 

WPUAWaaaaaaaaaaaaaaa Enter point of measurement (max. 15 characters) 

a = ASCII character: blank, ”0” ... ”9”, ”A ” ... ”Z”, ”–”, ”+”, ”/” 



Clock 

RPRTM 

WPRTM0 

WPRTM1 

RPRTDF 

WPRTDF0 

WPRTDF1 

WPRTDF2 

WPRTDF3 

Query marker 



Query date format 

Set date format ”D.M.Y“ 

Set date format ”D/M/Y“ 

Set date format ”M/D/Y“ 

Set date format ”Y–M–D“ 

For setting time/date: see page 12–27 

For query of time/date: see page 12–5 

Manual Calibration – Entry of Saturation 

RPCAB 

WPCABp 

Query settings of manual saturation setpoint 

Enter manual saturation setpoint p 

Calibration by Data Entry 

RPCA7Z 

WPCA7Zp 

RPCA7S 

WPCA7Sp 

RPCAH 

WPCAHp 

Query currently measured zero point 

Enter zero point p 

Query currently measured slope 

Enter slope p 

Query relative humidity (only for calibration in air) 

Enter relative humidity p (only for calibration in air) 


RPTFS 

WPTFS0 

WPTFS1 

Query temperature probe adjustment settings 

Disable temperature probe adjustment 

Enable temperature probe adjustment 

For input of adjustment value: see page 12–27 


Measurement Display 

RPDIMM 

WPDIMM0 

WPDIMM1 

RPDI4 

WPDI4G 

WPDI4P 

RPDIR4 

WPDIR4A 

WPDIR43 

WPDIR46 

RPDIMA 

WPDIMA2 

WPDIMA7A 

WPDIMA7O 

WPDIMA4 

WPDIMAPO 

WPDIMATRT 

RPDIMVA 

Query marker 



Query unit of concentration 

Set unit of concentration to ”mg/l, g/l“ 

Set unit of concentration to ”ppm, ppb“ 

Query defined concentration range 

Set concentration range to “auto” 

Set concentration range to “mg/l” or “ppm” 

Set concentration range to “g/l” or “ppb” 

Query process variable assigned 

Assign temperature value to measurement display 

Assign oxygen saturation (referred to air) to measurement display 

Assign oxygen saturation (referred to pure oxygen) to measurement display 

Assign concentration to measurement display 

Assign oxygen partial pressure to measurement display 

Assign time to measurement display 

Query viewing angle 

WPDIMVAn Adjust viewing angle (n = –2 ... 0 ... +2) 

Parameter Setting of Left Secondary Display 

RPDISLA 

WPDISLA2 

WPDISLA7A 

WPDISLA7O 

WPDISLA2 

WPDISLAPO 


Display temperature 

Display oxygen saturation (referred to air) 

Display oxygen saturation (referred to pure oxygen) 

Display concentration 

Display oxygen partial pressure 



WPDISLAPA 

WPDISLA5 

Display pressure 

Display input current 

WPDISLAI1 Display output current 1 

WPDISLAI2 Display output current 2 (only with option 350) 

WPDISLAiPO 

WPDISLATRT 

WPDISLADRT 

WPDISLATCA 

WPDISLARS 

WPDISLATM 

Display input current measuring input 

Display time 

Display date (format depending on setting) 

Display calibration timer interval 

Display sensor impedance 

Display manual temperature 

Parameter Setting of Right Secondary Display 

RPDISRA 

WPDISRA2 

WPDISRA7A 

WPDISRA7O 

WPDISRA2 

WPDISRAPO 

WPDISRAPA 

WPDISRA5 


Display temperature 

Display oxygen saturation (referred to air) 

Display oxygen saturation (referred to pure oxygen) 

Display concentration 

Display oxygen partial pressure 

Display pressure 

Display input current 

WPDISRAI1 Display output current 1 

WPDISRAI2 Display output current 2 (only with option 350) 

WPDISRAIPO 

WPDISRATRT 

WPDISRADRT 

WPDISRATCA 

WPDISRARS 

WPDISRATM 

Display input current at measuring input 

Display time 

Display date (format depending on setting) 

Display calibration timer interval 

Display sensor impedance 

Display manual temperature 


Input Filter 

RPIFM 

WPIFM0 

WPIFM1 

RPIF 

WPIF0 

WPIF1 

RPLF 

WPLF0 

WPLF1 

Query marker 



Query setting of pulse suppression 

Disable pulse suppression 

Enable pulse suppression 

Query setting of low-pass filter 

Disable low-pass filter 

Enable low-pass filter 

Pressure Correction 

RPPRMM 

WPPRMM0 

WPPRMM1 

RPPRMA 

WPPRMAA 

WPPRMAP 

WPPRMA5 

RPPRMPV 

WPPRMPVp 

RPPR5A 

WPPR5A0 

WPPR5A1 

RPPRCA 

WPPRCAA 

WPPRCAP 

WPPRCA5 

RPPRCPV 

WPPRCPVp 

Query marker 



Query pressure detection during measurement 

Set pressure detection ”air pressure” 

Set pressure detection ”manual” 

Set pressure detection ”current input” 

Pressure correction during measurement, query manual pressure correction 

Set manual pressure correction p 

Pressure detection during measurement, query current input 

Set current input for absolute-value sensor 

Set current input for differential-value sensor 

Query pressure detection during calibration 

Set pressure detection ”air pressure” 

Set pressure detection ”manual” 

Set pressure detection ”current input” 

Pressure correction during calibration, query manual pressure correction 

Set manual pressure correction p 



Sensor Data 

RPMDM 

WPMDM0 

WPMDM1 

RPMD1 

WPMD1p 

RPMDTF 

WPMDTFp 

RPMDIMR 

WPMDIMR0 

WPMDIMR1 

WPMDIMR2 

Query marker 



Query polarization voltage 

Set polarization voltage p 

Query TC factor 

Set TC factor p 

Query current range 

Set current range ”auto“ 

Set current range ”250 nA“ 

Set current range ”5 A“ 

WPMDIMR3 Set current range ”250 A“ 

RPMDSCS Query Sensocheck ® 

WCSCR Reset Warn Sensocheck ® 

WPMDSCS0 

WPMDSCS1 

Set Sensocheck ® ”Off“ 

Set Sensocheck ® ”On” 

Temperature Detection 

RPTOT 

WPTOT0 

WPTOT1 

WPTOT2 

RPTOMA 

WPTOMA0 

WPTOMA1 

RPTMMV 

WPTMMVp 

RPTOCA 

WPTOCA0 

WPTOCA1 

RPTMCV 

WPTMCVp 

Query temperature probe 

Set NTC 22 k temperature probe 

Set Pt 1000 temperature probe 

Set Pt 100 temperature probe 

Query measuring temperature 

Set measuring temperature ”manual“ 

Set measuring temperature ”auto“ 

Query manual measuring temperature 

Set manual measuring temperature p 

Query calibration temperature 

Set calibration temperature ”manual“ 

Set calibration temperature ”auto“ 

Query manual calibration temperature 

Set manual calibration temperature p 


Salt Content 

RPSAM 

WPSAM0 

WPSAM1 

RPSAA 

WPSAA0 

WPSAA1 

WPSAA2 

RPSA0V 

WPSA0Vp 

RPSA1V 

WPSA1Vp 

RPSA2CV 

WPSA2CVp 

RPSA2TV 

WPSA2TVp 

Query marker 

Set marker ”Off 


Query input mode 

Set input mode ”Salinity” 

Set input mode ”Chlorinity” 

Set input mode ”Conductivity” 

Query salinity 

Set salinity p 

Query chlorinity 

Set chlorinity p 

Query conductivity 

Set conductivity value p 

For conductivity: query temperature 

Set temperature p 

Temperature Alarm 

RPALF2S 

WPALF2S0 

WPALF2S1 

RPALF2FL 

WPALF2FLp 

RPALF2WL 

WPALF2WLp 

RPALF2WH 

WPALF2WHp 

RPALF2FH 

WPALF2FHp 

Query settings 

Disable alarm 

Enable alarm 

Query failure limit Lo 

Set failure limit Lo p 

Query warning limit Lo 

Set warning limit Lo p 

Query warning limit Hi 

Set warning limit Hi p 

Query failure limit Hi 

Set failure limit Hi p 



Saturation Alarm 

RPALF7AS 

WPALF7AS0 

WPALF7AS1 

RPALF7AFL 

WPALF7AFLp 

RPALF7AWL 

WPALF7AWLp 

RPALF7AWH 

WPALF7AWHp 

RPALF7AFH 

WPALF7AFHp 


Disable alarm 

Enable alarm 









Partial Pressure Alarm 

RPALFPOS 

WPALFPOS0 

WPALFPOS1 

RPALFPOFL 

WPALFPOFLp 

RPALFPOWL 

WPALFPOWLp 

RPALFPOWH 

WPALFPOWHp 

RPALFPOFH 

WPALFPOFHp 


Disable alarm 

Enable alarm 









Concentration Alarm 

RPALF4S 

WPALF4S0 

WPALF4S1 

RPALF4FL 

WPALF4FLp 

RPALF4WL 

WPALF4WLp 


Disable alarm 

Enable alarm 


Set failure limit Lo p (in g/l) 


Set warning limit Lo p (in g/l) 


RPALF4WH 

WPALF4WHp 

RPALF4FH 

WPALF4FHp 


Set warning limit Hi p (in g/l) 


Set failure limit Hi p (in g/l) 

Pressure Alarm 

RPALFPAS 

WPALFPAS0 

WPALFPAS1 

RPALFPAFL 

WPALFPAFLp 

RPALFPAWL 

WPALFPAWLp 

RPALFPAWH 

WPALFPAWHp 

RPALFPAFH 

WPALFPAFHp 


Disable alarm 

Enable alarm 









Zero Point Alarm 

RPALFZS 

WPALFZS0 

WPALFZS1 

RPALFZFL 

WPALFZFLp 

RPALFZWL 

WPALFZWLp 

RPALFZWH 

WPALFZWHp 

RPALFZFH 

WPALFZFHp 


Disable alarm 

Enable alarm 











Slope Alarm 

RPALFSS 

WPALFSS0 

WPALFSS1 

RPALFSFL 

WPALFSFLp 

RPALFSWL 

WPALFSWLp 

RPALFSWH 

WPALFSWHp 

RPALFSFH 

PALFSFHp 


Disable alarm 

Enable alarm 









Cal Timer Alarm 

RPALFTS 

WPALFTS0 

WPALFTS1 

RPALFTWH 

WPALFTWHp 

RPALFTFH 

WPALFTFHp 


Disable alarm 

Enable alarm 





Impedance Alarm 

RPALFRSS 

WPALFRSS0 

WPALFRSS1 

RPALFRSFL 

WPALFRSFLp 


Disable alarm 

Enable alarm 




RPALFRSWL 

WPALFRSWLp 

RPALFRSWH 

WPALFRSWHp 

RPALFRSFH 

WPALFRSFHp 







Current Output 1 

RPOC1M 

WPOC1M0 

WPOC1M1 

RPOC1A 

WPOC1A2 

WPOC1A7A 

WPOC1A7O 

WPOC1A4 

WPOC1APO 

RPOC1Z 

WPOC1Z0 

WPOC1Z1 

RPOC1L 

WPOC1Lp 

RPOC1H 

WPOC1Hp 

RPOC1F 

WPOC1F0 

WPOC1F1 

RPOC1BX 

Query marker 




Assign measuring temperature as process variable 

Assign oxygen saturation (referred to air) as process variable 

Assign oxygen saturation (referred to pure oxygen) as process variable 

Assign concentration as process variable 

Assign partial pressure as process variable 

Query operating mode 0 – 20mA / 4 – 20mA 

Set operating mode 0 – 20mA 


Query initial value 

Set initial value p 

Query end value 

Set end value p 

Query curve settings 

Set curve linear 

Set curve trilinear 

Curve trilinear: query settings 1st corner point X 



WPOC1BXp 

RPOC1BY 

WPOC1BYp 

RPOC1EX 

WPOC1EXp 

RPOC1EY 

WPOC1EYp 

WPOC1F2 

RPOC1PX 

WPOC1PXp 

Curve trilinear: set 1st corner point X p 

Curve trilinear: query settings 1st corner point Y 

Curve trilinear: set 1st corner point Y p 

Curve trilinear: query settings 2nd corner point X 

Curve trilinear: set 2nd corner point X p 

Curve trilinear: query settings 2nd corner point Y 

Curve trilinear: set 2nd corner point Y p 

Set curve ”Function” 

Curve ”Function”: query settings 50% point 

Curve ”Function”: set 50% point p 

Current Output 2 (only with Option 350) 

RPOC2M 

WPOC2M0 

WPOC2M1 

RPOC2A 

WPOC2A2 

WPOC2A7A 

WPOC2A7O 

WPOC2A4 

WPOC2APO 

RPOC2Z 

WPOC2Z0 

WPOC2Z1 

RPOC2L 

WPOC2Lp 

RPOC2H 

WPOC2Hp 

Query marker 


Set Marker ”Off” 


Assign measuring temperature as process variable 

Assign oxygen saturation (referred to air) as process variable 

Assign oxygen saturation (referred to pure oxygen) as process variable 

Assign concentration as process variable 

Assign partial pressure as process variable 




Query initial value 

Set initial value p 

Query end value 

Set end value p 


RPOC2F 

WPOC2F0 

WPOC2F1 

RPOC2BX 

WPOC2BXp 

RPOC2BY 

WPOC2BYp 

RPOC2EX 

WPOC2EXp 

RPOC2EY 

WPOC2EYp 

WPOC2F2 

RPOC2PX 

WPOC2PXp 

Query curve settings 

Set curve linear 

Set curve trilinear 

Curve trilinear: query settings 1st corner point X 

Curve trilinear: set 1st corner point X p 

Curve trilinear: query settings 1st corner point Y 

Curve trilinear: set 1st corner point Y p 

Curve trilinear: query settings 2nd corner point X 

Curve trilinear: set 2nd corner point X p 

Curve trilinear: query settings 2nd corner point Y 

Curve trilinear: set 2nd corner point Y p 

Set curve ”Function” 

Curve ”Function”: query settings 50% point 

Curve ”Function”: set 50% point p 

Alarm Settings 

RPALM 

WPALM0 

WPALM1 

Query marker 



NAMUR Contacts 

RPCNM 

WPCNM0 

WPCNM1 

RPCNUO 

WPCNUO0 

WPCNUO1 

RPCNUOTF 

WPCNUOTFp 

RPCNUOTW 

WPCNUOTWp 

Query marker settings 



Query normally open/normally closed contacts 

Set normally closed contacts 

Set normally open contacts 

Query failure delay 

Set failure delay p 

Query warning delay 

Set warning delay p 



Limit Contacts 

RPCIM 

WPCIM0 

WPCIM1 

Query marker 



Limit Contact 1 

RPLI1A Query process variable assigned to limit 1 

WPLI1A2 Assign measuring temperature as process variable for limit 1 

WPLI1A7A Assign oxygen saturation (referred to air) as process variable for limit 1 

WPLI1A7O Assign oxygen saturation (referred to pure oxygen) as process variable for limit 1 

WPLI1A4 Assign concentration as process variable for limit 1 

WPLI1APO Assign partial pressure as process variable for limit 1 

WPLI1A5 Assign input current as process variable for limit 1 

RPLI1D Query effective direction limit 1 

WPLI1D0 Set effective direction Min for limit 1 

WPLI1D1 Set effective direction Max for limit 1 

RPLI1V Query limit 1 

WPLI1Vp 

RPLI1H 

WPLI1Hp 

Set limit 1 p 

Query limit 1 hysteresis (deadband) 

Set hysteresis (deadband) limit 1 p 

RPLI1CN Query limit contact 1 

WPLI1CN0 

WPLI1CN1 

Set limit contact 1 as normally closed 

Set limit contact 1 as normally open 

Limit Contact 2 

RPLI2A Query process variable assigned to limit 2 

WPLI2A2 Assign measuring temperature as process variable for limit 2 

WPLI2A7A Assign oxygen saturation (referred to air) as process variable for limit 2 

WPLI2A7O Assign oxygen saturation (referred to pure oxygen) as process variable for limit 2 

WPLI2A4 Assign concentration as process variable for limit 2 

WPLI2APO Assign partial pressure as process variable for limit 2 

WPLI2A5 Assign input current as process variable for limit 2 


RPLI2D Query effective direction limit 2 

WPLI2D0 Set effective direction Min for limit 2 

WPLI2D1 Set effective direction Max for limit 2 

RPLI2V Query limit 2 

WPLI2Vp Set limit 2 p 

RPLI2H Query limit 2 hysteresis (deadband) 

WPLI2Hp Set hysteresis (deadband) limit 2 p 

RPLI2CN Query setting of limit contact 2 

WPLI2CN0 Set limit contact 2 as normally closed 

WPLI2CN1 Set limit contact 2 as normally open 

Current Input 

RPICM 

WPICM0 

WPICM1 

RPICZ 

WPICZ0 

WPICZ1 

RPICA 

WPICA0 

WPICA1 

RPICL 

WPICLp 

RPICH 

WPICHp 

Query marker 




Set operating mode 0 – 20 mA 

Set operating mode 4 – 20 mA 

Query application (only for option 352 probe rinsing) 

Application as signal input (only for option 352 probe rinsing) 

Application as control input for probe rinsing 

(only for option 352 probe rinsing) 

Query pressure value for 0/4 mA 

Set initial pressure value p for 0/4 mA 

Query pressure value for 20 mA 

Set end pressure value p for 20 mA 

Current Input Alarm 

Not available with probe rinsing enabled! 

RPALF5S 

WPALF5S0 

WPALF5S1 

RPALF5FL 

WPALF5FLp 


Disable alarm 

Enable alarm 





RPALF5WL 

WPALF5WLp 

RPALF5WH 

WPALF5WHp 

RPALF5FH 

WPALF5FHp 







Probe Rinsing (Option 352) 

RPUCM 

WPUCM0 

WPUCM1 

RPUCCN 

WPUCCN0 

WPUCCN1 

RPUCS 

WPUCS0 

WPUCS1 

RPUCTI 

WPUCTIp 

RPUCT01 

WPUCT01p 

RPUCT02 

WPUCT02p 

RPUCT03 

WPUCT03p 

RPUCT04 

WPUCT04p 

RPUCT05 

WPUCT05p 

Query marker 



Query probe contact 

Set probe contact as normally closed 

Set probe contact as normally open 

Query probe rinsing 

Disable probe rinsing 

Enable probe rinsing 

Query interval 

Set interval p [h] 

Query rinsing lead time 

Set rinsing lead time p [s] 

Query first rinsing time 

Set first rinsing time p [s] 

Query cleaning time 

Set cleaning time p [s] 

Query second rinsing time 

Set second rinsing time p [s] 

Query measurement lead time 

Set measurement lead time p [s] 


RS 485 Interface 

RPINM 

WPINM0 

WPINM1 

RPMSR 

WPMSR0 

Query marker setting 



Query ready message 

Set: no return after write command 

WPMSR1 Set: Send return after write command: the Model 73 O 2 

sends a message terminator after executing the command 

(not with bus operation, only with point-to-point operation) 

RPINWP 

WPINWP0 

WPINWP1 

Query write protection 

Set write protection ”Off” 

Set write protection ”On” 

Automatic Device Diagnostics 

RPTEM 

WPTEM0 

WPTEM1 

RPTES 

WPTES0 

WPTES1 

RPTETI 

WPTETIp 

Query marker 



Query self test 

Disable self test 

Enable self test 

Query interval time 

Set interval time p (h) 

DEVICE Commands: Device Description 

RDMF 

RDUN 

RDUS 

RDUV 

RDUP 

Query manufacturer 

Query device type 

Query serial number 

Query software/hardware version: 

“70;01” means ”software version 7.0, hardware version 1” 

Query option numbers 



COMMAND Commands: Control Commands 

The Process Unit 73 O 2 -2 can be controlled with the ”command” commands. ”Command” commands 

are write commands which call up functions or change device states. 

With the first write command, the controlling computer (PC, SPS, ...) assumes control 

of the Process Unit 73 O 2 -2. Many security prompts must then be implemented in the 

computer! With the “WCOMIN0” command (go to local) the computer returns control 

to the Process Unit 73 O 2 -2. The Process Unit 73 O 2 -2 restarts in the measuring 

mode. 

When the write protection is switched on, any write attempts without switching off the 

write protection beforehand or with an invalid passcode are entered in the logbook. 

As delivered, write protection is switched off. 

The command sequence corresponds to the description given in chapters 3, 4, 5, 8 and 9. 

First Calibration 

WCCASTI 

Store present data set as First Calibration 

Automatic Calibration in Water or Air 

WCOU1 

WCCAAW1 

WCCAAW2 

WCCAAA1 

WCCAAA2 

WCOU0 

Freeze output currents, disable limit values 

Calibration in water, 100 % medium 

Calibration in water, 0 % medium 

Calibration in air, 100 % medium 

Calibration in air, 0 % medium 

Enable output currents and limit values 

Manual Calibration – Entry of Saturation 

WCOU1 

WCCAM1 

WCOU0 

Freeze output currents, disable limit values 

Start manual calibration (First, write setpoint using WPCABp) 

Enable output currents and limit values 


WCTEA 

Start device diagnostics (without display, keypad test) 


Clock 

WCRTThhmmss 

WCRTDddmmyy 

Set time hhmmss 

Set date ddmmyy (format depending on setting) 

Measurement Point Maintenance 

WCOM08MA 

Enable measurement point maintenance (output currents frozen, 

limit values disabled) 

Probe Rinsing (Option 352) 

WCUCR 

Start rinsing cycle 

Following commands only with measurement point maintenance enabled (WCOM08MA, RSP = 08): 

WCUCCNR0 

WCUCCNR1 

WCUCCNC0 

WCUCCNC1 

Open rinsing contact 

Close rinsing contact 

Open cleaning contact 

Close cleaning contact 

Current Source Function 

WCOM08CS 

WCCSI1p 

Enable current source function 

Set output current 1 to value p 

WCCSI2p Set output current 2 to value p (only with option 350) 


WCTFVp 

Temperature probe adjustment: set process temperature p 

Parameter Setting 

WCOM01 

WCPZM0 

WCPZM1 

WCOM00 

Activate Parameter Setting menu (functional check active) 

Erase all markers 

Set all markers 

Return to measuring mode 



RS 485 Interface 

WCOMIN0 

WCDIW0aaaa... 

WCINPWpppp 

WCINPD 

Goto local, enable complete keypad 

Activate write protection if enabled 

Write free text as display message: max. 40 characters, 

Can only be written on bottom display line during functions such as 

current source, maintenance, etc! 

a = ASCII character: blank, ”0” ... ”9”, ”A” ... ”Z”, ”–”, ”+”, ”/” 

Deactivate write protection, pppp = administrator passcode, 

required for writing parameters and control commands 

Activate write protection 

Interface Point-to-Point 

When you have selected “Point-to-Point” coupling, the data are transmitted as ASCII characters. A 

checksum (CRC) is not required. Please observe the changeover of the data flow direction on the 

RS 485 (see Pg. 9–35). 

Query 

PC → Process Unit: R V 2 (ASCII) 

52 56 32 OD (hexadecimal) 

Response 

Process Unit → PC: 2 5 • 3 (ASCII) 

32 35 2E 33 OD (hexadecimal) 


Interface Bus Protocol 

Applies only if you have selected BUS coupling! 

The protocol is based on a master/slave relationship. The participants addressed by the master (host 

computer) are called slave. They have to execute the communication sequence as prescribed by the 

controlling master. 

Each communication sequence between participants on the bus is basically determined by two sections, 

the command section and the response section: 

In the command section the master defines meaning and function of the currently transferred message. 

The command information is accepted by the slave and correspondingly evaluated. 

The response section shows the master if a bus transfer has been properly executed. It can also contain 

data, if required. 

Data Format 

Hardware: RS485 2-wire. 

The data format is permanently set to 9600 bauds, 8 data bits, no parity. 

Each slave has a bus address that may be in the range 01...31. 

Each slave on a bus system must have a unique address. 

The address 00 is a broadcast address (message for ALL). 

Structure of a Message 

1 Byte 1 Byte n Bytes 2 Bytes 

slave address 

status flags 

length: 

n + 2 

ASCII message, 

as with point-to-point connection, 

but without message terminator 

CRC16 

according to 

CCITT–X.25 



1st Field: Slave Address, Status Flags 

7 6 5 4 3 2 1 0 

”1” master / 

slave 

error 

slave address 01...31, 00 = broadcast 

Bit 7: ”1” This bit must be set to logical One. 

Bit 6: Master / Slave: ”1” means that the message was sent from master to slave. 

The slave address indicates the data sink. 

”0” means that the message is a response from slave to master. 

Here, the slave address indicates the data source. 

Bit 5: Error During transmission master→slave always ”1”. 

During response slave→master erased if an error has occurred. 

(e.g. syntax error; not for CRC error since in that case there won’t be a 

response). 

Slave address 00 has a special function: 

00 addresses all slaves. No slave may send a response. Therefore, the master does not know if the 

message was completely understood by all participants. Nevertheless, this function can be useful for 

synchronizing all participants (e.g. to set clock). Afterwards, each participant can be individually 

checked if it has successfully received the respective message. 

2nd Field: Length 

7 6 5 4 3 2 1 0 

”0” more length of message field and CRC16 

The length field indicates the remaining message length, i.e. length of message block and CRC (message 

+ 2 bytes). In the case of correct reception, exact length bytes must follow after having read the 

length. 

Up to 63 bytes can be transmitted in each block (61 data bytes + 2 bytes CRC). Longer transmission 

strings must be divided into blocks. 

The ”more” bit is set if another complete data block follows. In a block sequence, the ”more” bit of the 

last block is erased. If the ”more” bit is erased (normal case), the message is complete with this 

block. 

3rd Field: ASCII Message 

This message field contains the command to the Process Unit 73 O 2 . The message has the same 

structure as the string of the point-to-point connection (e.g. RV2). The message terminator is omitted. 

The message is immediately followed by CRC16. 

All characters in this field must have bit 7 erased (as 7 data bits, space parity). 


4th Field: CRC16 

CRC16 (16-bit Cyclic Redundancy Check) is calculated according to CCITT–X.25. 

Check polynominal according to CCITT–X.25 = x 16 + x 12 + x 5 + 1 

CRC is the check sum of all transmitted bytes. CRC is transmitted as 2 binary bytes. First, the more 

significant bit and then the less significant bit is transmitted. The structure of the transmitted CRC16 

is such that it always supplements the total CRC to 0000 hex . The completely received string is only 

valid and must be interpreted if CRC = 0000 hex . If not, the complete message must be ignored. 

CRC16 has a Hamming distance of 4 and is used in the bus protocols HDLC, SDLC and ADCP, 

among others. 

Procedure for Generating a CRC: 

To supplement the string to CRC = 0000 hex , the CRC in the string is first set to 0000 hex . The CRC 

calculated from this string (incl. CRC) is then entered into the string. Like this, the CRC supplements 

to the total CRC of 0000 hex . 

Calculating a CRC: 

Variables: 

BUFFER = 

BUFPOINTER = 

memory area of complete message incl. header and CRC field 

pointer to character in BUFFER 

LENGTH = length of complete message (fields 1 to 4) 

BYTE = 

FLAG = 

character in BUFFER being processed 

temporary storage for most significant bit (MSB) 

CRC = 

CRC16 

BEGIN crc 

. CRC = 0000 hex 

. BUFPOINTER = points at beginning of BUFFER 

. WHILE (LENGTH != 0) 

. . bitcounter = 0 

. . BYTE = character the BUFPOINTER points at 

. . BUFPOINTER to next character (increment) 

. . DO 

. . . FLAG = highest bit Bit 15 of CRC 

. . . shift CRC 1 bit to the left (CRC = CRC * 2) 

. . . IF (highest bit Bit 7 of BYTE == ”1”) 

. . . . CRC = CRC + 1 

. . . ENDIF 

. . . shift BYTE 1 bit to the left (BYTE = BYTE * 2) 

. . . IF (FLAG == ”1”) 

. . . . CRC = CRC Exclusive Or 1021 hex 

. . . ENDIF 

. . . bitcounter = bitcounter + 1 

. . WHILE (bitcounter < 8) 

. . LENGTH = LENGTH – 1 

. END WHILE 

END crc 



Interface Bus Protocol of Slave (Model 73) 

Timeouts: 

A = 3-byte transmission rates 

(approx. 3.1 ms at 9600 bauds) 

Error States at Slave: 

1) timeout A expired 

(approx. 3-byte 

transmission rates) 

2) CRC error 

3) unknown target address 

(not addressed) 

4) framing (UART) error 

Reaction to Error: 

Do not send response, 

reject received string, return to 

standby mode, 

wait for new receive characters. 


Interface Bus Protocol of Master 

Timeouts: 

A = 

B = 

3-byte 

transmission rates 

(approx. 3.1 ms at 

9600 bauds) 

approx. 1 s 




13 Product Line and Accessories 

Instrument 

Ref. No. 

Process Unit 73 O 2 -2 73 O 2 -2 

Options 

English display texts 348 

French display texts 362 

Second current output 350 

Power supply 24 Vac/dc 298 

Power supply 115 Vac 363 

RS 485 interface 351 

Probe rinsing 352 

Logbook 354 

Improved resolution 430 

Mounting Accessories 

Mounting plate, extruded profile, AlMg3, 20 m anodized 

(not required for direct wall mounting, see Fig. 10–2, page 10–2) ZU 0126 

Bracket kit, brackets galvanized, screws stainless steel, thumb nuts aluminum anodized 

(only with ZU 0126 mounting plate, see Fig. 10–2, page 10–2) ZU 0125 

Protective hood, aluminum AlMg1, 25 m anodized 

(only with ZU 0126 mounting plate, see Fig. 10–2, page 10–2) ZU 0123 

Protective polyester case, IP 65, protective panel made of polycarbonate, 

complete with mounting kit, see Fig. 10–3, page 10–3 ZU 0124 

Bracket kit for protective case, brackets galvanized, screws stainless steel, 

thumb nuts aluminum anodized (only with ZU 0124) ZU 0128 

Terminal box made of polycarbonate ZU 0307 

8-core measuring cable, for extension ZU 0075 

Product Line 13–1


Sensors 

Sensors 

Ref. No. 

Model SE 704 12 mm dia., insertion length 120 mm (without connecting cable) SE 704 

Model SE 705 12 mm dia., insertion length 320 mm (without connecting cable) SE 705 

Accessories 

Membrane kit 

4 membrane modules, 25 ml electrolyte, replacement O rings ZU 0228 

Membrane module ZU 0230 

5 m connecting cable with 4-pole connector and open cable ends ZU 0231 

10 m connecting cable with 4-pole connector and open cable ends ZU 0232 

Polarization module, for sensor prepolarization ZU 0248 

Connector for power supply input instead of Pg threaded cable gland, ZU 0271 

made by Harting, Model HAN 7D with pin insert 

Connector for current output instead of Pg threaded cable gland, ZU 0272 

made by Harting, Model HAN 8U with socket insert 

13–2 Product Line

14 Specifications 

Oxygen input 

Current-sensitive measuring input for amperometric SE 704/705 sensors 

(also for galvanic sensors, input for an additional electrode for potentiostatic 

operation [3-electrode arrangement]), 

Ranges Saturation 0.0 to 600.0 % Air 

0.0 to 120.0 % O 2 

Concentration 0.0 g/l to 90.00 mg/l 

0.0 ppb to 90.00 ppm 

Partial pressure 0 to 2000 mbar 

Air pressure 

700 to 1100 mbar 

Sensor monitoring 

Sensocheck ® , monitoring of membrane and electrolyte 

Measuring current Range 1: 0 to 250 nA, resolution 5 pA (opt. 430: 2 pA) 

Range 2: 0 to 5 A, resolution 100 pA 

Range 3: 0 to 250 A, resolution 5 nA 

Range selection automatic or manual 

Polarization voltage 

0 to -1500 mV 

Additional input 

-2000 to +2000 mV 

Accuracy ( 1 count) Measuring voltage < 0.5 % of meas. value, +0.2 mV 

Temperature 

< 0.2 % of meas. value, +0.2 K (for 0 to +50 C) 

< 0.3 % of meas. val., +0.3 K (for -10 to +80 C) 

Air pressure 

< 12 mbar (operating temp 0 to 40 C) 

Calibration 

Operating Modes *) 

(sensor standardization) 

● automatic calibration in air-saturated water 

● automatic calibration in air 

● automatic zero-point calibration 

(for measurements in the g/l range) 

● manual – entry of saturation 

● data entry 

Temperature input 

Pt 100/Pt 1000/NTC 22 k 

2-or 3-wire connection 

Temperature probe adjustable 

Ranges Pt -50.0 to +250.0 C 

NTC 

-40.0 to +150.0 C 

Accuracy ( 1 count) 

< 0.2 % of measured value, 0.2 K 

Temperature compensation 

membrane diffusion 

Nonlinear, preset for SE 704 and SE 705 sensors, 

user defined for other sensors 

Current input 0(4) to 20 mA (0 to 100 %) 

input resistance 50 , overload 100 mA, 

e.g. for limit monitoring 

In conjunction with power output complete 2-wire loop, 

e.g. for flow meter, level meter or pressure transducer 

Accuracy 

< 1 % full scale 

Specifications 14–1


Display 

Graphic LCD, 240 x 64 matrix with CFL 1) backlighting 

Main display 

character height approx. 25 mm 

Secondary display character height approx. 6 mm 

Dialog display 7 lines, character height approx. 4 mm 

Display options Main display Secondary display 

saturation saturation [% Air] 

[% O 2 ] 

concentration concentration [mg/l; g/l] 

[ppm; ppb] 

partial pressure partial pressure [mbar] 

temperature temperature [C] 

pressure 

[mbar] 

time time [h,min] 

date [d,m,y] *) 

current output 1 [mA] 

current output 2 [mA] 

current input [%] 

cal timer 

[h] 

Output 1 *) 

Output 2 *) 

(Option 350) 

0 to 20 mA or 4 to 20 mA, max. 10 V, floating 

user defined for %AIR, %O 2 , conc., p O2 , C 

Current characteristic definable: linear, bilinear, trilinear, function 

Error message if load is exceeded 

0 to 20 mA or 4 to 20 mA, max. 10 V, floating 

user defined for %AIR, %O 2 , conc., p O2 , C 

Current characteristic definable: linear, bilinear, trilinear, function 

Error message if load is exceeded 

Anywhere within range 

Beginning/end of scale *) 

Spans *) Saturation 10.0 to 600.0 % Air; 2.0 to 120.0 % O 2 

Concentration ≥ 20.0 g/l, min. 10 % full scale 

Partial pressure 20 to 2000 mbar 

Temperature 

10.0 to 300 C 

Current source function 0.00 mA to 20.50 mA, separately definable for output 1 and 2 

Output current error 

< 0.25 % of measured value 20 A 

Power output 

24 Vdc/30 mA, floating, short-circuit-proof 

Typical applications: loop current for current input, 

signal current for switching outputs 

Switching contacts *) 

Salt correction 

Remote interface *) 

(Option 351) 

8 switching contacts, floating 

Contact ratings ac < 250 V/5 A < 1250 VA resistive 

dc < 120 V/5 A < 120 W 

NAMUR 2) contacts functional check 

warning (maintenance required) 

failure 

Failure/warning delays separately definable 

Limit contacts limit 1 

limit 2 

Cleaning contacts rinsing 

(option 352) 

cleaning 

probe 

0.0 to 45.0 g/kg 

RS 485, galvanically isolated 

Baud rate 300/600/1200/9600 

Data bit/parity 7/even, 7/odd, 8/no 

Point-to-point or bus connection of up to 31 devices 

14–2 Specifications

Logbook 

(Option 354) 

Probe rinsing *) 

(Option 352) 

Recording of 

Storage capacity 

Retrievable via 

function activations, appearance and 

disappearance of warning and failure 

messages, with date and time 

200 entries available 

keypad/display or remote interface 

Automatic probe rinsing and cleaning 

via timer-controlled cleaning contacts, e.g. splash rinsing 

Data retention Parameters and factory settings > 10 years (EEPROM) 

Clock and logbook, statistics 

> 1 year (battery backed) 

Unit self-test 

Clock 

RFI suppression to EN 50 081-1 

Immunity to interference 

(without sensors) 

Protection against electrical shock 

Test of RAM, PROM, EEPROM, display and keypad, 

Record for quality management documentation (QM) to ISO 9000 

Data retrievable via display and remote interface 

Real-time clock with date, self-contained 

to EN 50 082-2 and to NAMUR EMC recommendation for process and 

laboratory control equipment 

Inputs and outputs are isolated against 230 V and 115 V power supply 

and against switching contacts by the protective measure “Functional 

extra-low voltage with protective separation” as defined in DIN 57100/ 

VDE 0100 Part 410 and DIN VDE 0106 Part 101. 

Power supply AC 230 V -15 % +10 % < 10 VA 48 to 62 Hz 

Opt. 363 AC 115 V -15 % +10 % < 10 VA 48 to 62 Hz 

Opt. 298 AC/DC 24V AC: -15 % +10 % < 10 VA 

DC: -15 % +25 % < 10 W 

Protection class II Overvoltage category III/I 

Ambient temperature Operation 3) -20 to +50 C 

Transport and storage -20 to +70 C 

Enclosure 

Case with separate terminal compartment, suitable for outdoor mounting 

Material: acrylonitrile butadiene styrene (ABS), Front: polyester 

Protection: IP 65 

Cable glands 

10 Pg 13.5 threaded cable glands 

Dimensions Refer to dimension drawing Fig. 10–1, page 10–2 

Weight 

approx. 3 kg 

*) user defined 

1) Cold Fluorescent Lamp 

2) German committee for measurement and control standards in the chemical industry 

3) With ambient temperatures below 0 C, display readability can be restricted. This does not affect instrument functions. 

Specifications 14–3


Sensors 

Model SE 704 / SE 705 (12 mm dia., insertion length 120 mm / 320 mm) 

Measuring principle 

Cathode 

Anode 

Polarization voltage 

Amperometric mode of operation 

Platinum (Pt) 

Silver (Ag) 

-675 mV 

Temperature compensation Integrated NTC 22 k temperature probe, 0 to 80 °C 

Sensor signal in room air (25 °C) 

Residual signal in 

oxygen-free medium 

30 to 65 nA 

< 1 % of signal in room air 

Temperature range 0 to 130 °C 

Response time 

Detection limit 

Flow error 

Long-term stability 

Max. permissible gauge pressure 

Cable connection 

For 98 % full scale: 

< 90 s at 25 °C 

< 40 s at 37 °C 

0.1 % of air saturation (0.01 mg/l) 

Max. 5 % of displayed value between resting and 

strongly agitated solution 

Better than 2 % of displayed value per week (p = const., T = 30 °C) 

4 bar 

4-pole receptacle with bayonet joint 

for ZU 0231 / ZU 0232 connecting cable 

Material Membrane PTFE coated 

Sensor body stainless steel 1.4435 

Gaskets 

Viton 

Insertion length SE 704 120 mm 

SE 705 

320 mm 

14–4 Specifications

15 Appendix 

Warning 

Remember that the voltage across accessible parts of the open apparatus 

may be dangerous to life. 

If opening the apparatus is inevitable, it shall first be disconnected from 

all voltage sources. 

Make sure that the mains supply has been disconnected. 

Operations on an opened apparatus shall be carried out only by a 

skilled person who is aware of the hazard involved. 

Caution 

Observe the handling precautions for ESD sensitive components 

when acting on the opened apparatus! 

Appendix 15–1


EPROM Replacement 

You need: 

< 2 mm 

+ 

1. 

2. 

3. 

15–2 Appendix

4. 

5. 

6. 

7. 

8. Remount the instrument in reverse sequence. 

Appendix 15–3


15–4 Appendix

16 Technical Terms 

3-wire connection 

Administrator level 

administrator passcode 

alarm limit 

cal 

Calibration menu 

calibration passcode 

cleaning 

concentration 

current input 

cursor keys 

Connection of the temperature probe with a (third) 

sense line to compensate for the lead resistances; 

required for exact temperature measurement with 

long leads 

”adm” – menu level of parameter setting. All instrument 

settings and the passcodes can be edited. 

Protects access to Administrator level; can be 

edited on the Administrator level 

For each measured variable, you can define high 

and low warning and failure limits, respectively. 

Alarm can be activated individually for each variable. 

When an alarm limit is exceeded, an error 

message will be displayed and the corresponding 

NAMUR contact be activated. 

Menu key for Calibration menu 

Menu for calibrating the sensor 

Protects access to calibration; can be edited or 

disabled on the Administrator level 

User defined time during which the cleaning contact 

is closed during a rinsing cycle 

Membrane-covered oxygen sensors supply a current 


Henry’s Law allows to calculate the oxygen concentration 

from the oxygen partial pressure using 

a solubility coefficient. 

In the Process Unit 73 O 2 -2 the solubility coefficient 

for water is stored for the proper temperature 

from -5°C to +60°C as a table according to 

EN 25814 1992. In addition, you can take account 

of the influence of the medium’s salt content (salinity) 

on the solubility. The salt content can either 

be entered directly as salinity or chlorinity or you 

specify values for conductivity and temperature of 

the medium. Calculation of salinity from conductivity 

and temperature is according to: International 

Oceanographic Tables, Unesco / National Institute 

of Oceanography of Great Britain Volume 2, 

Wormley/Godalming/Surrey. 

Processes an input current of 0 (4) to 20 mA. The 

current can be displayed (in % full scale) and 

monitored via alarm limits. 

and – select entry positions or digits during 

number input. 

Technical Terms 16–1


delay time 

diag 

Diagnostics menu 

enter 

failure 

first rinsing 

functional check 

GMP 

information display 

interval 

limit contacts 

logbook 

main display 

maint 

Maintenance menu 

maintenance passcode 

meas 

measurement lead time 

User defined time until contacts ”warning” and 

”failure” react to an alarm message 

Menu key for Diagnostics menu 

Displays all relevant information on instrument status 

Key for confirming entries 

Alarm message and NAMUR contact; 

indicates that equipment does not function properly 

or that certain process parameters have 

reached a critical value. 

Failure is not enabled during ”functional check”. 

User defined time during which contact ”rinsing” is 

closed at the beginning of a rinsing cycle 

NAMUR contact – always enabled when Process 

Unit does not output the selected measured value 

Good Manufacturing Practice: guidelines for performance 

and documentation of measurements 

Information text for operator guidance or indication 

of instrument status; marked with i . 

Time from beginning of one rinsing cycle until beginning 

of the next rinsing cycle, user defined 

Controlled by a user-defined measured value. Are 

activated when the value falls below or exceeds 

the limit, depending on the user-defined effective 

direction 

The logbook shows the last 200 events with date 

and time, e.g. calibrations, warning and failure 

messages, power failure etc. This permits quality 

management documentation to ISO 9000. 

Large measurement display in measuring mode. 

You can select a measured variable to be displayed. 

Menu key for Maintenance menu 

The Maintenance menu comprises all functions for 

maintaining the sensors and adjusting connected 

measuring equipment. 

Protects access to maintenance, can be edited or 

disabled on the Administrator level 

Menu key – allows return to measuring mode 

from all other menus. 

User defined time at the end of the rinsing cycle, 

after deactivation of contact ”probe” 

16–2 Technical Terms

measuring mode 

menu 

menu level 

message list 

NAMUR 

NAMUR contacts 

Operator level 

operator passcode 



oxygen saturation index 

par 

partial pressure 

passcode protection 

point of measurement 

polarization time 

rinsing cycle 

rinsing lead time 

When no menu function is activated, the Process 

Unit is in measuring mode. The selected measured 

value is output. Pressing always returns 

you to measuring mode. 

Pressing a menu key (, , or ) 

gives access to a menu from which you can select 

the corresponding functions. 

The menu is divided into several menu levels. You 

can switch between different levels by pressing 

the menu key or the cursor keys and . 

The message list shows the number of currently 

activated messages and displays the individual 

warning or failure messages in plaintext. 

German committee for measurement and control 

standards in chemical industry 

”functional check”, ”warning” and ”failure” – indicate 

status of measured variable and Process Unit 

”opl” – menu level of parameter setting. You can 

edit the settings that have been enabled on the 


Protects access to the Operator level; can be 

edited or disabled on the Administrator level 

See concentration 

See partial pressure 

See saturation index 

Menu key for Parameter Setting menu 

Share of a gas to the total pressure of the gas 

mixture 

The passcodes protect access to calibration, 

maintenance, Operator and Administrator level. 

The passcodes can be edited or disabled on the 


Can be defined for identifying the instrument; can 

be displayed in the diag menu or read out via remote 

interface 

Time after instrument power-on until the sensor 

delivers stable measured values (see instruction 

manual for sensor) 

User defined sequence for cleaning sensors; controls 

contacts ”probe”, ”rinsing” and ”cleaning” 

User defined time at the beginning of the rinsing 

cycle, after activation of contact ”probe”, before 

closing of contact ”rinsing” 

Technical Terms 16–3


saturation index 

scrolling key 

second rinsing 

secondary display 

Sensocheck ® 

sensor 

temperature compensation 

Viewing level 

wait position 

warning (maintenance required) 

Percentage of measured quantity of O 2 to highest 

possible quantity (saturation) either referred to air 

or to pure oxygen 

and – for selecting menu lines or entering 

numeric digits 

User defined time during which contact ”rinsing” is 

closed at the end of the rinsing cycle 

Two small displays that appear at the lower left 

and right sides of the main display during measuring 

mode. The process variables displayed can be 

selected using / and / . 

Error signal in the case of mechanical stress of the 

sensor membrane that might modify the calibration 

data. After a Sensocheck ® message, recalibration 

is necessary. The Sensocheck ® message ”Warn 

Sensocheck” can be reset without having to carry 

out a calibration. 

Oxygen-sensitive sensor 

A) Correction of temperature dependence of membrane 

diffusion 

B) Consideration of oxygen solubility in water and 

of water vapor pressure 

”view” – menu level of parameter setting; display 

of all configuration settings, no editing possible 

Position between ”Second Rinsing” and ”Measurement 

Lead Time” where the probe remains as long 

as a start current of 10 to 20 mA is applied to the 

current input (only when current input has been 

set as control input) 

Alarm message and NAMUR contact; 

means that measuring equipment still operates 

properly but should be maintained, or that certain 

process parameters have reached a value that 

requires intervention 

Warning is not enabled during ”functional check”. 

16–4 Technical Terms

17 Index 

3–wire connection, 9–11 

definition, 16–1 

A 

adm, 8–1 

Administrator level, 8–1 


example, 8–3 

administrator passcode 


setting, 8–5 

alarm limit, 2–2 


alarm settings, 9–24 

interface commands, 12–21 


appendix, 15–1 

automatic calibration, 3–6 

B 

bracket kit, 10–1, 13–1 

C 

cal, definition, 16–1 

cal timer, 9–5 


cal timer alarm, 9–24 

calibration, 3–1 

automatic, 3–6 


data entry, 3–10 


First Calibration, 3–4 

freeze outputs, 3–6, 3–9, 3–10 

manual input of saturation, 3–9 

interface commands, 12–10, 12–26 

monitoring functions, 3–2 

calibration menu, 3–3 


calibration passcode 



calibration record, 4–3 


calibration sequence, selection of, 3–3 

cleaning, 10–8 


clock 



COMMAND, interface commands, 12–26 

concentration, definition, 16–1 

concentration alarm, 9–24 


concept of instrument, 1–1 

connection of sensors, 10–7 

connections 

block diagram, 9–20 

terminal assignments, 10–6 

control elements, 2–3 

corner point 

bilinear output curve, 9–15 

trilinear output curve, 9–15 

Index 17–1


CTIME, 2–2 

current input, 9–22 




current input alarm, 9–24 



current output, 9–13 

falling curve, 9–14 

output curve, 9–14 


error messages, 9–18 

span, 9–14, 9–15, 9–16 

current output 1, 9–13 


current output 2, 9–17 


current source function, 5–3 


cursor key, definition, 16–1 

D 

date 



date format, setting, 4–6 

delay time, 9–26 


DEVICE, interface commands, 12–25 

device description, 4–6 

device diagnostics, 4–7 




diag, definition, 16–2 

Diagnostics menu, 4–2 

capabilities, 4–1 


display, viewing angle adjustment, 9–4 

dual point calibration, 3–5 

E 

effective direction, 9–27 

enter, definition, 16–2 

EPROM, replacement, 15–2 

error messages 

according to error code, 11–4 

alphabetical, 11–1 

F 

failure, 9–26 


First Calibration, 3–4 


first rinsing, definition, 16–2 

functional check, 9–26 


G 

GMP, definition, 16–2 

grounding conditions, 10–7 

H 

hysteresis, 9–27 

I 

I–IN, 2–2 

impedance alarm, 3–2, 9–24 


17–2 Index

input filter, 9–4 


installation, 10–5 

terminals, 10–5 

instrument concept, 1–1 

interface, 9–33 

bus protocol, 12–29 

command set, 12–5 

contents, 12–1 

information, 9–35 


point to point, 12–28 


transmission behavior, 12–4 

write protection, 9–35, 12–28 


interval, definition, 16–2 

marker setting, 8–2 

meas, definition, 16–2 

measurement data, point of measurement, 4–2 

measurement display, 9–3 


measurement lead time, definition, 16–2 

measurement point, 4–2 



measurement point maintenance, 5–2 


measuring mode, 2–1 


menu, definition, 16–3 

menu level, definition, 16–3 

L 

limit contacts, 9–27 


display, 2–2 

effective direction, 9–27 

hysteresis, 9–27 



logbook, 4–5 



M 

main display, definition, 16–2 

maint, definition, 16–2 

maintenance, 10–8 

Maintenance menu, 5–1 


maintenance passcode 



menu structure, 1–3, 2–4 

message list, 4–2 


mounting, 10–1 

mounting accessories, list, 13–1 

mounting plate, 10–1, 13–1 

N 

NAMUR, definition, 16–3 

NAMUR contacts, 9–26 




numeric value, input, 2–5 

O 

Operator level, 7–1 



Index 17–3


operator passcode 



opl, 7–1 

options, list, 13–1 

output current 1 



output current 2 



output curve 

bilinear, 9–15 

function, 9–16 

linear, 9–14 

logarithmic, 9–16 

trilinear, 9–15 

oxygen concentration, definition, 16–3 

oxygen measurement, connections, 9–20 

point of measurement, 4–2 



polarization time, 10–7 


power output, 9–22 

power supply, 9–1, 10–5 

pressure alarm, 9–24 


pressure correction, 9–5 


probe rinsing, 9–29 



operation, 9–31 


protective case, 10–1, 13–1 

protective hood, 10–1, 13–1 

oxygen partial pressure, definition, 16–3 

oxygen saturation index, definition, 16–3 

P 

par, definition, 16–3 

parameter setting 

Administrator level, 8–1 

marker setting, 8–2 

passcodes, 8–4 


Operator level, 7–1 

Viewing level, 6–1 

partial pressure, definition, 16–3 

partial pressure alarm, 9–24 


passcode protection, definition, 16–3 

passcodes 

factory settings, 8–5 


R 

rinsing cycle, 9–29 


disable, 9–29 

rinsing lead time, definition, 16–3 

RS 485 interface, 9–33 

bus protocol, 12–29 

command set, 12–5 

contents, 12–1 



point to point, 12–28 


transmission behavior, 12–4 

write protection, 9–35, 12–28 

S 

salt content, 9–21 


17–4 Index

saturation alarm, 9–24 



saturation index, definition, 16–4 

scrolling key, definition, 16–4 

second rinsing, definition, 16–4 

secondary display, 2–1 



Sensocheck, 9–10 


sensor 

connection, 10–7 


sensor data 


parameter setting, 9–8 

sensor statistics, 4–3 


sign, change, 2–5 

single point calibration, 3–5 

slope alarm, 3–2, 9–24 


span, 9–14 

specifications, 14–1 

STATUS, interface commands, 12–5 

temperature detection, 9–10 


temperature probe, connection, 9–11 

temperature probe adjustment, 5–4 


terminal assignments, 10–6 

U 

user interface, 1–1 

V 

VALUE, interface commands, 12–5 

view, 6–1 

viewing angle adjustment, 9–4 


Viewing level, 6–1 



W 

wait position, 9–30 


warning, 9–26 


T 

technical terms, 16–1 

temperature alarm, 9–24 


Z 

zero point alarm, 3–2, 9–24 


temperature compensation, 9–10 



manual, 9–12 

Index 17–5


17–6 Index

Process Unit 73 O2 -2 - Knick

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