II - DCE FEL ČVUT v Praze

SIMATIC S7 Ex Analog Modules
3.6 Basic Requirements for the Use of Analog Modules
In this chapter
3-38
In this chapter you will find:
Explanations of fundamental definitions for analog value processing.
How to set measuring ranges of analog input channels.
What diagnostic options the individual analog modules make available.
The parameters you can use to set the functions of the individual analog
modules.
Characteristics of the individual analog modules
3.6.1 Conversion and Cycle Time of Analog Input Channels
Introduction
Conversion time
Cycle time
The definitions and interrelationships of conversion time and cycle time for
analog input modules are described in this section.
The conversion time is made up of the basic conversion time and additional
processing times for wire break monitoring.
The basic conversion time depends directly on the conversion method
(integral action, successive approximation or sigma-delta method) of the
analog input channel. In the case of integral action conversion, the
integration time is included directly in the conversion time. The integration
time has a direct influence on the resolution. The integration times of the
individual analog modules are specified in Section 3.6.3. These times are set
in STEP 7.
Analog/digital conversion and transfer of the digitized measured values to the
memory or on the backplane bus of the S7-300 take place sequentially, i.e.
the analog input channels are converted one after the other. The cycle time,
i.e. the time necessary until an analog input value is converted again, is the
sum of the conversion times of all activated analog input channels of the
analog input module. The conversion time is based on channel groups when
the analog input channels are combined in channel groups by means of
parameterization. In the analog input modules SM 331; AI 8 x TC/4 x RTD,
2 analog input channels are combined to form one channel group. You must
therefore subdivide the cycle time into steps of 2. Unused analog input
channels should be deactivated by means of parameterization in STEP 7 in
order to reduce the cycle time.
Fig. 3-14 shows and overview of how the cycle time is made up for an
n-channel analog input module.
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04