LED TE-TC Temperature Controller for Thermoelectric Cooler

TE-TC 

Temperature Controller for 

Thermoelectric Coolers Manual 

1. Introduction 

The TE-TC is a precision temperature controller designed to control thermoelectric (Peltier) 

coolers for infrared detectors and light-emitting diodes. 

The controller senses temperature by measuring the resistance of a thermistor mounted on the 

cooler. The TE-TC operates with a one, two, or three stage Peltier cooler and thermistor 

temperature sensor. Control and display can be either in temperature or resistance units. The 

controller output current can also be displayed and the maximum cooler current can be set. Either 

the set point or actual value of temperature, resistance or current can be displayed. 

The TE-TC incorporates an RS-232 serial interface for computer communication and control. 

Additional features include automatic cooler shutdown when thermistor short or open circuit is 

detected. 

PLEASE READ THIS GUIDE BEFORE USING THE CONTROLLER 

2. Control Principle 

The TE-TC employs a full three-term digital control algorithm to control the temperature, 

minimizing overshoot, eliminating steady-state temperature error and allowing fast settling time 

to a selected temperature. For set temperatures above ambient, the controller reverses the current 

polarity to force the Peltier device to act as a heater, enabling a controlled temperature range 

from –42° to +32° Celsius. 

3. Controls 

The front panel consists of: 

• 4 digit LED display 

• MODE push button and LED indicators, selecting either SET or READ SET displays the 

set value in the selected units. READ displays the actual value of the selected unit. 

• UNITS push button and LED indicators, selecting either temperature (T), resistance (R) 

or current (I). 

• Increase (INC) and decrease (DEC) push buttons, to adjust the setpoint temperature or 

resistance. 

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445 

(800)347-5445 or (617)566-3821 * fax (617)731-0935 * boselec@boselec.com * www.boselec.com

• Current limit potentiometer (screwdriver slot) used to adjust the maximum allowable 

output current. 

• Power ON/OFF switch - AC inlet ON/OFF (on Rear Panel). 

• OUTPUT switch, controlling current to the coolers. 

4. Connecting the Cooler and Thermistor 

1. Unplug the TE-TC controller from the AC supply. 

2. Attach the leads from the Peltier cooler to the connector on the rear panel. See Appendix 

1 for wiring details. 

WARNING! The supplied current can KILL. Ensure that the controller is unplugged from the 

power and turned OFF. 

CAUTION! Observe the correct polarity. Reversed connections will cause overheating and 

possible failure of the cooler and any device mounted on it. 

The cooler connections must not be grounded. 

3. Attach the leads from the thermistor to the connector on the rear panel. See Appendix 1 

for details. 

CAUTION! The controller is normally calibrated to a linearised thermistor having a resistance 

of 8.2kΩ+/-5% at 25°C. (Betatherm 8.2KΩ MCDG). If any other variety of thermistor is to be 

used, the TE-TC must either be factory calibrated or used in CONTROLLED RESISTANCE 

mode (see section 8 below). Use of CONTROLLED TEMPERATURE mode in this 

circumstance will lead to gross temperature errors and possible damage to the cooler and any 

device mounted on it. 

The Thermistor connections must not be grounded. 

5. Identification of Controller 

As the calibration of the TE-TC controller depends on the type of thermistor used, the unit can 

display an identification code to identify the calibration permanently stored in its memory. To 

display the identification code: Press and hold down the MODE key whilst switching on. The 

code will be displayed until the MODE key is released. The code for specially-calibrated units is 

"SP-X where X is a number. The variations from the standard setting, if programmed, are 

described in Appendix 2. The standard code is AP-1. 



6. Setting the Current Limit 

1. Plug the controller into the power and switch power ON. 

2. Ensure the OUTPUT is OFF. 

3. Using the push buttons, select SET mode and I units to display current. 

4. Using a small screwdriver, adjust the current limit potentiometer until the display shows 

the desired value in amperes. 

NOTE: Adjusting the potentiometer at any time will adjust the maximum current, whether or not 

it is displayed. It is advisable to initially set to half the recommended current for the Peltier 

cooler being used. The current can subsequently be increased if inadequate. 

7. Setting the Operating Temperature 

The set point units (i.e. temperature or resistance) must be selected and set before switching the 

controller output to ON. Once the output is activated, only the initial setpoint units can be altered 

in SET mode; all other units can only be read. 

1. Set output to OFF. 

2. Select T units for temperature. 

3. Select SET mode. 

4. Using the INC and DEC push buttons, increase or decrease the setting. Holding down the 

buttons increases the speed of change. 

NOTE: Temperatures BELOW 0°C are displayed without a minus sign and with 0.01°C 

precision. For example, -18.5°C is displayed as 18.50. Temperatures ABOVE zero are shown 

with a plus sign: e.g. 14°C is displayed as +14.0. 

CAUTION! CONTROLLED TEMPERATURE mode should be used only with linearised 

thermistors having a resistance of 8.2 kilohms at 250 C. For other thermistors, see Section 8 

below. 

5. Turn output to ON. The controller will supply current to the cooler to bring the actual 

temperature to the setpoint value. 

With output ON, the actual thermistor resistance, cooler temperature and current can be viewed 

by selecting READ mode and the appropriate units. 

8. Setting the Operating Resistance 

If a non-standard thermistor is used, the temperature calibration of the controller is not valid; 

instead, the thermistor resistance must be monitored and controlled. 

1. Consult the thermistor specifications to determine its resistance at the desired setpoint 

temperature. 



2. Set output to OFF. 

3. Select R units for resistance. 

4. Select SET mode. 

5. Use the INC or DEC push buttons to increase or decrease the setpoint for resistance. 

6. Turn output to ON. The controller will supply current to the cooler to bring the measured 

resistance to the setpoint value. 

NOTE: A resistance range for 2OOKΩ to 6.7KΩ may be used, Above 200KΩ the controller 

assumes an open circuit and displays –0C-. Below 50Ω, a short circuit is assumed and -SC- is 

displayed. 

With output ON, the actual thermistor resistance or cooler current can be viewed by selecting 

READ mode and the appropriate units. Note that the displayed temperature will NOT be correct. 

9. Display Format 

As explained above, temperature is displayed to four significant figures below 0°C and to three 

figures above 0°C; e.g. -30.45°C is shown as 30.45, while 10.23°C is shown as 

10.22 Resistance is displayed in kilohms to four figures. For example, 12 kilohms is shown as 

12.00 and 120 kilohms as 120.0. 

Current is displayed as a three figure value in amperes, with a resolution of 0.02A. 

-OC- indicates an open circuit for the thermistor. 

-SC- indicates a short circuit for the thermistor. 

10. RS-232 Serial Interface 

The serial interface allows communication with a computer. This section describes interfacing 

details. 

10.1 Description 

The interface is implemented as a simple three-wire system which uses software handshaking 

procedures to allow the system to work with any computer having an RS232 type serial I/O port. 

10.2 Pin-outs 

The connector pin-outs are shown in figure 1. A 9-pin D connector is assumed at the computer 

end; if this is not the case, pin numbers will change. A null modem cable may be used since no 

other pins are connected at the TE-TC controller end. 

10.3 Communication Protocol 

4800 baud 

1 start bit 

8 data bits 

no parity (if there is, it is ignored) 

1 or 2 stop bits 



RS232 9-way D-plug on controller 

Pin No Usage 

2 TXD - output from TE-TC 

S RXD - input to TE-TC 

5 Ground 

10.4 Handshaking 

Handshaking (i.e. verification of proper communication) is performed by a character echoing: a 

character sent to the temperature controller causes a reply with either the same character, data, or 

an error character. There is no further response from the temperature controller until another 

command is sent. A ‘character’ is any valid ASCII code for upper case characters, numbers 0 to 

9, ".","+", and "". 

Command characters are T, R, S, L, G, and H. These are always echoed. 

10.5 Units selection 

Select R to select resistance units. 

Send T to select temperature units. 

The LED's on the front panel will respond in the same manner as if the front panel controls were 

being used. Note that the front panel controls will still operate when remote commands are sent. 

It is good practice to use only the RS232 link when operating remotely to avoid confusion. 

Send G (for GO) to turn on the output. 

Send H (for HALT) to switch off the output. 

Send L to load the setpoint once T or R has been selected. 

The standard procedure is as follows: 

Send T or R (wait for echo) 

Send L (wait for echo) 

Send setpoint data, character by character, waiting after each character for its echo. 

The exact data format must be followed; otherwise the temperature controller will not accept the 

data and will send an error character. 

• For resistance setpoints, send four digits with decimal point; e.g. 123.245KΩ is sent as 

123.3 

• For negative temperatures, send first two numbers, then decimal point, and finally two 

numbers; e.g. 17.42 for –17.42°C. 

• For positive temperatures, send first a ‘plus’ sign, the two numbers, then decimal point 

and finally one number, e.g. +07.6 for + 7.6°C. For example, to set a temperature of - 

12.32°C via RS 232 follow this procedure: 

Send T 

Send L 

Send 1 

(await echo) 

(await echo) 

(await echo) 



Send 2 

Send . 

Send 3 

Send 2 

(await echo) 

(await echo) 

(await echo) 

(await echo) 

The front panel should now show SET mode, TEMPERATURE units and a display of 12.32. 

Any format error will result in a “D” being sent by the TE-TC after the last number. Any 

unrecognized character will be echoed by "Q" (for Query); this will also cause the controller to 

revert to normal idle state, awaiting another command or setpoint. 

The controller automatically loads the setpoint value after receiving five characters, including the 

decimal point, providing they are valid characters and the decimal point is correctly positioned. 

For example, 12.345 would be accepted as 12.34 but a"" would be returned on receipt of the “5” 

which would be interpreted as an unrecognized command. 

10.6 Reading Actual Values 

Send T or R 

Send S 

Send X 

Send X 

to select temperature or resistance. (await echo) 

to order the value to read into an output buffer. (await Echo) 

to receive the first digit of the value. The digit character will be sent 

without echoing the “X”. 

to receive the other four characters, repeat “X”. 

For example, to read a temperature of -21.59°C, follow this procedure: 

COMPUTER TE-TC REPLY 

T 

T 

S 

S 

X 2 

X 1 

X . 

X 5 

X 9 

If another S or any other character other than “X” is sent while data is being transferred, the old 

command will be cleared and the new command will be carried out More than five “X” 

characters will be echoed by “E” for 'END'. 

10.7 RS-232 Command Summary 

Control character 

T 

R 

S 

X 

L 

G 

H 

Action 

Select temperature units 

Select resistance units 

Read temperature or resistance 

Send next character of the measured value 

Load setpoint value 

Go (turn output on) 

Halt (turn output off) 

Error Character 

Meaning 



D Decimal point wrongly placed or missing 

Q Invalid data character 

Unrecognized command 

E End of buffer 

11. Improving Temperature Stability 

If the controller is being used at a temperature which needs much less than the maximum 

allowable current for the Peltier cooler, the temperature can sometimes be improved by 

decreasing the set current limit. To reduce the set current, first check the operating current at the 

set temperature whilst the controller is operating. Select READ mode and I units. Next set the 

current limit to about 10 to 20% greater than the required value. Switch to READ mode and 

temperature units again to see if the temperature has stabilized. Note that it may take a little 

longer to reach a set value. If the set value is not regained, increase the current limit slightly and 

repeat. 

NOTE: If the Peltier cooler has inadequate capacity to reach the set temperature, the controller 

will supply the maximum allowable current. Temperature stability is likely to suffer. 

12. Specifications 

Sensor Type 

Thermistor (8.2KΩ @ 25°C) 

Sensor Current 10 µA 

Output Stage 

Bipolar, constant current type 

Output Current Range 

0 to 2.0 amperes 

Maximum Output Voltage 

3 volts 

Temperature Range (with calibrated Thermistor) -42°C to +32°C 

Thermistor Resistance Range 

200KΩ to 6.7KΩ 

Temperature Setting Readout Resolution below 0.01°C 

100KΩ 

Resistance Setting and Readout Resolution 10Ω 

below 100KΩ 

Short-term Temperature Stability (using +/- 0.01°C 

calibrated thermistor) 

Ambient Temperature Tempco 

50 ppm/°C 

Current Limit set and Readout Range 0 to 2.5A 

Display 

4 digit seven segment LED 

Serial Interface 

RS-232 compatible 

Protection 

Automatic shutdown for open or 

short circuit of thermistor 

Power Requirement 

115 or 220V AC (+/- 10%) @ 24VA 

Identification 

AP-1 



Appendix 1: Cooler/Thermistor Connector 

The back panel includes RS232 connector, AC power switch and cooler/thermistor connector. 

The cooler/thermistor connector is used both for thermistor input and cooler output. One 9-pin 

D-plug to 9-pin D-plug is supplied with the controller. 

The plug is wired as follows: 

Pin Number Connection 

6 Cooler positive 

1 Cooler negative 

5 Thermistor 

9 Thermistor 

The AC fuse is internal - lA for 240V AC, 2A for 120V AC. 

Appendix 2: Special settings for SP-1 Calibrated Units 

1. The thermistor resistance varies nonlinearly with temperature (see Fig 2) 

2. Sensor current is 100uA. 

3. The open circuit symbol (-OC-) is displayed for resistance above 17KΩ instead of 

200KΩ. 

4. For thermistor resistance below 10KΩ, the display and RS-232 formats are to 1Ω 

resolution, not of 10KΩ resolution. 

Appendix 3: Calibration of the Thermistor Probe, standard unit AP-1 

The following data has been used to calibrate the Type 8.2K7MCD6 thermistor: 

Resistance Temperature °C Resistance Temperature °C 

178423.1 -40 23165.13 0 

134078.2 -35 18582.49 5 

101723.2 -30 15005.79 10 

77882.2 -25 12194.57 15 

60147.8 -20 9970.69 20 

46839.5 -15 8199.88 25 

36766.07 -10 6781.67 30 

29077.81 -5 5638.84 35 

4712.54 40 



Appendix 4: Identification of Units 

Press the mode key when switching ON: an identification code will appear on the display until 

the mode key is released. For standard unit it is AP-1. 

For SP-3 Unit 

This unit is calibrated against the RT curve supplied (see appendix 3 for standard RT curve), 

with end curve extrapolation to –27°C and +20°C. The excitation current is 

100uA. 

- OC- will be displayed and unit will shut off load power. If the resistance goes above 17KΩ, 

then the display will be – SC - (i.e. very low input resistance). 

The RS 232 format differs only for transmitted resistance value (i.e. 1.2K is sent as 1.200 with 

normal units this would be 01.20). Resistance is now displayed with a resolution of 1Ω for 

resistance values below 10KΩ. 

NOTE: Both sensor inputs and cooler output connections must not be grounded. 

Propriety Notice 

This publication contains information partly derived from propriety data of Laser Monitoring 

Systems. The express purpose of this information is to assist in the operation and maintenance of 

the equipment described herein. The publication of this information does not convey any right to 

reproduce or use the information for any purposes other than in the operation or maintenance of 

the equipment described herein. 

Disclaimer 

Laser Monitoring shall not be liable for any incidental or consequential damages in connection 

with any deletions, errors or omissions in this manual. 

It is the user's responsibility to use the controller as described in this manual. Using too high a 

limiting current or an incompatible thermistor, or an inadequate heatsink could damage the 

Peltier cooler and/or any device mounted on it. 

Laser Monitoring Systems Limited disclaims all responsibility for damage caused by misuse of 

the TE-TC controller Evidence of misuse will void the warranty.

LED TE-TC Temperature Controller for Thermoelectric Cooler

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