TE Technology TC-24-12 - Manual (Page 5)

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standard thermistor. The thermistor should be a negative temperature coefficient device.
Because the temperature controller is really measuring the thermistor’s resistance and converting
this to a temperature, the temperature controller will be “fooled” into thinking that the thermistor
is at a different temperature than it really is, and the Set-Temperature will be skewed
accordingly. A loss of resolution, control range, and control stability may occur as a result. The
user assumes all risks associated with making any substitutions and TE Technology assumes no
liability whatsoever for the operation of the controller when a non-standard thermistor is used.
The controller is pre-programmed to enter into a “Fault Mode” if the controller senses the
resistance of control thermistor as either a short circuit or an open circuit. When a fault is
sensed, the controller will perform the following tasks:
1. Turn off the output to the thermoelectric module(s)
2. Flash LEDs to indicate a control thermistor fault has been sensed (see Fault
Detection Indications)
3. Electrically short Pins JP2-3 and JP2-4 to the circuit ground through the drain of the
alarm output transistor
The controller will return to normal operating mode as soon as the resistance of control
thermistor is no longer sensed as an open or short circuit.
4.0 Over-Temperature Thermistor / Thermostat Inputs
Two additional thermistors may be used as over-temperature sensors. Generally, these would be
attached to the hot and cold sides of the cooling assembly. The controller is pre-programmed to
enter into a “Fault Mode” if the resistance of either over-temperature thermistor drops below
approximately 2620 ohms, which corresponds to a fault temperature of 70 °C with the standard
series thermistors. When a fault is sensed, the controller will perform the following tasks:
1. Turn off the output to the thermoelectric module(s)
2. Flash LEDs to indicate a fault temperature has been sensed (see Fault Detection
Indications)
3. Pins JP2-3 and JP2-4 are shorted to the circuit ground through the drain of the alarm
output transistor
The return to normal operating conditions depends on the placement of the two-pin jumper at
JP4. If the jumper is installed (pins are shorted together) then the output to the TE load will
latch off if a fault temperature is detected. With this jumper setting the controller will need to
have its power removed in order to unlatch and reset the controller. This mode allows the user to
correct the problem that caused the fault condition, and it prevents the thermoelectric cooling
system from being destroyed by over-temperature conditions and/or thermal cycling. This is the
recommended operating mode.
If the jumper is removed then the controller will return to normal operating conditions when the
fault sensor’s resistance increases beyond approximately 5390 ohms, which corresponds to a
temperature of 50 °C with the standard thermistors. NOTE: If the cause of the fault condition
continues to exist, this mode would thermally cycle the cooler because power is being removed
and then reapplied. Thermal cycling could eventually destroy the thermoelectric cooling system.
Therefore, this mode should only be used if the thermoelectric cooler is protecting expensive or
critical equipment and failure of the thermoelectric cooling system, while undesirable, is
preferable to having absolutely no cooling in the system.