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STT40 / STT70
Troubleshooting 9-4
Problem Possible cause Corrective action
No setting change possible on
temperature controller.
The key protection switch is set
to ON.
Set the key protection switch to
OFF.
Input polarity on thermo-couple
is wrong or connection is wrong.
Properly wire the terminals.
Input-type setting is incorrect.
Properly set the input with the
input-type selector rotary
switch.
No compensating lead wires
used for extension of the
thermocouple.
Use proper compensating lead
wires and terminals.
Thermocouple and controller are
connected by wires other than
proper lead wires.
Use a dedicated thermocouple
connector. If a connector is a
metal different from the
thermocouple and controller, a
temperature error may result.
Process thermocouple not in
airflow.
Verify that the thermocouple is
properly installed in the inlet
tube.
Sensor is broken or short-
circuited.
Replace with a good sensor.
The controller is influenced by
noise or other induction.
Separate input wires as far as
possible from the origin of the
noise.
Process value is abnormal or
not obtained.
Celsius temperatures used
instead of Fahrenheit or vice
versa.
Check to see that proper
temperature setting is in the
temperature controller.
9.2. Determining Temperature Controller Errors or Sensor Errors
Using a Thermocouple
If the controller displays a temperature that is close to room temperature (70ºF/21ºC)
when you short-circuit controller input terminals, the controller is normal and the
sensor is probably broken, short-circuited, or incorrectly wired.
Using a Platinum Resistance Thermometer
If the controller displays a temperature of about 0.0°C (32ºF) when you insert a 100-
ohm resistor between terminals A and –B of the controller, and you short-circuit
controller terminals +B and –B, the controller is normal and the sensor is probably
broken, short-circuited, or incorrectly wired.
Other service problems or questions can be answered by contacting the Service
Department.