Watlow Series TM - Manual (Page 17)

Wa t l o w S e r i e s C • 1 5 • Tr o u b l e s h o o t i n g
Troubleshooting
Indication Probable Cause(s) Corrective Action
On indicating controls, the
display is not illuminated. • Power supply switch off. • Turn switch on.
• Fuse blown. • Replace fuse (check cause of failure).
• Breaker tripped. • Reset breaker (check cause of failure).
• Safety interlock door switch activated. • Close door.
• Separate system limit control latched. • Reset limit controller.
• Wiring incorrect or open. • Check wiring.
• Power supply voltage incorrect. • Verify input power.
• Defective controller. • Repair or replace controller.
Troubleshooting thermocouple inputs
Temperature reading is
incorrect, showing a sen-
sor error,
[Er;In] , or LOAD
LED is switching at the
wrong temperature.
• Calibration offset is incorrect (tactile
models only). Check calibration offset.
• Settings for degree C or F is incorrect. Check model part number for degree C or F.
If model has Increment/Decrement keys then
C/F setting is adjustable.
• Sensor or controller may be bad.
Sensor connections may be bad. • Place a jumper wire across the thermo-
couple input terminals. The display should
indicate ambient temperature. If it does, the
controller is OK.
For controllers without the ability to view
process temperature:
- Decrease set point below ambient tempera-
ture, LOAD LED should be off for heating
controllers and on for cooling controllers.
- Increase set point above ambient tempera-
ture. LOAD LED should be on for heating
controllers and off for cooling controllers.
• Ambient temperature in the control
cabinet is over 70°C. • Measure temperature in cabinet to ensure
it is below 70C. Vent cabinet or add fans if
necessary.
• Ground loop problem. Can occur
when using a switched DC output and
a grounded thermocouple. • Remove power from the system. Use an
ohm meter to measure resistance between
output DC- and the thermocouple sheath. If
there is continuity, replace sensor with an
ungrounded thermocouple.
Temperature reading is de-
creasing, but actual process
is increasing. • Thermocouple polarity is reversed. In
the US, red wire insulation denotes the
negative wire. • Check thermocouple connections. All con-
nections, including extension wire must
maintain the correct polarity. Correct polarity
problems.
Temperature reading is
reading low and not increas-
ing while actual process
temperature is increasing. • Sensor is bad. Thermocouple is short-
ed. • Check thermocouple connections. Check
thermocouple wire insulation to make sure
it is not damaged, causing the wires to short
(making a new junction).
Temperature reading is
offset from actual process
temperature, or the output
switches on or off at the
wrong temperature. The off-
set changes with changes in
process temperature. • Copper wire was used instead of ther-
mocouple extension wire. Connectors
of metals different than thermocouple
metal were used to splice or make con-
nections. • Check thermocouple connections. Check to
make sure that only thermocouple extension
wire of the correct type was used to extend
thermocouple leads. Replace if necessary.