User`s manual

Watlow Series C ■ 11 ■ Troubleshooting
On indicating controls, the
display is not illuminated
• Power supply switch off.
• Fuse blown.
• Breaker tripped.
• Safety interlock door switch activated.
• Separate system limit control latched.
• Wiring incorrect or open.
• Power supply voltage incorrect.
• Defective controller.
• Turn switch on.
• Replace fuse (check cause of failure).
• Reset breaker (check cause of failure).
• Close door.
• Reset limit controller.
• Check wiring.
• Verify input power
• Repair or replace controller.
Troubleshooting thermocouple inputs
Temperature reading is in-
correct, showing a sensor er-
ror, [Er;In] , or LOAD LED
is switching at the wrong
temperature.
• Sensor or controller may be bad. Sensor
connections may be bad.
• Ambient temperature in the control
cabinet is over 70°C.
• Ground loop problem. Can occur when
using a switched DC output and a
grounded thermocouple.
• Place a jumper wire across the ther-
mocoup le 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 tem-
perature, LOAD LED should be off for
heating controllers and on for cooling
controllers.
- Increase set point above ambient tem-
perature. LOAD LED should be on for
heating controllers and off for cooling
controllers.
• Measure temperature in cabinet to en-
sure it is below 70C. Vent cabinet or add
fans if necessary.
• Remove power from the system. Use an
ohm meter to measure resistance be-
tween output DC- and the thermocouple
sheath. If there is continuity, replace sen-
sor 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
connections, including extension wire
must maintain the correct polarity. Cor-
rect polarity problems.
Temperature reading is read-
ing low and not increasing
while actual process temper-
ature is increasing.
• Sensor is bad. Thermocouple is shorted. • 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 off-
set from actual process tem-
perature, 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 connections.
• Check thermocouple connections.
Check to make sure that only thermocou-
ple extension wire of the correct type was
used to extend thermocouple leads. Re-
place if necessary.
Troubleshooting