Troubleshooting
Symptom
Process control temperature dif-
fers from setpoint when read
with an external pyrometer.
Deviation meter nulls and
process is stable.
Probable Cause
- T/C lead wires shorted close
to process
- Wrong type of T/C being used,
etc.
- Standard electrical wiring
being used in place of T/C
wire
- Gradient error
Symptom
Temperature overshoots, or
oscillates.
Probable Cause
- Process overpowered
- Bandwidth too narrow
- Process or sensor lag
Symptom
Process control temperature
stabilizes above or below set-
point as read on deviation
meter.
Probable Cause
- Offset (manual reset) incor-
rectly adjusted
- Partial short to ground in
heater when used on 240 V
line
- No output from suspect con-
trol
- Controller reading other zones
of multi-controlled process
- Full output from suspect con-
trol
- Apparent stabilization from
other zones of multi-controlled
process
- Improperly sized heater
NOTE: Fuse blowing is not caused by
the controller. Blown fuses are caused
by shorts in the heater circuit, and
must be corrected to prevent damage
to the controller.
Check
Check T/C lead wires at back of probe
Wire color indicates type of T/C
Verify type of wire
Corrective Action
- Replace defective wiring
- Install correct T/C for temperature range of instru-
ment. See instrument serial number tag for T/C type.
- Run only T/C wire between process and controller.
- Use electronic indicator in parallel with suspect
instrument’s T/C input.
Check
Check bandwidth
Loose heater or sensor fit. Poor
relative location.
Corrective Action
- Reduce total heater power
- Widen band
- Improve fit, locate closer together
Check
Offset (manual reset)
Heater to ground resistance
Design parameters for process heat required
Corrective Action
- Adjust (+) to increase controlled temp. (-) to
decrease temp.
- Replace defective heater
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