Watlow Series TM - Manual (Page 18)

Wa t l o w S e r i e s C • 1 6 • Tr o u b l e s h o o t i n g
Indication Probable Cause(s) Corrective Action
Troubleshooting RTD inputs
Temperature reading is in-
correct, showing a sensor er-
ror,
[Er;In] , or LOAD LED
is switching at the wrong
temperature.
• Calibration offset 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. Sen-
sor connections may be bad. • Place a 110 ohm resistor across the sensor
input terminals. The display should indicate
25°C (77°F). If it does, the controller is OK.
Sensor or connections may be bad.
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 (158°F). • Measure temperature in cabinet to ensure
it is below 70°C (158°F). Vent cabinet or add
fans if necessary.
• Sensor connections may be bad. Ex-
cessive lead wire resistance. • Check sensor connections. Measure lead
wire resistance. There will be a 2.6°C (4.7°F)
error for every ohm of lead wire resistance.
Troubleshooting controller outputs
Controller output signal is
not on when it should be.
Load LED is not on. • Temperature reading is incorrect on
display of indicating controls or limit.
See input troubleshooting. • See input troubleshooting.
• Set point is not set correctly. • Verify set point setting.
Controller output signal is
not on when it should be.
Load LED is on. • Output wiring is incorrect. • Verify wiring. Relay outputs act as a
switch, they do not source power.
For DC output controls, voltage should be
about 20VDC with no load. Greater than 5
volts with load of 500
Ω or greater.
Control output signal is on
when it should not be on.
Load LED is on. • Temperature reading is incorrect on
display of indicating controls or limit.
see input troubleshooting. • See input troubleshooting.
• Set point is not set correctly. • Verify set point setting.
• Control output is defective. • Repair or replace controller.
Load is on when it should
not be on. Load LED is off. • Power switching device (SSR, HG
relay, mechanical relay) is shorted. Con-
troller outputs shorted. • Remove wires from output of control to in-
put of power switching device. If load is still
on, replace power switching device. If load
turns off, replace controller or sensor. See in-
put troubleshooting.
• Output wiring is incorrect. • Verify wiring.