Watlow Series L
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13
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Chapter 5: Troubleshooting
Indication
Possible Cause(s)
Corrective Action
On indicating limits, the dis-
play is not illuminated.
• Power supply switch off
• Fuse blown
• Breaker tripped
• Safety interlock door switch activated
• Wiring incorrect or open
• Power supply voltage incorrect
• Defective limit
• Turn switch on
• Replace fuse (check cause of failure)
• Reset breaker (check cause of failure)
• Close door
• Check wiring
• Verify input power
• Repair or replace limit
Troubleshooting Thermocouple Inputs
Temperature reading is incor-
rect, showing a sensor error,
[Er;In]
, or ALARM LED is
switching at the wrong tem-
perature.
• Setting for degree C or F is incorrect • Check the model part number for
Degree C or F. If the model has Incre-
ment/Decrement keys, then the C/F
setting is adjustable
• Sensor or limit may be bad. Sensor
connections may be bad
• Place a jumper wire across the ther-
mocouple input terminals. The display
should indicate ambient temperature.
If it does, the limit is OK
- For high limit: Start with limit set
point above ambient temperature,
ALARM LED should be off. Decrease
limit set point until ALARM LED goes
on. It should be approximately ambi-
ent temperature
- For low limit: Start with limit set point
below ambient temperature, ALARM
LED should be off. Increase limit set
point until ALARM LED goes on. It
should be approximately ambient tem-
perature
• 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 thermo-
couple sheath. If there is continuity,
replace sensor with an ungrounded
thermocouple
Temperature seems to be 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.
Correct polarity problems
Temperature seems to be read-
ing low and not increasing
while actual process tempera-
ture is increasing.
• Sensor is bad. Thermocouple is shorted • Check thermocouple connections.
Check thermocouple wire insulation
to make sure it is not damaged, caus-
ing the wires to short (making a new
junction)
Temperature seems to be off-
set from actual process tem-
perature, or the ALARM LED
switches on at the wrong tem-
perature. The offset changes
with changes in process tem-
perature.
• 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 thermo-
couple extension wire of the correct
type was used to extend thermocouple
leads. Replace if necessary
Troubleshooting
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