Watlow Series L Temperature Limit - Manual (Page 13)

Wa t l ow S e r i e s L • 11 • C h a p te r 5 : Tro u bl e s h o o t i n g
Indication Probable 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