Watlow Series 935A User’s Manual
3 7
To Troubleshoot Sensor
• Remove sensor wires from Terminals 1 and 2.
• For a thermocouple sensor Series 935A, place a jumper wire on Terminals 1 and 2.
Control should display the ambient temperature at the back of the control.
• For an RTD sensor Series 935A, place a 110 +/- 10
Ω
resistor on Terminals 1 and 2.
The control should read 100
Ω
= 32°F, 110
Ω
= 77°F, 120
Ω
= 127°F.
• An RTD sensor Series 935A can be configured in software as if it were a
thermocouple unit, and then tested as above.
• You can restore factory calibration
[`rST]
Table 13 - Error Codes and Actions
Display
Probable Cause
Recommended Action
Reversed thermocouple
Change the sensor
A-D
conn to –.
leads on Terminals 1 and 2.
under flow
Sensor type
Go to In prompt, check selection (see p. 20),
Sensor
mismatch or open RTD.
or check RTD, replace as necessary.
under range
Sensor type
Go to In prompt,
Sensor
mismatch.
check selection (see p. 20).
over range
Open Thermocouple, bad
Check the sensor,
A-D
connection, or broken wire.
replace as necessary.
over flow
Electrical noise.
Cycle power to system. See if error clears.
Check system for electrical interference.
Control is inoperable.
Check for line voltage at
terminals 7 and 8.
Table 14 - Troubleshoot Control Outputs
When indications such as significant differences between set point and
actual temperatures point to no output action, check output configurations
as described on p. 23. Check wiring, p. 44.
Measure
Output
Terminals
Load-on State
Load-off State
“C” Output 1
3 & 4
LED 1 on
LED 1 off
3.0 to 7.0V
Î
(dc)
0.0V
Î
(dc)
“C” Output 2
5 & 6
LED 2 on
LED 2 off
3.0 to 7.0V
Î
(dc)
0.0V
Î
(dc)
“D” Output 2
5 & 6
LED 2 on
LED 2 off
0V
Î
(dc)
line voltage.
Load sees line voltage
Load sees 0V
Î
(dc)
“K” Output 2
5 & 6
LED 2 on
LED 2 off
<2V
Î
(dc)
line voltage
Load sees line voltage
Load sees 0V
Î
(dc)
[`Er1]
[`Er2]
[`Er3]
[`Er4]
[`Er5]
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