Watlow CPC400 - Manual (Page 163)

CPC400 Series User’s Guide Chapter 6: Troubleshooting and Reconfiguring
Doc. 0600-2900-2000 Watlow Anafaze 149
5. Verify the sensors:
• For thermocouples, remove the thermocouple
leads and use a digital voltmeter to measure the
resistance between the positive and negative
thermocouple leads. A value of 2 to 20
Ω
is nor-
mal. Readings in excess of 200 Ω indicate a prob-
lem with the sensor.
• For RTDs, measure between the IN+ and IN- ter-
minals of TB1. RTD inputs should read between
20 and 250
Ω .
6. To verify that the controller hardware is working cor-
rectly, check any input (except the pulse input or an
RTD) as follows:
a) Disconnect the sensor wiring.
b) In the Input menu, set the Input type parameter
to J T/C.
c) Place a short across the input. On the loop that
you are testing, the controller should indicate the
ambient temperature.
Earth Grounding
If you suspect a problem with the ac ground or a ground
loop:
• Measure for ac voltage between ac neutral and panel
chassis ground. If ac voltage is above 2V
Å (ac), then
there may be a problem with the ac power wiring. This
should be corrected per local electrical codes.
• With ac power on, measure for ac voltage that may be
present between control panels’ chassis grounds. Any
ac voltage above 2V
Å (ac) may indicate problems with
the ac ground circuit.
• With the heater power on, check for ac voltage on ther-
mocouples. A control output providing power to the
heaters will increase the ac voltage if there is heater
leakage and an improper grounding circuit. Measure
from either positive or negative thermocouple lead to
ac ground. AC voltage above 2V
Å (ac) may indicate the
ground lead is not connected to the CPC400 TB2
ground terminal.
If the above tests indicate proper ac grounding but the con-
troller is indicating incorrect temperatures or process read-
ings:
• Verify which type of sensor is installed and that the
Input type parameter in the Input menu is set accord-
ingly.