Watlow CLS200 - Manual (Page 187)

CLS200 Series User’s Guide Chapter 9:Troubleshooting and Reconfiguring
Doc.# 0600-3050-2000 Watlow Anafaze 171
Checking Analog Inputs
If the process variable displayed in the software and on the
controller do not agree:
1. Verify that the controller is communicating.
2. If the process variable indicated on the controller dis-
play is incorrect:
a) Verify that you have selected the correct input
type for the affected loops.
b) Verify that sensors are properly connected.
3. If the sensors are correctly connected, with power on to
the heaters check for high common mode voltage:
a) Set a voltmeter to measure volts ac.
b) Connect the negative lead to a good earth ground.
c) One by one, check each input for ac voltage by
connecting the positive lead on the voltmeter to
the positive and negative sensor input connec-
tions. The process variable should indicate ambi-
ent temperature. If it does not, contact your
supplier to return the unit for repair. See Return-
ing Your Unit on page 164.
NOTE! Noise in excess of 1V Å (ac) should be elimi-
nated by correctly grounding the CLS200.
See Wiring the Power Supply on page 25.
4. 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 .
5. 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) Set the INPUT TYPE to J T/C in the SETUP LOOP
INPUT menu.
c) Place a short across the input. The controller
should indicate the ambient temperature on the
channel you are testing.