CLS200 Series User’s Guide
Chapter 8: Troubleshooting and Reconfiguring
146
2. If the process variable indicated on the controller display 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 connections.
NOTE! Noise in excess of 1VAC should be eliminated by correctly grounding the
CLS200. See Wiring the Power Supply on page 29.
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 20Ω is normal. Readings in excess of 200Ω indicate a problem with the sensor.
• For RTDs, measure between the IN+ and IN- terminals of TB1. RTD inputs should read
between 20 and 250Ω.
5. To verify that the controller hardware is working correctly, 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 loop you are testing.
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 above
2VAC is observed, 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 2VAC may indicate problems with the ac ground
circuit.
• Check for ac voltage on thermocouples with the heater power on. 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 2VAC may indicate the ground lead is not connected to the CLS200 TB2
ground terminal.
If the above tests indicate proper ac grounding but the controller is indicating incorrect temperatures
or process readings:
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