Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 163)

Rockwell Automation Publication 1756-UM540A-EN-P - May 2014 163
Troubleshoot Your Module Chapter 9
2. Check the module wiring to verify the following:
–
The wiring is correct.
– The wiring is intact.
– The CJC sensors, if being used, are installed correctly.
3. If the status indicators indicate that the module is communicating as
expected and all module wiring is correct, complete the following tasks.
a. Disconnect the thermocouple from the channel in question.
b. Connect a thermocouple emulator directly to the channel in question.
The emulator provides voltage at the channel that is equivalent to the
voltage expected for the thermocouple type it is emulating.
– If the emulator temperature report is correct, the module is performing
as expected. In this case, the thermocouple and wiring are likely the
cause and should be checked again.
– If the emulator temperature report is incorrect, the module hardware,
configuration, or the software application are likely the cause. In this
case, check the Logix Designer application project.
We highly recommend using a thermocouple emulator for initial
troubleshooting. In lieu of an emulator, you can apply a millivolt signal to
the input. The module must be configured to read a millivolt signal. If the
module is reading back the millivolt correctly, then the module is
performing as expected.
IMPORTANT Remember, if you choose to use CJC sensors with the 1756-IRT8I
module, you must use the sensors at both connection positions, that is,
the top and bottom of the module.
You cannot use only one CJC sensor with the module.
For more information on using CJC sensors with the 1756-IRT8I
module, see
Cold Junction Compensation on page 82 .