Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 165)

Rockwell Automation Publication 1756-UM540A-EN-P - May 2014 165
Troubleshoot Your Module Chapter 9
1756-IRT8I Module - Incorrect RTD Readings
To determine the cause of the incorrect reading, first determine the nature of the
incorrect reading. For example, the module can perform as follows:
• The module always reads maximum.
• The module always reads minimum.
• The module reads erratically (data jumping around).
• The module reads with an offset over the entire range.
First, complete the following tasks.
1. Check the status indicators to verify that the module is powered and
communicating.
Red or flashing green status indicators indicate a problem. For more
information on the 1756-IRT8I module status indicators,
page 158 .
2. Make sure wiring is intact and correct.
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 RTD from the channel in question.
b. Connect an RTD emulator directly to the channel in question.
The emulator provides voltage at the channel that is equivalent to the
voltage expected for the RTD type it is emulating.
– If the ohms value reports back correctly then the module is performing
as expected. In this case, the RTD and wiring are likely the cause and
should be checked again.
– If the ohms value reports back incorrectly, 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 an RTD emulator for initial
troubleshooting. In lieu of an emulator, you can apply a known ohms value
to the input. The module must be configured to read an ohms value. If the
module is reading back the ohms correctly, then the module is performing
as expected.