Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 168)

168 Rockwell Automation Publication 1756-UM540A-EN-P - May 2014
Chapter 9 Troubleshoot Your Module
1756-IF8I Module - Incorrect Input Voltage/Current 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/zero/negative.
• The module reads voltage/current 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-IF8I module status indicators,
page 157 .
2. Make sure wiring is intact and correct, current or voltage input wired to
the corresponding terminals and with proper polarity.
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 transmitter from the channel in question.
b. Connect a known voltage/current source directly to the module.
A known voltage/current source provides voltage/current at the
channel equivalent to the voltage/current expected from the
transmitter.
– If the voltage/current reports back correctly then the module is
performing as expected. In this case, the transmitter or wiring are likely
the cause.
– If the applied voltage/current source is not reporting back correctly,
then the module hardware, configuration, or the software application
are likely the cause.
We highly recommend using a known voltage/current source for initial
troubleshooting.