Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 171)

Rockwell Automation Publication 1756-UM540A-EN-P - May 2014 171
Troubleshoot Your Module Chapter 9
1756-OF8I Module - Incorrect Output 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 outputs maximum.
• The module always outputs zero.
• The module outputs a smaller value than expected.
• The module outputs erratic voltage/current data.
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-OF8I module status indicators,
page 159 .
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 load from the channel in question.
b. Insert a resistor with the module’s voltage/current output range.
c. With a voltmeter or in line current meter, verify that the voltage or
current is as expected.
– If the voltage/current reads correctly the module is performing as
expected. In this case, the load or wiring are likely the cause.
– If the sourcing voltage/current is not read back correctly, then the
module hardware, configuration, or the software application are
suspect.