Rockwell Automation 1771-IFF/A,D17716.5.116 FAST ANALOG INPUT MODULE - Manual (Page 23)

2–7 Troubleshooting Your Input Module
Publication 1771Ć6.5.116 - July 1996
After determining that the module is operating correctly,
troubleshoot any faulty inputs by:
•
measuring each input with respect to module common
•
disconnecting inputs from the field wiring arm one at a time
while observing module action
•
testing for input channel functionality
Measuring Each Input with Respect to Module Common
During this procedure, monitor the input data table of the
programmable controller and observe any changes which occur.
1. Make sure the field wiring arm is in position on the module.
2. Apply power to the 1771 I/O chassis.
3. Check each input (either single-ended or differential) for common
mode voltages exceeding +35V with respect to module common.
A. Hold the positive probe of the voltmeter on the first input
terminal.
B. Hold the negative probe of the voltmeter on a module
common terminal (terminals 20 or 21).
4. If any voltage is seen that exceeds +35V, remove that channel’s
input wiring and observe the affect on the input data table of the
programmable controller.
!
ATTENTION: Remove power from the 1771 I/O
chassis backplane and field wiring arm before
removing or installing input wiring.
•
Failure to remove power from the backplane or
wiring arm could cause module damage, degradation
of performance, or injury.
•
Failure to remove power from the backplane could
cause injury or equipment damage due to possible
unexpected operation.
If no other common mode voltages are present, the input data for
all other channels should stabilize to some predictable value.
Troubleshooting a Bad
Input