Allen-Bradley CompactBlock LDX 1790D-4T0, User Manual

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Publication 1790-UM003A-EN-P
4-4 Diagnostics and Troubleshooting
Channel Diagnostics
When an input channel is enabled, the module performs a diagnostic
check to see that the channel has been properly configured. In addition,
the channel is tested on every scan for configuration errors, over-range
and under-range, and open-circuit conditions.
Over- or Under-Range Detection
Whenever the data received at the channel word is out of the defined
operating range, an over-range or under-range error is indicated in input
data word 4.
Possible causes for an out-of-range condition include:
•
The temperature is too hot or too cold for the type of thermocouple
being used.
•
The wrong thermocouple is being used for the input type selected, or
for the configuration that you have programmed.
•
The input device is faulty.
•
The signal input from the input device is beyond the scaling range.
Open-Circuit Detection
On each scan, the module performs an open-circuit test on all channels.
Whenever an open-circuit condition occurs, the overrange bit for that
channel is set in input data word 4.
Possible causes of an open circuit include:
•
the input device is broken
•
a wire is loose or cut
•
the input device is not installed on the configured channel
•
a thermocouple is installed incorrectly