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Channel diagnostics, Channel diagnostics -4 – Rockwell Automation 1790P-T4T0 CompactBlock LDX I/O Thermocouple Modules User Manual

Page 54

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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