Channel Diagnostics; Over- Or Under-Range Detection; Open-Circuit Detection - Allen-Bradley CompactBlock LDX 1790D-T4T0 User Manual

4-4 Diagnostics and Troubleshooting

Channel Diagnostics

Publication 1790-UM003A-EN-P
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