Channel-Status Leds (Green); Open-Circuit Detection (Bit 12); Out-Of-Range Detection (Bit 13 For Under Range, Bit 14 For Over Range) - Allen-Bradley 1746-NT8 User Manual

6-4 Troubleshooting Your Module
Publication 1746-UM022B-EN-P - January 2005

Channel-status LEDs (Green)

The channel-status LED operates with status bits in the channel status
word to indicate the following faults detected by the module:
• invalid channel configuration
• an open-circuit input
• out-of-range errors
• selected filter frequency data acquisition or auto-calibration
errors
When the module detects any of the following fault conditions, it
causes the channel-status LED to flash and sets the corresponding
fault bit in the channel status word. Channel fault bits (bits 12 through
15) and channel-status LEDs are self-clearing when fault conditions
are corrected.

Open-circuit Detection (Bit 12)

If open-circuit detection is enabled for an input channel, the module
tests the channel for an open-circuit condition each time it scans its
input. Open-circuit detection is always performed for the CJC inputs.
Possible causes of an open circuit include:
• broken thermocouple or CJC sensor
• thermocouple or CJC sensor wire cut or disconnected
• millivolt input wire cut or disconnected
Out-of-Range Detection (Bit 13 for Under Range, Bit 14 for Over
Range)
The module tests all enabled channels for an out-of-range condition
each time it scans its inputs. Possible causes of an out-of-range
condition include:
• the temperature is too hot or too cold for the thermocouple
being used.
• a type B thermocouple may be registering a °F value in
Engineering Units x1 beyond the range allowed by the SLC
processor (beyond 32,767) for the data word.
• a CJC sensor may be damaged or the temperature being
detected by the CJC may be outside the CJC sensor range limits.