Spectrum Controls 1746sc-NI8u - Manual (Page 77)

Chapter 6: Testing Your Module 65
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 blink and sets the corresponding fault bit in the
channel status word. Channel fault bits (bits 12-15) and channel-status
LEDs are self-clearing when fault conditions are corrected.
Open-circuit Detection (Bit 12)
If open-circuit is enabled for an applicable 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. Open
circuit does not apply to ±2V, 0-5V, 1-5V, ±10V, 0-10V, or 0-20mA ranges.
Possible causes of an open circuit include:
• broken thermocouple, RTD or CJC sensor
• thermocouple, RTD or CJC sensor wire cut or disconnected
• millivolt, volt or milliamp input wire cut or disconnected
• less than 3 ohms has been detected on an RTD input.
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 or RTD
being used
• a type B thermocouple may be registering a °F value in EU 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
• the millivolt, Volt, or milliamp input is outside of its selected input range