Instrument Fail Check

Instrument Fail Check can be configured on rate and analog records to generate alarms when Remote Terminal Units (RTUs) receive values outside their measurable range.

Sometimes, due to instrument or sensor malfunction, analog and rate instruments and/or their associated transducers try to send a value to the RTU that is outside of the RTUs’ measurable range. If the Instrument Fail Check checkbox is selected for RTUs capable of sensing instrument failures, an analog or rate point alarm is generated when an instrument failure occurs.

If the RTU is not capable of sensing "out-of-range" failures, select Instrument Fail Check to generate alarms whenever the raw value is not within the raw value range.

Note: Instrument failure handling is protocol-specific.

For analog points, instrument failure alarms "clamp" a value that exceeds the minimum or maximum alarm threshold to the value of the threshold it exceeded. For example, if the maximum pressure value allowed is 50, and this value increases from 45 to 55, the value will be locked in at 50.

For rate points, instrument failure alarms "clamp" a value that exceeds the minimum or maximum alarm threshold to the last known good value. For example, if the maximum flow rate value allowed is 50, and this value increases from 45 to 55, it will be locked in at 45.

For rate points receiving accumulated pulse counts, instrument failure alarms are generated when the raw value received is negative, or equal or greater than the configured rollover value. In both cases, the flow rate and the accumulated values will display the last good polled value. For cases when accumulator rollover results in instrumentation failure state alarm, the instrument failure deadband configuration is not applicable.