State-based Instrument Failure alarms

For state-based Instrument Failure alarm behavior, the instrument failure condition is a state on a tank record. The record can only be in one state at any given time. For example, if the Tanking system is functioning normally, the tank is considered to be in a NORMAL state. However, if the next level reading exceeds the HIGH-HIGH limit, the NORMAL state is replaced by the HIGH-HIGH state. If the next reading exceeds the maximum Engineering Units (EGU) limit, the HIGH-HIGH state is replaced by the INST FAIL HIGH state, and so on. When a state is replaced by another state, the associated state alarm is also replaced by the new alarm.

If the Instrumentation High Inhibit checkbox is selected for a tank record, and the level reading exceeds the maximum instrument limit, no INST FAIL HIGH alarm is issued.

If the Instrumentation Low Inhibit checkbox is selected for a tank record, and the level reading drops below the minimum instrument limit, no INST FAIL LOW alarm is issued.

The Instrument Fail Inhibit setting does not apply to the state-based Instrument Failure alarms but does apply to the attribute-based Instrument Failure alarms. For more information, see Attribute-based Instrument Failure alarms.

Note: Occasionally, the state-based Instrument Failure alarm obscures the underlying condition when the new state replaces the current state. For example, if the current state of the tank record is in HIGH-HIGH and the next level reading triggers an instrument failure, the HIGH-HIGH alarm is replaced by the INST FAIL HIGH alarm. If this scenario causes concern, consider using the attribute-based Instrument Failure alarm.