Check for tank level or volume creep

A tank can be configured to track either level creep or volume creep. If the tank is in an Idle state (either set by the Controller or automatically), there should be no change in the tank level/volume. Level/volume changes can occur, however, due to instrumentation drift. When this happens, it is referred to as level/volume creep or deviation.

When a tank goes into an Idle state and creep checking is enabled, a base level/volume for creep checking is set to the current level. A Creep or Deviation state exists if a configured positive change or negative change limit is exceeded.

If a Deviation state exists, an alarm is issued and the base level/volume is reset to the current level/volume. On the next processing cycle where the required time between creep checks has elapsed, if one or both Creep or Deviation state conditions have cleared, the tank returns to a Normal state. Otherwise, the Deviation state will persist. Each time Deviation persists, the base level/volume is reset.

Once the alarm has been issued, it is not cleared until a configured time interval has elapsed and the Deviation state no longer exists.