WITS Field Devices support either:
- a single Persistence duration that applies when entering and leaving a state
- a Persistence duration for entering a state and a separate Persistence duration for leaving a state.
Entering a state means that the point value is moving into a different state, away from Normal. A point only enters a new state if its value has been equal to, or beyond the limit threshold for the Persistence duration.
Leaving a state means that the point value is moving into a different state, towards Normal. A point only leaves a state (and therefore enters a new state) if its value has been beyond the limit value (with Hysteresis where applicable) for the Persistence duration.
The Device Profile for your Field Device specifies whether the device supports separate Persistence for entering and leaving (see Display a WITS Device Profile).
When you configure WITS database points, the Persistence settings on the Point Form reflect the Persistence supported by your Field Device:
- If there is one Persistence field (for the point or for each limit/state), the Persistence duration you specify will apply to both entering and leaving a state.
- If there are a pair of Persistence fields (for the point or for each limit/state), you can specify separate Persistence durations for entering and leaving a state.
For more details on configuring the Persistence durations, see: