Point signals can experience transient changes ('spikes') that can result in unwanted point state changes. To help prevent these transient changes from being recorded, and causing alarms and events to be generated or logged, you can configure Persistence on the point limits/states (if supported by your Field Device).
When Persistence is used, any change of point state is not reported unless the point remains in the new state for a specified amount of time (the Persistence Duration). Only then is the new state recorded.
NOTE: You can use the Device Profile to determine if your WITS Field Device supports Persistence (see Display a WITS Device Profile). The Device Profile also specifies various Persistence-related settings.
To configure the Persistence for a WITS analog point or WITS binary point, refer to the following sections:
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Single Persistence Per Point. One Persistence Duration is applied to all of the point's limits or states.
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Separate Persistence Per Point Limit/State. There are separate Persistence Durations for each of a point's limits/states. If Persistence Per Point Limit is supported, you can configure sequential or non-sequential Persistence durations (analog points only).
Sequential Persistence is when equal or longer Persistence Durations are applied as the limits move further away from Normal. For example, if an analog point has three High limits (H1, H2, and H3), the Persistence for H1 is shorter than the Persistence for both H2 and H3. The Persistence for H2 is shorter than the Persistence for H3. This means that the Persistence Durations expire in limit order.
Non-Sequential Persistence is when shorter Persistence Durations are applied as the limits move further away from Normal. For example, if an analog point has three High limits (H1, H2, and H3), the Persistence for H1 can be longer than the Persistence for either H2 or H3. This means that the Persistence Durations may not expire in limit order.
If Persistence is supported, a Field Device may also support separate Persistence Durations for entering a point state and leaving a point state (analog points only). The entering/leaving state persistence can be used with both Single Persistence Per Point and Separate Persistence Per Point Limit/State as explained in those topics.