Use the Persistence field near the top of the DDE tab to stop a change in value from affecting the point state until the point has been in that state for a specified time. This allows the driver to ignore fleeting changes in point value. It also stops ClearSCADA raising change of state alarms and logging change of state events when a point value is fluctuating.
When the point changes value, any change of point state is delayed until the point remains in the new state for a specified amount of time. If the point does not remain in the new state for the required amount of time, no change in point state is recorded.
If, within the persistence time, the value of a multi-bit point continues to increase or decrease in the same direction, the persistence period does not restart as the value crosses to a further state. If the point value remains within the new state as the original persistence time elapses, the outstation updates the point state.
If the value of a multi-bit point reverses its direction of travel before the persistence time has elapsed (for instance, it starts to increase when it was previously decreasing), the point does not change state, and a new persistence time starts for the point value traveling in the new direction.
- Persistence—Use this field to specify the period, in seconds, that a point needs to remain in a new state before the DDE driver updates the ClearSCADA database with a change of value.