Use the fields within the Persistence section of the Digital Point tab to stop fleeting changes in value from causing a change in point state. With the Persistence feature, a change in value will only cause a change in point state if that point remains in the new state for a specified time.
Example:
A 1-bit digital point is configured to show the state of a pump (running, or stopped). The point states are configured as:
State 0 = Pump Running
State 1 = Pump Stopped
The Persistence settings are
The pump is not running so the point is in State 1. The pump starts to run then stops again after 2 seconds. The point state remains unchanged as the pump did not run for the duration of the Leaving Other States persistence time (three seconds).
The pump starts to run and remains running. After three seconds, the pump is still running so the point state changes to 0. The change is reported to the server the next time that the driver scans the outstation. The reported data is processed and ClearSCADA raises or logs any alarms or events that are configured for State 0.
The pump stops running and remains stopped. After five seconds (the Leaving State 0 persistence time), the pump is still not running. The point state changes to 1. The change of state is reported to the server the next time that the driver scans the outstation. The reported data is processed and ClearSCADA raises or logs any alarms or events that are configured for State 1.
The persistence interval should be equal to or greater than the scan rate of the point so that point values are recorded within the persistence period.