Use Persistence to Stop Fleeting Changes in Value from Changing a Point State
Use Persistence to stop momentary changes in point value from changing the state of a point. This stops the driver from processing fleeting changes in point state and reporting those fleeting changes to the server. When a point that supports persistence 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.
Use the Persistence feature to stop Geo SCADA Expert from raising change of state alarms and logging change of state events when a point value is fluctuating.
On Trio radios, points other than String points support persistence.
Configure the required persistence settings using the Persistence field for analog points, and the Persistence section for digital points. In both cases, these fields are on the <Point Type> tab of the Point Form.
Persistence does not apply if an analog point becomes over range (above Full Scale) or under range (below Zero Scale), as these states are reported immediately.
Remember that if you also use the Hysteresis feature with analog points, this can further affect whether the value that the driver reports to Geo SCADA Expert triggers a change in point state. When both Persistence and Hysteresis are used, the change in a point's value has to persist for longer than the Persistence time, and then exceed the Hysteresis value to trigger a change in point state. (For more information Hysteresis, see Specify the Hysteresis - the Minimum Value Change that can Clear an Alarm in the Geo SCADA Expert Guide to Core Point Configuration.)
Example 1 - Using Persistence with an Analog Point
An analog point has this configuration:
High-High Alarm Limit = 80
High Alarm Limit = 70
Low Alarm Limit = 20
Low-Low Alarm Limit = 10
with this Persistence setting:
At 12:00:00 the point value is 50 (Normal).
At 12:00:23 the point value increases to 73, which is above the High Limit.
At 12:00:28 the point value is still 73, so the point state changes to High, as it has been 5 seconds since the value crossed the High Limit from the Normal state.
At 12:00:38 the point value rises further to 84 (the High-High Limit).
At 12:00:40 the point value drops to 78, so the point state of High remains unchanged, as the point was in the High-High range for less than the Persistence time.
Example 2 - Using Persistence with a Digital Point
A 1-bit digital point is configured to show the state of a switch (on, or off). The point states are configured as:
State 0 = Switch On
State 1 = Switch Off
The Persistence settings are:
The switch is off so the point is in State 1. The switch goes on then off again after 2 milliseconds. The point state remains unchanged as the switch did not remain on for the duration of the Leaving Other States persistence time (3 milliseconds).
The switch goes on and remains on. After 3 milliseconds, the switch is still on so the point state changes to 0. The change is reported to the server the next time that the driver scans the radio. The reported data is processed and Geo SCADA Expert raises or logs any alarms or events that are configured for State 0.
The switch goes off and remains off. After 5 milliseconds (the Leaving State 0 persistence time), the switch is still off. The point state changes to 1. The change of state is reported to the server the next time that the driver scans the radio. The reported data is processed and Geo SCADA Expert raises or logs any alarms or events that are configured for State 1.