The following are examples of how you might use a calculation point:
Example 1:
You have two analog points called Flow 1 and Flow 2.
You have an analog calculation point called Total Flow in the same group as Flow 1 and Flow 2.
The calculation point has the trigger condition Tag Processed and the expression: ".Flow 1" + ".Flow 2".
The calculation point calculates the total measured flow of Flow 1 and Flow 2. It updates the total flow each time that ClearSCADA processes either of the flow points.
Example 2:
You have two analog points called Flow and Pressure and a digital point called Valve.
You have a digital calculation point called Alarm Summary in the same group as these three points. The calculation point has the following properties:
- 1-bit digital with a state 0 description of Inactive and a state 1 description of Active.
- The trigger conditions Method and Tag Processed.
- The expression: IIF((".Flow.AlarmState" = 2) OR (".Flow.AlarmState" = 4) OR (".Pressure.AlarmState" = 2) OR (".Pressure.AlarmState" = 4) OR (".Valve.AlarmState" = 2) OR (".Valve.AlarmState" = 4),1,0).
The calculation point summarises the alarm state of the three points. The point's state will be Active if any of the three points have an active alarm, otherwise its state will be Inactive.
The calculation point's state updates each time that ClearSCADA processes any of the three points or when the Execute method is called.
Example 3:
You have an analog point called Flow with historic data enabled.
You have an analog calculation point called Average Flow Today in the same group as the analog point Flow.
The calculation point has a trigger condition of Periodic. The period Interval is 1H, the Offset is D and the time zone is UTC. The calculation point has the expression: ".Flow;Average;D;1D".
The calculation point calculates today's average flow from the historic data collected by ClearSCADA from the analog point Flow. The expression uses a historic tag.
The calculation point updates the average flow every hour throughout the day.
Example 4:
You have an analog point called Flow.
You have an analog calculation point called Percentage Flow in the same group as the analog point Flow.
You also have a constant double variable called Maximum Flow that defines the maximum flow value. For example, maximum flow value=50 litres/second.
The calculation point has the trigger conditions Method and Tag Processed and the expression: (".Flow" / ".Maximum Flow") * 100.0.
The calculation point calculates the last measured flow as a percentage of the maximum flow. For example, if the analog point Flow measured the flow as 30 litres/second, and the maximum flow value is 50 litres/second, then the percentage flow is 60%. The calculation point updates the percentage flow value every time that ClearSCADA processes the analog point Flow.
The expression uses a variable so that users can change the maximum flow without having to modify the expression.
Further Information
Periodic execution and trigger conditions: see Configure the Execution Settings for a Calculation Point.
Execute method: see Execute.
Variables: see Variables in the ClearSCADA Guide to Core Configuration.