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Calculation example: sum of analog values

In this first example of the use of Calculation, we need to fetch two values from two different IGSS analog objects, for instance tanks, and display the result as a total value.

To illustrate clearly what we’re doing, we create a third tank on the process diagram whose data input does not come from the process but from simply fetching values already collected from the process by the two tanks on the diagram. In the Definition module, our process visualization looks like the illustration below, where Tank_FR1 and Tank_FR2 are the two tanks whose sum we wish to display.

1. Let's start by creating a third analog object and placing it on the diagram underneath Tank_FR1 and Tank_FR2, and we’ll call it Intake_Main.

2. The only work to be done on the Intake_Main analog object is on its Calculation tab. Remember that we don’t actually receive data directly from the process for this tank but via the two other tank objects. Double click on the new object Intake_Main and then find the tab Calculation and open it.

3. Put a check mark in the Actual Value atom as shown above.
4. Under Execution trigger to the right, make sure the On object changes in expression is selected.
5. In the field under Expression key in the following parameters: Value('Tank_FR1')+Value('Tank_FR2'). The latter are called IGSS object functions.
6. Click on the button Test Expression… and the following message box appears confirming that the expression syntax is valid.

7. Click OK.
8. In the field called Comment, the system designer may write a brief note about what occurs. If operators are permitted to view an object's properties in Supervise, then this note will be viewable for them.
9. Now go to the Display tab and under Show select Name > Enable and select State /Value > Enable.
10. At the bottom left of the Display tab remove the checkmark from Selectable, which prevents operator access to the object's properties.
11. Click OK to save and close.
12. Save and install the configuration.
13. Start the configuration up by clicking on the IGSS Starter.
14. Try changing the Actual Value atoms on either of the two tanks Tank_FR1 or Tank-FR2.

• When either of the Actual Value atoms on the two tanks Tank_FR1 or Tank_FR2 is changed, the Intake_Main tank reflects the changes immediately.

• If it's necessary to record the workings of the Calculation function, then make sure All changes and Log outgoing commands is selected on the object's Data Management Definitions tab.

For a complete list of the object functions available for Calculation, please click here.

For a complete list of the arithmetical functions and operators available for Calculation, please click here.

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