Calculation example: controlling a pump by setting a condition

In this example of using Calculation, we want to always ensure that when a specific condition is met, a specific state will be active.

We apply this control instance to a pump, which is called Pump_4. It’s purpose is to pump a liquid into a storage tank called Tank_FR1.

However, we want to ensure that the pump automatically stops when the level in the tank reaches a certain limit. To achieve this, we send a command to the pump to stop it when the condition of the tank having reached a certain level is fulfilled.

$images\DEF_Calc_Pump_4_Tank_FR1.gif$

Double click on the Pump_4 graphic and go to the Calculation tab.
Under Atom select Command.
Under Execution trigger select On object changes in expression.
Under Expression in the Command field, key in the command 0 (stop).
Select the check box Only execute expression if this condition is true and then key in the following: Value('Tank_FR1')>2310.11
Click the button Test Expression… to make sure the syntax is correct for both the expression and the condition.
In the Comment field, type in a short explanation of what takes place. (See the illustration below.)

$images\DEF_Calc_Pump_4_Calculation_tab.gif$

Click OK.
Save and install the configuration.
Activate the IGSS Starter and test the results by changing the PV (Process Value) atom of the tank to a value greater than 2310.11 and the pump changes its state to 0 (OFF).

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.