Create a Calculation

When you create a calculation, you can manually define your own expression based on either PI points or assets, or you can create a calculation from one or more existing symbols on a display. To create a calculation from one more symbols on your display, see Create a calculation based on symbols in a display. All PI points in a calculation must be from the same Data Archive. Assets in a calculation must be from the same AF database. You cannot use both PI points and assets in the same expression.

Note: Calculations can be resource-intensive and may slow down your system if used excessively. If AVEVA PI Vision does not allow you to add calculations by following the steps below, your system may be configured to restrict calcuation usage. For more information, see Restrict the use of calculations.

To manually define a calculation, perform the following steps:

1. On the left side of the screen, click Calculations and then click Add Calculation .

   

   The Calculation Editor window opens.

2. Give the new calculation a Name and a Description.

   Note: The calculation Name needs to be unique for the current display. You may reuse a Calculation Name on different displays.

3. Select the basis for the calculation:

   • Click to base the calculation on PI points from a Data Archive, and then select the PI Data Archive server from the drop-down menu.

   • Click to base the calculation on assets from PI AF.

   

4. Configure the Expression to calculate the data you need. Expressions can include tag variables with mathematical and logical operations. See Calculation syntax for additional information.

   Examples:

   'sinusoid' * 2

   ('cdt158'+'sinusoid')/2

   log('cdt158')

   ('sinusoid')/tagspan('sinusoid')

   Drag and drop a PI point or attribute from the Assets pane into the Expression to include it in the calculation. When a data source can be successfully dropped in the expression, it is outlined in green.

   

   By default, all data sources are added to the calculation with the + operator.

5. To change the asset context, drag and drop it from the Assets pane into the field next to the calculation basis buttons. When a data source can be successfully dropped in the field, it is outlined in green.

   

   Note: If the calculation is created in a display that has an asset context, that asset context is used as the default asset context for the calculation.

6. Click Preview to test the expression with data available at the current time.

7. Click Advanced Options to further configure the calculation.

8. Configure the Time Interval for the calculation. By default, this is set to Auto, but you can choose a Custom Time Interval if needed.

   If you set the Time Interval to Auto:

   • Set the Total Conversion Factor for the calculation. This only applies to the Total summary Column.

   • Click Stepped Plot to display this calculation with stepped data.

     

     If you set the Time Interval to Custom:

   • Set the Calc Interval for the calculation. The Calc Interval is the time range for which the data calculation is performed.

   • Set the Sync Time for the calculation. The Sync Time is the time of day (in 24-hour format) from which Calc Intervals are counted.

   • Set the Total Conversion Factor for the calculation. The Total Conversion Factor is used as a time basis for time-weighted totals. This only applies to the Total summary Column.

   • Click Stepped Plot to display the calculation with stepped data.

     

     Example of Calc Intervals and Sync Time defined for a calculation:

   • Calc Interval: 10m

   • Sync Time: 00:00:00 (default)

     The calculated value for each interval is plotted at the start of the interval. Since the Sync Time is set as 00:00:00, the start of the interval begins at the top of the hour. Since the Calc Interval is 10m, every 10 minutes, a new value is plotted. In this example, there is a new plotted value at the following timestamps (among many more):

   • 1:00:00

   • 1:10:00

   • 1:20:00

   • 1:30:00

   • 1:40:00

   • 1:50:00

9. When you have finished configuring the calculation, click Save.