Specify the sampling

You specify how the SourceTag will be sampled on the Sampling tab. The choices you make here determine when the PI Totalizer will look at the SourceTag: whenever there is a new event, on a timed basis, or when an expression changes.

• To create a PI Totalizer that processes the value every time there is a new event for the SourceTag, select Whenever a new source tag event occurs (Natural).

• To create a PI Totalizer to evaluate the SourceTag whenever an expression changes, select Whenever the event expression changes. You can test the expression by clicking the Test button.

• To create a calculation that samples the SourceTag on a timed basis (for example, every 20 minutes beginning at midnight, select Periodically.

  • Then select how the periodically sampled value is derived: Interpolate or Extrapolate. The time period when the sample is to be taken is not guaranteed to correspond to a new event on the SourceTag (unlike Natural sampling) so you must determine whether you will extrapolate the previously recorded value or wait until the next value and interpolate.

  • For new PI Totalizers, the Totalizer tool uses the Step attribute of the SourceTag. If Step is turned on, the tool will default to Extrapolate. If Step is turned off, the tool will default to Interpolate. For details, see Set archive attributes.

    Caution: You may override the default, but you should use caution due to possible data representation conflicts.

  • If you edit an existing PI Totalizer with timed sampling, the tool displays the configured choice.

    

To filter the source events that the PI Totalizer uses, check the Filter source data with the following expression option. Then enter an expression to filter incoming SourceTag events. For example, you can look at a flow only when the fresh water valve is closed. You can test the expression by clicking the Test button.