Blog Post 3 - PIAFC

Time Weighted vs Event Weighted Average

1. Explanation of Time-Weighted and Event-Weighted Average

The following tags are used for this example: ExampleTag1 and ExampleTag2. The table below shows the values in the archive for the two tags for a one minute interval. ExampleTag1 has an archive value every 10 seconds, whereas ExampleTag2 has the same values in the archive as ExampleTag1, but stored at varying intervals.

When using the PI Tag data reference in PI AF to retrieve the average value for the same minute as in the table above

Event-Weighted

Weights each event equally and uses events at each boundary.

Event-Weighted Exclude Earliest Event

Same as Event-Weighted, except the event at the start time (or earliest time) is not used in the calculation.

Event-Weighted Exclude Most Recent Event

Same as Event-Weighted, except the event at the end time (most recent time) is not used in the calculation.

Event-Weighted Include Both Ends

Same as Event-Weighted.

Time-Weighted

Weighs each event value by the length of time over which it applies.

Time-Weighted Continuous

Time-weighs the values, but uses linear interpolation between values regardless of whether the attribute is configured as stepped.

Time-Weighted Discreet

Time-weighs the values, but uses stepped interpolation between values regardless of whether the attribute is configured as stepped.

2. Calculation Details

Event-Weighted

The results ignore any time effect, since it only uses the event values and nothing else.

Time-Weighted (Continuous)

ExampleTag1

The result is calculated as the sum of the areas (A1 – A6) divided by 60 seconds.

ExampleTag2