Introduction to analyses

An analysis performs calculations on a specified schedule. An analysis takes existing PI AF attribute values as inputs and produces new outputs, either new calculated values or new event frames. Every analysis has an associated element or element template.

The following types of analyses are available:

• Expression

  Calculates one or more output values from specified functions, operators, and input values.

• Rollup

  Calculates standard statistical functions for a group of selected attributes. This group is selected from attributes on an element or from the set of all attributes on its sub-elements.

• Event frame generation

  Starts or ends event frames based on specified conditions.

• SQC

  Uses Statistical Quality Control (SQC) methods to monitor that attribute values lie within predetermined boundaries.

All analyses can be created from analysis templates with either Enabled or Disabled status; by default, analyses will be enabled when created. To create an analysis with Disabled status, make sure to clear the Enable analyses when created from template check box in the analysis template.

For event frame generation analyses and SQC analyses with event frame outputs, you can create a notification rule template by clicking Create a new notification rule template for Analysis Template Name.

For expression analyses and event frame generation analyses, you specify inputs in expressions.

For event frame generation analyses (running PI Analysis Service 2017 R2 or later versions), expression and rollup analyses, you can map analysis outputs to PI AF attributes. If you map outputs to attributes configured as PI point data references, the analysis saves the history of the output to a PI point. We recommend you save analysis outputs to PI points. You can use the PI point in visualization tools to view the trend of the analysis. Saving outputs to PI points also results in better PI AF performance than saving outputs to attributes without data references.

Note: PI Analysis Service does not use exception reporting while writing to output configured as PI point data references. Although exception settings for the output PI point are not used, compression settings for the output PI point will be used to determine the outputs that are written to Data Archive.

Beginning with PI AF 2018 SP2, analyses will honor the display digits configured on an attribute or attribute template. Values you see when you evaluate an analysis or preview results will display the same number of digits as your output attribute so long as you have mapped your output attribute. For more information, see Control the display of attribute and attribute template values.