Expressions

In PI DataLink, expressions are performance equations that you can use in functions to incorporate mathematical operations and calculations based on PI System data items. For example, you might use an expression in a PI DataLink function to calculate values as they are retrieved from Data Archive.

Note: PI DataLink restricts data items that you can include in expressions. See Restrictions on data items in expressions.

Some PI DataLink functions accept either a data item or an expression as input. These functions have Data item and Expression options at the top of the task pane. Some PI DataLink functions also have a Filter Expression field. Specify a filter expression to limit the values that a function returns.

PI DataLink functions that can use expressions include:

• Archive Value function

• Compressed Data function

• Sampled Data function

• Timed Data function

• Calculated Data function

• Time Filtered function

Subsequent sections describe basic information about expressions. PI DataLink supports all the syntax, operators, and functions that Data Archive supports.

For more information regarding syntax, see Performance equation syntax. For a complete list of PE equations, see Alphabetical reference for PE functions.