Span

The Span is the difference between the maximum and minimum of the range. It is required for all numeric data type points.

For float16 point types, Span is used with Zero for scaling values in the archive. The Span value must be positive. If the value for a point type float16 point is greater than the maximum of range, it is recorded in the archive as Over Range. For other point types, Zero and Span do not affect the values recorded in the archive.

The Span is also used when defining trends in client tools (such as PI Vision) with a vertical scale of database.

For digital points, the Data Archive server assigns the value for this attribute and ignores any edits made to it, such as with PI Builder.

This attribute is not used for non-numeric points.

You can change the Span for a point without affecting data already in the archive. For points of type float16, the old Span is used for retrieving the archive data collected before the edit. The new Span is used for data collected after the edit. If you change Span, the exception and compression deviation percentages are preserved but the ExcDev and CompDev fields, which are expressed in engineering units, are modified internally. If you specify any of the deviation fields in the editing operation, they take precedence.

Note: Some interfaces use Span information to filter incoming data. These interfaces often convert out-of-range data to digital states over range and under range. However, interfaces can use Span configuration in other ways. The PI Server computer itself does not change out-of-range data, except for points of type float16.