Compression attributes

Compression settings enable you to store just enough data to reproduce the signal, discarding any data that is not significant. Compression is performed on Data Archive unless PI Buffer Subsystem is running on the interface node, in which case compression is performed on the interface node by PI Buffer Subsystem.

For more information about compression, see the PI Server System Management Guide.

The following attributes define the compression settings:

• Minimum compression reporting interval

  Minimum frequency (compmin) attribute value, in seconds for recording updates. Values are recorded to Data Archive no more frequently than the specified interval.

• Maximum compression reporting interval

  Maximum time (compmax) attribute value, in seconds, for recording values from the interface to Data Archive.

• Compression deviation

  The compression deviation (compdev) attribute, or deadband, is the acceptable variation used to determine the amount of variation that is considered meaningful. The interface records exceptions, or values whose variation exceeds the deadband.

• Compression deviation percentage

  The compression deviation percentage value is stored in the compdevpercent attribute and specifies what percentage of the span attribute constitutes an exception.

The compdev attribute is related to the compdevpercent attribute as shown in the equation compdev = compdevpercent * span / 100. If either attribute is changed, the other attribute is automatically updated to be compatible.