About the PI status variable

It is optional to specify a status variable. Without a status variable, by default, AVEVA Production Management attempts to poll variables in each group every 10 seconds with a 10 minute moving-forward window regardless of whether new samples are available from the PI server. With a status variable, the PI connector monitors the status variable at the configured poll interval, and if the value of this variable changes, AVEVA Production Management makes a request for variables in the group that uses the status variable. This option can reduce the number of unnecessary polls and improve the efficiency of data acquisition.

The StatusVariable property of a group defines the variable that the group uses as the status variable. This can be any variable, such as a stored variable, calculated variable, PiVariable item, or PiStatusVariable item.

Polling scenarios

The following list describes different polling scenarios:

• Without a status variable - The connector attempts to poll tags in a group in one request at the configured poll interval. The connector polls from the end time of the stream to Current Time minus Offset, and it updates the end time of the stream to Current Time minus Offset. The MaximumTimeDomain moves forward regardless of whether new samples are available from the data source. This configuration does not account for late-arriving data.

• With a status variable that is a PiVariable item, stored variable, or calculated variable - The connector monitors the status variable at the configured poll interval, and if the value of this variable changes, AVEVA Production Management makes a request for variables in the group that uses the status variable. This configuration is suited for a slowly changing dimension where the status variable does not participate in the aggregation, particularly for accumulative values. In this configuration, the status variable and the other variables may not have the same end-of-stream time. The connector updates the status variable to the last good sample, but it updates the stream of the other variables to Current Time minus Offset. This configuration obtains late-arriving values for the status variable, but it may miss late-arriving values for the other variables. In this configuration, the status variable cannot belong to the group that uses it as a status variable.

• With a status variable that is a PiStatusVariable item - The connector monitors the status variable at the configured poll interval, and if the value of this variable changes, AVEVA Production Management makes a request for variables in the group that uses the status variable. This configuration is suited for a slowly changing dimension where the status variable does participate in the aggregation, particularly for non-accumulative values such as hertz and kilowatts. This configuration does not miss any late-arriving values. The connector polls the status variable from the end time of the stream to Current Time minus Offset, ignores the MaximumTimeDomain setting, and updates the end time of the stream to the last good sample.

Related topics

• PI connector

• Add and configure a PI variable