Archived data collection

AVEVA™ PI System Connector 3 (PSC3) supports the replication of archived data from the source PI System to the destination PI System for source PI points that have compression enabled/on as indicated by the PI point attribute compressing=1.

When the compressing attribute is set to compressing=1, archived data is transferred from the source PI System to the destination PI System based on the PI points associated with AF objects selected by the data source configuration. By default, the connector sets the compressing attribute to compressing=0 on the destination Data Archive for PI points that have the compressing attribute set to compressing=1 on the source Data Archive. Archive data is transferred for all PI points associated with a Replicate Data Archive only data source configuration, or AF objects selected by a Replicate AF and Data Archive data source configuration.

Note: There is an exception regarding PI points that match the Snapshot Query under the data source configuration. In that case, PI points that match the snapshot query replicate the PI Point attribute as it is defined on the source Data Archive through the compressing setting.

PI points associated with AF objects selected by the data source configuration and all the PI points associated with a Replicate Data Archive only data source configuration or AF objects selected by a Replicate AF and Data Archive data source configuration will have archive data transferred from the source PI System to the destination PI System with the compressing attribute set to compressing=0.

The exception to this rule relates to PI points that match the global Send snapshot data for PI Points that match this query of the data source configuration. In this case, PI points that match the snapshot query replicates the PI Point attribute compressing setting as defined on the source Data Archive.

By default, all archive data moved from the source PI System to the destination PI System has its compressing attribute set to 0 at the destination. The only exception is for any PI Point that is part of a Snapshot Query. In such cases, the PI Point retains the same compressing attribute on the destination as it had on the source, whether that value is 0 or 1.

If desired, archive data replication for a PI point that currently sends snapshot data replication from the source PI System can be edited to send only archive data replication by setting the compressing attribute to compressing=1 on the source PI point to allow replication of archive only data from the source to destination PI System. In this scenario, the PI point must not match a defined snapshot query.

When a PI point is configured for archive only data replication, the destination PI System snapshot will contain the last archived value/timestamp contained in the source PI System. Therefore, the snapshot value/timestamp for a PI point on the destination PI System will be one archived value/timestamp behind the PI point snapshot value found on the source PI System. In other words, the source PI System will contain the latest snapshot value/timestamp of a PI point, whereas the destination will contain the last archived value/timestamp on the source PI System for the PI point.

Note: Slow changing archive only PI point data may result in the destination PI System not reflecting the desired value/timestamp for a PI point. This is a result of the destination PI point only containing the last archived value contained on the source PI System for the PI point.