OPC HDA connector

The OLE Process Control Historical Data Access (OPC HDA) connector library provides connection to and data retrieval from OPC HDA servers that implement the OPC HDA Specification 1.1 or greater. It is a true historical connector.

Rather than monitor a tag in real time and then historize the data, the OPC HDA connector can directly obtain historical information about a tag.

Elements

The OPC HDA connector library contains the following items:

• Data source

• Data connection

• Group

• Variable

• Status variable

Guidelines

• The OPC HDA connector supports only OPC Historical Data Access servers that implement the OPC HDA Specification 1.1 or greater.

• Verify that the OPC server is installed as a service rather than a WinForms application.

Connecting and disconnecting

• Start an OPC HDA data source to initiate connection to the respective OPC HDA server.

• Stop an OPC HDA data source to disconnect it from the respective OPC HDA server.

• If a connector becomes disconnected, the update to the stream of stored values stops. When it regains communications with the OPC HDA server or restarts, it queries the OPC HDA server from the time it lost connection up to the current time to verify that data is not lost.

Authentication

The user account running the service requires security permissions to launch and activate the OPC HDA server. If you run the OPC HDA server on a remote PC, there may be additional authentication.

Polling rate

The PollInterval property of an OPC HDA group sets the polling rate for the group of variables. Without a specified status variable, the OPC HDA connector attempts to poll tags in a group in one request. Limit the number of tags in a group to reduce the request size.

With a specified status variable, however, the OPC HDA connector monitors the status variable at the configured poll interval, and if the value for this variable changes, AVEVA Production Management makes a request for variables in the group that uses the status variable.

Related topics

• Add and configure an OPC HDA group

• About the OPC HDA status variable

• Add and configure an OPC HDA data source

• Add and configure an OPC HDA data connection

• Add and configure an OPC HDA variable