OPC Historical Data Access (OPC HDA) is used to retrieve and analyze historical process data for the purpose of analysis, optimization, inventory control, regulatory compliance, etc. OPC HDA Servers typically retrieve data stored in a Process Data Historian, a relational database, or an RTU (Remote Terminal Unit).

Software applications can use OPC HDA to write historical data as well. This enables applications to write historical data back to a database. This occurs when users need to input manual meter readings (which have a timestamp that occurs in the past), laboratory readings, or even corrections of previously dated information.

OPC HDA can also be used for the automated transfer of data between historians. Corporations can use this to synchronize process historians, or to compensate for interruptions in the real-time transfer of process data. That is, an application can buffer data during a communication outage, and when the real-time connection is restored, the receiving application can use OPC HDA to recover the buffered information. The OPC Foundation (www.opcfoundation.org) is responsible for defining and maintaining the OPC HDA specification.

See also: OPC DA