Save data quality (VTQ) as historical data

The Historian supports the OPC Quality definition. A 16-bit value for OPC data quality is sent to the Historian in the VTQ packet. Within the 16-bits, the low-order byte is the standard OPC portion. The high order byte is reserved and is currently unused. The Good, Bad, Initializing (which is a form of Bad) and Uncertain quality states are specified in the low-order byte.

Any change in the mapped Historian Quality Detail saves a new record to the Historian, regardless of whether the attribute value has changed. If an attribute value remains constant over a period of time with varying changes in quality, multiple records are stored in the Historian. The OPC quality stored in the Historian is the actual quality of the attribute in Application Server without modification.

The Historian can create and insert additional (non-System Platform generated) VTQ records that modify quality in the database. These additional VTQ records provide additional information about network outages or other events to client applications that use historical data from the Historian.