VQT Data

VQT stands for Value, Quality, Timestamp.

The three characteristics of each data point in the system are compliant with the OPC or OPC UA specification.

Value

Value of the data point, can contain different data types.

Examples:

  • 32 (Integer)

  • 38.5 (Real number)

  • helloworld (string)

Quality

Quality of the value, also available as numeric code. Determines how trustworthy the value is, described in detail in the OPC specification.

Examples:

  • Good (0x0 in OPC UA and 0xC0 in OPC Classic).

  • BadWaitingForInitialData (0x80320000 in OPC UA)

Timestamp

The Timestamp, for the value.

Example:

  • 2018-07-26T14:23:45.000Z (ISO 8601 format)

  • 1532615025000 (milliseconds since Epoch)

When transferring data points from different source systems to the target system, note how the respective source system and the target system PI handle VQT.

Quality can be influenced at several levels in the data flow. It can already be bad in the "bad" source, that is, it can also be bad due to the failure of a component involved in the data transfer.

The following section describes the special cases that data transfer takes into account.