VQT Data Ingress and Egress
Ingress
The different source systems and interface types usually provide Value and Timestamp. Depending on the interface, the only remaining question is whether the timestamp includes a local time offset. The Quality, on the other hand, can be completely different depending on the source system type or the interface used. Since not every system and interface provides quality information according to the OPC specification, the available status information must be converted into a valid OPC Quality Code for recording in the system.
Source Type OSI PI
Value and Quality are available in UTC time format via the PI Bridge. Connections with the PI OPC HDA server will receive OPC HDA-compliant qualities. Connections using the PI-Bridge (SDK calls), will be automatically translated from PI Status to OPC UA Status.
Source Type AspenTech IP.21
AspenTech IP.21 includes an OPC HDA server.
Historical data can also, be realized via an ODBC query.
The ODBC interface of AspenTech IP.21 transmits value and timestamp in UTC format, but no OPC quality.
Instead, a status code is transmitted, which must be translated into an OPC Quality.
| This is also generally the same situation for the Wonderware Historian/InSQL. |
Source Type PHD
For the read access to PHD no special interface is used, but the standard OPC HDA server.
Source Type HDA
If a query of historical data is executed via an OPC HDA interface, the result contains VQTs according to the OPC specification. Therefore no logics concerning quality have to be executed.
Source Type OPC DA
An OPC DA data source provides only VQT of the current value, and is therefore not linked to the History Transporter object. OPC DA data sources are connected with the standard functionality of the system, and provide VQT according to the OPC specification. Therefore no logics concerning quality have to be executed, but a QT can be taken over as read after the system.
Egress
The target system is unable to treat quality as a separate parameter and cannot process it independently. As a result, the system must receive quality information as part of the current value, with the specific format depending on the interface being used. Note: In case of poor quality, the V information is lost in the target system.
A selection of states is available that are permitted as values during the write process. The data transfer must therefore map incoming "not good" qualities to the permitted, available states of the target system.