In a DA server, Automation Data is represented by Value, Quality and Time Stamp for a Tag.
The COM UA Wrapper maps the VQT data to the Data Value and Diagnostic Info structures.
The Error codes returned by the DA server are based on the HRESULT type. The COM UA Wrapper maps this error code to an OPC UA Status Code. Figure A.13 illustrates this mapping.
Figure A.13 – OPC COM DA to OPC UA data and error mapping
The data values in the DA server are represented as Variant data type. The COM UA Wrapper converts them to the corresponding OPC UA DataType. The mapping is shown in Table A.60:
Table A.60 – DataTypes and mapping
|
Variant Data Type (In DA server) |
OPC UA Data type Mapping in COM UA Server (DataValue structure) |
|
VT_I2 |
Int16 |
|
VT_I4 |
Int32 |
|
VT_R4 |
Float |
|
VT_R8 |
Double |
|
VT_BSTR |
String |
|
VT_BOOL |
Boolean |
|
VT_UI1 |
Byte |
|
VT_I1 |
SByte |
|
VT_UI2 |
UInt16 |
|
VT_UI4 |
UInt32 |
|
VT_I8 |
Int64 |
|
VT_UI8 |
UInt64 |
|
VT_DATE |
Double |
|
VT_DECIMAL |
Decimal |
|
VT_ARRAY |
Array of OPC UA types |
.
The Quality of a Data Value in the DA server is represented as a 16 bit value where the lower 8 bits is of the form QQSSSSLL (Q: Main Quality, S: Sub Status, L: Limit) and higher 8 bits is vendor specific.
The COM UA Wrapper maps the DA server to the OPC UA Status code as shown in Figure A.14:
Figure A.14 – Status Code mapping
The primary quality is mapped to the Severity field of the Status code. The Sub Status is mapped to the SubCode and the Limit is mapped to the Limit Bits of the Status Code.
Please note that the Vendor quality is currently discarded.
Table A.61 shows a mapping of the OPC COM DA primary quality mapping to OPC UA status code
|
OPC DA Primary Quality (Quality & Sub status QQSSSS) |
OPC UA Status Code |
|
GOOD |
Good |
|
LOCAL_OVERRIDE |
Good_LocalOverride |
|
UNCERTAIN |
Uncertain |
|
SUB_NORMAL |
Uncertain_SubNormal |
|
SENSOR_CAL |
Uncertain_SensorNotAccurate |
|
EGU_EXCEEDED |
Uncertain_EngineeringUnitsExceeded |
|
LAST_USABLE |
Uncertain_LastUsableValue |
|
BAD |
Bad |
|
CONFIG_ERROR |
Bad_ConfigurationError |
|
NOT_CONNECTED |
Bad_NotConnected |
|
COMM_FAILURE |
Bad_NoCommunication |
|
DEVICE_FAILURE |
Bad_DeviceFailure |
|
SENSOR_FAILURE |
Bad_SensorFailure |
|
LAST_KNOWN |
Bad_OutOfService |
|
OUT_OF_SERVICE |
Bad_OutOfService |
|
WAITING_FOR_INITIAL_DATA |
Bad_WaitingForInitialData |
The Timestamp provided for a value in the DA server is assigned to the SourceTimeStamp of the DataValue in the COM UA Wrapper.
The ServerTimeStamp in the DataValue is set to the current time by the COM UA Wrapper at the start of the Read Operation.