The value according to the OPC specification consists from three informations:
- specifies if the value is Bad (value <64), Uncertain (value >=64 and <192) or Good (value >=192).
- specifies closer reason (see the table).
- specifies the relation to the limits: when the value 0 is added to the table value, then the value is not limited. When 1 is added, then the value is on low limit, 2 on high limit and 3 means that the value is constant and cannot be changed.
The following data correspond to the recommended values according to the OPC specification:
- Bad: Non-specific
- Bad value with unspecified reason.
4 (&h4) - Bad: Configuration Error - There is some server specific problem with the configuration. For example the item has been deleted from the configuration.
8 (&h8) - Bad: Not Connected - The input is required to be logically connected but it isn't.
12 (&hC) - Bad: Device Failure - A device failure has been detected.
16 (&h10) - Bad: Sensor Failure - A sensor failure had been detected.
- Bad: Last Known Value
- Communication has failed. However, the last known value is available. The 'age' of the value may be determined from the TimeStamp
- Bad: Comm Failure
- Communication has failed. There isn't the last known value available.
28 (&h1C) - Bad: Out of Service - The block is off the scan or otherwise locked.
- Bad: Waiting for Initial Data
- Wrong value. The value has not been read from the communication so far, or the opposite side does not have the correct initial value.
64 (&h40) - Uncertain: Non-specific - There is no specific reason why the value is uncertain.
- Uncertain: Last Usable Value
- The return value should be regarded as 'stale'. The 'age' of the value may be determined from the TimeStamp
80 (&h50) - Uncertain: Sensor Not Accurate - The sensor is out of the calibration.
84 (&h54) - Uncertain: Engineering Units Exceeded - The value is outside the limits defined for this parameter.
- Uncertain: Sub-Normal
- The value is derived from multiple sources and has less than the required number of Good sources.
- Good: Non-specific
- The value is good. There are no special conditions.
216 (&hD8) - Good: Local Override - The value has been Overridden. Typically this means that the input has been disconnected and a manually entered value has been 'forced'.