The value according to the OPC specification consists from three informations:
- Specifies whether 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: If the value 0 is added to the table value, then the value is not limited. If 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 by means of the TimeStamp
- Bad: Comm Failure
- Invalied value caused by communication error. The last value is no longer 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 returned value is to be considered as inaccurate due to interrupted data reading. Value is to be considered as old. The age of the value may be determined by means of 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 flag. Typically this means that the input has been disconnected and a manually entered value has been 'forced'.