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OPC DA Quality Codes

What do the OPC DA Quality Codes indicate?

The OPC quality code is made up of 16 bits.

  • The high 8 bits are available for vendor specific use and should be all 0's when not used.
  • The low 8 bits are broken into three sections:
    • The first two bits can pass the meaning Good, Bad or Uncertain. If a server does not support quality codes, a good value will always be passed.
    • The next four bits can be used to provide additional specific information about the general quality.
    • The last two bits are used if limit information is supported by the server.* In VB these are returned as Hex values that can them be converted to meaningful information.

The two most common OPC quality codes are:

  • 192 or hex C0 is good quality.
  • 0 (decimal or hex) is bad quality.

Below is a listing of the OPC specification quality codes:

Hex Value Decimal value OPC Specification Definition
C0 192 Good
D8 216 Good--Local Override, Value Forced
0 0 Bad
4 4 Bad - Configuration Error in Server
8 8 Bad - Not Connected
C 12 Bad - Device Failure
10 16 Bad - Sensor Failure
14 20 Bad - Last Know Value Passed
18 24 Bad - Comm Failure
1C 28 Bad - Out of Service (also happens when item or group is inactive)
40 64 Uncertain
44 68 Uncertain - Last Usable Value - timeout of some kind
50 80 Uncertain - Sensor not Accurate - outside of limits
54 84 Uncertain - Engineering Units exceeded
58 88 Uncertain - Value from multiple sources -----------with less then required good values

*If limit quality is supported, then the above numbers mean the value can change:

  • If the value is one greater - value is pegged at Lower Limit
  • If the value is two greater - value is pegged at High Limit
  • If the value is three greater - value is constant - can't change

OPC Quality Flags Explanation

For more information see the OPC specifications. (Note: not all servers will support all these codes)