Operating Instructions
Appendix A – OPC Quality Flags
Siemens Building Technologies, Inc. 39
Appendix A – OPC Quality Flags
The OPC quality flags represent the quality of an item’s data value. The lower byte is a bit-field used to
convey standard quality values. The high byte is available for vendor-specific use complementary to the
standard values. The following table lists the range of valid quality values (ignoring the vendor-specific
bits). See the OPC DA 2.0 specification for more information.
Table 8. Valid Values for OPC Quality.
Binary Decimal Definition Description
00000000 0 Bad, Non-specific The value is bad (no specific reason).
00000100 4
Bad, Configuration
Error
A server-specific problem exists in the
configuration.
00001000 8 Bad, Not Connected
The input should be logically connected to
something, but is not.
00001100 12 Bad, Device Failure A device failure has been detected.
00010000
00010001
00010010
00010011
16
17
18
19
Bad, Sensor Failure
+ Low Limit
+ High Limit
+ Constant
A sensor failure has been detected. The value
may be “pegged” as indicated by the limit field.
00010100 20 Bad, Last Known Value
Communications have failed. The item value
represents the last known.
00011000 24 Bad, Comm Failure
Communications have failed. There is no last
known value.
00011100 28 Bad, Out of Service
The block is off-scan or otherwise locked, or
the group or item is inactive.
01000000 64 Uncertain, Non-specific The value is uncertain (no specific reason).
01000100 68
Uncertain, Last Usable
Value
Whatever was writing this value has stopped
doing so. The value is “stale.”
01010000
01010001
01010010
80
81
82
Uncertain, Sensor Not
Accurate
+ Low Limit
+ High Limit
The value may be “pegged” at one of its limits
or it is detected as being out of calibration.
01010100
01010101
01010110
01010111
84
85
86
87
Uncertain, EU
Exceeded
+ Low Limit
+ High Limit
+ Constant
The returned value is outside of the engineering
unit limits defined for this parameter.
01011000 88 Uncertain, Sub-normal
The value is derived from multiple sources, an
insufficient number of them are GOOD.
11000000 192 Good, Non-specific The value is good (no specific reason).