OPC Quality

OPC Toolbox™ software uses specific quality attributes defined by the OPC Foundation, based on a major quality value, a substatus for that major quality value, and a limit status indicating how the value is limited. This appendix describes the standard quality attributes defined by the OPC Foundation that are used in the toolbox, and describes any special extensions that the toolbox uses.

An OPC quality value is a number ranging from 0 to 65535, made up of four parts. The high 8 bits of the quality value represent the vendor-specific quality information. The low 8 bits are arranged as QQSSSSLL, where QQ represents the major quality, SSSS represents the quality substatus, and LL represents the limit status.

OPC HDA quality values are layered on top of OPC DA quality values.

The following topics describe the OPC quality values and texts associated with each quality part.

For more information, see the Quality property reference page. The quality of an item is also stored in native value format in the QualityID property of the daitem object.