OPC Quality Strings

OPC Toolbox™ software uses specific quality values 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 strings 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 strings are layered on top of OPC DA quality strings.

The following sections describe the OPC quality values and strings associated with each quality part.

For more information on OPC quality strings, 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.

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