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Quality |
Quality fields represent a quality status of an item's value. They are formed by a 16-bit word, in which the first eight bits are defined as three bit fields, Quality, Substatus, and Limit.
The other eight bits of higher order are available for each manufacturer's usage. If these bits are used, default quality bits are still used to indicate which deductions could be performed on returned data. So, it is a client's responsibility to interpret quality's specific information field, to ensure that a server providing this information uses the same rules as a client.
Available options in the Quality field
Quality |
Quality Field |
Description |
---|---|---|
0 - 63 |
Bad |
This value cannot be used for the reasons indicated in the Substatus field |
64 - 127 |
Uncertain |
This value's quality is uncertain for the reasons indicated in the Substatus field |
128 - 191 |
(Reserved) |
Not used by the OPC standard |
192 - 255 |
Good |
This value's quality is good |
A server that does not support information on quality always returns 192 (Good). It is also acceptable that a server simply returns 0 or 192 (Bad or Good) and always returns 0 (zero) for Substatus and Limit.