5 Using the PHD OPC Server
5.4
PHD OPC Data Standards for Client Applications
Uniformance - PHD OPC Server User Guide
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Interpreting data quality
The PHD Server represents data quality as a percentage of confidence, with a range of 0 to
100 %. Under most conditions, a data value is always represented by a confidence of 100%,
indicating a good value, a confidence of 0, indicating a uncertain value. Normally, values
between 0 and 100 are reserved for representation of confidence as a result of extrapolation
from known good values.
A special confidence factor value of –1 is reserved to indicate when data is not available and
must be considered bad quality. This Bad Data status normally indicates a period of outage
caused by server shutdown or loss of communications with the DCS.
The confidence factor assigned to a value is derived at the time the data value is collected
from the remote data owner, such as the DCS. The confidence is derived from the specific
status of the value as reflected by the underlying DCS system.
Using a simple percentage of confidence in value storage relieves the PHD Server from
having to store specific status indication that would require distinct interpretation for each
type of DCS or other equipment from which data is collected.
The PHD OPC Server translates the PHD confidence factor to the appropriate OPC Data
Quality indications.
PHD Confidence
OPC Quality
Factor Quality
Sub-Status
100 Good
Non-Specific
-1 Bad
No
Data
(Comm Failure, Nan)
>0 and <100
Uncertain
Non-Specific
Summary of Contents for Uniformance R300
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