Data retrieved from external systems, such as historians, often have an associated confidence, which can be important in various calculations and applications.
P2 Server passes confidence through the system from the datasource unchanged.
The consuming application applies the rules to the data according to their requirements, since those rules might be specific to the application.
P2 Server does not perform any filtering, except where data is passed into a calculation function. This is because many of the calculation functions transform many points into fewer points. For example, we don’t want to include 274564638363 with a confidence of 0 in our calculation for Daily Production. So we need some handling for confidence in that case, but otherwise the data is passed through unchanged.
The default behaviour is to remove and extrapolate from past or future data when confidence is below 80. In some cases where there is no valid data, P2 Server will throw an error because there is nothing it can extrapolate from.
The trend and page controls in P2 Explorer do not currently show low confidence indicators based on a threshold configurable in Explorer, except for the process control shapes such as the Level Meter.
These are the configuration settings in P2 Server that controls filtering:
- CalculationConfidenceCutoffBehavior: Determines how data values with a confidence less than or equal to the configured threshold are treated when performing calculations. Options: Disabled, ReplaceWithLastKnownValue, ReplaceWithDatumError. Default: ReplaceWithLastKnownValue
- CalculationConfidenceCutoffThreshold: A value is regarded as bad if it is less than or equal to this confidence value. This must be an integer number between 0 and 100. Default: 80
As these are usually set once and then not changed, they are located in the configuration file. See the P2 Server Installation Guide for further details.
P2 Server also has 3 calculation functions related to confidence:
- CatchLowConfidence lets you replace values below a threshold with a manual value.
- Confidence returns the confidence of an expression.
- ConfidenceCutoff overrides the default CalculationConfidenceCutoffThreshold and CalculationConfidenceCutoffBehavior configuration parameters when fetching tags referenced within the Expr argument.