Each Historic View has a Quality Filter setting that you can use to specify which values are included in the calculation, based on quality. By default, the values for a Historic View table are calculated using all quality types - Good, Bad, and Uncertain. You can change the Quality Filter to suit your preferences, or in the case of advanced drivers, to avoid undesirable results.
With the default settings in place, the values for a Historic View table are calculated using all of the values in the defined time range, irrespective of their quality.
For simple drivers, using values of any quality produces results that have a clear relationship with the raw values that were reported from a device. This is also true for advanced drivers that do not use the Log Historic Value on Communication Failure feature. At some stage, a device reported the raw values, which were then used to create processed historic values. The processed historic values were then used to create the values for the Historic View. So irrespective of the Quality Filter, the data spread in the Historic View has a relationship with the original raw values.
However, for advanced drivers that use Log Historic Value on Communication Failure, having Bad included in the Quality Filter can produce undesirable results. This is because the Log Historic Value on Communication Failure feature causes ClearSCADA to log an ‘extra’ historic value in the event of an unsuccessful communications attempt. This ‘extra’ historic value has a Bad quality to indicate the loss of communications, but is not a value that has been measured or reported by the device. So if you include Bad in the Quality Filter, the Historic View calculation will include all Bad quality values, including any ‘extra’ loss of communications values. The result is a Historic View that contains undesirable drops in value. To avoid this, we recommend that you do not include Bad in the Quality Filter for drivers that use Log Historic Value on Communications Failure.
For algorithms that relate to quality, such as DurGood, DurBad, PerGood and PerBad, the default filter of Good, Bad and Uncertain being included should be in place. If you filter out a Quality with quality-related algorithms, the results may be undesirable. For example, if you use the DurBad algorithm and filter out the Bad quality values, the results will be calculated without using any Bad values, and so will be of no use.