ClearSCADA has built-in historic algorithms that you can use with historic Trends and other historic features such as Historic Views. Each historic algorithm performs a calculation on the relevant raw historic values and returns the result, which can be used as a data source on a Trend or displayed in Queries. (For more information on raw historic values, see Raw Historic Data on Trends).
Each historic algorithm is applied to the values in a defined 'resample interval' (a time period).
If the resample interval is 30M (day) and you use the 1hAverage algorithm, ClearSCADA calculates the average hourly value at 30 minute intervals.
The resample interval is defined in the configuration of the Historic item, for example the Historic Trend, Historic Calculation, Historic View, and so on.
The topics in this section explain the historic algorithms that are often used when working with historic data. For more information, see the topics that are listed in the gray footer section at the bottom of this topic. Select the relevant entry to display the topic that you require.
In addition to the algorithms listed below, ClearSCADA also supports the following historic algorithms, many of which are specified as part of the OPC historic standard:
The difference between the first value and the last value in the data for the resample interval. The time stamp of the result matches the start time of the sample.
The duration (in seconds) of good data in the data for the resample interval.
The duration (in seconds) of bad data in the data for the resample interval.
The last value in the data for the resample interval. The timestamp is the time at which the last value was reported.
Returns either the last value in the data for the resample interval or the latest value in the data prior to the resample interval (if there are no values in the defined resample interval). For example, if there are values in the defined resample interval, the EndLast algorithm works in the same way as the End algorithm: it will return the last value in the resample interval. However, if there are no values in the defined resample interval, the EndLast algorithm will return the last value prior to the resample interval. The timestamp is the time at the end of the defined resample interval, even if the actual value was taken from a sample prior to the defined resample interval. So the timestamp may not correspond with the time at which the last value was reported.
The sum of the absolute differences between each pair of values in the resample interval.
The percentage of bad data in the data for the resample interval (1=100%).
The percentage of good data in the data for the resample interval (1=100%).
The difference between the maximum value and the minimum value in the data for the resample interval.
The first value in the data for the resample interval. The timestamp is the time at which the first value in the sample was reported.
This is specific to ClearSCADA and is an obsolete algorithm that is included for backwards compatibility reasons. The Stepped algorithm was designed to allow traces to be stepped, but this functionality is now provided by the Step First and Step Last Trace Style settings (see Configure a Trace).
For more information on the algorithms listed above (with the exception of Stepped), please refer to the OPC Foundation documentation or visit:
http://www.opcfoundation.org
ClearSCADA also supports any custom historic algorithms that have been created on your system (see Historic Algorithms (Custom)). When you are configuring a Historic item, any custom historic algorithms are included in the list of available algorithms.