This Tech Tip describes how to calculate statistics on tags in Wonderware InTouch, assuming those tags are being historized in InSQL Historian 9.0. The statistic functions provided in this application are Min, Max, Avg and StDev. For the Min, Max and Avg calculations, the queries take advantage of the advanced retrieval modes provided by Historian 9.0, allowing for very fast calculations of these statistics. Since Standard Deviation (StDev) is not one of the advanced retrieval modes in Historian, we use the standard SQL “StDev” function – calculation time is dependent on the duration over which you calculate this statistic. Since this application uses InTouch SQLAccess functionality, the SQLAccess features needs to be added to the InTouch installation, if that option was not checked during the original installation.
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