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Increasing the dynamic range of compressed data

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Originally posted on UserVoice

I see too often customers struggling to find the right exception and compression settings. When exception/compression are not well defined, they end up having too many values or missing values, what causes a lot of problems when the affected tag is being used in other calculations (totalizations, for example).

Consider the tag attributes " zero" and "span": today, values near the "zero" are more penalized than the values near the "span"  value, because the exception/compression deviation may be too big for the values in the lower scale of the entire tag range. It translates in poor dynamic range.

We could have the option to use logarithm exception/compression scale, similar to the mechanism used in telecommunications (A-law or u-law, for example). Small changes near " zero"  would be more prone to pass exception/compression testing than the small changes near the "span"  value. This way we improve the dynamic range of the archive data, which may be very important in a totalization scenario (oil & gas production, for example). As a result, the robustness of the PI System exception/compression mechanism would be greatly improved.

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