How data compression works in Tag Historian Module?


Need more understanding on how tag historian module compress the real time data and to store in DB( Felt Point covered related to this on Doc was limited, Configuring Tag Historian - Ignition User Manual 7.9 - Ignition Documentation) .It was mentioned, Its a modified version of the ‘Sliding Window’ algorithm. I hope answers to this doubt will make us to understand purpose of Tag Historian module more clearly.

~hari gb

The explanation immediately below that chart at the manual page you linked runs through the details. I’ll try putting it in slightly different words. Points 1-5 are raw data points on the blue line and the red line shows the compressed data that is actually stored.

  1. To run through how it works, start at point 1

  2. The vertical line at point 2 is the height of the deadband and creates the initial deadband limits (L1, U1). for this sequence.

  3. The vertical line at point 3 is also the height of the deadband and creates new upper limit U2. It does not create a new lower limit as the bottom of it is outside lower limit L1 set by deadband at point 2.

  4. The same thing happens at point 4, except that it creates new lower limit L3 and doesn’t create a new upper limit as it is limited by U2 upper limit.

  5. Point 5 is outside the deadband limits set by previous points so point 4 is stored and the process repeats.

To sum this up, point 1 is stored, point 4 is stored, and then point 4 becomes the new point 1 and point 5 becomes the new point 2 for the next sequence.


Thank you witman,

~hari gb

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