[PLC Sample Code] - Lowpass filter function block

[pat.stave]

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Lowpass filter function block

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Lowpass filter for Omron PLCs.

Only tested on CJ-series CPU. Use at own risk!

Many thanks to Peter Nachtwey @ PLCS.net for providing the mathematical formula.

Unfiltered = raw unfiltered value in INT.

TC = Time constant tau, given in seconds.

Filtered = Filtered value in INT.

FilteredReal = Filtered value in REAL.

- The FB can be duplicated.

- The FB can only be used in program parts that are scanned every CPU cycle, as it relies on the "P_Scan_Time_Value" variable.

According to the working principles of a lowpass filter, it will take the filtered value tau amount of seconds to reach 63% of the unfiltered value.

The value will reach within 1% of the unfiltered value in approx 5x tau.

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• Submitter
  pat.stave
• Submitted
  11/21/2013
• Category
  PLC Sample Code