Ladder logic 402: Data manipulation and filtering

The prior post on ladder logic discussed using a programmable logic controller (PLC) to capture values from an analog card. Once those values have been captured, there are methods to filter the data and methods to simulate a filter using Microsoft Excel before it is coded into a PLC. There are several filtering algorithms that can be found on the Internet currently being used on a PLC (see links below). For the formulas, the same variable names were used even though they differed extensively in the various posts: N = New value calculated and substituted for the input value. In other words, the calculated filtered value. L = The previous captured input value. F = The previous calculated filtered value. k = The manipulated factor for all calculations (sometimes known as Alpha). i = The current analog input value. Avg = A running average over x number of previous samples,


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