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Median SCL Code

This document describes a median filter function that can reduce the effects of random noise spikes. The function uses a buffer to hold the most recent values and their ages. It identifies the oldest value, removes it, and inserts the new incoming value into the sorted list. The median (middle) value of the sorted list is then output to reduce the impact of outliers.

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Bassel Almouie
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274 views2 pages

Median SCL Code

This document describes a median filter function that can reduce the effects of random noise spikes. The function uses a buffer to hold the most recent values and their ages. It identifies the oldest value, removes it, and inserts the new incoming value into the sorted list. The median (middle) value of the sorted list is then output to reduce the impact of outliers.

Uploaded by

Bassel Almouie
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as TXT, PDF, TXT or read online on Scribd
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//

***********************************************************************************
**
// ** MEDIAN FILTER
**
// ** v1.0 August 2018 C. Laffoon
**
// ** Median filter function for use in reducing effects of random noise spikes
**
// ** To increase/decrease number of filter elements, change constant
FILTER_ELEMENTS **
// ** and also edit size of arrays to match.
**
//
***********************************************************************************
**
FUNCTION_BLOCK FB201

CONST
FILTER_ELEMENTS := 11;
END_CONST

VAR_INPUT
IN_VALUE : INT;
END_VAR

VAR_OUTPUT
OUT_VALUE : INT;
END_VAR

VAR_TEMP
// Temporary Variables
BFR_VAL : ARRAY[0..10] OF INT;
BFR_AGE : ARRAY[0..10] OF INT;
BFR_IDX : INT;
VAL_IDX : INT;
TMP_IDX : INT;
OLDEST_DELETED : BOOL;
OLDEST_AGE : INT;
OLDEST_IDX : INT;
INCOMING_VALUE_WRITTEN : BOOL;
MEDIAN_IDX : INT;
END_VAR

VAR
// Static Variables
VALUE : ARRAY[0..10] OF INT;
AGE : ARRAY[0..10] OF INT;
END_VAR

LABEL
LAB1, LAB2;
END_LABEL

// ***********************************************************
// ** Statement Section **
// ***********************************************************
BEGIN
BFR_IDX := 0; // Initialize Index
VAL_IDX := 0; // Initialize Index
OLDEST_DELETED := FALSE;
OLDEST_AGE := -1;
INCOMING_VALUE_WRITTEN := FALSE;
MEDIAN_IDX := (FILTER_ELEMENTS / 2);

// Find oldest element (this will be removed from updated list)


FOR TMP_IDX := 0 TO FILTER_ELEMENTS-1 DO
IF AGE[TMP_IDX] > OLDEST_AGE THEN
OLDEST_AGE := AGE[TMP_IDX];
OLDEST_IDX := TMP_IDX;
END_IF;
END_FOR;

WHILE BFR_IDX < FILTER_ELEMENTS DO


// If this is oldest element, then just skip over it so that it falls out
of list.
IF VAL_IDX = OLDEST_IDX THEN
VAL_IDX := VAL_IDX + 1;
END_IF;

// If new value is smaller than current index value, then write incoming
value to buffer
IF INCOMING_VALUE_WRITTEN = FALSE AND IN_VALUE <= VALUE[VAL_IDX] OR VAL_IDX
> (FILTER_ELEMENTS-1) THEN
// Write incoming value and age to buffer
BFR_VAL[BFR_IDX] := IN_VALUE;
BFR_AGE[BFR_IDX] := 0;
BFR_IDX := BFR_IDX + 1;
INCOMING_VALUE_WRITTEN := TRUE;
END_IF;

// Write current value and incremented age to buffer


IF BFR_IDX < FILTER_ELEMENTS THEN
BFR_VAL[BFR_IDX] := VALUE[VAL_IDX];
BFR_AGE[BFR_IDX] := AGE[VAL_IDX] + 1;
BFR_IDX := BFR_IDX + 1;
VAL_IDX := VAL_IDX + 1;
END_IF;
END_WHILE;

// Write buffer to values/ages


FOR TMP_IDX := 0 TO (FILTER_ELEMENTS-1) DO
VALUE[TMP_IDX] := BFR_VAL[TMP_IDX];
AGE[TMP_IDX] := BFR_AGE[TMP_IDX];
END_FOR;

// You've been waiting for it! Here it is...


// Return median of dataset (middle element)
OUT_VALUE := VALUE[MEDIAN_IDX];

END_FUNCTION_BLOCK

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