From the OSCAT open source library run through the S7-1200 SCL Converter tool, here are a couple of functions used to perform a running average of an input signal. Check the library for more filtering options :

[code]

// Automatically Edited - Old code marked with SCLConverter
//~ - (UTC) 10/2/2012 5:11:57 PM

FUNCTION INC1 : INT
TITLE = 'INC1'
//
//This is a increment function which increments the variable X by 1 and if M is reached, it begins with 0 again.
//_inc1(3,X) will generate 0,1,2,3,0,1,.....
//
VERSION : 1.2
AUTHOR : hugo
NAME : INC1
FAMILY : MATH

VAR_INPUT
X : INT;
N : INT;
END_VAR
VAR_TEMP
END_VAR

BEGIN

IF X >= N - 1 THEN
INC1 := 0;
ELSE
INC1 := X + 1;
END_IF;

(* this elegant version is 50% slower
INC1 := X := (x + 1) MOD N;
*)

(* revision history
hm 13. oct. 2008 rev 1.0
original version

hm 22. oct. 2008 rev 1.1
added statement to return value for compatibility reasons

hm 23. feb. 2009 rev 1.2
when inc1 is called with X >= N inc will continue with 0
*)
END_FUNCTION

// Automatically Edited - Old code marked with //~ - (UTC) 10/2/2012 5:11:57 PM

FUNCTION_BLOCK FILTER_MAV_DW
TITLE = 'FILTER_MAV_DW'
//
//FILTER_MAV_DW is a moving average filter with programmable length N for DWORD Data.
//
//uses: INC1 [FC53]
//
VERSION : 1.3
AUTHOR : hugo
NAME : FIMAVDW
FAMILY : SIGPRO

VAR_INPUT
X : DWORD;
N : INT;
RST : BOOL;
END_VAR
VAR_OUTPUT
Y : DWORD;
END_VAR
VAR_TEMP
init: BOOL;
buffer : ARRAY[0..31] OF DWORD;
i: INT;
END_VAR
VAR_TEMP
tmp: INT;
tN : INT;
END_VAR

BEGIN

(* limit N to size of buffer *)
tN := MIN(IN1:=N, IN2:=32);

(* startup initialisation *)
IF NOT init OR rst OR tN = 0 THEN
init := TRUE;
tmp := tN - 1;
FOR i := 0 TO tmp DO
buffer[i] := X;
END_FOR;
Y := X;
ELSE
tmp := tN;
i := INC1(X:=i, N:=tmp);
Y := DINT_TO_DWORD(DWORD_TO_DINT(Y) + (DWORD_TO_DINT(X) - DWORD_TO_DINT(buffer[i])) / INT_TO_DINT(tN));
buffer[i] := X;
END_IF;

(*
hm 13. oct. 2008 rev 1.0
original version

hm 27. oct. 2008 rev 1.1
added typecast to avoid warnings

hm 24. nov. 2008 rev 1.2
added typecasts to avoid warnings
avoid divide by 0 if N = 0

hm 23. feb. 2009 rev 1.3
limit N to max array size

*)
END_FUNCTION_BLOCK
[/code]