Filter
- Block name
- ST call
- Library
- Version
- Description
- Inputs
- Outputs
- Function
- Application example

Filter

Block name

B86_FILTER

ST call

PROGRAM TEST FILTER
    VAR
 REAL1,REAL2,REAL3 :REAL;
    FB: LIB.CORE.V1_0.B86_FILTER;
   END_VAR
     FB(IN:= REAL1, INDT:=REAL2, OUT=>REAL3);
END_PROGRAM

Library

LIB\CORE

Version

V1.0

Description

The block is an analogue filter of the input signal in time.

Inputs

Input	Type	Description	Default value
IN	REAL	Input signal, distorted by noise, fluctuations, etc.	0
INA	REAL	DO NOT USE	0
INDT	REAL	Effective filtering time. Set DT = 10-30% of the period of the useful signal (Tperiod = 900s ⇒ DT = 90-270s)	90

Outputs

Output	Type	Description
OUT	REAL	Filtered signal

Function

The block is an analogue filter. There is weighted average at the output out, where older values are less important, they are weighed with lower factor. The importance is set by the indt parameter according to q=1/(1+4Dt/t) (aka exponential decay).

B86 Filter – Sine wave with period T=10 s. X is a white noise signal.

B86 Filter – x - sine wave with white noise, y - filtered signal with parameter indt = 3.

B86 Filter – x - sine wave with white noise, y - filtered signal with parameter indt = 6.

B86 Filter – x - sine wave with white noise, y - filtered signal with parameter indt = 9.

B86 Filter – x - sine wave with white noise, y - filtered signal with parameter indt = 20.

Increasing of the indt parameter out of recommended bounds increases the output signal delay. The original sine signal is flattened at the same time, which causes its lower amplitude.

Application example

The filter is used for e.g. outside temperature signal filtering where the outside temperature sensor is influenced by an exhaust air from an air-handling unit. It makes the weather-based controls more stable.

Table of Contents