LPF – Low-pass filter

Block SymbolLicensing group: STANDARD
PIC

Function Description
The LPF block implements a second order filter in the form

Fs = 1 a2s2 + 2ξas + 1,

where

a = 2 2ξ4 2ξ2 + 1 2ξ2 + 1 2πfb

and fb and ξ = xi are the block parameters. The fb parameter defines the filter bandwidth and xi is the relative damping coefficient. The recommended value is xi = 0.71 for the Butterworth filter and xi = 0.87 for the Bessel filter.

If ISSF = on, then the state of the filter is set to the steady value at the block initialization according to the input signal u.

Input

u

Input signal to be filtered

double

Output

y

Filtered output signal

double

Parameters

fb

Filter bandwidth [Hz]; the frequencies in the range 0,fb pass through the filter, the attenuation at the frequency fb is 3 dB and approximately 40 dB at 10 fb; it must hold fb < 1 10TS for proper function of the filter, where TS is the block execution period  1.0

double

xi

Relative damping coefficient (recommended value 0.5 to 1)  0.707

double

ISSF

Steady state at start-up

bool

off ..

Zero initial state

on ...

Initial steady state

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