LowpassButterworthOutput the input signal filtered with a low pass Butterworth filter of any order 
This information is part of the Modelica Standard Library maintained by the Modelica Association.
This block defines the transfer function between the input u and the output y as an nth order low pass filter with Butterworth characteristics and cutoff frequency f. It is implemented as a series of second order filters and a first order filter. Butterworth filters have the feature that the amplitude at the cutoff frequency f is 1/sqrt(2) (= 3 dB), i.e., they are always "normalized". Step responses of the Butterworth filter of different orders are shown in the next figure:
If transients at the simulation start shall be avoided, the filter should be initialized in steady state (e.g., using option initType=Modelica.Blocks.Types.Init.SteadyState).
n 
Value: 2 Type: Integer Description: Order of filter 

f 
Value: Type: Frequency (Hz) Description: Cutoff frequency 
initType 
Value: Modelica.Blocks.Types.Init.NoInit Type: Init Description: Type of initialization (1: no init, 2: steady state, 3: initial state, 4: initial output) 
x1_start 
Value: zeros(m) Type: Real[m] Description: Initial or guess values of states 1 (der(x1)=x2) 
x2_start 
Value: zeros(m) Type: Real[m] Description: Initial or guess values of states 2 
xr_start 
Value: 0.0 Type: Real Description: Initial or guess value of real pole for uneven order otherwise dummy 
y_start 
Value: 0.0 Type: Real Description: Initial value of output (states are initialized in steady state if possible) 
x1 
Type: Real[m] Description: states 1 of second order filters (der(x1) = x2) 

x2 
Type: Real[m] Description: states 2 of second order filters 
xr 
Type: Real Description: state of real pole for uneven order otherwise dummy 
u 
Type: RealInput Description: Connector of Real input signal 


y 
Type: RealOutput Description: Connector of Real output signal 