HVM200 Reference Manual Downloading Data 3-15
% y output signal, acceleration
% x input signal, acceleration
% fs sampling frequency Hz
% bilinear transformation algorithm is used
f1 = 0.4;
f2 = 100;
f3 = 12.5;
f4 = 12.5;
Q4 = 0.63;
f5 = 2.37;
Q5 = 0.91;
f6 = 3.35;
Q6 = 0.91;
% Note that in the function “butter” the variables Ql and Q2 are
% effectively set to equal to l/sqrt(2), therefore they don't need
% to be explicitly set here.
w3 = 2*pi*f3;
w4 = 2*pi*f4;
w5 = 2*pi*f5;
w6 = 2*pi*f6;
nyq = fs/2; % Nyquist frequency
% determine parameters for band limiting high pass and low pass
[b1,a1] = butter (2,f1/nyq, 'high' ); % High pass
[b2,a2] = butter (2,f2/nyq); % Low pass
% determine parameters for a-v transition
B3 = [1/w3 1];
A3 = [1/w4/w4 1/Q4/w4 1];
[b3,a3] = bilinear (B3, A3, fs);
% determine parameters for upward step
B4 = [1/w5/w5 1/Q5/w5 1]*w5*w5/w6/w6;
A4 = [1/w6/w6 1/Q6/w6 1];
[b4,a4] = bilinear (B4, A4, fs);
% Apply filter to input signal vector x (output to signal vector y)
y = filter (b2, a2, x); % Apply low-pass band limiting
y = filter (b1, a1, y); % Apply high-pass band limiting
y = filter (b3, a3, y); % Apply a-v transition
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