How to to filter non-uniformly sampled data?

I've a series of force sensor data acquired by an industrial robot controller. Sadly the data has to be read out in a background task, so the sampling time differs between 1m and 20ms. Due to high oscillation in the process, I have to low-pass filter these force values.

What is the best way to filter this data? Right now, I'm interpolating linear between the data points and than resample with a sampling rate of 1kHz (1ms sampling time). Then I'm using a moving average filter to smooth and filter these data.

But I'm not happy with this method because I neither know how this is changing the validity of my data.

Help is highly appreciated. Thank you.

Answer 1

[Star Strider]

Your approach is correct. Rather than using interp1, use the Signal Processing Toolbox resample (link) function. It incorporates an anti-aliasing filter, and is preferred for signal processing purposes.

A useful lowpass filter design prototype is:

Fs = 360;                                                   % Sampling Frequency (Hz)
Fn = Fs/2;                                                  % Nyquist Frequency (Hz)
Wp = 100/Fn;                                                % Passband Frequency (Normalised)
Ws = 101/Fn;                                                % Stopband Frequency (Normalised)
Rp =   1;                                                   % Passband Ripple (dB)
Rs = 150;                                                   % Stopband Ripple (dB)
[n,Ws] = cheb2ord(Wp,Ws,Rp,Rs);                             % Filter Order
[z,p,k] = cheby2(n,Rs,Ws);                                  % Filter Design
[soslp,glp] = zp2sos(z,p,k);                                % Convert To Second-Order-Section For Stability

figure(3)
freqz(soslp, 2^16, Fs)                                      % Filter Bode Plot

filtered_signal = filtfilt(soslp, glp, original_signal);    % Filter Signal

Make appropriate changes for your signal.

[riss]

Hello Star Strider,

thank you a lot for your answer. It helped me a lot.

[Star Strider]

As always, my pleasure.