How the increase the affect of lowpass filter on a field data?
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Hello,
I would like to apply lowpass filter to my temperature data to remove the high frequency noise. I have applied simply 'lowpass' and could not see a significant affect on my data. I have seen several question regarding the lowpass but I am quite new to this area, so maybe missed the point.
sampling_rate=10; %seconds
fs=1/sampling_rate; %Hz
fpass=0:0.01:fs/2;
T35_lp=lowpass(T35,0.01,fs);
Here you can see the applied filter and original data below. They are almost same.
Is there any way to improve the affect of lowpass filter? I appreciate any suggestions.
Thanks!
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Star Strider
le 28 Nov 2023
The cutoff frequency of the lowpass filter is too high.
Try these —
LD = load('T35.mat');
T35 = LD.T35;
sampling_interval = 10;
Fs = 1/sampling_interval;
L = numel(T35);
t = linspace(0, L-1, L)/Fs;
[FTT35,Fv] = FFT1(T35, t);
figure
semilogx(Fv, abs(FTT35)*2)
grid
xlabel('Frequency')
ylabel('Magnitude')
title('T35: Fourier Transform')
xlim([0 Fs/2])
Fco = 1E-5;
T35_filt1 = lowpass(T35, Fco, Fs, 'ImpulseResponse','iir');
Fco = 8E-7;
T35_filt2 = lowpass(T35, Fco, Fs, 'ImpulseResponse','iir');
figure
plot(t, T35, 'DisplayName','Original (Unfiltered)')
hold on
plot(t, T35_filt1, 'DisplayName','Filtered (F_{co} = 1\times 10^{-5})', 'LineWidth',2)
plot(t, T35_filt2, 'DisplayName','Filtered (F_{co} = 8\times 10^{-7})', 'LineWidth',2)
hold off
grid
legend('Location','best')
function [FTs1,Fv] = FFT1(s,t)
s = s(:);
t = t(:);
L = numel(t);
Fs = 1/mean(diff(t));
Fn = Fs/2;
NFFT = 2^nextpow2(L);
FTs = fft((s - mean(s)).*hann(L), NFFT)/sum(hann(L));
Fv = linspace(0, 1, NFFT/2+1)*Fn;
Iv = 1:numel(Fv);
FTs1 = FTs(Iv);
end
.
4 commentaires
Star Strider
le 30 Nov 2023
As always, my pleasure!
Your interpretation of the spectrogram is correct.
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