Removing 60Hz from ECG using digital band stop filter
Let’s make a filter, which filters off the 60Hz frequency from ECG signal. As
we know American power supply is 60Hz. This is common noise in biomedical
signals, while they are powered from industrial power supply. This type of noise
can be defined easily and can be filtered as parameters of noise are
known.
Here is one example of how to implement FIR filter using mathematical
tools, like Matlab. This can be done by using microcontroller, like ARM or even
ARM, because the frequencies are up to 1 KHz.
Initial conditions:
f0=60Hz - pover supply frequency;
fs=500Hz - sampling rate;
frequencies
who define complex zeros:
we get w0=0.754;
Positions of complex zeros:
Zeros and poles in z plane
System Function
From it we can calculate filter coefficients:
And filter coefficients:
Also we know that:
And here we get filter characteristics:
Ve have band stop filter at 60Hz and its jam at 60Hz is -300dB. Bellow is filter structure:
Now using this filter we can filter ECG signal:
As you can see this is simple FIR filter. In other words there is nothing more than average function which doesn’t need much of resources. The other benefit of FIR filter is that we can get linear Phase characteristics, there fore filtered signal isn’t distorted because of different spectra frequency delay. As result wee see that ECG become more smooth. FIR filter
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May 23rd, 2006 at 2:32 am
Good article.
July 3rd, 2006 at 9:43 am
Click right mouse button and select open/view image for better image quality.
October 3rd, 2006 at 4:26 pm
hi, i’m developping an application for removing 60 Hz noise from ECG diagram, and i’m newbie in all of this.
I have an array on 2000 points for 4 secs. So Fs=500Hz, how can i remove the 60 Hz noise.
Ok…if i anderstood w0=0.754 and If the sampling frequency is 500 Hz, the zero at +43,2 degres will completely eliminate any signal at
60 Hz is it correct??
October 5th, 2006 at 1:42 pm
As far as I remember yes. Because we get band-stop filter at 60Hz.
February 20th, 2007 at 1:26 pm
hello Dear
I want remove 50Hz noise of EKG with 500Hz sps. please help me for writing m file(mATLAB pROG.) of your technic.
February 20th, 2007 at 3:02 pm
Just change
w0=2*pi*((60)/(fs));
to
w0=2*pi*((50)/(fs));
in attached file bellow article. That should help.
August 23rd, 2007 at 11:50 am
hi
i want to remove 50Hz noise of ECG..please help me where i can find the source code..i prefer c language..please help me..
December 4th, 2007 at 8:54 pm
The Fs in the zip file is 200, why?
December 5th, 2007 at 12:00 am
Probably a mistake, but as ECG signal is low freq, it is even enough of 200Hz sampling freq.
May 13th, 2008 at 8:29 pm
Hi,
I am using digital filters,but since i am new to this concept,i have stuck at one doubt.Please help me out. i am designing a LPF having 6Hz & 30Hz passband & stopband edge freq Also Fs(Sampling) is 512Hz. I have got the filters coefficient by implementing it in matlab but on the site from where i am taking guidance of this topic they have got coeff. in integer forms like
//Lowpass FIR filter coefficients for 17 taps to filter > 30Hz
static const int coeffslp[9] = {
5225, 5175, 7255, 9453, 11595, 13507, 15016, 15983, 16315 };//
I am not getting that how can we get such a large integer no. as a coeff.Is there any scaling process.
Please guide me about this
March 26th, 2009 at 2:18 pm
Hi,
am working on something like that and am trying to understand your article. You are talking about a sample frequency of 500Hz, but yout code only works with 200Hz. i tried to tune it to get it to work, but that didn’t help at all ^^.
So why the fs=200 in the code?
March 26th, 2009 at 10:49 pm
Probably it was left after some tweaks. The change of fs to 500 didn’t work?