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Date: Tue, 11 Aug 2020 08:59:09 -0700
Subject: Re: [EE] averaging multiple samples to reject AC interference
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I did a filter some years back where I averaged up enough samples to get a =
complete cycle of the AC line, inverted it, and added it back to the data, =
which worked pretty well at getting rid of line based interference.

________________________________
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Richar=
d Prosser <rhprosser@gmail.com>
Sent: Monday, August 10, 2020 2:34 PM
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Subject: Re: [EE] averaging multiple samples to reject AC interference

I did something similar a longish time ago - synchronised my sampling with
the mains frequency & averaged over a full  cycle. I can't remember the
details but It worked well. I think I was using a Keithly meter as the adc
and it handled the AC triggering side of things.

RP

On Tue, 11 Aug 2020 at 08:17, Jim <jim@jpes.com> wrote:

>
>
> A .1 second worth of samples is 30 samples at a 1/300 sampling period.
>
> If my calculations are correct, 30 samples, at a 1/300 second sampling
> period, that would reduce interference below about 5 Hz, if I am
> thinking correctly about the Nyquist theory.
> If the interference is low frequency, this method should provide some
> degree of reduction.  If the interference is higher frequency than that,
> there may be little to no reduction.
> The best way to find the answer is probably to just write the code to
> implement the algorithm, and test it under actual conditions.
>
> Regards,
>
> Jim
>
> > -------- Original Message --------
> > Subject: [EE] averaging multiple samples to reject AC interference
> > From: Bob Blick <bobblick@outlook.com>
> > Date: Mon, August 10, 2020 2:44 pm
> > To: "piclist@mit.edu" <piclist@mit.edu>
> >
> >
> > I have sensors that feed an instrumentation amplifier running a voltage
> gain of 10 before going into the A/D converter of a microcontroller.
> >
> > There is AC line interference. It is small, but if I can reduce the
> effect, that would be good. I'm in the 60 Hertz part of the world, but
> ultimately this will be used in both 50Hz and 60Hz locations. Battery
> operated, this is not conducted interference or power supply ripple.
> Shielding is not possible. I only need to process the signal about 4 or 5
> times per second. The signal is changing, so long-term averaging is bad.
> Actually any averaging will result in a tradeoff between response time an=
d
> accuracy that I will need to evaluate.
> >
> > These sensors are multiplexed with others and I can't sample
> continuously.
> >
> > If I average multiple samples taken at 1/300 second intervals over a
> 1/10 second period, that should give some improvement at 50Hz and 60Hz
> without getting too involved, correct? This would fit into my existing
> multiplexing constraints.
> >
> > I seem to recall being in this situation before but forget what I did a=
t
> the time.
> >
> > Thanks for any suggestions.
> > Bob
> > --
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