From: Sean Breheny <shb7@cornell.edu>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Mon, 10 Aug 2020 15:11:20 -0700
Subject: Re: [EE] averaging multiple samples to reject AC interference
Thread-Topic: [EE] averaging multiple samples to reject AC interference
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Most multimeters still use dual-slope ADCs. One major advantage of this
technique (averaging over a multiple of the line frequency) is that it
actually places a notch (zero) of the transfer function at the line
frequency. It is MUCH better than simply a low-pass filter since it will
pass some frequencies above the line frequency and can pass frequencies up
to more than half the line frequency will very minimal attenuation.

On Mon, Aug 10, 2020 at 4:15 PM Dwayne Reid <dwayner@planet.eon.net> wrote:

> Hi there, Bob.
>
> Old-time Dual-Slope digital meter systems did exactly what you
> describe, with great effectiveness.
>
> dwayne
>
>
> At 01:44 PM 8/10/2020, Bob Blick wrote:
> >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 and accuracy that I will need to evaluate.
> >
> >These sensors are multiplexed with others and I can't sample continuousl=
y.
> >
> >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 at the time.
> >
> >Thanks for any suggestions.
> >Bob
>
>
> --
> Dwayne Reid   <dwayner@planet.eon.net>
> Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> 780-489-3199 voice   780-487-6397 fax   888-489-3199 Toll Free
> www.trinity-electronics.com
> Custom Electronics Design and Manufacturing
>
> --
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