From: Jim <jim@jpes.com>
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Date: Mon, 10 Aug 2020 13:17:08 -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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A .1 second worth of samples is 30 samples at a 1/300 sampling period.=20

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.=20
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>
>=20
>=20
> I have sensors that feed an instrumentation amplifier running a voltage g=
ain of 10 before going into the A/D converter of a microcontroller.
>=20
> There is AC line interference. It is small, but if I can reduce the effec=
t, that would be good. I'm in the 60 Hertz part of the world, but ultimatel=
y this will be used in both 50Hz and 60Hz locations. Battery operated, this=
 is not conducted interference or power supply ripple. Shielding is not pos=
sible. 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 ne=
ed to evaluate.
>=20
> These sensors are multiplexed with others and I can't sample continuously=
..
>=20
> 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.
>=20
> I seem to recall being in this situation before but forget what I did at =
the time.
>=20
> Thanks for any suggestions.
> Bob
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