From: David C Brown <dcb.home@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Tue, 11 Aug 2020 02:08:50 -0700
Subject: Re: [EE] averaging multiple samples to reject AC interference
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Does that mean that multimeters from America are disadvantaged in Europe?
And vv?
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: 01663 733236
Derbyshire                eMail: dcb.home@gmail.com
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Mon, 10 Aug 2020 at 23:12, Sean Breheny <shb7@cornell.edu> wrote:

> 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 u=
p
> 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
> 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 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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