>
> 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
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>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

>
>
> 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
>

>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

> 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   <@spam@dwaynerKILLspamplanet.eon.net>
> Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> 780-489-3199 voice   780-487-6397 fax   888-489-3199 Toll Free
> http://www.trinity-electronics.com
> Custom Electronics Design and Manufacturing
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

> 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 <spamBeGonedwaynerspamBeGoneplanet.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   <TakeThisOuTdwaynerEraseMEspam_OUTplanet.eon.net>
> > Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> > 780-489-3199 voice   780-487-6397 fax   888-489-3199 Toll Free
> > http://www.trinity-electronics.com
> > Custom Electronics Design and Manufacturing
> >
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > mailman.mit.edu/mailman/listinfo/piclist
> >
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

>
>
> 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
>

> David C Brown wrote:
> > Does that mean that multimeters from America are disadvantaged in Europe?
> > And vv?
>
> Not at all. Averaging for 1/10 second, which is 5 whole cycles of 50 Hz or
> 6 whole cycles of 60 Hz, works equally well in both systems.
>
> -- Dave Tweed
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

> That's a great idea David, but with averaging, much performance is lost.
> And, even without averaging, there is a finite propagation delay (phase
> error) through the electronics-whether digital or analog.
>
> It occurred to me that I might use a second A/D converter to quantify
> the 60Hz powerline frequency and apply that correction digitally. There
> will still be propagation delay and the amplitude of the 2 data streams
> will never match precisly, but the sampling of the realtime data can be
> delayed and sync'd by some amount by delaying the digital clock time
> sampling of one of the waveforms.
>
> Such a practice probably improves the line frequency interference
> problem, but might require lots of time to figure our whether it is usable.
>
> I know that a similar technique is used in analog receiver inputs in
> order to reduce line noise arcing, and it does work. MFJ makes the
> hardware, but it takes a very long time to find the correct amount of
> delay/phase/amplitude as the tuned circuit has nearly infinate
> combinations of possible settings. Once the sweet spot is found, it
> works well until the ambient temperature in the shack changes and
> everything needs retweaking::>
>
> The same concept cannot be applied to very low 50 or 60 Hz interference,
> there is no way to make variable inductors and capacitors to make the
> concept work.
> -
> Aloha,
>
> W1ABA
>
>
> On 8/11/20 11:59 AM, David Van Horn wrote:
> > 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.
> >
>
>
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

>
>
> On Tue, 11 Aug 2020, Art wrote:
>
> > That's a great idea David, but with averaging, much performance is lost..
> > And, even without averaging, there is a finite propagation delay (phase
> > error) through the electronics-whether digital or analog.
> >
> > It occurred to me that I might use a second A/D converter to quantify
> > the 60Hz powerline frequency and apply that correction digitally. There
> > will still be propagation delay and the amplitude of the 2 data streams
> > will never match precisly, but the sampling of the realtime data can be
> > delayed and sync'd by some amount by delaying the digital clock time
> > sampling of one of the waveforms.?
>
> assuming the time it takes to aquire a sample is constant, how about
> taking 3 readings A, B, C such that A and C are from the signal to be
> measured and B is from the mains reference then the adjusted signal
> becomes:
>
> S = (A+C)/2 - B
>
> Since (A+B)/2 should correspond to the time when B was aquired
>
> Regards
> Sergio Masci
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>