Vladimir Vassilevsky wrote:> > > DigitalSignal wrote: > >> To follow up with this question, I wonder if there is a way to >> adaptively notch out the power line harmonics in the analog domain >> before it enters the A/D. Have you seen such a solution? > > IIRC Maxim has ADCs with the built in rejection of 50 and/or 60 Hz. > Don't know whether they do the filtering before or after conversion. > BTW, making a comb filter in the analog domain is not a very big deal > either. >The ones that I know of implement a sigma-delta with a CIC filter that has a 1/60th (or 1/50th) second filter length. But they would still be subject to problems if your "60Hz" energy were coming from a generator on an inverter instead of from a nice steady power line. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html
notching filter that removes the power line harmonics?
Started by ●October 23, 2008
Reply by ●October 27, 20082008-10-27
Reply by ●October 27, 20082008-10-27
Jerry Avins wrote:> DigitalSignal wrote:(snip)>> To follow up with this question, I wonder if there is a way to >> adaptively notch out the power line harmonics in the analog domain >> before it enters the A/D. Have you seen such a solution?> I think digital is the way to go for anything adaptive. I can imagine a > system with servo-driven variable capacitors and inductors, but I > wouldn't want to build (or maintain) one.I would go for varactor diodes instead of servo driven capacitors, but I agree that digital is a better choice. Phase lock on some (large) multiple of 60Hz and divide down. Tap off the divider for each harmonic you want to cancel, then filter, a voltage controlled amplifier, and whatever actual cancels the signal. The control is still digital, but the signal processing is analog. -- glen
Reply by ●October 27, 20082008-10-27
Tim Wescott wrote: (snip)> If part of your problem is huge, narrow spikes, consider making your > analog front-end so that it doesn't get upset by them for any long > duration, then sense the spikes and blank them (by not paying attention > to those ADC readings, and interpolating over them) digitally as part of > your noise rejection.I believe that is what they used to do for analog (LP) records. I never had one, but there were boxes with a description like that, except I believe using analog electronics. Also, there is error concealment for CD players. If you can't read the bits interpolate over them and hope the listener doesn't notice. -- glen
Reply by ●October 27, 20082008-10-27
Glen Herrmannsfeldt wrote:> Jerry Avins wrote: > >> DigitalSignal wrote: > > (snip) > >>> To follow up with this question, I wonder if there is a way to >>> adaptively notch out the power line harmonics in the analog domain >>> before it enters the A/D. Have you seen such a solution? > > >> I think digital is the way to go for anything adaptive. I can imagine >> a system with servo-driven variable capacitors and inductors, but I >> wouldn't want to build (or maintain) one. > > > I would go for varactor diodes instead of servo driven capacitors, > but I agree that digital is a better choice. Phase lock on some > (large) multiple of 60Hz and divide down. Tap off the divider > for each harmonic you want to cancel, then filter, a voltage controlled > amplifier, and whatever actual cancels the signal. The control is > still digital, but the signal processing is analog. > > -- glen >I wonder *IF* ;/ I'm not sure how to phrase it AND *definitely* NOT how to deal with interference is INTEGER multiple of "fundamental" *BUT* _phase_ said multiple wanders
Reply by ●October 27, 20082008-10-27
Glen Herrmannsfeldt wrote:> Jerry Avins wrote: > >> DigitalSignal wrote: > (snip) > >>> To follow up with this question, I wonder if there is a way to >>> adaptively notch out the power line harmonics in the analog domain >>> before it enters the A/D. Have you seen such a solution? > >> I think digital is the way to go for anything adaptive. I can imagine >> a system with servo-driven variable capacitors and inductors, but I >> wouldn't want to build (or maintain) one. > > I would go for varactor diodes instead of servo driven capacitors, > but I agree that digital is a better choice. Phase lock on some > (large) multiple of 60Hz and divide down. Tap off the divider > for each harmonic you want to cancel, then filter, a voltage controlled > amplifier, and whatever actual cancels the signal. The control is > still digital, but the signal processing is analog.Locking on a harmonic and dividing allows a phase ambiguity unless the phase reference is the fundamental. But then we're actually locking on the fundamental, are we not? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 27, 20082008-10-27
Tim Wescott wrote:> Vladimir Vassilevsky wrote: > >> >> >> DigitalSignal wrote: >> >>> To follow up with this question, I wonder if there is a way to >>> adaptively notch out the power line harmonics in the analog domain >>> before it enters the A/D. Have you seen such a solution? >> >> >> IIRC Maxim has ADCs with the built in rejection of 50 and/or 60 Hz. >> Don't know whether they do the filtering before or after conversion. >> BTW, making a comb filter in the analog domain is not a very big deal >> either. >> > The ones that I know of implement a sigma-delta with a CIC filter that > has a 1/60th (or 1/50th) second filter length. > > But they would still be subject to problems if your "60Hz" energy were > coming from a generator on an inverter instead of from a nice steady > power line. >Wouldn't that be solved by the sampling clock being locked to the 50/60 Hz base? -- Inquiring minds want to know - [stolen from some source ;]
Reply by ●October 27, 20082008-10-27
Do like minds go in same direction? We posted ~simultaneously. Jerry Avins wrote:> Glen Herrmannsfeldt wrote: > >> Jerry Avins wrote: >> >>> DigitalSignal wrote: >> >> (snip) >> >>>> To follow up with this question, I wonder if there is a way to >>>> adaptively notch out the power line harmonics in the analog domain >>>> before it enters the A/D. Have you seen such a solution? >> >> >>> I think digital is the way to go for anything adaptive. I can imagine >>> a system with servo-driven variable capacitors and inductors, but I >>> wouldn't want to build (or maintain) one. >> >> >> I would go for varactor diodes instead of servo driven capacitors, >> but I agree that digital is a better choice. Phase lock on some >> (large) multiple of 60Hz and divide down. Tap off the divider >> for each harmonic you want to cancel, then filter, a voltage controlled >> amplifier, and whatever actual cancels the signal. The control is >> still digital, but the signal processing is analog. > > > Locking on a harmonic and dividing allows a phase ambiguity unless the > phase reference is the fundamental. But then we're actually locking on > the fundamental, are we not? > > Jerry
Reply by ●October 27, 20082008-10-27
Richard Owlett wrote:> Glen Herrmannsfeldt wrote: > >> Jerry Avins wrote: >> >>> DigitalSignal wrote: >> >> (snip) >> >>>> To follow up with this question, I wonder if there is a way to >>>> adaptively notch out the power line harmonics in the analog domain >>>> before it enters the A/D. Have you seen such a solution? >> >> >>> I think digital is the way to go for anything adaptive. I can imagine >>> a system with servo-driven variable capacitors and inductors, but I >>> wouldn't want to build (or maintain) one. >> >> >> I would go for varactor diodes instead of servo driven capacitors, >> but I agree that digital is a better choice. Phase lock on some >> (large) multiple of 60Hz and divide down. Tap off the divider >> for each harmonic you want to cancel, then filter, a voltage controlled >> amplifier, and whatever actual cancels the signal. The control is >> still digital, but the signal processing is analog. >> >> -- glen >> > > I wonder *IF* ;/ > > I'm not sure how to phrase it > AND *definitely* NOT how to deal with > interference is INTEGER multiple of "fundamental" > *BUT* > _phase_ said multiple wandersIt can certainly wander in general. Consider the spectrum of a triac motor controller as the load varies. One can hope that the wandering is slow enough for an adaptive notch to follow it. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 27, 20082008-10-27
Richard Owlett wrote:> Do like minds go in same direction? > We posted ~simultaneously.We had different ambiguities in mind. Consider a nice, steady, rock-solid square wave driving a bunch of divide-by-tens. How many dividers are needed to ensure that at least two of their outputs are in sync? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������> Jerry Avins wrote: > >> Glen Herrmannsfeldt wrote: >> >>> Jerry Avins wrote: >>> >>>> DigitalSignal wrote: >>> >>> (snip) >>> >>>>> To follow up with this question, I wonder if there is a way to >>>>> adaptively notch out the power line harmonics in the analog domain >>>>> before it enters the A/D. Have you seen such a solution? >>> >>> >>>> I think digital is the way to go for anything adaptive. I can >>>> imagine a system with servo-driven variable capacitors and >>>> inductors, but I wouldn't want to build (or maintain) one. >>> >>> >>> I would go for varactor diodes instead of servo driven capacitors, >>> but I agree that digital is a better choice. Phase lock on some >>> (large) multiple of 60Hz and divide down. Tap off the divider >>> for each harmonic you want to cancel, then filter, a voltage controlled >>> amplifier, and whatever actual cancels the signal. The control is >>> still digital, but the signal processing is analog. >> >> >> Locking on a harmonic and dividing allows a phase ambiguity unless the >> phase reference is the fundamental. But then we're actually locking on >> the fundamental, are we not? >> >> Jerry
Reply by ●October 27, 20082008-10-27
Jerry Avins wrote: (snip)> It can certainly wander in general. Consider the spectrum of a triac > motor controller as the load varies. One can hope that the wandering is > slow enough for an adaptive notch to follow it.Most of the Seattle bus system is ordinary diesel engine buses, but there are some using overhead DC wiring. When a bus starts up from a stop, spikes from the power inverter run down the wires and are easily picked up by AM radios. Also, it is somewhat higher than 60Hz, maybe 360Hz, but a relatively constant frequency. (It doesn't change with the speed of the bus.) -- glen
