Jerry Avins wrote: (snip, I wrote)>> 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?You could use a different phase off the divider to run the PLL than is used for the taps. Even separate dividers and phase selection for each harmonic. As someone said, hopefully things change slow enough to follow the changes (in either the analog or digital case). -- glen
notching filter that removes the power line harmonics?
Started by ●October 23, 2008
Reply by ●October 27, 20082008-10-27
Reply by ●October 28, 20082008-10-28
I did similar project before. The key idea is not to design any filter. To remove harmonics, filter has to be very narrow and it is not plausilble. I put my answer in my blog at here: http://www.ecvale.com/index.php?main_page=user_blogs_info&upar=169126437&blgspar=9 let me know how it works for you.>Is there good notching filter that can effectively remove the >powerline harmonics? This is a real tough project for at least two >reasons: > >1. Frequency of power line signals flucturates. It is not a constant >50/60Hz >2. Harmonics can go 10th or beyond. > >Thanks for the advice in advance. > >James >www.go-ci.com >
Reply by ●October 28, 20082008-10-28
seafrn wrote:> I did similar project before. The key idea is not to design any filter. To > remove harmonics, filter has to be very narrow and it is not plausilble. I > put my answer in my blog at here: > > http://www.ecvale.com/index.php?main_page=user_blogs_info&upar=169126437&blgspar=9 > > let me know how it works for you. > > >> Is there good notching filter that can effectively remove the >> powerline harmonics? This is a real tough project for at least two >> reasons: >> >> 1. Frequency of power line signals flucturates. It is not a constant >> 50/60Hz >> 2. Harmonics can go 10th or beyond. >> >> Thanks for the advice in advance.Nice! Before I start hunting, can you point me to an explanation of mud-pulse telemetry? It intrigues me. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 28, 20082008-10-28
I am not sure about the mud thing either. I guess you find it in their patent. When I did the project years ago, I read the inventerss' paper first and it is for sure much more understandable than the patent. I couldn't find the paper so i post the patent link instead.>seafrn wrote: >> I did similar project before. The key idea is not to design any filter.To>> remove harmonics, filter has to be very narrow and it is notplausilble. I>> put my answer in my blog at here: >> >>http://www.ecvale.com/index.php?main_page=user_blogs_info&upar=169126437&blgspar=9>> >> let me know how it works for you. >> >> >>> Is there good notching filter that can effectively remove the >>> powerline harmonics? This is a real tough project for at least two >>> reasons: >>> >>> 1. Frequency of power line signals flucturates. It is not a constant >>> 50/60Hz >>> 2. Harmonics can go 10th or beyond. >>> >>> Thanks for the advice in advance. > >Nice! Before I start hunting, can you point me to an explanation of >mud-pulse telemetry? It intrigues me. > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� >
Reply by ●October 28, 20082008-10-28
On Tue, 28 Oct 2008 11:04:31 -0400, Jerry Avins <jya@ieee.org> wrote:>seafrn wrote: >> I did similar project before. The key idea is not to design any filter. To >> remove harmonics, filter has to be very narrow and it is not plausilble. I >> put my answer in my blog at here: >> >> http://www.ecvale.com/index.php?main_page=user_blogs_info&upar=169126437&blgspar=9 >> >> let me know how it works for you. >> >> >>> Is there good notching filter that can effectively remove the >>> powerline harmonics? This is a real tough project for at least two >>> reasons: >>> >>> 1. Frequency of power line signals flucturates. It is not a constant >>> 50/60Hz >>> 2. Harmonics can go 10th or beyond. >>> >>> Thanks for the advice in advance. > >Nice! Before I start hunting, can you point me to an explanation of >mud-pulse telemetry? It intrigues me. > >JerryJerry, ask Julius. ;) Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org Blog: http://www.dsprelated.com/blogs-1/hf/Eric_Jacobsen.php
Reply by ●October 28, 20082008-10-28
seafrn wrote:> I am not sure about the mud thing either. I guess you find it in their > patent.I googled a bit, and I'm more confused than befire. Mud-pulse telemetry is what is sounds like: signaling by means of modulating the pressure of the circulating drilling mud. So where does the electrical interference come from? Is it introduced at the down-hole modulator, or noise getting into the pressure sensor at the surface? If the latter, shame on those who accept it! Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 28, 20082008-10-28
Guys, Thank you so much for the advice and various throughts. The applications are related to the very weak signal measurement, usually in the range of a few uV, that is damaged by the interference of powline signals. The analog signal contains very large power line harmonics, say near 1Vac, as well as the weak signals that we are interested. If we feed all the signals without analog treatment into A/ D, the dynamic range will be suffered. If we can remove the power line harmonics in the analog domain first, the A/D dynamic range can be fully utilized. Therefore I am looking into this direction now. James www.go-ci.com
Reply by ●October 28, 20082008-10-28
On Tue, 28 Oct 2008 13:11:48 -0400, Jerry Avins <jya@ieee.org> wrote:>seafrn wrote: >> I am not sure about the mud thing either. I guess you find it in their >> patent. > >I googled a bit, and I'm more confused than befire. Mud-pulse telemetry >is what is sounds like: signaling by means of modulating the pressure of >the circulating drilling mud. So where does the electrical interference >come from? Is it introduced at the down-hole modulator, or noise getting >into the pressure sensor at the surface? If the latter, shame on those >who accept it!The noise to be removed comes from the pulsing nature of the mud pump discharge, which can be only partially removed by finite sized accumulators (fluidics analog to a capacitor, stores pressure rather than voltage).
Reply by ●October 28, 20082008-10-28
Glen Walpert wrote:> On Tue, 28 Oct 2008 13:11:48 -0400, Jerry Avins <jya@ieee.org> wrote: > >> seafrn wrote: >>> I am not sure about the mud thing either. I guess you find it in their >>> patent. >> I googled a bit, and I'm more confused than befire. Mud-pulse telemetry >> is what is sounds like: signaling by means of modulating the pressure of >> the circulating drilling mud. So where does the electrical interference >> come from? Is it introduced at the down-hole modulator, or noise getting >> into the pressure sensor at the surface? If the latter, shame on those >> who accept it! > > The noise to be removed comes from the pulsing nature of the mud pump > discharge, which can be only partially removed by finite sized > accumulators (fluidics analog to a capacitor, stores pressure rather > than voltage).So it isn't line noise, but rather an analog if it. That makes sense. I'd need to study the details to understand why noise and signal can't be made orthogonal, but differential methods seem to be unavailable. Separating signal from noise after digitizing can lead to poor dynamic range, as Walpert points out in another post, and that means some sort of analog processing. I wonder if synchronous demodulation (ala lock-in amplifier) has been tried? There's plenty of stray infrared in most living spaces, but IR remote controls work quite well. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 28, 20082008-10-28
DigitalSignal wrote: (snip)> The analog signal contains very large power line > harmonics, say near 1Vac, as well as the weak signals that we are > interested. If we feed all the signals without analog treatment into A/ > D, the dynamic range will be suffered. If we can remove the power line > harmonics in the analog domain first, the A/D dynamic range can be > fully utilized. Therefore I am looking into this direction now.I was wondering not so long ago about the state of the art in A/D conversion. It seems that 24 bit audio is reasonably common in digital recorders. Is the analog electronics up through the A/D converter really that good? Amplifiers with 144dB signal to noise ratio? The A/D converter itself? Microvolt signal in 1V background is only 120dB. -- glen
