I have some more information: It is a piezoelectric element that is not crystalline. I was mistaken when I described it as a crystal. The resonance is totally mechanical, not electrical. The piezoelectric actuating element drives a diaphragm. Here is where I suspect the problem is. I suspect the elastic properties of the diaphragm change with usage, and that changes the resonance frequency. -- To email me directly remove sj. from my email address's domain name. This is a spam jammer.
Crystal Controlled Oscillator
Started by ●January 3, 2022
Reply by ●January 4, 20222022-01-04
Reply by ●January 4, 20222022-01-04
On Tuesday, January 4, 2022 at 7:55:23 PM UTC+11, Artist wrote:> I have some more information: > > It is a piezoelectric element that is not crystalline. I was mistaken > when I described it as a crystal. > > The resonance is totally mechanical, not electrical. > > The piezoelectric actuating element drives a diaphragm. Here is where I > suspect the problem is. I suspect the elastic properties of the > diaphragm change with usage, and that changes the resonance frequency.You should be able to monitor the changing properties of the resonant assembly by looking at relationship between the current driving the oscillation and the displacement produced (which should show up in the voltage appearing across the piezoelectric element). You've got to tell us more about the system you are driving if you want more specific help. You can certainly e-mail me at my ieee address, it you want to do it privately. -- Bill Sloman, Sydney
Reply by ●January 4, 20222022-01-04
Artist wrote:> I have some more information: > > It is a piezoelectric element that is not crystalline. I was mistaken > when I described it as a crystal. > > The resonance is totally mechanical, not electrical. > > The piezoelectric actuating element drives a diaphragm. Here is where I > suspect the problem is. I suspect the elastic properties of the > diaphragm change with usage, and that changes the resonance frequency. >Quartz crystals are mechanical resonators too, but their electrical and mechanical characteristics are coupled via the piezoelectric effect. There's nothing magic about quartz--lots of lower-performance oscillators use ceramic resonators. Shifting the mechanical resonance shifts the electrical one as well, because the piezoelectric effect is intrinsically wideband--it's precisely the mechanical motion that's responsible for the electrical frequency selectivity. Resonator parameters such as peak amplitude, zero phase shift, and minimum impedance appear close together at high Q values--with 'high' meaning 'above about 3'. So your piezo should be fine. For a fixed drive amplitude and a nonresonant diaphragm, tuning for the maximum _in-phase_ current will get you the maximum mechanical amplitude, because there's nowhere for the power to go except into the mechanical motion. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●January 4, 20222022-01-04
BS Artist wrote: =============> I have some more information: >** We had none before.> It is a piezoelectric element that is not crystalline. I was mistaken > when I described it as a crystal. > > The resonance is totally mechanical, not electrical. >** Something I picked up on immediately while other are still baffled by.> The piezoelectric actuating element drives a diaphragm.** So just like a piezo tweeter. Have you never seen one? The load presented by such a piezo transducer is purely capacitance. About 100 to 200nF.> Here is where I > suspect the problem is. I suspect the elastic properties of the > diaphragm change with usage, and that changes the resonance frequency.** Exactly. So you tweak it. ..... Phil
Reply by ●January 4, 20222022-01-04
On 5/1/22 1:20 am, Phil Hobbs wrote:> Artist wrote: >> I have some more information: >> >> It is a piezoelectric element that is not crystalline. I was mistaken >> when I described it as a crystal. >> >> The resonance is totally mechanical, not electrical. >> >> The piezoelectric actuating element drives a diaphragm. Here is where >> I suspect the problem is. I suspect the elastic properties of the >> diaphragm change with usage, and that changes the resonance frequency. >> > > Quartz crystals are mechanical resonators too, but their electrical and > mechanical characteristics are coupled via the piezoelectric effect.As they are with piezo-ceramics. But in P-Cs the resonance of the ceramic isn't dominant, but the resonance of the substrate, often brass or some other thin metal, like in birthday-card sounders. Clifford Heath
Reply by ●January 4, 20222022-01-04
Clifford Heath wrote:> On 5/1/22 1:20 am, Phil Hobbs wrote: >> Artist wrote: >>> I have some more information: >>> >>> It is a piezoelectric element that is not crystalline. I was mistaken >>> when I described it as a crystal. >>> >>> The resonance is totally mechanical, not electrical. >>> >>> The piezoelectric actuating element drives a diaphragm. Here is where >>> I suspect the problem is. I suspect the elastic properties of the >>> diaphragm change with usage, and that changes the resonance frequency. >>> >> >> Quartz crystals are mechanical resonators too, but their electrical >> and mechanical characteristics are coupled via the piezoelectric effect. > > > As they are with piezo-ceramics. But in P-Cs the resonance of the > ceramic isn't dominant, but the resonance of the substrate, often brass > or some other thin metal, like in birthday-card sounders. > > Clifford HeathDepends on the situation. The OP was talking about an optical scanner, which needs to be stiff (i.e. nonresonant in the band of interest) in order for the optical wavefront not to get screwed up by the mirror bending. Greeting cards may well present a more complicated picture. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●January 4, 20222022-01-04
"the concepts "male" and "female" are essentially social constructions" (Bill Sloman) "the Mueller investigation was about Trump only because Trump made it so" (Bozo paraphrased) Bozo Bill Sloman is a chronic liar who cannot be reasoned with... -- Anthony William Sloman <bill.sloman@ieee.org> wrote:> X-Received: by 2002:ac8:6d35:: with SMTP id r21mr40185544qtu.9.1641196068408; Sun, 02 Jan 2022 23:47:48 -0800 (PST) > X-Received: by 2002:a25:4e03:: with SMTP id c3mr39283382ybb.266.1641196068150; Sun, 02 Jan 2022 23:47:48 -0800 (PST) > Path: eternal-september.org!reader02.eternal-september.org!news.misty.com!border2.nntp.dca1.giganews.com!nntp.giganews.com!news-out.google.com!nntp.google.com!postnews.google.com!google-groups.googlegroups.com!not-for-mail > Newsgroups: sci.electronics.design > Date: Sun, 2 Jan 2022 23:47:47 -0800 (PST) > In-Reply-To: <squ740$eh0$1@dont-email.me> > Injection-Info: google-groups.googlegroups.com; posting-host=123.243.66.234; posting-account=SJ46pgoAAABuUDuHc5uDiXN30ATE-zi- > NNTP-Posting-Host: 123.243.66.234 > References: <squ740$eh0$1@dont-email.me> > User-Agent: G2/1.0 > MIME-Version: 1.0 > Message-ID: <2329404f-444c-4d7c-bb9f-5f946d9f96c6n@googlegroups.com> > Subject: Re: Crystal Controlled Oscillator > From: Anthony William Sloman <bill.sloman@ieee.org> > Injection-Date: Mon, 03 Jan 2022 07:47:48 +0000 > Content-Type: text/plain; charset="UTF-8" > Content-Transfer-Encoding: quoted-printable > Lines: 38 > Xref: reader02.eternal-september.org sci.electronics.design:656582 > > On Monday, January 3, 2022 at 6:03:34 PM UTC+11, Artist wrote: >> I have been tasked with designing a piezoelectric actuator driver at its > >> resonant frequency. This is to replace an arrangement where the sine >> wave source is a function generator chip (the obsolete XR-2206) that >> must be individually tweaked on a unit, by unit basis, to match the >> crystal� Ts resonant frequency. >> >> The crystal is used as an actuator to vibrate a mirror used in a laser >> system. We have had systems come back from the field because the >> function generator� Ts sinewave frequency became too different for > the >> system to work. >> >> My idea is to use the crystal itself as part of an oscillator circuit so > >> that frequency is always exactly the crystal� Ts resonant frequency > . I >> have prepared an abbreviated concept schematic that can be viewed here: > >> https://i.imgur.com/4eBFQuD.png >> >> This is an op amp version of a Colpitts Oscillator. > > <snip> > > I suspect that what you want is a phase-locked loop. > > I did it once, but forced the sustaining current to be exactly in-phase with the voltage across the device, which didn't give the maximum excursion. If I'd been able adjust the phase match to hit the actual resonant frequency of the actual device (and my circuit did offer a straight=forward way of doing it, but I was on holiday in Australia when the hardware came together) it probably would have gone in to production, but production device ended up having a remarkably consistent resonant frequency, so we didn't need it. > > -- > Bill Sloman, Sydney > >
Reply by ●January 4, 20222022-01-04
"the concepts "male" and "female" are essentially social constructions" (Bill Sloman) "the Mueller investigation was about Trump only because Trump made it so" (Bozo paraphrased) Bozo Bill Sloman is a chronic liar who cannot be reasoned with... -- Anthony William Sloman <bill.sloman@ieee.org> wrote:> X-Received: by 2002:a05:620a:9c3:: with SMTP id y3mr32730941qky.367.1641261509488; Mon, 03 Jan 2022 17:58:29 -0800 (PST) > X-Received: by 2002:a25:ae13:: with SMTP id a19mr42789756ybj.327.1641261508993; Mon, 03 Jan 2022 17:58:28 -0800 (PST) > Path: eternal-september.org!reader02.eternal-september.org!news.misty.com!border2.nntp.dca1.giganews.com!nntp.giganews.com!news-out.google.com!nntp.google.com!postnews.google.com!google-groups.googlegroups.com!not-for-mail > Newsgroups: sci.electronics.design > Date: Mon, 3 Jan 2022 17:58:28 -0800 (PST) > In-Reply-To: <fdb23c12-119c-b0a3-cdec-da53833c28aa@electrooptical.net> > Injection-Info: google-groups.googlegroups.com; posting-host=123.243.66.234; posting-account=SJ46pgoAAABuUDuHc5uDiXN30ATE-zi- > NNTP-Posting-Host: 123.243.66.234 > References: <squ740$eh0$1@dont-email.me> <fdb23c12-119c-b0a3-cdec-da53833c28aa@electrooptical.net> > User-Agent: G2/1.0 > MIME-Version: 1.0 > Message-ID: <44df5508-706a-4819-a188-49ad9e93ee34n@googlegroups.com> > Subject: Re: Crystal Controlled Oscillator > From: Anthony William Sloman <bill.sloman@ieee.org> > Injection-Date: Tue, 04 Jan 2022 01:58:29 +0000 > Content-Type: text/plain; charset="UTF-8" > Content-Transfer-Encoding: quoted-printable > Lines: 123 > Xref: reader02.eternal-september.org sci.electronics.design:656633 > > On Tuesday, January 4, 2022 at 8:41:36 AM UTC+11, Phil Hobbs wrote: >> Artist wrote: >> > I have been tasked with designing a piezoelectric actuator driver at >> > its resonant frequency. This is to replace an arrangement where the >> > sine wave source is a function generator chip (the obsolete XR-2206) >> > that must be individually tweaked on a unit, by unit basis, to match >> > the crystal� Ts resonant frequency. >> > >> > The crystal is used as an actuator to vibrate a mirror used in a >> > laser system. We have had systems come back from the field because >> > the function generator� Ts sinewave frequency became too differen > t for >> > the system to work. >> > >> > My idea is to use the crystal itself as part of an oscillator circuit > >> > so that frequency is always exactly the crystal� Ts resonant freq > uency. >> > >> That's a good approach in general. >> > I have prepared an abbreviated concept schematic that can be viewed >> > here: https://i.imgur.com/4eBFQuD.png >> > >> > This is an op amp version of a Colpitts Oscillator. >> > >> > RV2 adds energy to the crystal to sustain its oscillations. I do not >> > know right now its optimum value. >> You're going to want a better oscillator circuit than that, for sure. >> >> I doubt it would actually oscillate, for one thing--unless the resonator > >> has a lot of delay (e.g. a SAW device) it'll just look like an inductor > >> or a capacitor depending on frequency. There may be a higher-order >> resonance that has enough delay. >> > U1 controls the oscillation amplitude by controlling the voltage on >> > the op amp� Ts power supply lines. The circuit is designed to hav > e a >> > single supply so two regulators need not be ganged together. >> Most of the piezo actuators I've used have resonated in the 30 kHz >> region, with Qs around 30. That's low enough that the nonsinusoidal >> waveform of a self-limited oscillator can cause all sorts of uglies in >> the motion--when the Q is low, the mechanical overtones often aren't far > >> enough from the electrical harmonics to get good rejection. >> >> The other issue is that the electrical resonance won't be the same as >> the mechanical resonance in general, so the vibration amplitude will be > >> tuning-sensitive. The mechanical resonance is what it is, and generally > >> coincides closely with the electrical series resonance. >> >> A Colpitts has to run at a frequency where the piezo looks inductive. >> Getting it to run exactly at its series resonance requires a series >> inductor of just the right size. >> >> <snip> >> > The cable to the crystal might be as long as five feet. >> Not a giant problem for a kilohertzy oscillator. >> > >> > My questions are whether this should work in principle, and whether >> > there are any bettor ways to do it. >> If you want to avoid tuning issues, I'd suggest using an external >> sinusoidal VCO and driving the piezo via a resistor. Servo the VCO >> frequency to where the phase shift across the resistor is zero. That >> should nearly coincide with the amplitude minimum. >> >> You might need an amplitude adjustment to take out unit-to-unit >> variations in the piezoelectric sensitivity, but at least it'll be >> running at its mechanical resonance. > > As usual Phil has got it pretty right. My problem was with a micro-stirrer which didn't need to produce a well-controlled excursion, but we did want to run it at the mechanical resonance , which was pretty sharp. > > My problem was that maximum amplitude didn't happen when the phase shift across the resistor was zero. > > The argument is that the phase shift goes from leading below resonance to lagging about resonance, but the reality is that it isn't exactly zero at resonance. > > If you want to define resonance as maximum excursion, you can't use amplitude monitoring to get it exactly, because the amplitude doesn't change with frequency at the peak. Happily, phase does change quite rapidly at that frequency. > > An approach that can work is to measure the phase when the amplitude is 50% down from the peak below resonance , and 50% down above resonance - both give well defined frequencies and thus phases, and set the system to lock the phase half-way between. > > There's no guarantee that this will give the absolute maximum amplitude, but it will get you close, and close enough to let you work out almost the exact phase shift that will give you the maximum amplitude at the time. > > The over-kill approach would be to use a direct digital synthesis (DDS) chip to generate the sine wave drive, and waveforms to drive in-phase and quadrature phase detectors. You'd have to digitise the outputs of both phase detectors and turn them into amplitude and phase signal and let a microprocessor do the tweaking. > > There are simpler, cruder approaches. You can make a crude approximation to a sine wave as a "modified sine wave" - which is a switched drive which is off from 0 degrees to 30 degrees, high from 30 degrees to 150 degrees, off again from 150 degrees to 210 degrees, low from 210 degrees to 330 degrees and off again from 330 degrees to 360 degress. > > That can be done with voltage controlled oscillator (VCO) in 4046 running at twelve times the desired frequency, and a bunch of digital dividers to spit out the drive waveforms and the outputs to drive the in-phase and quadrature phase detectors. > > If you run the VCO faster you can push out waveforms at the operating frequency that can drive the "in-phase" detector to pick up the output amplitude at the phase you get when the system is operating at resonance and the "phase detector" so that its output goes through zero as the system goes through resonance, but you do have to know roughly where these points are. That was what I was trying to do back in 1992, but I hadn't spelled it out to my colleagues in enough detail. > > -- > Bill Sloman, Sydney > >
Reply by ●January 4, 20222022-01-04
The John Doe troll stated the following in message-id <sdhn7c$pkp$4@dont-email.me>:> The troll doesn't even know how to format a USENET post...And the John Doe troll stated the following in message-id <sg3kr7$qt5$1@dont-email.me>:> The reason Bozo cannot figure out how to get Google to keep from > breaking its lines in inappropriate places is because Bozo is > CLUELESS...And yet, the clueless John Doe troll has itself posted yet another incorrectly formatted USENET posting on Wed, 5 Jan 2022 02:07:45 -0000 (UTC) in message-id <sr2uhh$jeh$6@dont-email.me>. nxPG9WsoBGo5
Reply by ●January 4, 20222022-01-04
The John Doe troll stated the following in message-id <sdhn7c$pkp$4@dont-email.me>:> The troll doesn't even know how to format a USENET post...And the John Doe troll stated the following in message-id <sg3kr7$qt5$1@dont-email.me>:> The reason Bozo cannot figure out how to get Google to keep from > breaking its lines in inappropriate places is because Bozo is > CLUELESS...And yet, the clueless John Doe troll has itself posted yet another incorrectly formatted USENET posting on Wed, 5 Jan 2022 02:09:07 -0000 (UTC) in message-id <sr2uk2$jeh$7@dont-email.me>. MDqmsKWPklxN
