Re: [time-nuts] Frequency of LC Tank
On 04/12/2014 03:23 PM, d...@irtelemetrics.com wrote: > Magnus, > You are very much on the track that I was thinking. I belive you are > absolutly correct in that a 90 degree phase shift would be ideal. Coming into the conversation kinda late. Sounds like you're building an induction heater which is what I do professionally. You might want to read this page http://inductionheatertutorial.com/ I gave Jonathan the circuit. He improved on it and inserted a microprocessor into the PLL to stabilize it and make it more noise resistant. He has some very nice videos on Youtube under the handle "imsmoother". Here's my page http://www.neon-john.net/Induction/Index.htm John -- John DeArmond Tellico Plains, Occupied TN http://www.fluxeon.com <-- THE source for induction heaters http://www.neon-john.com<-- email from here http://www.johndearmond.com <-- Best damned Blog on the net PGP key: wwwkeys.pgp.net: BCB68D77 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank
On 12/04/14 21:23, d...@irtelemetrics.com wrote: Magnus, You are very much on the track that I was thinking. I belive you are absolutly correct in that a 90 degree phase shift would be ideal. I did a bit more digging last night, and it turns out that an XOR phase comparator looking at the tank voltage and drive voltage may be ideal, as you have suggested here. My main concern was that I plan to adjust the pulse width of the push-pull the drive circuit to adjust the power into the tank circuit. (Actually the drive will be full bridge, transformer coupled to the tank). That change in pulse width is where I was stuck, mentall. However since I'm in the 10Khz to 100Khz range and am generating the push-pull PWM digitally, I can just generate a second output at the same frequency and phase (or even different phase) than the drive signal to compare to the tank voltage. As you say "away you go with a phase detector"! I propose to sample the voltage rather than just using a XOR-gate (and a limiter in front of it to square things up). Thing is, the voltage from your LC tank is very analogue, so make use of this fact. I would put a PI-loop (one op-amp, two resistors and a cap) in there. As for frequency, your actual drive-oscillator can run at 4 times the rate and then use a frequency divider to provide the phases. This can provide you with in-phase and quadrature signals. Look at Tayloe detector in a search engine near you. The driven frequency will remain in your range, but you now have a quadrature signal to compare with. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank
It is very easy to make an impedance phase detector by inserting a toroidal current transformer in series with the load under test. The center of the secondary is connected to the load through a capacitor. Each end of the secondary goes to a diode detector. When the load is resistive, the DC outputs of the two detectors are equal. You can see this in the literature back as far as at least the 1950's for autotuning antennas. It is closely related to various FM discriminator circuit like the ratio detector. Rick On 4/12/2014 12:23 PM, d...@irtelemetrics.com wrote: Magnus, You are very much on the track that I was thinking. I belive you are absolutly correct in that a 90 degree phase shift would be ideal. I did a bit more digging last night, and it turns out that an XOR phase comparator looking at the tank voltage and drive voltage may be ideal, as you have suggested here. My main concern was that I plan to adjust the pulse width of the push-pull the drive circuit to adjust the power into the tank circuit. (Actually the drive will be full bridge, transformer coupled to the tank). That change in pulse width is where I was stuck, mentall. However since I'm in the 10Khz to 100Khz range and am generating the push-pull PWM digitally, I can just generate a second output at the same frequency and phase (or even different phase) than the drive signal to compare to the tank voltage. As you say "away you go with a phase detector"! Didier, I guess the thing that's different here than in most situations, is that normally you try not to load the tank circuit more than necessary. Here I'm loading the tank circuit considerablly, knowing that it will change frequency with the change in Q. This change in frequency is what I need to find, track, and follow. The tank will be very lossy (Maybe consuming 20Kw to 30Kw of power if all goes well). I'm also certian Q will move all over the place. I just want to stay near the peak of the bell, even if it's a short fat bell shaped curve. Since the frequecny is low, I was thinking that even a modern optocoupler should get me phase information well. At these power levels a little loading souldn't be a big deal! :) Dan As you drive it with a pulse, you induce energy to it. If you sample the voltage (or current) 90 degrees of from your drive-pulse, that quadrature will indicate if you are early, late or prompt. As your sampling point is also a sign of your current rate, and the pulse forced the LC tank and your oscillator into sync, the frequency error will cause the phase difference and hence voltage difference to be observeable. As you are fairly close in frequency, so will the phase error and you can assume the phase to voltage to be almost linear and away you go with a phase detector. Cheers, Magnus -- Keep in mind that anything you connect across your tank circuit will affect its resonant frequency and Q (signal source and measuring device). You need to make sure your equipment is very loosely coupled to the UUT through small value capacitors for instance. Didier KO4BB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank
Magnus, You are very much on the track that I was thinking. I belive you are absolutly correct in that a 90 degree phase shift would be ideal. I did a bit more digging last night, and it turns out that an XOR phase comparator looking at the tank voltage and drive voltage may be ideal, as you have suggested here. My main concern was that I plan to adjust the pulse width of the push-pull the drive circuit to adjust the power into the tank circuit. (Actually the drive will be full bridge, transformer coupled to the tank). That change in pulse width is where I was stuck, mentall. However since I'm in the 10Khz to 100Khz range and am generating the push-pull PWM digitally, I can just generate a second output at the same frequency and phase (or even different phase) than the drive signal to compare to the tank voltage. As you say "away you go with a phase detector"! Didier, I guess the thing that's different here than in most situations, is that normally you try not to load the tank circuit more than necessary. Here I'm loading the tank circuit considerablly, knowing that it will change frequency with the change in Q. This change in frequency is what I need to find, track, and follow. The tank will be very lossy (Maybe consuming 20Kw to 30Kw of power if all goes well). I'm also certian Q will move all over the place. I just want to stay near the peak of the bell, even if it's a short fat bell shaped curve. Since the frequecny is low, I was thinking that even a modern optocoupler should get me phase information well. At these power levels a little loading souldn't be a big deal! :) Dan As you drive it with a pulse, you induce energy to it. If you sample the voltage (or current) 90 degrees of from your drive-pulse, that quadrature will indicate if you are early, late or prompt. As your sampling point is also a sign of your current rate, and the pulse forced the LC tank and your oscillator into sync, the frequency error will cause the phase difference and hence voltage difference to be observeable. As you are fairly close in frequency, so will the phase error and you can assume the phase to voltage to be almost linear and away you go with a phase detector. Cheers, Magnus -- Keep in mind that anything you connect across your tank circuit will affect its resonant frequency and Q (signal source and measuring device). You need to make sure your equipment is very loosely coupled to the UUT through small value capacitors for instance. Didier KO4BB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank.
Keep in mind that anything you connect across your tank circuit will affect its resonant frequency and Q (signal source and measuring device). You need to make sure your equipment is very loosely coupled to the UUT through small value capacitors for instance. Didier KO4BB On April 11, 2014 3:15:37 PM CDT, Dan Kemppainen wrote: >Hi all, > >I'm thinking about an upcoming project, if this is off topic please >disregard or contact me off list. :) > >I have a large LC tank, with a very lossy inductor. Being driven by a >pulse width push pull driver, that is digitally controlled. The driver >circuit will couple through a N:1 transformer. I need to be able to >adjust the push/pull driver frequency to match the frequency of the >tank >circuit. (See frequency/time is involved :) ) The tank components can >vary and are not adjustable, so the drive frequency needs to vary. > >I'm thinking some sort of a phase detector may be the way to go. I'm >just not sure were to sample the V and I signals to look for phase >differences, or where to get a good clean reference from. > >So the question is, when actively driving a tank circuit, how do you >know you are driving it with the same frequency ad the same phase it >naturally oscillates at. > >Any thoughts, suggestions, or readily available papers you guy could >point me to? > >Thanks! >Dan >___ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank.
On 11/04/14 22:15, Dan Kemppainen wrote: Hi all, I'm thinking about an upcoming project, if this is off topic please disregard or contact me off list. :) I have a large LC tank, with a very lossy inductor. Being driven by a pulse width push pull driver, that is digitally controlled. The driver circuit will couple through a N:1 transformer. I need to be able to adjust the push/pull driver frequency to match the frequency of the tank circuit. (See frequency/time is involved :) ) The tank components can vary and are not adjustable, so the drive frequency needs to vary. I'm thinking some sort of a phase detector may be the way to go. I'm just not sure were to sample the V and I signals to look for phase differences, or where to get a good clean reference from. So the question is, when actively driving a tank circuit, how do you know you are driving it with the same frequency ad the same phase it naturally oscillates at. Any thoughts, suggestions, or readily available papers you guy could point me to? As you drive it with a pulse, you induce energy to it. If you sample the voltage (or current) 90 degrees of from your drive-pulse, that quadrature will indicate if you are early, late or prompt. As your sampling point is also a sign of your current rate, and the pulse forced the LC tank and your oscillator into sync, the frequency error will cause the phase difference and hence voltage difference to be observeable. As you are fairly close in frequency, so will the phase error and you can assume the phase to voltage to be almost linear and away you go with a phase detector. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank.
Some terminology to consider. There is the natural and damped frequency to consider. That is, as you load the circuit, the resonance changes. If you drive it with infinite impedance, you are at the natural frequency. Loading it will shift the frequency, hence the damped frequency. I would try to lose the transformer if possible. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank.
That's why you want to look for the phase of the tank impedance. The phase goes through zero at resonance. It is far more precise. The steepness of the phase v. frequency plot is steep w/ a high Q circuit... flatter w/ a low Q tank. Either way, it does go through zero at resonance. The phase v. freq looks kinda like this: Phase: /\ -/ \ /---Freq \/ ^ resonance The dither sweep, amplituse measurement, lock-in will tune the oscillator to maximize the amplituse. Either on should pretty much steer you to resonance. -John == > >> I have a large LC tank, with a very lossy inductor. ... > >> So the question is, when actively driving a tank circuit, how do you >> know >> you are driving it with the same frequency ad the same phase it >> naturally >> oscillates at. > > If it's lossy, the peak will be broad so tuning the driving frequency > won't > be critical. > > How about just measuring the amplitude and tune for a max? I'm thinking > of > something like a diode and R/C filter feeding an ADC. > > > -- > These are my opinions. I hate spam. > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank.
I would have done exactly what Hal said. I do this all the time when trying to figure out the LC tanks operating frequency. An example keeping this time nuts friendly, the d-psk-r circuits at 60 Khz. I am lucky in that I can add or subtract C on the stuff I work on. Regards Paul WB8TSL On Fri, Apr 11, 2014 at 6:05 PM, Hal Murray wrote: > > > I have a large LC tank, with a very lossy inductor. ... > > > So the question is, when actively driving a tank circuit, how do you know > > you are driving it with the same frequency ad the same phase it naturally > > oscillates at. > > If it's lossy, the peak will be broad so tuning the driving frequency won't > be critical. > > How about just measuring the amplitude and tune for a max? I'm thinking of > something like a diode and R/C filter feeding an ADC. > > > -- > These are my opinions. I hate spam. > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank.
> I have a large LC tank, with a very lossy inductor. ... > So the question is, when actively driving a tank circuit, how do you know > you are driving it with the same frequency ad the same phase it naturally > oscillates at. If it's lossy, the peak will be broad so tuning the driving frequency won't be critical. How about just measuring the amplitude and tune for a max? I'm thinking of something like a diode and R/C filter feeding an ADC. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank.
First order approximation of course would be to sweep the frequency and look for a dip (peak for series resonant) in the DC current drawn by the driver. On Fri, Apr 11, 2014 at 4:15 PM, Dan Kemppainen wrote: > when actively driving a tank circuit, how do you > know you are driving it with the same frequency ad the same phase it > naturally oscillates at > -- --Jim Harman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency of LC Tank.
At resonance, an LC looks pure resistive. For a parallel LC, sample the voltage across the LC and the drive current, and tweek the frequency until they are in-phase. For a series LC, sample the voltage across the L or C and tweek as above. If you want to do it analog, dither the frequency a bit. With the quardature of the sweep signal as reference for a lock-in. The output of thye L-I is the tuning signal. (Roughly Pound Locking) YMMV, -John === > Hi all, > > I'm thinking about an upcoming project, if this is off topic please > disregard or contact me off list. :) > > I have a large LC tank, with a very lossy inductor. Being driven by a > pulse width push pull driver, that is digitally controlled. The driver > circuit will couple through a N:1 transformer. I need to be able to > adjust the push/pull driver frequency to match the frequency of the tank > circuit. (See frequency/time is involved :) ) The tank components can > vary and are not adjustable, so the drive frequency needs to vary. > > I'm thinking some sort of a phase detector may be the way to go. I'm > just not sure were to sample the V and I signals to look for phase > differences, or where to get a good clean reference from. > > So the question is, when actively driving a tank circuit, how do you > know you are driving it with the same frequency ad the same phase it > naturally oscillates at. > > Any thoughts, suggestions, or readily available papers you guy could > point me to? > > Thanks! > Dan > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Frequency of LC Tank.
Hi all, I'm thinking about an upcoming project, if this is off topic please disregard or contact me off list. :) I have a large LC tank, with a very lossy inductor. Being driven by a pulse width push pull driver, that is digitally controlled. The driver circuit will couple through a N:1 transformer. I need to be able to adjust the push/pull driver frequency to match the frequency of the tank circuit. (See frequency/time is involved :) ) The tank components can vary and are not adjustable, so the drive frequency needs to vary. I'm thinking some sort of a phase detector may be the way to go. I'm just not sure were to sample the V and I signals to look for phase differences, or where to get a good clean reference from. So the question is, when actively driving a tank circuit, how do you know you are driving it with the same frequency ad the same phase it naturally oscillates at. Any thoughts, suggestions, or readily available papers you guy could point me to? Thanks! Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
