Re: [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors
OK, note taken. Usually large capacitors are not available with tantalum dielectric, it seems that the last is a 1000uF 6.3V. On Fri, Jan 6, 2012 at 6:54 PM, Bob Camp wrote: > Hi > > Oddly enough, if you use a tantalum electrolytic as C2, it's not very happy > in that circuit. Their leakage with low voltages on them can be pretty > nasty. > > Bob > > -Original Message- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Poul-Henning Kamp > Sent: Thursday, January 05, 2012 5:50 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors > > In message > > , Azelio Boriani writes: > > >I have googled extensively trying to find something about the dual > >capacitor method of reducing the leakage current... nothing found. Please, > >can you indicate anything for me to learn more? > > It is very simple: > > R1 charges C1 to the DC potential and therefore C2 sees > (almost) no DC voltage, which means (almost) no leakage > current. C2 is still a capacitor for any AC or dV component. > > I belive I picked this trick up from a datasheet or app-note relating > to precision voltage references. > > Poul-Henning > > >> [Some op-amp] >-+-R2-+--> > >> || > >> | - C2 > >> | - > >> || > >> +---||---+ > >>R1 | > >> | > >> - C1 > >> - > >> | > >> GND > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > ___ > 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 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] Thunderbolt? (re simple gpsdo.) >> capacitors
Hi Oddly enough, if you use a tantalum electrolytic as C2, it's not very happy in that circuit. Their leakage with low voltages on them can be pretty nasty. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Poul-Henning Kamp Sent: Thursday, January 05, 2012 5:50 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors In message , Azelio Boriani writes: >I have googled extensively trying to find something about the dual >capacitor method of reducing the leakage current... nothing found. Please, >can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning >> [Some op-amp] >-+-R2-+--> >> || >> | - C2 >> | - >> || >> +---||---+ >>R1 | >> | >> - C1 >> - >> | >> GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
I have used that trick also for HV supplies when leakage through a capacitor (typically the capacitor used to compensate the HV divider used for regulation) exposed to 10 or 20kV is hard to eliminate. At the time, I did not know it had already been invented... Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: "Poul-Henning Kamp" Sender: time-nuts-boun...@febo.com Date: Thu, 05 Jan 2012 22:49:55 To: Discussion of precise time and frequency measurement Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors In message , Azelio Boriani writes: >I have googled extensively trying to find something about the dual >capacitor method of reducing the leakage current... nothing found. Please, >can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning >> [Some op-amp] >-+-R2-+--> >> || >> | - C2 >> | - >> || >> +---||---+ >>R1 | >> | >> - C1 >> - >> | >> GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
Thanks. Me too: now I got it, sort of bootstrap and now I see that R2 is needed because the real filter is R2*C2 and the leakage is not totally compensated if C1 has to move to a new value -> R*C1 wrote: > Poul > Thanks have been kind of following this thread and the diagram did not make > a lot of sense. > I figured I missed part of the thread. But this clears it up nicely. > Regards > Paul. > WB8TSL > > On Thu, Jan 5, 2012 at 5:49 PM, Poul-Henning Kamp >wrote: > > > In message > g...@mail.gmail.com> > > , Azelio Boriani writes: > > > > >I have googled extensively trying to find something about the dual > > >capacitor method of reducing the leakage current... nothing found. > Please, > > >can you indicate anything for me to learn more? > > > > It is very simple: > > > > R1 charges C1 to the DC potential and therefore C2 sees > > (almost) no DC voltage, which means (almost) no leakage > > current. C2 is still a capacitor for any AC or dV component. > > > > I belive I picked this trick up from a datasheet or app-note relating > > to precision voltage references. > > > > Poul-Henning > > > > >> [Some op-amp] >-+-R2-+--> > > >> || > > >> | - C2 > > >> | - > > >> || > > >> +---||---+ > > >>R1 | > > >> | > > >> - C1 > > >> - > > >> | > > >> GND > > > > -- > > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > > p...@freebsd.org | TCP/IP since RFC 956 > > FreeBSD committer | BSD since 4.3-tahoe > > Never attribute to malice what can adequately be explained by > incompetence. > > > > ___ > > 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 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] Thunderbolt? (re simple gpsdo.) >> capacitors
Poul Thanks have been kind of following this thread and the diagram did not make a lot of sense. I figured I missed part of the thread. But this clears it up nicely. Regards Paul. WB8TSL On Thu, Jan 5, 2012 at 5:49 PM, Poul-Henning Kamp wrote: > In message g...@mail.gmail.com> > , Azelio Boriani writes: > > >I have googled extensively trying to find something about the dual > >capacitor method of reducing the leakage current... nothing found. Please, > >can you indicate anything for me to learn more? > > It is very simple: > > R1 charges C1 to the DC potential and therefore C2 sees > (almost) no DC voltage, which means (almost) no leakage > current. C2 is still a capacitor for any AC or dV component. > > I belive I picked this trick up from a datasheet or app-note relating > to precision voltage references. > > Poul-Henning > > >> [Some op-amp] >-+-R2-+--> > >> || > >> | - C2 > >> | - > >> || > >> +---||---+ > >>R1 | > >> | > >> - C1 > >> - > >> | > >> GND > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > ___ > 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] Thunderbolt? (re simple gpsdo.) >> capacitors
In message , Azelio Boriani writes: >I have googled extensively trying to find something about the dual >capacitor method of reducing the leakage current... nothing found. Please, >can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning >> [Some op-amp] >-+-R2-+--> >> || >> | - C2 >> | - >> || >> +---||---+ >>R1 | >> | >> - C1 >> - >> | >> GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
... don't know but judging from the very simple ASCII schematic I'll say no because the lower capacitor is grounded. There is some sort of feedback I can't figure out, too simple that schematic. On Thu, Jan 5, 2012 at 11:27 PM, wrote: > Perhaps the dual cap is a differential implementation of the > filter/integrator. > > ___ > 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] Thunderbolt? (re simple gpsdo.) >> capacitors
Perhaps the dual cap is a differential implementation of the filter/integrator. ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
I have googled extensively trying to find something about the dual capacitor method of reducing the leakage current... nothing found. Please, can you indicate anything for me to learn more? Thank you On Thu, Jan 5, 2012 at 9:18 PM, WarrenS wrote: > > Yes almost as long as you include ONE more Resistor, R2 added below. > The dual cap thing does not get rid of leakage entirely, but close enough > in most cases. > That configuration is most useful for slow open loop filters when you want > low leakage errors. > > It may be a bit of an overkill for a closed loop filters when a 10 % > leakage would be tolerable. > I tested a 10,000 sec TC filter using a 10 meg and 1000 uF, and got under > 1% leakage error open loop. > > ws > > > ******* > > [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors > Poul-Henning Kamp phk at phk.freebsd.dk > > > The leakage current noise I measured was way below insignificant when >>> things are properly scaled. >>> >> > Couldn't the "double condensor" from voltage references trick be used to >> eliminate the leakage entirely ? >> > > > [Some op-amp] >-+-R2-+--> > | | > | - > | - > | | > +---||---+ > >| > - > - >| >GND > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > > ___ > 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] Thunderbolt? (re simple gpsdo.) >> capacitors
Yes almost as long as you include ONE more Resistor, R2 added below. The dual cap thing does not get rid of leakage entirely, but close enough in most cases. That configuration is most useful for slow open loop filters when you want low leakage errors. It may be a bit of an overkill for a closed loop filters when a 10 % leakage would be tolerable. I tested a 10,000 sec TC filter using a 10 meg and 1000 uF, and got under 1% leakage error open loop. ws *** [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors Poul-Henning Kamp phk at phk.freebsd.dk The leakage current noise I measured was way below insignificant when things are properly scaled. Couldn't the "double condensor" from voltage references trick be used to eliminate the leakage entirely ? [Some op-amp] >-+-R2-+--> | | | - | - | | +---||---+ | - - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
In message <80B26DC756AA45DD84E4EB9E14B58998@Warcon28Gz>, "WarrenS" writes: >The leakage current noise I measured was way below insignificant when things >are properly scaled. Really stupid question: Couldn't the "double condensor" from voltage references trick be used to eliminate the leakage entirely ? [Some op-amp] >-++--> || | - | - | | +--||+ | - - | | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
this thread has wandered a bit. The thread was originally for "Simple"... Bottom line is that electrolytic caps can be made to work fine for a "SIMPLE" analog controller built for home NUT use, Not recommended for space or critical life support applications, or any production thing. Besides putting the crappie RC inside a closed loop the other thing that seems several are missing is to limit the correction range. If one sets up the simple loop to give say a 100 to 1 improvement, then all the other concerns become non-issues. "The noise created by the leakage current in an electrolytic will be an issue outside the loop bandwidth and only will be reduced by the available gain..." Loop Gain is not a problem when making a frequency lock loop, even with a P only controller, using any kind of phase detector because the gain is infinite. The leakage current noise I measured was way below insignificant when things are properly scaled. Such as when you scale it so you only care about a 1% of 5 volt change and not uv. If you're depending on a specific time constant for a SIMPLE controller using electrolytic caps then the problem is the design and not the caps. If you're want to make a 1e-10 to one correction with a simple controller the problem is not the cap but the configuration and the expectations. But making a 1e-13 correction to a 1e-9 Rb is no problem (1000 to one improvement) Hal Murray Posted: "I'm not interested in the frequency shift of the filter as the temperature but the voltage shift due to a fixed charge as the capacitance changes." Interesting question, so I tried it. No effect on the One I tested. I charged a cheapie 1000uf, 50V cap to 5 volts then changed it's temperature which did changed it's capacitance and leakage, but had no effect on it's charge voltage. I guess the charge is not Fixed, so not the same thing as changing the value by paralleling the cap. ws ** [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors Bob Camp lists at rtty.us Hi No argument there, but this thread has wandered a bit. If you are depending on the capacitor to provide a specific time constant, then you will have issues. If the control loop is not impacted by the changes, then they will track out. Often it's not quite an either / or, but a some of this and some of that. In any case the noise created by the leakage current in an electrolytic will be an issue outside the loop bandwidth and only will be reduced by the available gain... Bob *** On Behalf Of Chris Albertson Hi Using electrolytic caps in timing applications is a bit exciting. Their leakage current changes each time you change the voltage on them. It's enough of a change to significantly impact long time constants. In some cases the capacitance changes with voltage as well.. In general you are right. But in this case the electrolytic cap is inside a closed loop so as the temperature changes and the voltage in the cap changes, the loop will correct it, as long the temperature changes slowly compared to how frequently we measure the phase of the PPS signal. You could always place the entire system inside box and control it to a constant temperature. Chris Albertson Redondo Beach, California ___ ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
Hi No argument there, but this thread has wandered a bit. If you are depending on the capacitor to provide a specific time constant, then you will have issues. If the control loop is not impacted by the changes, then they will track out. Often it's not quite an either / or, but a some of this and some of that. In any case the noise created by the leakage current in an electrolytic will be an issue outside the loop bandwidth and only will be reduced by the available gain... Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Chris Albertson Sent: Tuesday, January 03, 2012 12:35 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors On Tue, Jan 3, 2012 at 9:14 AM, Bob Camp wrote: > Hi > > Using electrolytic caps in timing applications is a bit exciting. Their > leakage current changes each time you change the voltage on them. It's > enough of a change to significantly impact long time constants. In some > cases the capacitance changes with voltage as well.. > In general you are right. But in this case the electrolytic cap is inside a closed loop so as the temperature changes and the voltage in the cap changes, the loop will correct it, as long the temperature changes slowly compared to how frequently we measure the phase of the PPS signal. You could always place the entire system inside box and control it to a constant temperature. -- Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
On Tue, Jan 3, 2012 at 9:14 AM, Bob Camp wrote: > Hi > > Using electrolytic caps in timing applications is a bit exciting. Their > leakage current changes each time you change the voltage on them. It's > enough of a change to significantly impact long time constants. In some > cases the capacitance changes with voltage as well.. > In general you are right. But in this case the electrolytic cap is inside a closed loop so as the temperature changes and the voltage in the cap changes, the loop will correct it, as long the temperature changes slowly compared to how frequently we measure the phase of the PPS signal. You could always place the entire system inside box and control it to a constant temperature. -- Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.) >> capacitors
Hi Using electrolytic caps in timing applications is a bit exciting. Their leakage current changes each time you change the voltage on them. It's enough of a change to significantly impact long time constants. In some cases the capacitance changes with voltage as well. Temperature stability of capacitance for most processes is in the 10 to 20% change over 0 to 50C. Leakage at least doubles every 10C. Many ceramic bypass caps have similar TC and change in cap with voltage issues. NPO ceramics or *good* film capacitors are the stuff you make your analog computer out of. (Yes, I'm old enough that you had to check the course description to see if the "computer" course was analog or digital...) Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Monday, January 02, 2012 8:15 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) > Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you > have 1 second. In theory you could build 100s just by using a 100K resistor > but I think real world components are not perfect enough. Does anybody know anything about the temperature coefficients of large caps? I found data for ceramic caps, but when I added "electrolytic" all I got was lifetime stuff rather than capacitance change with temperature. I'm not interested in the frequency shift of the filter as the temperature but the voltage shift due to a fixed charge as the capacitance changes. -- These are my opinions, not necessarily my employer's. 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.
