Hi If you do a quick Google search for "insulation resistance" you get to:
http://www.electrocube.com/support/insulation_resistance.asp or a bunch of similar information. The capacitor it's self (no external resistance at all) has a time constant between it's capacitance and internal leakage. There's nothing the op amp can do to take care of this. Indeed the leakage of the op amp *adds* to the cap's leakage. Unless it's a very good op amp, the op amp leakage will have a noticable negative impact. Bob On Jan 1, 2012, at 3:56 PM, Don Latham wrote: > http://www.falstad.com/circuit/e-capmult.html > I did not take the time to analyze... > Don > > David >> Jim Williams did this in one of his designs for measuring low >> frequency reference noise. The large value low leakage wet tantalum >> capacitor he used was like $400 and it took 24 hours for the >> dielectric absorption to settle: >> >> http://www.linear.com/docs/28585 >> >> You can get the necessary time constant using a good 1uF film >> capacitor with good design and construction in this case. >> >> On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp <[email protected]> wrote: >> >>> Any real world capacitor will have a dielecric with an associated >>> insulation resistance. It's a "more money gets better performance" sort >>> of thing, but there are indeed limits. A 1000 uF cap that has a "good" >>> insulation resistance number might cost you more than some new cars…. >>> >>> On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: >>> >>>> On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray <[email protected]> >>>> wrote: >>>> >>>>> I think the main problem in this area is building a low pass filter >>>>> with a >>>>> long time constant. >>>>> >>>>> The time constant of the filter has to be: >>>>> long relative to the noise from the phase detector >>>>> short relative to aging of the oscillator >>>>> short relative to environmental changes >>>>> (so the osc can track temperature and voltage >>>>> those changes may be in the PLL system rather than the osc) >>>>> >>>>> If we are starting with PPS (rather than 10KHz), the filter time >>>>> constant >>>>> needs to be 10s or 100s of seconds. How do I build an analog filter >>>>> with a >>>>> time constant that long? >>>>> >>>> >>>> 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. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > -- > "Neither the voice of authority nor the weight of reason and argument > are as significant as experiment, for thence comes quiet to the mind." > R. Bacon > "If you don't know what it is, don't poke it." > Ghost in the Shell > > > Dr. Don Latham AJ7LL > Six Mile Systems LLP > 17850 Six Mile Road > POB 134 > Huson, MT, 59846 > VOX 406-626-4304 > www.lightningforensics.com > www.sixmilesystems.com > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
