Bruce wrote: > Analog time constants of several hours are generally considered > impractical due to the lack of suitable low noise components > principally high value resistors and capacitors.
> So how do you propose to get around this with an analog control loop? > Bruce Not that I'm recommending this approach, but for general info, Digikey sells a 1 Farad 5.5V cap for about $7.00CAD in singles: http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=131084;keywords=1%20farad A time constant of 1 hr would need a 3.6k resistor. That's not bad. I have some 5 Farad caps that might be even better. The typical leakage spec for electrolytics is I = K * C * V where C = capacitance in Farads V = applied voltage K = 0.002 for low leakage electrolytic caps, 0.02 for standard I have measured K values of 7e-7 for double layer caps. This is much, much better than any electrolytic I have ever seen. This enabled some advanced silver ion generators using differentiation that could not be done with electrolytics. The typical frequency response rolls off above a few hundred Hz. This is of little consequence in timing circuits intended for several hours duration. But I'd go with a digital approach for a low frequency PLL. Mike Monett _______________________________________________ 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.