On Thu, 18 Dec 2014 04:26:22 -0500 Charles Steinmetz <[email protected]> wrote:
> Gary <[email protected]> wrote: > > >Why not use a lower voltage transformer, preferably not at a lethal > >voltage. You only need a couple of volts to drive the rest of the > >circuit. > > As you can see from the schematic, the voltage is diode-clamped > almost immediately to ~ +/- 1.5v. The reason for using a 120v > winding is to take advantage of the free slope enhancement provided > by the higher voltage. The 120v winding provides a signal with a > zero-cross slew rate of ~65mV/uS. A 12v winding would slew only > ~6.5mV/uS. The faster the slew rate, the more accurately one can > locate the zero crossings. > I try to minimize dangerous voltages. Anyway, the filtering reduces the slew, so you can't have it both ways. > >If you are going to look at glitches, that should be done by sampling > >the AC (transformer coupled obviously). Basically the circuit to > >detect period is dedicated to that function. Since the frequency > >won't vary significantly, a high order filter wouldn't be an issue, > >as long as you don't care about delay. > > You are suggesting two separate data collections, one geared toward > grid frequency and one geared toward glitch detection. That's fine, > and might be preferable if it provided better results than using just > one data collection. But using a higher-order hardware filter does > not provide better frequency determination than post-processing the > ZCD data. > If by post processing you are averaging, then you certainly have lost frequency variation data. Averaging is a filter. > The circuit presented allows one data collection to do both functions > well. It has enough filtering to prevent local interference from > corrupting the data, it can locate 60Hz zero crossings to within 1uS > (i.e., frequency resolution significantly better than 0.01 Hz, > single-shot, which can be filtered/averaged to get whatever > resolution you want in post-processing), and it can locate transient > events to within 1uS. Win-win. If the event is due to noise, you resolved essentially garbage to a microsecond. If you average, you have done filtering. I don't see this as a win-win. > > Best regards, > > Charles > > > > _______________________________________________ > 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.
