Given that it sounds that these capacitors are mains connected I would recommend using Y rated capacitors for safety reasons. That should prevent them from going short circuit, Y caps being designed to "fail open".
Or did I misunderstand the proposed circuit? Wilko > On 22 Jan 2022, at 03:06, Lux, Jim <j...@luxfamily.com> wrote: > > On 1/21/22 4:43 PM, willl will wrote: >> Hi everyone, >> >> I have an recently finished project that also measuring AC waveform, full >> description here: >> https://github.com/will127534/RaspberryPiAtomicNixieClock/wiki >> >> Basically using an AC transformer and Ti's ADC8681 @ 50Khz sampling rate. >> >> This year I'm working on a earthquake sensor + AC mains monitor system (In >> an earthquake prone area, AC mains frequency will fluctuate by power >> generator and machine emergency stop like this one: >> https://twitter.com/kuriuzu/status/1360602496821911553). >> >> I want to improve AC measurement. Apart from the ADC sampling speed upgrade >> (previously bottlenecked by the SPI connection to FPGA). I'm currently >> debating about whether or not to bypass the transformer. How does the >> distortion of an AC transformer impact the accuracy of mains waveform and >> frequency? I'm not sure if it is worth it to go through the mains voltage >> safety requirements. > > You can use a capacitorsget your galvanic isolation, and a CR voltage divider > with minimal waveform distortion. Pick a burden current (say, 1 mA) and for > 120V line, you need 120k impedance at line frequency 60Hz > > X = 1/(377*C) --> C = 1/(377 * 120E3) = 22 nF > > Say you want ~100:1 ratio? so 22 nF in series with 1.2k (or 2.2uF) would do > nicely. Then feed your high Z ADC with a couple 0.1 uF capacitors from the > ends of the 1.2k. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
