[time-nuts] Re: Another reason to monitor line frequency :) - My AC measurement project & question

[Jan-Derk Bakker]

Hi Will,

Given that you already have an FPGA in the system I'll assume that you are
comfortable with digital solutions. Have a look at
https://www.analog.com/en/products/ad7402.html ; it's a 1-bit sigma-delta
modulator with a built-in galvanic isolation for its output. TI and ST have
similar parts (for some you need to add your own isolator); we've used them
in power quality analysis experiments. By having the modulator on the
primary side you can use a simple resistor divider, saving you from
possible group delay issues.

Good luck and let us know how it goes,

JDB.
[Disclaimer: I don't have my notes here to double check whether we ended up
using the AD7402 or a similar part; do double check the isolation offered
to see whether this particular chip suffices for your mains voltage safety
requirements]

On Sat, Jan 22, 2022 at 1:55 AM willl will <will at willwhang.com> 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.
>
> Thanks,
> Will
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