[time-nuts] Mains frequency

[Tom Van Baak]

> When you measure the mains signal, nominally 60 Hz in this case, spikes
> etc. is noise which is local and not of interest when comparing over a
> large area. Inter-area oscillations have much slower properties.
> If you go the time-stamping way, you *should* remove such noise.
> 
> Removing or padding over it by logic will mean dropping data, which is
> not helpful.

A time-stamping counter never drops *data*; instead you apply logic to drop *noise* when necessary.

> Turns out that professional gear for this does not do time-stamping in
> this regard. Rather, they I-Q demodulate the signal with a reference
> signal at the nominal rate, low-pass filter it and pay attention to
> details of filtering like group-delay and compensation thereof. It's a
> rather wise approach for the type of conditions you have.

I'd be happy to compare "professional gear" with a time-stamping counter. I have two or three years of data to show 60 Hz time-stamping works perfectly. Not to say your professional gear might also. But a zero-crossing counter never misses a cycle; you can set the s/w bandwidth just as you can set an IQ hardware bandwidth.  Both assume some reasonable limit of mains df/f/dt. You can either do it with a fancy $100 to $1000 reference signal generator + PLL or FLL + IQ detector + professional box -- or with a $1 PIC and $0 s/w.

/tvb