[time-nuts] Mains frequency

[Poul-Henning Kamp]

In message <77A742979E2849FD9CA585192F2F5AFC at pc52>, "Tom Van Baak" writes:

>For tau 0.01 to 0.3 s it would take more work to quantify which pieces are
>contributing to the instability pie.

It doesn't really make sense to talk about taus less than approx
0.1s for Mains.

It is not atypical to see 10% "harmonic distortion" on mains in a
household, most of it from switchmodes, but also single-phase
motors etc.  Music amplifiers, in particular played at "teenagerockgod"
volumes add a very interesting challenge too.

In theory harmonic distortion does not change your zero-crossings,
but it is not really "harmonic" in the Fourier sense, it's just
mostly centered around the overtones.

Either you include the "harmonic" distortion, and then your measurement
applies only to that specific outlet, when the dish-washer is running
exactly 20 minutes into programme 3 and no kids listen to loud
music.

Alternatively you can put mains through a 40-60 or 50-70 Hz
bandpassfilter to supress anything but the the fundamental, but
what exactly do you measure then ?

Once you get below about 1Hz, the most interesting thing you can
do with mains is to sample it at ~4kHz, make a water-fall plot and
try to identify your house-hold appliances by their distortion
patterns :-)

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