My past experiments in watching line frequency (actually,
watching 1/f or the period of a cycle with a Time-Interval
Counter) showed that line frequency varied only ever so
slightly - and fractionally (small fraction) at that.

Of course, that was monitoring our grid under normal
conditions here in 'Tejas' ...

I also once upon a time programmed up a BRG (Baud Rate
Generator) set for 60 Hz rate and applied this to a
dual-trace scope -

- allowing me to watch the 'phase' of the commercial
AC mains bounce around a little in relation to the
crystal-controlled BRG reference oscillator.

Jim

----- Original Message -----
From: "M. Adam Davis" <adampic@UBASICS.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, June 11, 2002 11:24 AM
Subject: Re: [EE] Phase control dimming on a cheap pic


> They also vary the line frequency so that  in any 24 hour period there
> are as close to 5184000 cycles as they can get (in the US on 60Hz AC
> lines).  This is for the many clocks that still base their time on the
> frequency of the line, and that loading during the day changes the
> frequency slightly.
>
> I suppose the matter is more complex than that, since they have to
> synchronize the AC on many grids, but it's easier to adjust the
> frequency when the load is lighter.
>
> -Adam
>

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