[time-nuts] Building a mains frequency monitor

[Hal Murray]

bill.iaxs at pobox.com said:
> You are looking for parts per thousand at most. Precision GPSDO 10 MHz is
> overkill.

That depends on the time scale you are interested in.

If you want to plot the line frequency on the scale of seconds or minutes, 
then a junk crystal is probably good enough.

If you are want to measure the drift over hours or days, then you want a 
reference with long term stability.  You can do that with either a PPS or a 
10 MHz reference.

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elfchief-timenuts at lupine.org said:
>   - The dropping resistor will slowly change the amplitude of the waveform
> (and thus the point in the cycle that the schmitt trigger fires) due to
> thermal and aging effects, if we're measuring anything that's not the exact
> zero crossing 

There is all sorts of crap on the line.

I think temperature and aging of a resistor will be lost in the noise of 
normal shifts in the line voltage.  When I run out of other things to do, I 
want to capture what happens when the washing machine or refrigerator turns 
on and compare that with random dips that the power company delivers.

The APC UPS units have a serial or USB port to tell your system when to shut 
down.  At least the one I have will also tell you the line voltage and the 
min and max since the last time you asked.

On a good day, my 120V line voltage wanders over about 5 volts.  On other 
days, there are 10-15 volt dips.




-- 
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