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Re: Wattmeter
Tesla List wrote:
>
> Original Poster: "jim jpl" <jimlux-at-jpl.nasa.gov>
>
> -----Original Message-----
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
> Date: Monday, January 25, 1999 10:51 AM
> Subject: Re: Wattmeter
>
> >Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
> >
> >Tesla List wrote:
> >
> >An electromechanical watt-hour meter probably measures correctly the
> >power for arbitrary waveforms. The mechanical inertia is just the filter
> >that averages the current x voltage product, and is not a problem for
> >long averages. And as the voltage is essentially a 60 Hz sinusoid for
> >any reasonable current, active power flows only at 60 Hz, so other
> >frequency limitations, as inductances of coils in the meter, are of
> >little importance.
> >
>
> I've played around with a watt hour meter I picked up at the local utility
> scrap yard. It has 5A full scale current (obviously designed to work with a
> current transformer) and has 240 V potential winding. I was originally using
> it to measure power factor on lightly loaded ac motors (which it did
> admirably). However, when looking at highly irregular current waveforms
> (like that into a lightly loaded capacitor input filter) where the current
> is very peaky, I noticed that there were some errors, typically, reading on
> the low side. I suspect it was the higher harmonic power in the current
> winding getting sucked up into eddy currents, or the like.
>
> In any case, it is easy to use. What you do need to do though, is to put a
> known load on it and time how long it takes for the disc to turn. It takes a
> long time to measure power if you actually use the dial, since it has 1 kWh
> resolution (that means running that 1 kW coil for an hour straight....)
But there is a Kh factor or some such on most labels, which is related
to one turn of the disk is one kwh or one turn of the least significant
digit. I never remember, and have to keep testing with lightbulb, and
count turns; to calilbrate mine.
--
Will; Amateur Radio call K 2 L B ; Rochester, New York, USA
e-mail <herzog-at-frontiernet-dot-net>