As a thank offering for all the good software advice I have received by 
lurking here over the years, I offer the following link for those interested:

http://www.analog.com/technology/dataConverters/energyMeasurement/reference.html

It is a complete reference design for a power meter such as one could hook 
up to a VAX.  There are appnotes on the site dealing with considerations on 
measuring using microprocessors. I suggest this not purely as a scientific 
benefit, but more so you can prove to your wives that these beasts really 
don't take that much current.


btw, I am happily chugging along on with NetBSD on my MicroVax IIs.  One of 
them has a Data Translation DT2765 millivolt isolated a/d that I am dying 
to use to measure dome kind of power line stuff, but anybody who suggests 
an experiment also has to come up with a driver!

cheers
Nigel Johnson
VAX Hardware Hacker.
VE3ID
At 09:50 02-10-25 -0700, Carl Lowenstein wrote:
> > Date: Fri, 25 Oct 2002 08:30:26 -0400
> > To: der Mouse <mouse@Rodents.Montreal.QC.CA>, port-vax@netbsd.org
> > From: Michael Thompson <m_thompson@ids.net>
> > Subject: Re: Just how many of the group are actively running NetBSD on
> >   their Vaxen?
> >
> > You could have simply said that the power factor of the load was low. The
> > power meter on your house measures loads as if the power factor is 1.0. The
> > power factor of an old power supply that has jumper selectable voltage
> > inputs is probably 0.65. Modern power supplies that have univeral
> > (85VAC-270VAC) inputs have power factor correction circuits to correct the
> > power factor to nearly 1.0.
>
>Come now.  The power meter on the house has been carefully designed to
>measure the time integral of power.  (energy in kilowatt-hours).
>
>To learn more about it than you probably wanted to know, visit the web site
>of the US Bureau of Reclamation.
>< http://www.usbr.gov/power/data/fist/fist3~10/3~10_3.htm >
>for a comprehensive article on "Watt-Hour Meter Operating Principles".
>
>Actually, reading at the above URL, I become uncertain about what
>rotating-disk watt-hour meter would do when the current drawn is not
>sinusoidal.
>
>With regard to modern switching-type power supplies, they draw current
>in short pulses at the peak of the input voltage, to charge a large
>capacitor which then supplies current to the switching circuitry.
>
>As a calculus exercise, one can compute the ratio of actual power consumed
>to the product of voltmeter and ammeter readings.  Under the reasonable
>assumption that both the voltmeter and ammeter read full-wave-average
>values but are calibrated to read correct RMS values of a sine wave,
>one finds that the product of the meter readings underestimates the
>power by a factor of pi/4.  A "power factor" greater than 1.
>
>Far away from the original subject.
>
>     carl
>--
>     carl lowenstein         marine physical lab     u.c. san diego
>                                                  clowenst@ucsd.edu