This looks like an oportunity for the Heisenberg Uncertainty Principle to
get involved. When you run the software on the VAX to measure the power
consumed by the VAX it will affect the power consumed by the VAX.


At 02:25 PM 10/25/02 -0400, Nigel Johnson wrote:
>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
>
>

Michael Thompson
E-Mail: M_Thompson@IDS.net