From: kolstad@cae.wisc.edu (Joel Kolstad)
Subject: Re: Tell me about electric blankets
Organization: U of Wisconsin-Madison College of Engineering
Distribution: na
Date: 26 Dec 92 06:06:58 CST

In article <1992Dec26.092022.3114@hpcvaac.cv.hp.com> billn@hpcvaac.cv.hp.com (bill nelson) writes:
>kolstad@cae.wisc.edu (Joel Kolstad) writes:
>: In article <1992Dec14.092120.20097@hpcvaac.cv.hp.com> billn@hpcvaac.cv.hp.com (bill nelson) writes:
>: >: 
>: Um, Bill, for someone who works for a very reputable company on the net
>: here, I'm surprised you'd use such language.
>
>I am me, not the company. So far, they have not chosen to censor me.
>I do not expect them to do so for my using a non-pc term.

You certainly have a right to say whatever you want, and I would never
suggest that you should be censored.  On the other hand, choosing to
sprinkle your language with vulgarities often suggests that you're rather
crude and uneducated, which looks bad when you're working for an employeer
that doesn't employ crude and uneducated people.

>An electromagnetic field has electric and magnetic components. As such,
>in this case, they cannot be separated.

Yes, this is the general definition, which (as I pointed out in my last
post) isn't a term applicable to DC circuits.  A direct (i.e.,
non-pulsating) current will produce a magnetic field, and not an electric
field.  A stationary charge will produce an electric field, and not a
magnetic field.

>If the blanket had a simple diode circuit (to produce the dc) - then the
>waveform would not be anywhere close to a square wave. It would be a 
>rectified sine wave - with a frequency of either 60 Hz or 120 Hz, depending
>on whether a half-wave or full wave rectifier was used. You still will have
>an electromagnetic field that builds and collapses - just like with an
>unrectified supply. To a test meter, you would not be able to tell the
>difference - nor would your body.

This is true.  Most people call what you describe above "pulsating DC".
When _I_ say DC, I _mean_ DC!

>The only way to avoid this would be to build a DC power supply that has
>some capacitors and a voltage regulator to smooth out the DC so there
>is no ripple.

That's what _I've_ been talking about all along.  Constructing DC power
supplies isn't rocket science; we've been doing it for years.  Building DC
electric blankets would not be difficult.

>Either I misunderstand what you are saying, or you are confused. Any time
>a current moves in a wire, you have an electromagnetic field. It does not
>matter if the current is AC or DC. 

>: If you like, I can drudge out Maxwell's equations and show this all
>: mathematically, but I don't think there's much point.
>
>What would you try to prove, that a DC current does not generate an
>EM field? I don't think you can do so.

Moving charges through a given surface at a constant rate (i.e., a constant
current vector J), such as through a wire at a given, non-changing current,
products only a magnetic field, and not an electric field.  Period, amen.
(At least in a Maxwellian Universe, which is very close to what we're
talking about here.)

Trust me.  Hook up one of your HP constant current power supplies to a coil
of wire or a resistor.  Set it to pump out 1A DC, constant current.  I
guarantee you that any E field you measure by the coil is not being
produced by that coil.  (Try inducing a voltage in another nearby coil for
starts.  It isn't going to happen, because you need an EM field to induce
voltages, and you only have a M field.)

>: P.S. -- Which division of HP do you work for?  Certainly not one where
>: they do anything with fields and waves?
>
>What does that have to do with my training? One of the people in my
>group got his degree in religious studies. He still is one of the
>brightest engineers in the division.

I would hope that he has an engineering degree (or a science degree)
_as well_.  I think it's rather obvious what training in a given field has 
to do with one's knowledge on the subject: It tends to lend credibility to 
your arguments.

					---Joel Kolstad
Newsgroups: misc.consumers