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Re: Re[2]: Radiant energy cooktops

This type of cooking element was first introduced by Westinghouse in the
70's. A pancake coil made of Litz wire is driven by a high frequency power
supply. The magnetic field couples to a suitable pan made of steel with a
copper clading to distribute heat more uniformily. The eddy currents in the
steel pan cause losses which heat the pan and cook the food. The only heat
on the ceramic top is the result of heat transfer from the pan backwards
into the caramic and the coil which is located just below the surface. It
is an expensive though entirely useful way to cook food. The trouble was
that the cost was 2-3 times a normal electric heating element type stove.
It caught on in England for awhile, because Princess Margaret bought one. A
buying surge resulted in trying to "keep up with the ..." One problem was
the field that existed without a pan. This high frequency field was not too
compatible with cooks that had pacemakers, so we added a "pan detector"
circuit that throttled back on the coil power supply if a pan was not
covering (an capturing) the high frequency magnetic field. It was an
interesting program. The Litz wire was necessary to reduce losses in the
coil itself.

H. B. Jim James, ex-Westinghouse R&D Engineer

At 02:22 PM 4/1/96 EST, you wrote:
I have a question concerning this also. I was watching one of
those cooking shows and they were showing the new Culinary Institute
of America school in CA. The chef doing the show mentioned the
"cutting edge" stoves and how nice they were. There was a pot of
something boiling on the stove and he put his hand right down on the
surface only an inch or less away and said it was not hot (the fact
that he kept his hand there for several seconds was a testament to
that). It looked like one of those radiant cooktops and he mentioned
something about magnetic induction. Could someone give us more info
on this? It sounds interesting and might make for a good topic to
introduce certain E&M ideas. Thanks.
Homer B. (Jim) James Home: 1636 Jamestown Place
Adjunct Professor of Physics Pittsburgh, PA 15235-4922
Community College of Allegheny County (412) 731-3239 (voice)
Allegheny Campus