It is a mechanical device, generally called an "infinite switch" in
the trade. A set of heavy contacts open and close on temperature;
there is a bimetallic strip that operates the contacts in response to
heat. The heat is supplied by a resistance element wound around the
bimetal strip that is in series with the element so that the heat
supplied to the bimetal is proportionate to the heat of the surface
element. Turning the knob from "warm" through the numbers to "hi"
turns a cam that supplies increasing bias tension to close the
contacts, such that it takes ever more heat to open them until, at
the "hi" setting, they never open.
I've never known one to cause RFI either; sounds like maybe a bad
connection is arcing, perhaps inside the switch. They carry some
fairly high currents; depending on the size of the surface element, 8
to 12 amps is normal. And you're right---the most common problem is
the female connectors in the receptacles burning up. When an infinite
switch fails, it usually fails to open, thus you get full heat at all
settings.
Travis
On Apr 8, 2007, at 5:50 PM, Ken Brown wrote:
> This is completely off topic, except that it is in a general sense
> about
> the production or RFI or the lack thereof. If you are one of those
> people whose blood pressure rises when you see a question that is not
> specifically about a Ten-Tec product on this reflector, please delete
> this message immediately to avoid any hazard to your health.
>
> I have an electric stove in my home, and have had them in many homes I
> have lived in. I have never heard any RF noise that I could
> attribute to
> the heat controls on an electric stove. I have also never
> experienced a
> failure in an electric stove other than at the connections to the
> heating elements. If they used electromechanical relays I would expect
> to have seen a failure at that point by now. If they use SCRs or other
> solid state controls I would have expected to hear some RFI from
> one by
> now. How do they do it?
>
> DE N6KB
>
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