moderately resistive materials?

If you sandwich a resistive material between two conductors, the current will flow mainly through the conductors, even at low voltage. Never mind the 'skin effect' of high voltages.

I would want to *insulate* the resistor to force all the current to go through the resistive material.

Start here:

R(T) =3D R0 * [1 + AT + BT^2]

with A =3D 3.9083 =D7 10-3

This gives a strong positive slope over the linear range. Standard Pt-100 sensors have 100 ohms resistance at 0=B0 C.

Platinum also meets your other criteria pretty well. as long as you aren't working in fluorine or aqua regia.

Tom Davidson Richmond, VA

call up people who make thermisters, Thermotron (sp?) is one. resistive heating is typically a type of steel wire,or ............. there is another type that is used too, forgot what name is. #3 needs a spec. Mechanically Stable ? thermal expansion? how much? #1 spec, 10 ohms per square ? that is a high value, for metals, you have a flat thin wafer

There does not appear to be sufficient info here, or I am missing something. Most metals exhibit a positive tempco, and they are approx linear (some more then others)

If the passage of current can be changed to lengthwise I think a metal film/foil may perform nicely. You may want to look at Minco. They make some very nice metal film/foil heaters.

M Walter PE

OK. That configuration sounds more like what they called a 'leaky capacitor' back on the soldering bench.

You need a poor dielectric. Paper runs about 5*10^4 ohm-cm resistivity according to my old copy of Eshbach's Handbook of Engineering Fundamentals. This can be 'adjusted' by impregnating the paper with different liquids. You willl probably need to do a little testing and literature searching.

Tom Davidson Richmond, VA

Good analogy. Of course, in this case, the leakiness would be both deliberate and carefully calibrated.

I worry that liquid-impregnated paper wouldn't hold up well to continual heating. So I would probably prefer something graphite-like, or maybe some composite material, if it exists with the right electrical and thermal properties.

Any suggestions concerning reference literature to look at? I'm delving into areas somewhat outside my normal practical expertise, though I understand the theory pretty well.

Thanks.

________________________________________ Prof. Grant W. Petty Atmospheric and Oceanic Sciences

snipped-for-privacy@aos.wisc.edu Tel: (608) 263-3265 Fax: (608) 262-0166

I don't know how to give a spec for this. Basically I'm ruling out anything that I'd have a hard time handling without breaking or degrading it. For that matter, I suppose a paste-like goo squeezed between the two conductors could work, if it won't change properties over time.

TBD. I'd say as long as it's not unusually high it's probably okay.

Yes. I'm thinking something comparable to graphite. In fact, maybe some kind of conductive graphite composite wafer, if such a thing exists.

________________________________________ Prof. Grant W. Petty Atmospheric and Oceanic Sciences

snipped-for-privacy@aos.wisc.edu Tel: (608) 263-3265 Fax: (608) 262-0166

Dont suppose a peltier array would be any help ??

description

You might pose your question on sci.materials. Mike

I don't know what that is ... is it related to the Peltier effect?

________________________________________ Prof. Grant W. Petty Atmospheric and Oceanic Sciences

snipped-for-privacy@aos.wisc.edu Tel: (608) 263-3265 Fax: (608) 262-0166

meteorological

Nichrome?

On 15 May 2006 15:31:01 -0700, "tadchem" Gave us:

Skin effect is a function of frequency, not voltage. It is just easier to prove in higher voltage settings.

Perhaps you can get some of the the material used in self-resetting fuses: a conductive polymeric concoction with a non-linear PTC.

-- Joe Legris