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moderately resistive materials?

Discussion in 'Electrical Engineering' started by Grant W. Petty, May 15, 2006.

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  1. In connection with a prototype design I'm developing for a meteorological
    measurement device, I'm looking for a readily available material with the
    following physical properties:

    1) Moderately resistive -- it will be used for resistive heating by passing
    a current through a thin sheet sandwiched between two metal conductors.
    Target resistivity should fall in the range 10 to 10**4 m*ohm at
    temperatures between 0 and 100 C.

    2) A marked increase in resistivity with increasing temperature (this
    apparently rules out silicon, for example).

    3) Mechanically stable and easy to work with in sheets or disks of order
    0.1 mm thickness, 30 cm diameter.

    4) Not subject to significant degradation or aging, even at sustained
    temperatures near 100 C.

    If anyone either knows offhand of a material matching the above description
    or can point me to a good tabulation of candidate materials, please let me
    know.

    thanks

    ________________________________________
    Prof. Grant W. Petty
    Atmospheric and Oceanic Sciences
    1225 W. Dayton Street
    University of Wisconsin-Madison
    Madison, WI 53706


    Tel: (608) 263-3265
    Fax: (608) 262-0166
     
  2. Johnny

    Johnny Guest

    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
     
  3. To clarify, one conductor is at one potential, the other is at a different
    potential. So the current flow is through (perpendicular to) the resistive
    sheet.
    ________________________________________
    Prof. Grant W. Petty
    Atmospheric and Oceanic Sciences
    1225 W. Dayton Street
    University of Wisconsin-Madison
    Madison, WI 53706


    Tel: (608) 263-3265
    Fax: (608) 262-0166
     
  4. 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
    1225 W. Dayton Street
    University of Wisconsin-Madison
    Madison, WI 53706


    Tel: (608) 263-3265
    Fax: (608) 262-0166
     
  5. 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
    1225 W. Dayton Street
    University of Wisconsin-Madison
    Madison, WI 53706


    Tel: (608) 263-3265
    Fax: (608) 262-0166
     
  6. Dont suppose a peltier array would be any help ??
     
  7. amdx

    amdx Guest

    You might pose your question on sci.materials.
    Mike
     
  8. I don't know what that is ... is it related to the Peltier effect?


    ________________________________________
    Prof. Grant W. Petty
    Atmospheric and Oceanic Sciences
    1225 W. Dayton Street
    University of Wisconsin-Madison
    Madison, WI 53706


    Tel: (608) 263-3265
    Fax: (608) 262-0166
     
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