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RTDs as heating elements?

Discussion in 'Electronic Design' started by Steve Lieberman, Jul 30, 2003.

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  1. Someone on my project suggested using an RTD as a heating element;
    they claimed one could supply the RTD with a constant current (and
    allow unlimited voltage) and that should allow for a somewhat constant
    temperature.

    Does this make sense? Is it reliable?

    Thanks,
    Steve
     
  2. Not really, as the RTD only varies about 0.4%/K around room
    temperature, but you could certainly control it so that it runs at a
    constant temperature. Or a constant current. But not both.
    You could always ask the RTD manufacturer. ;-)

    A resistor makes a much cheaper heating element.

    Best regards,
    Spehro Pefhany
     
  3. John Larkin

    John Larkin Guest

    It is feasible to use the RTD for both functions, heating and sensing,
    simultaneously, *if* that makes sense thermally. It pretty much does
    only for large-area etched-serpentine type heaters that are glued onto
    the gadget to be heated. Minco does this.... I think they have some
    appnotes on the technique.

    Seems like a cute trick/lot of trouble to me. I agree that heaters and
    sensors should generally be different things.

    A ceramic PTC element, run at constant voltage, gives fairly good
    temperature regulation... reduces delta ambient effects by 10:1 or so
    maybe.

    Could you drive a PTC from a negative resistance source and improve
    temperature regulation?

    John
     
  4. Yes they generally should be. I've done it for good reason, kind of
    the thermal analog of the typical high-speed photodiode amplifier.
    Sure, but I think that amounts to the same thing as above.

    Best regards,
    Spehro Pefhany
     
  5. John Larkin

    John Larkin Guest

    Oh, yeah. Right. Duh.

    John
     
  6. A simple bridge circuit can be used to force the RTD to a
    constant resistance. This automatically forces it to a
    a constant temperature.
     

  7. As non-native english speaker : what is an RTD ?

    Rene
     
  8. John Larkin

    John Larkin Guest

    Resistor, Temperature Dependent. Most commonly, these are 100 ohm
    platinum-wire elements used as very precise temperature sensors, used
    commonly in industry and science. Also available in platinum
    thin-film, and occasionally with other metals, like copper. Google
    "platinum RTD" for more.

    John
     
  9. Resistance Temperature Detector. A precision wire-wound or thin-film
    metal resistor that has a predictable temperature-resistance
    relationship. Often made from platinum, but also nickel, various
    base-metal alloys, copper. Not the same thing as a thermistor, the
    change per degree is much less, typically around +0.39%/K at room
    temperature (roughly PTAT).

    Perhaps "Platin Widerstandsthermometer" would be a familiar term for
    you?

    Best regards,
    Spehro Pefhany
     
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