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Inexpensive handheld thermistor probes?

Discussion in 'Electronic Components' started by Terran Melconian, Jan 16, 2007.

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  1. I have a handheld thermistor probe. It's a pretty standard 10k NTC
    thermistor in a stainless body with a plastic handle and some cable
    leading to banana plugs. It came for free with a Radio Shack DMM years
    ago and is perfectly functional.

    I'd like to get some more similar to it. I thought they would be
    trivial to find and cost $10. This has not proved to be the case. In
    fact, I have had great difficulty finding any whatsoever.

    I have found a lot of industrial ones designed to be permanently mounted
    and costing upwards of $50, neither of which are properties I want.
    There are also a great lot of thermocouples, and thermocouples are very
    nice, but I don't want them for this - I don't need the range and too
    many components are required to amplify the signal. It's also easy to
    get thermistors, but I have no desire to put my own bodies and handles
    on them, either.

    Does anybody know where I can get maybe a dozen of the right thing for
    under $20 each? If it costs much more than that, I can buy prebuilt
    handheld thermometer units and throw out the display.

    I am located in the United States.
     
  2. Things.consistent.org:
    As far as I know, the cheap probe thermometers you mention are also
    thermocouples, not thermistors. Mine are, anyway.
     
  3. Joerg

    Joerg Guest


    The ones I took apart over the years had mundane diodes.
     
  4. Interesting. I would have thought that per-unit calibration would be
    too costly for a $20-$30 consumer device, but so would opamps with a low
    enough input offset voltage to avoid the need for it. Do you recall how
    they measured the thermocouple voltage? Perhaps they have some smart
    technique I can steal... er, borrow. :)
     
  5. Things.consistent.org:
    I think it's likely I was wrong and Joerg is right. Without destroying one,
    I can't get at its innards enough even to test it. I was seeing just the
    wires to the probe, one is enamelled copper, the other is in what seems to
    be a teflon sheath, giving the impression of dissimilar metals. The range
    is -50C to +300C, which is definitely NOT a diode, maybe, or even a
    thermistor, unless it be PT100 type.

    I'd still lay odds on it being a thermocouple, even though I can't prove
    it. If you want to buy one to mutilate, go for it. :) They're on eBay,
    they're very good for the money, even without yielding their dark secrets.

    http://tinyurl.com/2mp95h (eBay listing. I was the buyer on that one.)

    There are others similar, many sellers, but I chose these after careful
    comparison, and I think I got the best deal by far.

    (Off-topic, but I'll take this shameless chance to suggest that if anyone's
    looking for an ITX computer, or an FS1R synthesizer (Yamaha), I'm selling
    them to raise money for a laser project. ITX machine will go up tomorrow
    night, is 1.2 GHz, tiny machine, built to keep, but I really need money
    fast to get some optics that won't wait around. I'll say no more here, it's
    not the place, but if anyone wants, they can post a question via a
    listing..)
     
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