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IR Temperature Measurement help

Discussion in 'Electronic Design' started by chapmjw, Apr 10, 2007.

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  1. chapmjw

    chapmjw Guest

    Hi,
    Can someone tell me what component I need or a project example for the
    following. I would like to measure the temperation of an RC engine
    using some sort of non contact method, like the IR temp devices.
    Output from this IR sensor will recieved by a PIC device. I'm sure
    there is a cheap method to do this but I haven't found a stand alone
    sensor that is less than $100. Yet you can buy a complete unit from
    TowerHobbies with lcd for less than $20.

    If the answer is a IR Phototransistor, could you please give me a
    little more info.
    thanks
    jim
     
  2. Tim Wescott

    Tim Wescott Guest

    The answer is _not_ an IR photo transistor, at least not one that isn't
    dipped in liquid nitrogen. Silicon IR photo transistors respond to IR
    around 1 micron wavelength through the visible spectrum (violet is 400
    nm or so). While a smart ass like me might suggest an indium-antimonide
    photo transistor to work in the 3-5 micron band, it would have to be
    cooled to liquid nitrogen temperatures which would raise the price of
    your device a little bit above $20.

    Most single-point radiometers use a thermopile, which is a collection of
    thermocouples which are heated by radiant energy from the target (your
    engine); you read the ambient temperature at the back of the thermopile,
    you read the voltage from the thermopile, you do some math, and you get
    a temperature reading.

    I suspect that the stand-alone sensors you can get are way more accurate
    than the Tower Hobbies one. That plus lower sales volume would be what
    makes them more expensive. If you could find a thermopile sensor in
    surplus you may be able to make something after a lot of learning.

    Frankly, if it's computer input you're after it may be cheapest to buy
    the Tower Hobbies one, reverse engineer it, then stick a PIC into the
    critical part of the thing. If your time is worth anything to you,
    getting one that already makes serial may be worth a couple C notes --
    but it won't be nearly as much fun.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  3. LVMarc

    LVMarc Guest

    you could use a PIR , a pyroeletric detector. then you physical modulate
    the incoming light path, with a shutter or mirror. this spatial
    modulation moves the signal onto a signal carrier. ie without the
    modualtion the energy wouldbe at dc and the pir does not respond to dc
    so you add spatial mos\dualtion. Then you measure the amplitude of
    thechopped signal. The amplitude will be proptoionate to the recieved ir
    (6-10 uM range) and this is proportionate to the balck body radiation,
    steffan -boltzman.

    Marc
     
  4. The bandwidth of neither the thermopile nor the PIR
    is large enough to allow for modulation. Take a
    chopper stabilized opamp to get a decent DC gain.

    Rene
     
  5. MassiveProng

    MassiveProng Guest


    The item needed is referred to as a "resistor bolometer", and can be
    bought with a germanium window, or pyrex window, or whatever is needed
    to narrow the band to fit the application desired.

    They are transistor sized packages and have 2mm diameter windows.
    All that is then needed is an optical focusing apparatus like a convex
    first surface mirror and a black tube. Lenses work, but they kill
    some of the energy as well. They are room temp devices. One would
    also need a proper circuit to deal with the output correctly.

    Much better off simply buying an off the shelf product.

    Even better would be to get non-contact out of your head (not you),
    and epoxy (thermal epoxy) a thermocouple onto the test article.
     
  6. MassiveProng

    MassiveProng Guest


    Actually, the original Fisher Price video camera (b&w) could be used
    with a window, and proper cooling! Imagine that! That was $150 back
    when our imager (LN cooled) was $90k! (1987)

    Now, even advanced imagers are a mere few grand up to 5x that for top
    of the line gear.
     
  7. vasile

    vasile Guest

    The thermopile does not require modulation for normal operation, but
    the PIR is OK with
    mechanical modulator (or optoacustic modulator, if you have one
    alowing IR passing through...)
    The silly question is why you need IR measurement as long you can
    measure directly
    on the motor body... ?
     
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