IR Temperature Measurement help

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

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

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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

--=20 Ing.Buero R.Tschaggelar -

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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... ?