# IR Temperature Measurement help

C

#### chapmjw

Jan 1, 1970
0
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
thanks
jim

T

#### Tim Wescott

Jan 1, 1970
0
chapmjw said:
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
thanks
jim
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 L #### LVMarc Jan 1, 1970 0 Tim said: 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

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.
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

R

#### Rene Tschaggelar

Jan 1, 1970
0
LVMarc said:
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.

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

M

#### MassiveProng

Jan 1, 1970
0
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).

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.

M

#### MassiveProng

Jan 1, 1970
0
I suspect that the stand-alone sensors you can get are way more accurate
than the Tower Hobbies one.

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.

V

#### vasile

Jan 1, 1970
0
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

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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