Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!think.com!mintaka!ogicse!milton!whit
From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Thermal imaging advice wanted
Message-ID: <1991May13.201218.15900@milton.u.washington.edu>
Date: 13 May 91 20:12:18 GMT
Article-I.D.: milton.1991May13.201218.15900
References: <1991May13.130630.51341@gmuvax.gmu.edu>
Organization: University of Washington, Seattle
Lines: 33

In article <1991May13.130630.51341@gmuvax.gmu.edu> juraschek@gmuvax.gmu.edu writes:
>Wanna build a device to allow me to scan an object to detect heat levels
>at different points.  For example, I aim it at a stationary, running car
>and get a scanned image of the car in terms of the heat eminating from it.

>(I want to do thermal imaging, in other words.)

	If you can get a mirror, there's a VERY old device that will
work for this.  It's called a galvanometer.  
	You get a thin quartz fiber for a torsion spring (pull your
own!  It's fun!), a single-turn loop with dissimilar metals (the
winding of the galvanometer is actually a thermocouple), and position
the bottom couple of the loop in the focus of the mirror.  Apply a
magnetic field to the loop, and you're set.
	To get fancy, operate a second current loop, from a D/A on
the PC, to null the galvanometer (i.e. balance the heat-generated
current with a known current).  It would also work to position a
light bulb to shine on the second couple, and  brighten/dim this
lamp from the PC.
        Imaging, however, will require motors and mirrors.
	In any case, a small mirror cemented to the
loop can bounce a light beam to make a massless 'pointer'.
A couple of photocells straddling the beam can generate a
difference signal whenever the pointer budges from center,
and the PC can detect this and close the feedback loop through the D/A.
There's an example in the British Museum science/technology section, that
purportedly could detect the heat of a candle at circa one mile.
The date on the exhibit was over a century ago, and it did
NOT employ a PC, as I recall.



	John Whitmore