Re: How does a Hands Free Temperature Measurement Device Work?

From: Jonathan Kirwan (jkirwan_at_easystreet.com)
Date: 03/11/05 

Date: Fri, 11 Mar 2005 23:39:00 GMT

On 11 Mar 2005 09:54:34 -0800, boats_ranger@yahoo.com wrote:

>I was at the price club a few days ago and there was a device that
>allow a hands free temperature measurement. I believe it can measure down
>to 150f (don't quote me).
>
>In general how is the temperature measured?

At 'low' temperatures of 150F and if there is no convective contact
and it appears to be an optical measurement, then it's likely this is
a longwave IR measurement. A great many things can complicate useful
measurements, though.

>Does ambient light contain temperature info

Yes, in the relative energy distribution over wavelength.

>does it need to be compensated for?

If it were measuring the apparent amplitude of a single wavelength,
yes. Dual wavelength techniques (or still more than two) can measure
the temperature by looking at the "slope" of the energy distribution
instead of the simple amplitude and this type of measurement can work
through uniform attenuation (so-called gray fog or interference that
doesn't act selectively) and still read out reasonably well.

>How does it ignore the temperature of the objects surrounding it?

Blocking can be done optically, but I think these things will often
read out what amounts to about the hottest target within optical view.

>If the temperature is XXX degrees f, what is the corresponding wavelength
>of light?

There isn't a single wavelength of light associated with one
temperature. There is a distribution that often is taken to follow a
"blackbody" distribution. You need to look up Planck's blackbody
equation, Wein's and Rayleigh's equations (which preceded Planck's),
and take a look at some of the displays of the curves at various
temperatures.

Jon

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