Re: [Phys-l] IR thermometer buy

[Bernard Cleyet <bernardcleyet@redshift.com>]

A few problems w/ this description from Vernier.

How the Infrared Thermometer Works and Measurement Tips
All objects emit infrared radiation, and the amount emitted is 
proportional to the
object’s temperature and its ability to emit infrared radiation. This 
ability called
emissivity is based on the material of the object and its surface 
finish. Emissivity
values range from 0.10 to 1.00 for a perfect black body. (See the chart 
below.) This
sensor makes its measurement based on a fixed emissivity of 0.95 which 
covers most
everyday objects. This sensor and all other infrared thermometers do not 
accurately
measure the temperature of shiny substances, e.g., polished metals, etc. 
To measure
the temperature of shiny objects, paint them with a flat paint or cover 
them with tape.
Also, if the object is covered by frost or another material, clean it to 
expose the
surface. If the sensor appears to measure incorrectly, check the front 
cone of the
sensor. It may be covered with condensation or debris. If necessary, 
wipe it with a
clean cloth.
To measure temperature, this sensor gathers infrared radiation in the 6 
to 14 mm
wavelength range. A Fresnel lens on the front of the sensor focuses the 
radiation
onto the sensing element. The observed spectral distribution is used to 
determine the
object’s temperature assuming standard blackbody radiation with an 
emissivity of
0.95.
Another consideration in this measurement is the field of view. The 
field of view is
the angle of vision at which the measurement is made. One of the 
valuable features
of this sensor is the laser sighting pattern which helps you identify 
the field of view.
The field of view and the spot almost coincide. The object that you are 
measuring
should fill the field of view, or better yet be 1.5 to 2 times size of 
the circular spot.
The laser sighting circle is great help in identifying the measurement 
region;
however be aware that if you are measuring small objects, e.g., 
approaching the size
of the sensor window, you will need to hold them close to the sensor. In 
that
arrangement parallax may prevent the laser circle from matching the 
measurement
reading.

bc, who hopes John G. of Vernier will read and respond.

Larry Woolf wrote:

> Such is the two color pyrometer
>
> <http://www.pyrometry.com/howitworks.php>
>
> Larry Woolf
> General Atomics
> www.ga.com
> www.sci-ed-ga.org
>
> -----Original Message-----
> From: Ludwik Kowalski
> Sent: Wednesday, January 24, 2007 2:52 PM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] IR thermometer buy
>
> The only things that do not change with r are the location of the
> maximum and ratios of partial intensities at two different wavelengths. 
> My guess is that T is determined from a ratio of two partial
> intensities. Some kind of a filter, and two detectors, would make this
> possible, at least in principle.
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