Re: [Phys-l] IR thermometer buy

[Bernard Cleyet <bernardcleyet@redshift.com>]

The m is a cut and paste error, but when I directly view the PDF w/ 
either the Mac. or Adobe version I still get 6 and 14.  This is a BTW.   
[Turns out a very much not so.]

I woke up from either a dream or hypnagogic state a few days ago w/ an 
answer.  One of which is in the Vernier instructions and directly 
addresses LK's point.  i.e. the subject  temperature area must fill 
(better 1.5 => twice) the view field as defined by the LASER's pattern.  
LK's point refers to point source or at least far field.  One must use 
near field wherein the energy received is independent of the distance.   
How it interprets the received energy is the other question.  My quick 
calc. * of  the emitted energy from a source at zero deg.  convinced me 
the 0.6. => 1.4 micron window could not be correct.  I suspect 
synchronous detection would be necessary!  Following JG's implied 
suggestion I found the majority of Omega's (and other's) detectors use 
an ~ 8 to 14 Micron band.  A vis./near IR one is used at high temps e.g. 
~ > 2k deg.   My other question related to how the thermometer would 
compensate for the deviation from T^4 that would come from detecting 
only a small portion of the total bandwidth.  I finally found the below 
which also answered by question on the detector.  [My old source 
suggests only doped Ge, TC, and thermisters would be suitable.]

http://archives.sensorsmag.com/articles/1099/80/main.shtml

*  Off scale on my GE slide rule.  Lazily I used:

http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/radfrac.html#c1

bc

John Gastineau wrote:

> That would be 0.6 to 1.4 micrometers, not millimeters. Near IR is in 
> the micrometer wavelength range. Our printed info shows the micro sign 
> correctly; I'm not sure where you grabbed that text, but it is a 
> common formatting error to replace a mu with an m when text is copied 
> and pasted.
>
> There are several ways to do IR thermometry, as you have probably read 
> on perusing the Omega web site: 
> http://www.omega.com/prodinfo/infraredthermometer.html
>
> The Vernier unit is made by Omega, and I confess to not knowing the 
> details of its operation. I think, but do not know, that it functions 
> with a single detector in a cavity that is brought into IR light 
> equilibrium with the target surface--then knowing the IR radiation and 
> the local temperature, the temp of the remote surface can be inferred. 
> I didn't supervise this project, and so don't have good contacts at 
> Omega to get more information. I'll see what I can do.
>
> The Fresnel lens is useful simply because you can get a short focal 
> length with very little lens material.
>
>
> --
> John Gastineau
> Staff Scientist and Partner
> Vernier Software & Technology
> jgastineau@vernier.com
>
>
>
> Bernard Cleyet wrote:
>
> > John!
> >
> > 1. A minor nit:  you mean nm not mm?  And 0.6 => 1.4 nm?
> > 2. A single detector?
> > 3. How does it measure the spectral distrib. w/ a single element and no dispersive element?
> >
> >
> > "To measure temperature, this sensor gathers infrared radiation in the 6 
> > to 14 mm [1] wavelength range. A Fresnel lens on the front of the sensor focuses the 
> > radiation onto the sensing element [2]. The observed spectral distribution is used to 
> > determine the object’s temperature assuming standard blackbody radiation with an 
> > emissivity of 0.95."
> >
> > bc, who wonders why a Fresnel instead of an ordinary and the material of the lens, etc.
> >  
> >
> >
> >
> >
> >
> >
> > John Gastineau wrote:
> >
> > > What specifically is your question regarding our description?
> > >
> > > --
> > > John Gastineau
> > > Staff Scientist and Partner
> > > Vernier Software & Technology
> > > jgastineau@vernier.com
> > >
> > >
> > >
> > > Bernard Cleyet wrote:
> > >
> > > > 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
> > > >
> > > >    
> > cut