Re: Optical pyrometers, was R = V/I ?

["Dewey Dykstra, Jr." <dykstrad@EMAIL.BOISESTATE.EDU>]

> Referring to a comment about a simple glowing wire pyrometer,
> Leigh wrote:
>
> > I don't understand. An optical pyrometer is used to measure
> > temperature objectively. "Pyrometer" merely means any
> > instrument or device (slump cones are also pyrometric devices) .
> > used to measure high temperatures. A calorimetric radiometer
> > is only one kind of pyrometer (usually calleda "bolometer").
>
> A measurement of T with a pyrometer in which we match colors
> (of a glowing wire and of the background behind it) is "subjective",
> in my terms, because abilities to compare colors are different for
> different people. A standard deviation s1 could be determined if
> many people were asked to measure T with the same color-based
> instrument. That deviation, I suspect, would be considerably wider
> than the one based on many measurements made by a single person.
> And mean values of T would probably be different for different
> observers. But that is only a guess. Another student project?
> Ludwik Kowalski

It could be argued that there is a degree of subjectivity in any
measurement, but a good optical pyrometer superimposes the view of the
glowing wire and the object to be measured.  The wire appears to disappear
against the object to be measured.  I'd say in this context our eyes are
pretty good at such comparisons.  I suppose that if the glowing wire is not
superimposed this way then there may be a reduction in ability to judge
that the two glows are the same.

Dewey


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Dewey I. Dykstra, Jr.                 Phone: (208)426-3105
Professor of Physics                  Dept:  (208)426-3775
Department of Physics/MCF421/418      Fax: (208)426-4330
Boise State University            dykstrad@email.boisestate.edu
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"As a result of modern research in physics, the ambition and hope,
still cherished by most authorities of the last century, that physical
science could offer a photographic picture and true image of reality
had to be abandoned."  --M. Jammer in Concepts of Force, 1957.

"If what we regard as real depends on our theory, how can we make
reality the basis of our philosophy? ...But we cannot distinguish
what is real about the universe without a theory...it makes no sense
to ask if it corresponds to reality, because we do not know what
reality is independent of a theory."--S. Hawking in Black Holes
and Baby Universes, 1993.
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