temperature measurement

Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file.

Is that possible and, if so, how?

I realize that the temperature varies along the length of the filament,
so hopefully this method would assign a temperature to each point of the
filament.
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

Allan Adler wrote:

Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file.

Is that possible and, if so, how?

I realize that the temperature varies along the length of the filament,
so hopefully this method would assign a temperature to each point of the
filament.


I don't know if these are good enough, but they're a start.

http://www.r2d2u.com/htm%20pages/col...ng%20chart.htm
http://www.lightbulbsdirect.com/Merc...emp_chart2.jpg
http://www.mediacollege.com/lighting...mperature.html


Getting the camera set properly may be a challenge. I don't know how
linear they are in their response.




mike

[A complimentary Cc of this posting was sent to
Allan Adler
], who wrote in article :
Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file.

Is that possible and, if so, how?

I realize that the temperature varies along the length of the filament,
so hopefully this method would assign a temperature to each point of the
filament.

[I never tried anything similar, but] I doubt very much that you will
be able to get any reasonable result without calibration.

On the other way, if you can measure similar temperatures by
independent means, it looks quite probable that you would be able to
calibrate your images, and get reasonable precision (I would say,
5-10%?).

Hope this helps,
Ilya

On 2008-02-21, Allan Adler wrote:
Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file.

Is that possible and, if so, how?

I realize that the temperature varies along the length of the filament,
so hopefully this method would assign a temperature to each point of the
filament.

Interesting question. What resources has your teacher suggested might
help with your assignment? rpd should not have been listed as a primary
resource.

--
Chris Savage Kiss me. Or would you rather live in a
Gateshead, UK land where the soap won't lather?
- Billy Bragg

Allan Adler wrote:
Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file.

Is that possible and, if so, how?

I realize that the temperature varies along the length of the filament,
so hopefully this method would assign a temperature to each point of the
filament.

Yes, not only is it possible, you could do it with great precision
with some calibration. The peak of the black body curve is in the
infrared and the red, green and blue filters they are on the blue
side of the filament black body peak. That means small changes in temperature
will result in a large change in intensity and a significant change
in color. You could compute the change in response given the
transmission of each filter and the spectral response of the detector
(I do it often with spectrometers, remotely determining temperatures).
Without knowing the spectral response of the filters, you would
need to calibrate the response using known temperatures (e.g. use
a blackbody; there are many around MIT; it is an instrument
that makes a precise temperature and lets the heat radiate out
a small hole). The digital camera must have raw output and you
use software that produces a linear response (e.g. dcraw).
With calibration, you could get temperature measurements
to a fraction of a degree.

Roger

On Feb 21, 8:47 am, "Roger N. Clark (change username to rnclark)"
wrote:
Allan Adler wrote:
Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file.

Is that possible and, if so, how?

I realize that the temperature varies along the length of the filament,
so hopefully this method would assign a temperature to each point of the
filament.

Yes, not only is it possible, you could do it with great precision
with some calibration. The peak of the black body curve is in the
infrared and the red, green and blue filters they are on the blue
side of the filament black body peak. That means small changes in temperature
will result in a large change in intensity and a significant change
in color. You could compute the change in response given the
transmission of each filter and the spectral response of the detector
(I do it often with spectrometers, remotely determining temperatures).
Without knowing the spectral response of the filters, you would
need to calibrate the response using known temperatures (e.g. use
a blackbody; there are many around MIT; it is an instrument
that makes a precise temperature and lets the heat radiate out
a small hole). The digital camera must have raw output and you
use software that produces a linear response (e.g. dcraw).
With calibration, you could get temperature measurements
to a fraction of a degree.

Roger

I also agree that the use of RAW is essential in this application.
JPEG is not known for its accuracy of color rendition, and this
application requires spot-on color accuracy. Incidently, filament
structures at operating temperatures ARE pretty close to black body.

[A complimentary Cc of this posting was sent to
Roger N. Clark (change username to rnclark)
], who wrote in article :
With calibration, you could get temperature measurements
to a fraction of a degree.

I doubt this very much. Luminosity channel is useless, and the color
one is going to be quite noisy (and changing quite insignificantly
when the temperature changes in such a cold range as a filament). I
would be (pleasantly!) surprised if even 1% error is achievable with a
digicam...

Hope this helps,
Ilya

In article BO7vj.45681$C61.13814@edtnps89, m II wrote:
Allan Adler wrote:

Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file.

Is that possible and, if so, how?

I realize that the temperature varies along the length of the filament,
so hopefully this method would assign a temperature to each point of the
filament.


I don't know if these are good enough, but they're a start.

http://www.r2d2u.com/htm%20pages/col...ng%20chart.htm
http://www.lightbulbsdirect.com/Merc...temp_chart2.jp
g
http://www.mediacollege.com/lighting...mperature.html


Getting the camera set properly may be a challenge. I don't know how
linear they are in their response.

The biggest challange may be keeping the filiment from saturation. I suppose
room light should be fairly bright, else use a small F stop and or filter.

greg

In article , wrote:
On 2008-02-21, Allan Adler wrote:
Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file.

Is that possible and, if so, how?

I realize that the temperature varies along the length of the filament,
so hopefully this method would assign a temperature to each point of the
filament.

Interesting question. What resources has your teacher suggested might
help with your assignment? rpd should not have been listed as a primary
resource.


Assignment ??? Why does this have to be an assignment ?

greg

"Roger N. Clark (change username to rnclark)" writes:

Allan Adler wrote:
Suppose I have a digital camera and an vacuum tube and I want to use the
camera to measure the filament temperature of the tube by studying a
digital photograph of the filament, saved as a computer file. Is that
possible and, if so, how? I realize that the temperature varies along the
length of the filament,so hopefully this method would assign a temperature
to each point of the filament.

Yes, not only is it possible, you could do it with great precision with some
calibration. The peak of the black body curve is in the infrared and the
red, green and blue filters they are on the blue side of the filament black
body peak. That means small changes in temperature will result in a large
change in intensity and a significant change in color. You could compute
the change in response given the transmission of each filter and the
spectral response of the detector (I do it often with spectrometers,
remotely determining temperatures). Without knowing the spectral response
of the filters, you would need to calibrate the response using known
temperatures (e.g. use a blackbody; there are many around MIT; it is an
instrument that makes a precise temperature and lets the heat radiate out
a small hole). The digital camera must have raw output and you use
software that produces a linear response (e.g. dcraw). With calibration,
you could get temperature measurements to a fraction of a degree.

Thanks, that is very helpful. How cheaply can I get a digital camera that
will have raw output?

Since posting this, I obtained a copy of Michael Covington's book,
"Astrophotography for the amateur, 2d ed", and located the chapter
on using CCD cameras. Of course I'm not going to do astrophotography,
but maybe some of the information can be used to make sense of the
raw output. If there is a better book to look at for this application
(i.e. the filament temperature, with a digital camera), I'd be glad to
know about it.
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.