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-   -   Tubed IR spectrophotometer (http://www.diyaudio.com/forums/tubes-valves/75384-tubed-ir-spectrophotometer.html)

7n7is 7th March 2006 03:52 PM

Tubed IR spectrophotometer
 
Check out this tubed infrared spectrophotometer.
http://chemapparati.topcities.com/PE337/PE337-1.htm
There's links to the schematic and other information on the 5th page. There is a chopper (rotating sector mirror) in the spec which creates a 13 Hz multiplex signal (sample beam and reference beam signals multiplexed). The circuit includes an impedance matching transformer between the thermocouple sensor and the preamp, some AC coupled circuits similar to typical audio circuits, a demultiplexer circuit and drive circuit for a two phase servo motor that drives the chart recorder and reference beam attenuator. The instrument is an optical null spectrophotometer.

Also see http://www.geocities.com/apis_mellif.../IRramble.html

SY 7th March 2006 07:29 PM

Cut my teeth on one of those. Candle for a source. Drum turned by a long stick with a donkey.

During my post-doc days, I worked for a prof who wouldn't even look at an FT-IR spectrum- that wasn't real data like the stuff on the graph paper. He would tell me, "FT-IR is not a well-established technique, use the Perkin-Elmer." This despite having a first-rate IBM FT-IR for department use... I hated using that damn dispersive instrument. But the prof would look at the FT-IR spectra blankly and say, "I'm sorry, I don't know how to read these."

Anyway, I interviewed at a company that made FT stuff, and the chief scientist suggested that I grab some Perkin-Elmer graph paper, use the FT-IR, set the plotter parameters to the P-E paper dimensions, plot on it, then lie to my prof. I tried that, showed the prof the spectra without mentioning what instrument I used. He exclaimed, "These are the finest spectra I've ever seen! Why can't the grad students get spectra as clean as these? They're BEAUTIFUL!!!"

EC8010 7th March 2006 08:27 PM

I'm sure there's a moral in there, somewhere. Nice story.

jackinnj 7th March 2006 11:23 PM

Quote:

Originally posted by SY
Cut my teeth on one of those. Candle for a source. Drum turned by a long stick with a donkey.
it also helps (or did 30 years ago in my case :) )if you have a good idea of what the answer should be.

i was fascinated by IR spectra as the Perkin Elmer spectrometer was the niftiest thing in the lab -- and as an undergrad spent hours and hours just looking at the plots in journals --

EC8010 7th March 2006 11:54 PM

Quote:

Originally posted by jackinnj
It also helps (or did 30 years ago in my case :) )if you have a good idea of what the answer should be.
Similarly, the best bit of advice I ever received was, "You should never measure anything unless you already know the result." The second good bit of advice (from a seriously good lecturer) was, "So long as you are twenty minutes ahead of the students, you're OK."

SY 8th March 2006 12:07 AM

Jack, I was lucky enough to snag my first job out of school on the design team of the top-of-the-line Nicolet FT-IR, then got to spend a year playing with it and publishing papers. Interestingly, the servo system used to drive the interferometer looked exactly like that of a servo woofer (but with optical rather than accelerometer sensing) right down to the LM1875 chip amp. In fact, it really WAS a servo woofer, but with a mirror rather than a cone.

No tubes, though. :dead:

7n7is 8th March 2006 01:01 AM

I never used an FT-IR spectrophotometer, but I have used a number of dispersive IR spectrophotometers at a community college and a university I went to. I used a Perkin Elmer Infracord (137?) in 1980 for one class on advanced organic synthesis. It drew a complete spectrum on one sheet of chart paper from what I can remember. The 337 draws half the spectrum on one sheet of chart paper and the second half on another sheet of chart paper. The 337 is good if you like working with tube electronics and optics, as well as chemistry. The optics are high quality. The lowest price I've seen for a new dispersive IR spectrophotometer is over eight thousand dollars (US). FT-IR spectrophotometers are even more expensive. Complicated solid state electronics is harder to figure out and service, too. You can sometimes buy a 337 or similar spec on Ebay for less than $100. Shipping is usually at least $50. They're heavy.


Here's the schematic in gif format. The gif image is smaller than the pdf file.
http://chemapparati.topcities.com/PE337/Schematic.htm

7n7is 10th March 2006 06:22 PM

Some interesting links on IR spectroscopy.


http://www.unodc.org/unodc/en/bullet...1_page005.html

http://www.pslc.ws/mactest/ir.htm

http://www.answers.com/topic/infrared-spectroscopy

http://hiq.linde-gas.com/internation...ias/anal_infra

SY 10th March 2006 09:16 PM

Interesting that photoacoustic methods (of great interest to audio folk) aren't mentioned. I confess that the PAS cell I built used a B&K condensor mike but didn't use tubes...

7n7is 11th March 2006 01:43 PM

Quote:

Originally posted by SY
Interesting that photoacoustic methods (of great interest to audio folk) aren't mentioned. I confess that the PAS cell I built used a B&K condensor mike but didn't use tubes...

Sounds like its similar to a Golay detector.


Quote:

The Golay detector is based on the volume or pressure change of an encapsulated gas with temperature. The volume change is measured e. g. by the deflection of lightrays resulting from the motion of properly positioned mirrors fastened to the walls of the gas container.
http://www.acreo.se/templates/Page____226.aspx


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