Teardown, Upgrade and Experiments with a Verity Visible Wavelength Monochromator - Page 1
Forum section: electronics / testgear

author: Hugoneus
author_rank: Frequent Contributor
timestamp: November 21, 2014, 05:41:22 pm
content: In this episode, Shahriar upgrades a Verity visible wavelength monochromator model EP200Mmd to be able to perform automatic scans. The instrument is retrofitted with a stepper motor and a microcontroller which performs wavelength scanning between 225nm to 875nm. The signal from the internal photomultiplier is sampled by the microcontroller and wirelessly sent to the computer. Matlab is used to plot the wavelength response.The principle operation of a monochromator is thoroughly reviewed starting with the grating mirror behavior. The operation of the photomultiplier is also described. Various mechanical and electronic of the upgraded system is also shown. The presented slides can be found on The Signal Path website.Watch the video directly here: [51 Minutes]http://youtu.be/veETVeEsaNMMore videos at The Signal Path:http://www.TheSignalPath.com

author: Hugoneus
author_rank: Frequent Contributor
timestamp: November 22, 2014, 06:01:16 am
content: Does anyone have any data on the photomultiplier inside this Verity unit? Also, any suggestions on the final version of this project would be good. O0

author: awallin
author_rank: Frequent Contributor
timestamp: November 22, 2014, 08:22:55 am
content: what is the noise floor, dynamic range, and resolution of a PMT-based spectrometer like this compared to the modern compact CCD-based ones (e.g. Ocean Optics)?Can you adjust a pinhole/slit in front of the PMT to trade off resolution vs. sensitivity?

author: Hugoneus
author_rank: Frequent Contributor
timestamp: November 22, 2014, 09:13:09 pm
content: Quote from: awallin on November 22, 2014, 08:22:55 amAll the slits are interchangeable to adjust optical bandwidth and sensitivity.

author: miguelvp
author_rank: Super Contributor
timestamp: November 23, 2014, 12:53:20 am
content: Thank you for the video, very interesting!

author: DJ
author_rank: Unknown
timestamp: November 23, 2014, 06:03:48 am
content: Nice video!PMT looks to be this one:http://www.hamamatsu.com/us/en/R928.htmlhttp://www.hamamatsu.com/resources/pdf/etd/R928_R955_TPMS1001E07.pdfSeewww.aps.anl.gov/.../20121018cycon.pdfETA: I have been looking for an inexpensive OSA:https://www.eevblog.com/forum/testgear/any-cheap-optical-spectrum-analyzers-available/The PMT units do have very good sensitivity, as you note in your video. Wonder if a cheap Gen1 Night Vision monocular could be adopted? Doubt it would be as well suited as the hamamatsu, but they do have compact, portable efficient power supplies, running from 1 or 2 AA or Li batteries. Looking for something between the PublicLab DIY spectrometer and a $$$ Ocean. The bench units like yours are great, but not sure how portable or rugged for outside the lab use.http://publiclab.org/wiki/spectrometer

author: Hugoneus
author_rank: Frequent Contributor
timestamp: November 23, 2014, 07:42:54 pm
content: Quote from: DJ on November 23, 2014, 06:03:48 amThanks for the information! Very helpful.In a dumpster dive recently I found a OSA which was thrown out. I have not turned it on yet, but I'll probably do a video of its teardown and repairs (if it needs one).It is very heavy as it is all based on free-space optics inside.

author: aargee
author_rank: Frequent Contributor
timestamp: November 24, 2014, 01:26:02 am
content: Nice vid.It's been a long time since I worked on Spectrometers. ICP using both mono- and poly-chrometers well into the UV spectrum with the light path under vacuum.3kV, 1A RF power supplies, 27MHz, 1600W RF generators, argon plasma, water cooling, 1kV PMT supplies, vacuum pumps, robotic samplers.... it had it all in the 80's!

author: HighVoltage
author_rank: Super Contributor
timestamp: November 24, 2014, 08:14:38 am
content: Thanks for another very nice video

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 24, 2014, 12:13:07 pm
content: Interesting video, I'd love something like this for testing lighting.

author: dentaku
author_rank: Frequent Contributor
timestamp: November 24, 2014, 01:51:24 pm
content: That was way more interesting than I expected.

author: radioFlash
author_rank: Regular Contributor
timestamp: November 25, 2014, 12:51:59 am
content: Nice video and very neat experiment. Would it be possible to calibrate the response of the setup using an incandescent lightblub and assume a black-body curve?

author: Dave
author_rank: Super Contributor
timestamp: November 26, 2014, 02:47:45 pm
content: Does the monochromator have some sort of filter to prevent second interference maximum from reaching the photodetector (so the 350nm light, for example, doesn't mess with the 700nm reading)?

author: ConKbot
author_rank: Super Contributor
timestamp: November 26, 2014, 05:49:09 pm
content: Quote from: radioFlash on November 25, 2014, 12:51:59 amFor calibrating wavelength, I'd expect a calibration with a lamp with known peaks would be easier than trying to fit a bulb of an unknown temperature.Looking at a fluorescent lamp should provide quite a few known mercury lines for a 2-3 point calibration, without even buying anything.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: November 26, 2014, 08:09:29 pm
content: Quote from: radioFlash on November 25, 2014, 12:51:59 amSodium D-line is the most common wavelength used for callibration. Thigns like these are my bread and butter, I use ones like this but on a much larger scale (typically full UV-Vis with large degrees of linerarity and fractional nanometer resolution. Use them daily for recording fluorescent dye and nanomaterials spectrums.