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ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
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Posted: Wed Jul 04, 2007 6:14 am Post subject: How to measure light wavelength?? |
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hello,
i need to build an instrument that can measure the wavelength of a light through a medium, such as water,etc, and display the wavelength
any idea about it? |
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bryon
Joined: 02 Oct 2005 Posts: 19
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ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
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Posted: Thu Jul 05, 2007 2:27 am Post subject: |
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hehehhe, search the globe and got the name
spectrophotometry
i need the number of light can be passed through a medium such as water and convert it to a number. found the sensor for it on Hamamatsu website as photomultiplier. pretty nice, simple, for measuring purity or concentration of a medium. |
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arief
Joined: 15 May 2007 Posts: 6 Location: Malang
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Posted: Thu Jul 05, 2007 11:43 am Post subject: Light to Frequency Converter |
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hi,
I suggest you, maybe you can using TSL230 Light to Frequency Converter.
TSL230 sensor precisely measures light using an array of photodiodes, with an output of digital square waves.
and you can buy at Toko-elektronika.com |
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ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
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Posted: Thu Jul 05, 2007 12:49 pm Post subject: |
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well, actually i've got the sensor. it is from an old saccharinmeter and i need to get the saccharin level using polarization of the light. pretty confusing too
any idea??
i've used that chip before, nice too |
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trinity772
Joined: 04 Jan 2007 Posts: 120 Location: MA
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Posted: Fri Jul 06, 2007 11:52 pm Post subject: |
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Hello ex4,
Quote: | hello,
i need to build an instrument that can measure the wavelength of a light through a medium, such as water,etc, and display the wavelength
any idea about it?
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After just finishing 2 semesters of optics, and advanced Laser optics, I do have some ideas. From what I read, you are trying to measure how much "light" passes through a medium such as water that contains something else? And, of course, what the wavelength of that light is.
Now you also mentioned something about polarization. Tell me a little more about that because that just may be your key to solving this problem.
In order for me to try and help, I have the following questions:
What wavelength(s) of light are you using?
Are you trying to measure what wavelengths emerge from, say, a glass jar that contains a liquid? If so, do you know what wavelengths you start with? (almost the same as the above question).
Are you using a LASER or regular uncollimated light?
Are you trying to measure the attenuation (ie, absorption, and scattering) of certain wavelengths by measuring which wavelengths come out?
These may sound like pretty stupid questions, but I don't want to assume anything.
In the meantime, I will have a look to the link on interferometry. Although, we usually used interferometry to measure distances on the order of a wavelength (10 power -9 meters or so). Also, have you tried googling spectroscopy?
Let me know if I can be of help,
Joe |
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ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
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Posted: Mon Jul 09, 2007 4:03 am Post subject: |
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thank you
Quote: |
What wavelength(s) of light are you using? |
300nm-650nm
Quote: |
Are you trying to measure what wavelengths emerge from, say, a glass jar that contains a liquid? If so, do you know what wavelengths you start with? (almost the same as the above question).
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after googling on wikipedia, i know the instrument name, it's saccharinmeter. it measure how much sugar is in a water solution based on its polarization angle (at least that what i've read from wikipedia)
Quote: | Are you using a LASER or regular uncollimated light? |
just ordinary 24V dc lamp focused using Nicol prism
Quote: | Are you trying to measure the attenuation (ie, absorption, and scattering) of certain wavelengths by measuring which wavelengths come out?
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the attenuation can be measured easily in term of voltage. i use photomultiplier from hamamatsu (PMT R931B). rather old, but that's what i got know |
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trinity772
Joined: 04 Jan 2007 Posts: 120 Location: MA
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Posted: Mon Jul 09, 2007 7:20 pm Post subject: |
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Hello ex,
Ok, so you are working from the Ultraviolet (300nm) to the red (650nm).
Quote: | just ordinary 24V dc lamp focused using Nicol prism |
So the lamp is white light then? White light would contain all the spectrum of your interest and more, including infrared.
A nicol prism is used to polarize light, if I remember correctly. It is a crystal.
Now if you are looking to measure wavelength, and not polarization, then I am confused.
Example, I go fishing once in awhile. When the sun hits the water, the horizontal surface of the water polarizes some of the light horizontally, which causes the glare and prevents you from seeing underwater with the naked eye. However, wearing polarized sunglasses of the opposite polarization, I can see into the depths (depending on water clarity), ie, if the glare is horizontally polarized, and the glasses are vertically polarized, then the glasses block the horizontally polarized light (the glare) and allow me to see into the water. There's a price though. You only see about half the intensity (Law of Malus, something to google).
To measure wavelength is a totally different procedure, google "Young's double slit experiment". He used a diffraction grating and a sodium lamp. He was able to determine the wavelengths present in the sodium lamp.
It is still widely used to determine wavelength, but you need a spectrometer.
Here is how I measure "wavelength" qualitatively, actually color. A CdS photocell has about the same sensitivity as the human eye. So you aim the photocell at something (it should be enclosed in a dark tube like a 35mm film canister or a piece of pvc pipe to avoid ambient light pickup. Then, on the sides of the canister or pipe are 3 LEDs. Red, green, and blue. By turning on each LED and reading the output from the CdS photocell (actually a resistor, so you need some voltage on it), using the micro, and by experiment, you can find all the colors of the spectrum (visible anyway, I have not worked with ultraviolet).
But it sounds to me that you are more interested in the polarization of the emitted light rather then wavelength. You could use polarizing sheets of plastic which are sold by different companies, again, google is your friend.
for wavelength (approximate)
Now they make ultraviolet LEDs, and I have found that an LED is like any other transducer. It absorbs at about the same wavelength it emits. So that is another option. Pass your white light thru the liquid, and use an ordinary prism to break it into its "colors". Determine the distance from the prism where you can mount some LEDs of all the different colors. ROYGBIV UV, and monitor them with the micro. They set up a voltage at their terminals when light hits them, which should be a maximum at around their emission wavelength. If you know the emission wavelength of each LED, then you can determine, within a pretty good degree of accuracy, what the wavelengths of the emerging light is.
Just try using a red LED and shine it onto another red LED (or infrared, or whatever you have handy), and monitor the voltage at the 'receiving' LEDs terminals (opposite polarity). That is how you would calibrate that setup. I have not tried this one yet.
hth,
Joe |
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ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
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Posted: Tue Jul 10, 2007 12:06 am Post subject: |
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for the short version, i need to measure sugar(suchrose mostly) concentration on a liquid, for instance orange juice,etc. some said it is a refractometer, saccharinmeter. any idea? |
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trinity772
Joined: 04 Jan 2007 Posts: 120 Location: MA
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Posted: Tue Jul 10, 2007 2:13 am Post subject: |
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Wow, why didn't you say so ?
Quote: | for the short version, i need to measure sugar(suchrose mostly) concentration on a liquid, for instance orange juice,etc. some said it is a refractometer, saccharinmeter. any idea? |
It just so happens that I live in the Northeastern US, and we harvest maple sugar up here for maple syrup. Best syrup in the whole world!
just a little plug there
Seriously though, it's a refractometer.
Check this site:
http://maple.dnr.cornell.edu/kids/refractometer.htm
That should get you started.
If you have a mind to use a LASER pointer, for a more high tech way, then check this one out:
http://www.sciencebuddies.org/mentoring/project_ideas/Phys_p028.shtml
Joe |
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ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
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Posted: Tue Jul 10, 2007 3:42 am Post subject: |
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got the idea and the hardware here (light source, nicol prism, and PMT R931B), so ready for testing. hope don't get sting by the HVDC of PMT
any circuit idea is welcome
oh yeah, care to send some maple syrup here??? |
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trinity772
Joined: 04 Jan 2007 Posts: 120 Location: MA
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Posted: Tue Jul 10, 2007 6:19 pm Post subject: |
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Quote: | got the idea and the hardware here (light source, nicol prism, and PMT R931B), so ready for testing. hope don't get sting by the HVDC of PMT
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I looked up the spec sheet on that instrument. Are you sure a pmt is what you need? It does have some hefty voltages. 1250 volts, I wouldn't even want to touch that.
We used to use pmts to count gamma rays during positron annihilation. I don't know what make it was though. That was off limits to students. My professor knew the ins and outs of it.
The impression I got of a pmt is that it amplifies the number of photons received in the form of a voltage. I could be wrong. I remember when an electron and positron collided, it was total annihilation of mass to pure energy with 2 511 Kev gamma rays going 180 degrees to each other. And we wouldn't just be annihilating a pair. There was several hundreds (maybe thousands) of them. We used to have to wear radiation dosimeters. That energy gamma ray would penetrate even lead.
But back to your pmt. If you do some very careful calibration using just plain (distilled) water, and then use a weak sugar solution, you may be able to see a difference. Do it with enough known samples, increasing the amount of sugar each time, plot it, and you have your calibration curve which you could then program into the micro.
I also think that measuring the refraction is a lot safer and could be more accurate.
As far as a circuit goes, I would have no idea. I only do low voltage stuff. I don't even like playing with the mains.
I don't know if I could afford the postage to send maple syrup to Indonesia. Besides, it's kind of difficult to find at this time of the year. Spring (March thru May) is the sugaring season. Maybe , ahem, a kind hearted Canadian on the forum could send you some of theirs.
Anyway, best of luck with your project.
Joe |
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ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
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Posted: Tue Jul 10, 2007 11:53 pm Post subject: |
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about the hvdc is just max of 1000V dc, and can be easily generated using ttl chips and CW multiplier, since pmt only consume very small current. but i'm considering using the low voltage version of the pmt from hamamatsu. they got several type. it should be a good subtitution, since i also don't wanna mess with HV. yesterday just checking the principal with the old saccharinmeter, and youknow that it's very easy.
turn on a light source,pass it through a prism (mine is nicol), and look at the refracto prism. move the refracto prism so the measured light beam is minimum, and voala we get the polarization angle of the liquid which show the concentration of the sugar from the movement of the motor. |
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trinity772
Joined: 04 Jan 2007 Posts: 120 Location: MA
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Posted: Wed Jul 11, 2007 4:54 am Post subject: |
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[quote]
turn on a light source,pass it through a prism (mine is nicol), and look at the refracto prism. move the refracto prism so the measured light beam is minimum, and voala we get the polarization angle of the liquid which show the concentration of the sugar from the movement of the motor.
Quote: |
So problem solved then.
What motor? |
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ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
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Posted: Wed Jul 11, 2007 5:16 am Post subject: |
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apparently what i got here is refracto prism that moved using motor, so the polarization angle is count using an optocoupler. 1 count represent an angle movement(haven't measure the resolution) |
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