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ArcticMyst Security by Avery

Laser Power Meter - DMM to LPM Adapter

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A little while back, I had a thread going about an LPM I made with a small TEC and a small analog panel meter. This simple device proved reliable and repeatable, so why not make something to attach to a DMM? I found a small black square heatsink from a junked PC and attached the small TEC to it. The TEC was coated with black sharpie marker this time. Since I needed some way to adjust the output of the TEC, I also stuck on a small multiturn 100k trimmer. The leads from the TEC go to the ends of the trimmer. Negative lead to the DMM goes to TEC negative. Positive lead to DMM goes to the trimmer wiper. I then grabbed a red laser and measured it at a steady 202mW with my Laserbee LPM. I shone this laser on my sensor, and adjusted the trimmer until I read 20.2mV on my DMM. Testing with various other lasers shows that this seems to work as reliably as my analog version. I haven't had it long enough to see how it does over time, but so far it looks quite promising. I checked a 2W handheld on my Coherent 210 and read 1.8W. On the DMM, I read 185.9mV or 1.859W so pretty close even at a higher power and IR.

Some pictures ...

The TECs used :

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The DMM and DMM to LPM Adapter :

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A closer shot of the sensor :

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With the DMM on and ready to measure :

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Taking a measurement (232mW) :

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This is another fairly simple way to measure laser power. The drawback, is of course the need to set it up either with another LPM, or a laser of known power. A DMM that can output to a PC would be interesting ...
 

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Awsome build! Dude, I think Jerry here is sweating already :D JK

Basically all you need is a trimmer with a TEC, and known power laser.
Know power is what bugs me...
 
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Awsome build! Dude, I think Jerry here is sweating already :D JK

Basically all you need is a trimmer with a TEC, and known power laser.
Know power is what bugs me...

Why would I be sweating.... :beer:

I think that this is a great idea for the DIY member...
just like all the other DIY projects on LPF... I even link to the
other DIY LPM projects from my own LaserBee I and HLPM II
Thread....

http://laserpointerforums.com/f39/laserbee-i-thermopile-based-laser-power-meter-40116.html


Jerry
 
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Haha dude, I'm just joking around, you know as in: everyone gonna build one of those, you sales dropping :p Right... Like that is gonna happen :D

You are always the first one to post a comment when Bill makes LPM project thread (like that analog head with TEC, making a LPM). You seem to be very much interested in such projects! I will also be making my own LPM through the first month next year or so, with Atmel 808x microcontroller and LED display , along with that TEC senzor head.
 

3zuli

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great! will u be selling those TECs? or where can I buy one?
 
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I only had a few of these TECs. They do show up on ebay, but only very rarely. The large TECs are quite common, but not useful for this application. Chris (heruur) did at one point have small TECs, another source is dead TO-3 LD's that still have a working TEC in them. These can also be purchased new, but could be $15 to $20 each. Digikey does not seem to have small ones.

Here, for example, is a European supplier : Thermoelectric Cooling Modules ML06 Series of small TECs.
 

Asherz

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I only had a few of these TECs. They do show up on ebay, but only very rarely. The large TECs are quite common, but not useful for this application. Chris (heruur) did at one point have small TECs, another source is dead TO-3 LD's that still have a working TEC in them. These can also be purchased new, but could be $15 to $20 each. Digikey does not seem to have small ones.

Here, for example, is a European supplier : Thermoelectric Cooling Modules ML06 Series of small TECs.

Thanks for the info Bill, I'll probably just buy a TO-3 diode from ebay and give this ago :)
 
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The TEC in a TO-3 diode can be a bit of a challenge to extract. First, the top must be popped off the TO-3. Then, you will see that the c-mount diode is indium-soldered to the TEC, which is in turn indium-soldered to the TO-3 mount base. You must heat the assembly just enough to part the indium solder, but not so much as to unsolder the TEC body itself into pieces. You do not want to pass 180 to 200 celsius at the max, as the TEC may start to come apart around 230 celsius. Once the TEC is free, wipe of any excess indium solder and as long as the TEC didn't burn out with the LD, you will be fine. Test it on a small heatsink, with a 1.5V battery, one side should warm, the other should cool. (Most small TECs will do something with 1.5V applied, even small ones are usually rated at least 2V.) You will also need to blacken one face of the TEC in order to enhance laser absorption. There are two easy ways, a black sharpie marker, or carbon black deposited from a candle, acetylene flame, etc.
 
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I've had a few people ask me about TECs, so I would like to add another experiment and its' results to this thread. It seems these small TECs are rarer than frog's milk and hen's teeth ... I decided to go to the other extreme, and I took a 96W 40 x 40 x 4mm TEC to try out. It was put on a square black heatsink, and connected to a 100k trimmer and my Amprobe DMM. This should simply not work, or be nearly useless, so which is it?
I got set up ...

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A closer view of the huge TEC ...

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(Yes I was feeling a little sarcastic ...)

Take a reading ...

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Fouled up the photo, oh well ...

The result is that the large TEC does not have the voltage output of the small one when used as an LPM sensor. It is 10x less sensitive and nearly unuseable although it does in fact work! It is slow to come up to a stable reading, and slow to cool down to zero afterwards. Too much mass ...
 

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Holy crap Bill, gotta love your machined hosts!!
And what is in them OFC...

Big TEC could be used for multiwatt measurents, although it would need a lot bigger heatsink.

Awsome collection....
BTW offtopic! When are you going to post some fresh pictures of your famous laser cabinet? We would all wanna see that!
 
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Haha dude, I'm just joking around, you know as in: everyone gonna build one of those, you sales dropping :p Right... Like that is gonna happen :D

You are always the first one to post a comment when Bill makes LPM project thread (like that analog head with TEC, making a LPM). You seem to be very much interested in such projects! I will also be making my own LPM through the first month next year or so, with Atmel 808x microcontroller and LED display , along with that TEC senzor head.

Hey Eudaimonium...

You are correct... I am very interested in DIY projects like this...
and others...
It reminds me of when we first started to try to build our own LPMs for
our shop using the Red and Green LED approach about 3-4 years
ago... (if anyone needs Red or Green LEDS at a fair price... just PM
me..:crackup:)

For the single person that does not want to go into mass production..
these DIY projects are great... you only need to find 1 or 2 surplus TECs
to do this project... and possibly end up with a fairly useable LPM..

But if you want to continually produce a consistent product then
surplus would not be the answer for consistency (accuracy variations)...

Just this year were were forced to have TECs made to our specific
specifications (because the ones we were using became obsolete..)
to assure compliance to consistency... Our new 8mm X 8mm TECs that
we use on the LaserBee I Thermopile... in large quantities cost us
$58.00US each.... But each one is the same as the last one....
or very close to it...:cool:

@ billg519..
at one point we tried 15mm X 15mm TECs from DigiKey... but found the
response time getting to a usable/stable reading much to slow... as you
noted with the 40mm X 40mm...


Jerry
 
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Holy crap Bill, gotta love your machined hosts!!
And what is in them OFC...

Big TEC could be used for multiwatt measurents, although it would need a lot bigger heatsink.

Awsome collection....
BTW offtopic! When are you going to post some fresh pictures of your famous laser cabinet? We would all wanna see that!

When I make a laser, I like to make the whole thing. The driver, body, laser head (I made a diode pocket reamer to make things easier ...) and lens nut all get made. I don't like the aixiz lens nut slop, plus I feel that I get slightly better heatsinking with the diode directly in the aluminum or brass head.

The big TEC is simply not a realistic option for an LPM sensor.

I will have to update the laser cabinet pictures as the existing cabinet is now too small, lasers are overflowing, so I got a new one, just have to bring it home.

Hmmm ... I just noticed ... It's New Year's Eve and this is my post #666 ...:eg::eg::eg: I wonder if any of my reds are off-spec a bit ... 666nm???
 
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Hey Eudaimonium...

You are correct... I am very interested in DIY projects like this...
and others...
It reminds me of when we first started to try to build our own LPMs for
our shop using the Red and Green LED approach about 3-4 years
ago... (if anyone needs Red or Green LEDS at a fair price... just PM
me..:crackup:)

...



Jerry
Dude, you mean like, shining a laser at a LED in front, it generates voltage? I've seen that experiment on youtube somewhere, another LED was connected on first one and it lit up! Powered by another LED :D
I'm guessing that it was (un)linearity of voltage supplied that made it unusable for sensor?
When I make a laser, I like to make the whole thing. The driver, body, laser head (I made a diode pocket reamer to make things easier ...) and lens nut all get made. I don't like the aixiz lens nut slop, plus I feel that I get slightly better heatsinking with the diode directly in the aluminum or brass head.

The big TEC is simply not a realistic option for an LPM sensor.

I will have to update the laser cabinet pictures as the existing cabinet is now too small, lasers are overflowing, so I got a new one, just have to bring it home.

Hmmm ... I just noticed ... It's New Year's Eve and this is my post #666 ...:eg::eg::eg: I wonder if any of my reds are off-spec a bit ... 666nm???
Yeah, aixiz' lens nut sucks because there is a 'wobbling' of lens... I hate that.
And I'm drooling arready hearing your cabinet is 'overflowing'...
TAKE PICS AS SOON AS YOU CAN!

Congrats on 666 post hehe :D I'm half way there I think...:crackup:
 




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