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 Laser Pointer Forums - Discuss Laser Pointers Simple Laser Power Meter Using IR Thermometer

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05-07-2009, 11:13 AM #33
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Warske
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Quote:
 Originally Posted by Benm I never realized those themometers had gotten that cheap by now. Could be useful for diagnosing electronic circuits as well.
Yes, if you get it close enough it will read an area on the circuit board as small as about 1/4 inch. Good for finding hot spots.

Quote:
 Originally Posted by Asherz Im trying this out soon looks great and will give a rough idea
Great! I don't think you will be disappointed. I'm looking forward to your feedback!

Quote:
 Originally Posted by DWells55 Harbor Freight also has helping hands available with two clamps and a magnifying glass for \$1.89 on sale...
I bought about 8 of those...

Quote:
 ...I'll build one of these as soon as I get home with the materials...
Excellent! It shouldn't take very long, I think.

Quote:
 The relationship between temperature and laser power is linear, correct? In other words, can I simply take the percentage difference in temperature and then multiply this by the output of the known laser in order to determine the output of the other laser?
Yes, linear within a few percent. The radiation and convection effects are, in fact, slightly non-linear over the range of interest, but a linear approximation works very well.

So if you take two stable lasers, measure the temperature rise of each separately, then the temperature rise of both hitting the target at the same time, the second temperature rise will be the sum of the first two. You can try this. The green lasers usually aren't very stable, so I expect this test will not work as well if you use green. But this meter does respond fast enough so that you can watch the temperature change as the green laser power changes.

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05-14-2009, 11:48 PM #34
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Hallucynogenyc
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Any accuracy numbers alredy? I'm waiting jerry to get his own one so we can compare with the calibrateds ;p

05-15-2009, 12:14 AM #35
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lasersbee
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I haven't had time to put it together yet... I'll post something when I have something...
I'm in the middle of a few production runs at the moment...

It's too bad that seoguy chased Warske off the Forum..
We won't have Warske's extensive electronic knowledge available
for this IR Thermometer LPM Project...

Such a waste...

Jerry

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Last edited by lasersbee; 07-01-2012 at 11:48 AM.

05-16-2009, 10:37 AM #36
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^ X2 Grrrrrr........ I was enjoying this bit of physics.

05-20-2009, 03:52 PM #37
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wohoooo... just found this. Great! So I don't have to design my own LPM

I haven't read all of this yet, however there's one thing I disagree with (don't know if that was tackled in the posts I didn't read): namely, that it's the area that matters but not the thickness. I say it's the total heat capacity of the sensor that matters, i.e. heat capacity times mass (times a fudge factor <1 to take the non-perfect black color into account). Only then will absorbing a given amount of energy (power multiplied by time) result in a given temperature rise. Area doesn't come into play (as long as all beam energy falls onto the target).
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05-24-2009, 05:40 PM #38
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c4r0
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I was searching for some information on how thermopile LPMs are made and just had a nasty idea :] This is a 40x40mm peltier module connected directly to a mV meter. I made a black bolt on it with a permanent marker pen for better absorption. The laser is 235mW 650nm based on a DVD-RW LD. Reading is 9mV and it gives 38mV/W without ANY additional electronic parts. The voltage becomes quite stable 45s after turning on the laser. I don't know if anybody here has tried this before but it looks awsome for me, actually I wonder if LaserBee sensor is not a tiny peltier module on a heatsink :P
And after all - bravo me, I posted it on the old forum first
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05-24-2009, 08:34 PM #39
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Hallucynogenyc
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That's also a nice idea

05-24-2009, 09:27 PM #40
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lasersbee
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That's called the Seebeck Effect....discovered in 1821....

Jerry

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Last edited by lasersbee; 07-01-2012 at 11:48 AM.

05-25-2009, 12:44 AM #41
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Have you tested the voltage response with various laser power levels, and is the relation linear?

While the fundamental principle is the same, i doubt a cpu-cooler type peltier element would ever give performance comparable to one designed for sensing applications. You should also measure generated current rather than voltage to make it work properly.

05-27-2009, 09:38 AM #42
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I've got these tiny peltier units I bought off ebay that are for more specialized purposes. I still haven't gotten around to rigging them up with an amp and ADC to see how they'd respond. That mostly has to do with the lack of some good high emissivity coating, like what would be on a real laser power meter element, and that I have good working meters so it isn't as urgent anymore. Ironically, one reason I wanted to get a meter is so I could compare the response.

05-28-2009, 08:04 PM #43
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c4r0
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Quote:
 Originally Posted by lasersbee That's called the Seebeck Effect....discovered in 1821.... Jerry
Yea, I know By the 'idea' I meant using peltier module that was designed for cooling stuff as a sensor. But anyway, I recently read some about power meters on Sam's Laser FAQ and this idea isn't new :P Old type thermal LPMs were made exactly this way.
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05-30-2009, 04:11 AM #44
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nikokapo
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Awesome, man, thanks for sharing new ideas

06-01-2009, 11:43 AM #45
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Where to buy IR-therm outside US?

Hello,

Does anyone have any idea as to where these Cen-Tech IR thermometers (or equivalent) can be found in Europe? I tried ordering from the HarborFreight site, but there is no option for international shipping... also all the ones I found on European sites are waaay overpriced, the least expensive was like 100€ and going up to 300€ At that price it would be far cheaper to get the LPM itself...

That being said, it looks like a nice mod and I wanted an IR thermometer for various applications anyway...

Thanks,
Mihnea

06-14-2009, 03:27 PM #46
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Uhm, i already tried times ago with peltier cells, and can say you a couple of things.

First, it works only on powers over a certain level, like, 15/20mw, not less, at least if you don't get a very special custom made peltier cell.

Second, you need to find a small pltier cell with a lot of little junctions, and build a particular enclosure, included a thermal compensation system, for some decent reading, and it's also more slow than thermopile.

The effect works only if there's difference of temperature between the two faces, and itìs also proportional to the difference ..... then, you need a semi-closed holder for the peltier cell, preferably a cell of 10x10mm or similar, and a thermistor on the cold side that act a compensation network on the amplification/output section ..... otherwise it work, but don't give you any precise reading.

The one i made, had a 150x150mm aluminium heatsink, with a fan, a thermal controller for the fan, a thermistor for the reaction, and a cell "enclosure" on the flat side, that was holding the cell away from air currents and disturbs, and still had from 10 to 15% of errors, also in the better cases, and never measured anything less than 10mw (i had not enough oney for order a custom peltier cell )

Anyway, it can work, as experiments ..... if you wany (and if i can found my old draws), can post them, or redraw on-the-fly a principle schematic and holder shape.
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06-24-2009, 02:26 PM #47
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Re: Simple Laser Power Meter Using IR Thermometer

You can get these in maplin (UK) - # N19FR £15
Or in germany @ conrad.de - # 122301-62 €19

I must try this when I get home....

Last edited by rcblob; 06-24-2009 at 02:40 PM.

06-24-2009, 05:16 PM #48
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Re: Simple Laser Power Meter Using IR Thermometer

Quote:
 Originally Posted by rcblob You can get these in maplin (UK) - # N19FR £15 Or in germany @ conrad.de - # 122301-62 €19 I must try this when I get home....
Now, why the hell just here they sell them over 47 Euro ? ..... damn thiefs
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