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Selling one of my LPMs (personal build)

HIMNL9

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Hi, i'm starting to put a bit of order in my laser items (just realized that i have waaaay too much laser related items around :p), so i'm placing something for sale, time by time (just need to check well anything, before, cause i don't want to sell non-working items).

I have some LPMs, around, so decided to sell one of them (maybe others in the future, but i need time for check all), thinking that someone can have an use for it, better than stay in my desk tire :p ..... it's a "pocket size" (sorta of :D) self-made LPM, that i built some times ago, when i needed a portable unit for some on-the-field measures ..... it uses a miniature 60-junctions 10x10mm TEC (so-called "wafer-type" thermopile, too), as sensor element, and this TEC is sensitive enough for detect also few mW (well, in fact, if i place my hand in front of the reading window, it read something, and another unit i've built with the same TEC type can read 1/10 of mW, so i suppose it's sensitive enough :p ..... originally, they costed me like 30$ each, and now i'm unable to found them anymore, anywhere) .....

The unit is an all-self-contained box, powered from a single 9V battery (uses a DC/DC converter for the dual power supply of the op-amps) with a power consumption around 50mA, and can measure til 2W (1,999 , being precise), with 1mW resolution ..... no backlighting of the display, when i built it, there was no backlighted panel meters available here ..... dimensions are 130x80mm, with a height of 32mm, and the reading thermopile is inside, rear a protective lid ..... i have repainted at new the sensor (cause the use had a bit signed with burn marks the paint i made originally :p), and recalibrated it with my other units, using red, green and BR, for check that the new coating have an almost-flat absorption band (in fact, it's not 100% flat, apparently it absorb a little bit better the UV band, and this means that reading a BR, you probably get around 1% to 2% more than the real power ..... sorry for this, but there's nothing i can do for correct it, cause this is the only matte black heat resistant paint that can be found around here)

As usual, pictures ..... first the inside, for the curious ones (so you can see the horrors of the DIY prototypes :p :D)





As you can see, it does not look "professional", it was built as prototype ..... it work decently, but, as non professional unit, it does not have any extra features like data logging or peak hold, just the bare reading of the power .....

This is the TEC, on its heatsink ..... after repainting, i used some copper piece "dipped" in thermal adhesive for increase the thermal mass of the heatsink, making the reading a bit more stable ..... the reason of the 4 wires, is that there is also a sort of "thermal compensation" circuit, with an NTC, glued in the heatsink ..... it cannot compensate the 100% of the thermal derive (due to the intrinsic different thermal characteristics from NTC and TEC), but i reached to reduce it of almost 90%, and this is not a too bad result, i think :p



Then some dimensions, and some readings from 3 of my pointers, a 65mW green, a 232mw BR from a 6X, and a 100mW red, with expositions of 15 seconds ..... a note about this time; as any other TEC based LPMs, the reading is not "immediate" as with a real thermopile ..... i mean, instead to reach the final reading in 2 or 3 seconds, like with a real thermopile, it need that you keep the beam on the sensor for at least 10 seconds, for permit a good reading ..... this is not a defect, anyway, it's a normal condition for any unit based on TECs as sensors.





Wondering what i can ask for this unit ..... do you think that around 100$ plus shipping can be a right price ? ..... also if i prefer to sell it inside Italy, for customs offices and shipping problems, if someone outside Italy want it, i have no problems .....

Let me know what you think .....


EDIT: on request, i made some tests for 445nm units at high power, and here are the results:

The LPM itself can hold til 2W, without problems, if the beam is defocused on at least 80% of the surface of the sensor (or, in other words, making a beam with at least 8mm of diameter) ..... for the other side, those 445nm diodes don't make a circular beam, so the thing is a little bit more complex .....

First, i've painted in the same way of the sensor another TEC, and tried to keep pointed a 1,6W beam, focused in a shape of 5mm lenght "bar", and the paint start to become damaged after 30 seconds ..... then tried focusing it at 8mm lenght, it start to become damaged only if i left it stable on the same place for 70 or more seconds, but it does NOT become damaged if i keep to move it, also just 3 or 4 millimeters (i mean, "sweeping" a small area, always the same, keeping the "bar", as example, horizontally, and moving the spot up and down for 3 or 4 mm, not staying on the same place for more than a pair of seconds) .....

Then i've tried on the meter, and i've found that, also keeping the "bar" moved on the surface of the sensor, it still measures correctly the value, in 15 or 16 seconds (this is due to the thermal conductivity of the ceramic plate of the TEC, that can measure the accumulation of heat also if the "spot" is moved on its surface, as long as it still hit the surface).

Then, used a correction optic on the labby unit, and made a "spot" almost round (almost square, being precise :p), of 8mm ..... it does not damage the surface in any way, at least not for the 5 minutes i've kept it pointed on the "decoy" TEC ..... and on the meter, it reads correctly, too .....

This means, practically, that if you have a laser that can make a ROUND (or almost round) spot, you can measure til 2W, defocusing the beam around 8mm, without the need to move it on the TEC surface ..... but, for lasers that make "thin bar" shaped spots, like the 445nm, you NEED to defocus it, til the "bar" have a lenght of 8 or 9 mm, and, preferably, keep it slightly moving on the sensor, for all the time that you need for make the measure ..... or, in alternative (always defocused to the same size), you can keep it on the same place, without moving it, but paying attention to not keep it pointed on the sensor for more than the 15 or 20 seconds that you need for stabilize the reading ..... otherwise, the surface of the sensor can become damaged.

Basically, this mean that you can use it for "on-the-fly" readings, but not as "lab instrument", keeping pointed high power units on it for long times.


I had to add these data, cause someone may want to use it with 445nm units too, and is better that you know what you can do or not, with it, before to buy it.
 

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aryntha

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Pics don't seem to be visible here, HIMNL9....
 

HIMNL9

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Very strange, i was seeing the pics in my post, and as forum attachments in the edit box (example, as "http://laserpointerforums.com/attachment.php?attachmentid=29964&stc=1&d=1287335686" address :confused:), but NOT as "attached thumbnails", where instead they are as usual ..... a forum glitch in the loading procedure ? ..... i don't know .....

I've reloaded them again, now, and now i see also the thumbnails bar, let me know if the problem persist or if now they are visible, thanks.

(and sorry for the delay, i was at lunch :p)
 
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HIMNL9

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Bumped and updated ..... :p

Also, i'm "refurbishing" the others 2, so soon i place also them for sale (probably next week).
 

ped

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Gday HLM...HMI9...forget it,

Are these calibrated?

Cheers
 

ElektroFreak

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You sell yourself short HIMNL9.. that looks very well-constructed for a homemade unit. Impressive!
 

HIMNL9

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@ ped: yes, i calibrated them with my "lab unit", and that is a thermopile based LPM that was calibrated with a Coherent commercial unit ..... ofcourse there are always some tolerances, but i suppose they are in the range of the unit itself ..... the main problem is that i don't know any other person around here with another calibrated LPM, so i have to suppose that they are calibrated only compared with the original calibration of the Coherent unit (i always wanted to check myself this thing, but as far as i know, there's no other peoples around here with a calibrated LPM, and shipping around LPMs for cross-calibrations is not the better thing to do, with Italian postal system :p ..... but i'm thinking about a possible system for turn around this, too :eg:)



@EF, well, they was there doing nothing, and i just thoughd they maybe can be more helpful to some other peoples, than sitting here doing nothing ..... also, they are old units, made with TECs as sensors, without any data logging or special functions ..... i can't honestly ask too much for them, i think .....
 

ped

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Im very tempted, even though i have a coherent based meter, i like the look of yours.
 




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