My primary personal meter uses a surplus Coherent thermopile, which turned out to be VERY accurate (i was lucky with the board i got!), only showing 1.96% too much, so i set the gain to 980.4 and now it's as accurate as it gets.
Brtaman's meter uses a Peltier "in reverse", thermal epoxied to a heatsink and coated, just like the LaserBee, yes, but possibly with a different coating (i don't know the coatting used on the LaserBee).. I call it a "Peltipile".. (- it was sold to me as a "thermopile", and when i finally saw what it really is, i started mocking the seller a little (since he did trick me), by calling it a peltiplie, and later it just kinda stuck)
On one hand, both a thermopile and a Peltier work on the same basic principle (the Peltier/Siebeck effect), but in the opposite way from each other, each optimised for a specific purpose. A Peltier for PUMPING heat, a thermopile for DETECTING it...
So while you can use a Peltier for heat detection, it will be a little slower in response, and less sensitive. But that also makes the reading more stable, by averaging it out a bit. Luckily a Peltier in reverse works better than a thermopile in reverse would (for pumping heat).. ;D
The secret of a good "Peltipile", is of course in the coating. I use a special coating, which only has +/-0.5% error over the visible spectrum! If it is set in the middle (to be spot on at 532nm), it will show 0.5% too much at 405nm (405nm absorbs a bit better) and 0.5% too little at 660nm. In practical terms, that's an error hardly worth mentioning. (Quite a few DIY meters are up to 7% off, some even more. And even that usually doesn't bother anyone too much.)
So if the meter is perfectly callibrated, the accuracy of a Peltipile meter could be as good as +/- 1.5%! But you would need a perfect calibration reference for that and a perfect calibration laser (with APC and constant temperature TEC thermal regulation for CONSTANT power). The calibration itself takes a lot of time without the special laser. And the accuracy will be as good as the accuracy of the reference, at best - if you do everything just right, or it could be slightly off, if you don't...
But if you have both a good coating, and a good calibration reference and special calibration lasers, the Peltier approach could yield surprisingly good results! Officially however, i won't claim more than +/-3% accuracy. But then again, that is the accuracy of many professional meters.
The only drawback is that PeltiPiles take longer to "climb" to the laser's full power on the display. But at the same time, they fluctuate MUCH less for the same reason. That actually makes them more stable (the slowness of the response averages the result out a little).... If there was a way to create a coating as good as the ones on real thermopiles, they would be just as accurate, only slower...
Anyway, the sensors my meters use...
I made two Coherent Thermopile meters so far, a third is in the making:
- One of them i made for a guy from Taiwan.
- The other is my main meter of course (that was my first meter).
- The handheld will also use a Coherent thermopile, it's my last one, it's also VERY accurate, currently at -1%! I can set the gain to 1010 and it will be "spot on". I am not selling that, i want to keep my last thermopile!
"Peltipile" meters i made:
- Brtaman's meter uses a Peltier on a heatsink with the special coating.
- My secondary meter also uses the same thing - Peltier in reverse on a heatsink....
- Jake's meter will use a Peltipile too...
You want to make your own? Do you know (want to know?) how to make a proper amplifier circuit?
A high precision PeltiPile amplifier is actually quite simple and easy to make, if you're used to "wire-wrapping" circuits together, or if you can etch it.
The circuits required for real thermopiles are much more complicated, if they are to be just as accurate. For example, my main meter now uses a high precision triple op-amp circuit, to eliminate certain errors present in the single op-amp design. Before that it had a single op-amp amplifier, which is now in Brtaman's meter... But since Brtaman's meter uses a "Peltipile", the single op-amp circuit classifies as "high precision" in that application.
This comes from the differences between how a thermopile and a PeltiPile work. But i won't go into details here..
In any case, i have the amplifier circuit schematics, optimised for "Peltipiles", if you want to make your own.... Other than that, you just need a tiny peltier and a good way to coat it.
No, i'm not gonna make any cheap ones anymore, it's just too much work, to be worth doing it cheap.. And the price that would be worth it to me, might be too high in other people's oppinion... If i sell anything, it will be my secondary meter in the white enclosure, with or without the computer interface...
I am making a "naked" meter for Jake, he will have to mount it in a box himself, so i don't have to do the hard part (electronics are the easy part, because i'm used to it....).
After that and my secondary meter, i don't know if i'll have any more. But the second white meter will most likelly be for sale.
It won't be ready in time for your reviews, i'm afraid. I'm way too busy, and the meter still needs some finishing touches.
Like the range switch switches the rage but doesn't move the dot on the LCD yet, have to add that. The low-battery LED is there, but not activated yet, need to do that too. Then there's the question of the computer interface....
Wow Traveller, you practicing necromany? Talk about bringing a thread back from the dead. :beer: :crackup:
The meter still works as great as the day I go it, though unfortunately it is more or less gathering dust nowadays. A couple of months ago I got into tesla coils, high voltage and power electronics. The new hobby has been eating away at what little time/$$ I actually have for myself.
I test red diodes I find in burners from time to time just to "blueprint" them, that's about it.
I would check paypal history normally, but I paid with bank transfer, it was much easier for me and him since we live 100km apart. In Slovenia, you cannot link a bank account to a paypal account, so paypal money is basically just virtual money to be spent on hobbies.
I do remember he gave me a great deal on it for waiting so long for it, TBH I think I just covered the expenses of the parts, he got practically nothing for the time he put into it.:yabbem: Great dude.
If ballpark is ok, I think it was in the ballpark area of yours and Kenoms LPM's, but take that with a grain of salt.
Of course, now it has become a priceless collectors item of epic proportions.