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Power Meter Calibration and Comparison

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While contemplating the varying powers observed by different members of the forum and the varying powers measured by different types of meters for 405nm lasers, I came to an idea of how to reconcile these differences. Everyone that has a meter seems to get self-consistent data from their meter, so the meters in use, on the whole, seem to be precise. But with the wide variation seen diode-to-diode shown by tests done by IgorT, among other tests, says that comparing one person's tests to the tests of others can't be done in order to calibrate the power meters being used. Instead, what we need is a common calibration source. Labs use pre-calibrated light sources to test and adjust photometers and the like, so why can't we do the same thing?

My proposal: We get a common light source of our own and use it to compare and calibrate each other's meters. Our common light source? A single PHR diode, in good condition, in a housing, with a driver. This small item would be fairly inexpensive. Then, Starting with whoever makes the test light source, check the power of the diode with your home meter. Each person wanting to chip in and test their own meter can post that they are interested, and shipping addresses can be communicated via pm or e-mail. Each person pays the shipping to the next person on the list, and everyone interested gets to test their own meter with a common diode, only having to chip in a few bucks for the diode, pay shipping once on a very small package, and add their own batteries. Once everyone has tested their meters, the first person to measure the diode gets it back, and tests it again just to make certain that there has been no change in the diode's output.

An example of how I envision this going: a PHR, an Aixiz, and a Rckstr driver comes up to around $50 (just for round numbers). We get 10 people interested, each sends $5 to one person (possibly whoever has the "best", or most certain to be exactly correct, meter). This person assembles the laser in the Aixiz module, tests it on their meter, and sends it to the next person on the list. It goes around the list, back to the first person, who tests it again, and everyone compares their results. If the 1st test and the last test, both done on the same meter by the same person, match, then we have calibration factors for every meter the diode was tested on, and each person paid $5, a small amount for a battery (a 9V battery is cheap and easy, I figure everyone has one for this quick test), and 1 shipping charge A steal for confirming that you meter is accurately calibrated, if I do say so myself. I'm sure there are some meters on this forum that owners are completely confident of, but I also know there has been quite a bit of uncertainty about some meters.

Maybe even if someone wants to, the person who builds the laser could just foot the bill for the laser by himself/herself, and get to keep it in the end? Ideas? Comments? Suggestions?
 

styropyro

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I think this is a great idea. I don't have a meter, but this could solve the inconsistencies we have been having recently.

We'll have to have some rule about being trusted by the community though, there have been quite a few scammers on here and I could see somebody trying to pull off a free violet laser by saying they want to see how their meter does.
 

jayrob

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Excellent idea! I have an LPM-1, and would love to know comparisons of the same laser on different meters, so I can get a more accurate multiplier for my LPM-1.

DDL tested a blu-ray with his LPM-1 against a thermal meter, and came up with a 2.58 multiplier:
http://www.laserpointerforums.com/forums/YaBB.pl?num=1211579193#3

I have my money ready to send to who ever wants to start. If we get less people interested, just chip in more per person!
Jay

Update: Using my Coherent PowerMax 5200 with Coherent PM3 thermal head for measurements now...
 
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IgorT

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I agree. It's a good idea. I would gladly give one of my diodes for this and put it in a box. But it could take up to two weeks before it would reach the US and start circulating.


Otherwise, i think it would be good to set it to 100mW, cos i've seen some degradation at higher powers. Less than 100mW would obviously be safer, but then the callibration results would not be as precise - the smaller the number, the less obvious the measurement error becomes. To prevent any changes in the output, each person would have to do a certain number of tests, but not play with the laser, and the lens would always have to be covered, when not testing. In fact, i think it would be best, if the lens nut would be glued in place, as a small shift in focus can cause the lens to collect more or less light, and change the results.

Also, if a rkcstr driver and a 9V are used, we'd have to ensure it is actually regulating when the testing is being done. If i have room, i usually put a Low-Bat LED in, that lights up, when the batteries are going low, to warn, that the current will start dropping soon. Otherwise, the measurement can be useless, and it's not immediatelly obvious why.


Other than that, everyone doing the measurement would also have to write down the room temperature, as the power can drop a few mW from a few degrees more. And at 100mW, a few mW means a few percent, and then you're back where you started... Better yet, everyone doing the measurement would have to wait for the ambient temp to be as close as possible to the original measurement temperature.
 

electron

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jayrob said:
Excellent idea! I have an LPM-1, and would love to know comparisons of the same laser on different meters, so I can get a more accurate multiplier for my LPM-1. DDL tested his LPM-1 against a thermal meter, and came up with a 2.58 multiplier:
http://www.laserpointerforums.com/forums/YaBB.pl?num=1211579193#3

I have my money ready to send to who ever wants to start. If we get less people interested, just chip in more per person!
Jay
Hello Jayrob,

I just bought a brand new $3,700.00 Coherent solution and I will be testing it against  the LPM-1 and a few other meters I have, I hopefully should be able to do that project this Sun or Mon; I'd be happy to let you know how the LPM-1 compares.
 

jayrob

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electron said:
[quote author=jayrob link=1217029972/0#2 date=1217033279]Excellent idea! I have an LPM-1, and would love to know comparisons of the same laser on different meters, so I can get a more accurate multiplier for my LPM-1. DDL tested his LPM-1 against a thermal meter, and came up with a 2.58 multiplier:
http://www.laserpointerforums.com/forums/YaBB.pl?num=1211579193#3

I have my money ready to send to who ever wants to start. If we get less people interested, just chip in more per person!
Jay
Hello Jayrob,

I just bought a brand new $3,700.00 Coherent solution and I will be testing it against  the LPM-1 and a few other meters I have, I hopefully should be able to do that project this Sun or Mon; I'd be happy to let you know how the LPM-1 compares.
[/quote]

Excellent! DDL used his LPM-1 set on the 473nm ND filter setting. Using the filter, he found that a 2.58 multiplier was accurate. When you do your test, try to note the 'peak', as well as the 'steady' readings. I notice that the peak reading with my optical meter, is always when I first turn on the laser, which is already pointing at the sensor. I would venture to guess, that with a thermal meter, the peak may be after a few seconds...
Jay
 

electron

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I'll post a graph from the LPM-1 and the Coherent solution, I will let the Laser cool off for 30mins before the next test along with fresh batteries, the room temperature will be controlled at 72F; you'll then be able to compare the Graphs for yourself, I think it's going to be interesting to see how this goes.  It's something I want to do before I sell off any of my "hobby type" meters in favor of the commercial solution.
 

rkcstr

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I have everything (including the driver ;) )... if we want to do this, I can build it.

I also have a 9V switching AC adapter I've been using to power one of mine that I could include as well... it works off of universal voltage (100-240VAC 50/60hz), it would just need an adapter for plugs outside of the US.
 

electron

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Crap! when I first read this thread I had the forum show me the last 40 new posts and I didn't notice or read too closely as I was multitasking at the time; mostly all I saw was "Power Meter Calibration and Comparison" and thought I could help.
But I'm sorry, I don't have a Blue-Ray at this moment to make the comparisons with. I was referring to Green & Red Lasers, I have tons of those and was planning on some tests over the next few days between the meters; my bad I just realized the subject was blu-ray, my apologies; I'd be glad to help if I had one, I do have the proper safety glasses though.  :-/
 

daguin

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electron said:
Crap! when I first read this thread I had the forum show me the last 40 new posts and I didn't notice or read too closely as I was multitasking at the time; mostly all I saw was "Power Meter Calibration and Comparison" and thought I could help.
But I'm sorry, I don't have a Blue-Ray at this moment to make the comparisons with. I was referring to Green & Red Lasers, I have tons of those and was planning on some tests over the next few days between the meters; my bad I just realized the subject was blu-ray, my apologies; I'd be glad to help if I had one, I do have the proper safety glasses though. :-/

You NEED a blu-ray laser, Dude!

Peace,
dave
 

Zom-B

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I think this is a great idea.

I have a thermal meter calibrated with a Nova Alpha125 and verified with a Nova X-105. I have subsequentially extended the meter with a new 200mW range, while trying to keep it calibrated (I think I succeeded).

I would however suggest some changes to the plan. I suggest everyone pays the full price of the laser to whoever he is getting it from, before it is shipped. If there is a greedy participant, he at least paid for what he took. If this happens, we'll have to start over, but with the same people minus the thief. If we then instead of repeating with the same people, start from the next one in the chain that hasn't got it yet, we can rule out remaining thiefs more quickly (as the people who have passed the laser to the next person have proven themselves to be honest (to some extent)). I think this is not a big problem because I think most people here are capable of creating such a calibration reference laser (I can).

I would indeed run it at 100mW because that is the speculated rated CW rate (if it is indeed the Sharp diode). It does not have to be exact, because we are measuring relative intensities and not absolute ones. The focus has to be fixed for sure, as I have seen for myself that small focus changes yield large power differences. I would also have to establish a measurement distance, as the halo of the beam will also feed the sensor. I would suggest a standard distance of 10cm/4in. For the power, I would suggest that everyone uses their own battery, and not ship it with the laser. The total time the laser will be used by all participants will likely drain it prematurely. Also, this way, the responsibility of powering the laser reliably for an equally reliable measure, is for the participant alone.

Furthermore I would suggest everyone who has calibrated his meter, to make or obtain his own reference laser (which is long-term stable), and whenever making new measurements, use this reference laser to obtain a correction ratio (to compensate for fluctuations like temperature) This way, ambient temperature has not to be taken into account at all. (when the reference laser is measured right after the calibration laser (the latter one being the one being shipped to everyone)

Finally, only the person with the most precise meter should publish his measurements so that other people can see what their measurement error was. (Other people are welcome to publlish their results too, of course)
 

jamilm9

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i have a cheap laserbee one that connects to a dmm.Does that count.It said that for 405nm you have to multiply by5.42 when on red setting.
 

rkcstr

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Zom-B said:
For the power, I would suggest that everyone uses their own battery, and not ship it with the laser.
An AC adapter, like I mentioned, would prevent any problems like that... and since it can operate on foreign voltages (with a simple adapter), anyone should be able to use it.

As for the payment each time, that's a reasonable idea to prevent any unscrupulous person from having off with the laser.
 

jayrob

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Kenom

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Ok this is a great idea.  I think it would be very important to note however that each person is going to pay a bit different for shipping.  So I think it would be better if the person recieving the laser pays for shipping.  That way if I have to ship the laser on to someone in slovokia or somewhere expensive, I am not the one that has to fork out the additional funds necessary to ship the laser.  it would make things a bit more difficult but would in my assesment make things a bit more fair.  

Secondly, we need to be cognizant of the possibility of customs confiscating the laser at some point and just like the thief scenario, be out a laser.  I think it would also be a good idea to send along a laser that is on the opposite end of the spectrum.  A stonetek set to precisely the same output would work well.  that way not only are you calibrating and verifying your meter for 405nm but also for 660nm.

As to the adapter rckstr, the easiest thing to do and what I did with my Laser power meters so that my customers didn't have to worry about hooking them up was wire in a universal plug (we've all seen them) I'll picture it below.  It's a basic computer power supply plug and most of us have probably 2-10 of the cords laying around taking up space.  Then all you have to do is enclose your psu into a project box with the plug and everyone can just plug in the cord.  My phihong psu's were universal and worked on 110-240v so there was no button to push or flip. I will donate this plug if you want it.

I think that everyone that is going to be involved in this is going to be pretty honest.  There are pass arounds all the time on CPF and yeah they pay for the laser in advance but in this instance for somthing that is very easily replaced by the forum cooperatively, I don't think we need to worry about theft.  The consequences of being banned and shunned by the community outweighs the profit from the laser.
 

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