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FrozenGate by Avery

Power Meter Calibration and Comparison

IgorT said:
If both lasers are set to 100mW, the red will actually dissipate less heat, than the blu ray.

For the blu ray at 100mW, it's 0.575W, and for the red, it's around 0.36-0.4W of heat.. Hardly worth mentioning.
Or is the red gonna be set to 200mW? Also, both lasers should be set to 100mW by the same person on the same meter. Otherwise the results won't be usefull.
Click to expand...


I was thinking that, using the FlexDrives, just set the current on the lasers. Not trying to set the power.

Set the 803T blu-ray at 100mA's. And set the Sony/Senkat build at 250mA's. If you guys wanted me to do the red build, I would send the laser to Kenom, and he could easily check that the FlexDrive was set at 250mA's.

I mean, we're going to get lots of different power readings, so why not start with a nice commonly known current setting?

Just a suggestion...
Jay
 





It would be easiest if both lasers are set to show the exact same power on the most precise meter.
And if this power is 100mW, any discrepancies would be immediatelly noticable, and obvious.

Of course, the calculation can be done regardless of what power the lasers are set to. It would just be easier this way.
Also, if both lasers are at the same power, it is also immediatelly noticable, if the coating isn't spectrally flat. This is important for thermopile meters. Again, it can be calculated regardles of the actual power of course.



The current a laser is set to is completelly meaningless here tho. If you include current in the calculation, you are making assumptions about what the power should be at that current. Even if the lasers are set to different powers, current has to be ignored completelly for this experiment to work. (except for making sure it is being regulated and the same every time)


If a laser is set to a higher power, the calculation would be more precise. But it would also warm up faster. And then we would have a different precision for reds and for blu rays....
 
On the other hand, exactly 100mW could also be misleading, if someone got 94, and thought they have to add 6%, or 110, and take 10% away..

Whatever the powers, everyone will have to follow the formula preciselly.


It would make sense to set the lasers as high as possible, for beter precision, but not so high, that one could die in the middle. For the same reason, the amount of use should be limited to the measurements. People who don't yet have a blu ray would want to play with it..  :-/ Having a blu ray of your own should be one of the conditions for joining, i think..
 
Just my opinion, but it seems to me that, using FlexDrives (the most efficient drivers we know of for DIY), we should set them at the agreed upon current, like 100mA's for the blu-ray & 250mA's for the Senkat red - (and nobody should adjust the current, or even test the current - because testing the current could lead to accidents, like killing a diode) We can just make our power reading comparisons. We should be able to get a pretty good idea of what the average power is.
That's one suggestion...
Jay
 
is this only usa or is it canada to because dr.lava is close to canada i think.
 
i just ordered 21 blu-ray diodes recently (15 kes-400's and 6 803's)
now im looking for a good laser meter... thats what u guys are doing? trying to find out what meters are reliable?
the only one i found recently that looks like it might be good is the laserbee on ebay. i missed out on the kenometers :(

has anyone tested those laserbee's against a known accurate meter?
 
Kind of what the idea is. A lot of the meters around don't have a setting for 405nm light, and you have to use a setting for a different wavelength and use a calibration factor to calculate the power of the 405. To find the calibration factor is well, pretty close to a crap shoot unless you have a way to calibrate it, with a known light source. With tests like IgorT's, we have shown that all 405nm diodes are NOT created equal, therefore the way to have a known 405nm lightsource is to use the same diode, since the diodes can vary so much from one to another. This way, instead of comparing "my diode and my meter" to "your diode and your meter", since the diodes can vary, it's "our meters and THIS diode", and it takes out that variable.

So, that calibration factor, and the fact that even without such a thing, people have seen quite large differences in the readings with their meters, such as people who bought completed lasers from IgorT and measured a different amount than he did. These are just examples, but the overall idea is that the meters in use are not coming up with the same results, and we want to correct that so that everyone has the same results, and hopefully accurate results.

Evaluations of which meters are best could very well be a result of this, though, as I think most people plan on doing multiple measurements, and they can therefore find the standard deviation of their meter, theoretically.
 
jayrob said:
(and nobody should adjust the current, or even test the current - because testing the current could lead to accidents, like killing a diode)
Click to expand...

Oh absolutelly. I did not suggest anyone change or measure the current, except for the person, who sets it.

I just said, that other than making sure it is always in regulation we have to ignore the current in the results. And by making sure i meant that the design should make sure of the current not being able to change, not that people should test it or adjust it. The LavaDrive would make sure the current is always the same, if it is used with protected Li-Ions.

Fiddling with the lasers should definitelly be limited to the absolute minimum. Dissasembly should not be attempted by anyone. Even the focus shouldnt be messed with. Never mind the current. It would render the results useless.



But 100mA would be too little for the blu ray, as then the precision would be less than 1%. The blu ray should be set to whatever current is necessary to get 100mW, or a little more.

I would imagine, that we want the highest resolution with the blu ray. Unfortunatelly, that is not possible safelly, as it can not be set higher, than the red, without the risk of dropping in power or even dying. But if the blu is set to 100mA and the red to 250, we will have ~1.25% resolution for the blu and ~0.66% resolution for the red (depending on individual diode efficiency). The blu measurements would have half the resolution of the red measurements.

Having a higher resolution with red might not be a problem. But we should definitelly try for a 1% resolution with the blu, as there will be enough other factors, that will reduce the precision anyway.
 
::slightly confused::

You're saying 1.25% resolution, is that based on having 1mW resolution with an 80mW laser? So your meter measures to within 1 mW of power?

Does this match everyone elses level of significant figures reported on their meters? Also, how repeatable are the results on all the meters being looked at here? ie when retest the same diode lots of times, how repeatable are the numbers? (Good, simple statistical way to report this is the % standard deviation: take the mean of the set, take the standard deviation of the set, and report the percentage of the mean that the standard deviation is, ie mean is 100, standard deviation is 5, % standard deviation is 5%)
 
I'm talking about resolution of a measurement in percentage, not precision.. The higher the resolution, the more precise our results will be. There will inevitably be errors, but low resolution would only increase them.

So yeah, the ~1.25% was based on ~80mW measured with a 1mW resolution meter. My meter measures to 0.1mW, but i don't use the fractional digit. I still like having it for more precise zeroing in, and to see for example, if a power is closer to a higher or a lower number.. You can probably imagine, that it fluctuates a lot, but i can usually get it quite stable. Especially if i use a tube on my meter.... But i still consider the resolution to be 1mW.

Many thermal meters, will have a 1mW resolution, which is 1% if we use a 100mW laser and 1.25%, if we use an 80mW laser. And a smaller percentage will give better results.


Otherwise my meter shows the same numbers as two thermal sensors Daedal callibrated for me. But Scopeguy's meter shows 7% more on two blu rays, so i have no idea about the accuracy.

But i am not as interested in absolute accuracy, as i am in us being able to compare our findings.. At the moment we don't know if it's 4% off or 20% off. I would be happy with an average between all meters, but if one or two of them are proffesional high accuracy meter, so much better! Then we could take the average between the best meters for a baseline.
 
Yes, I was just making sure I understood your resolution amount. It's always nice when people speak the same language (in my experience, most people wouldn't understand the differences between accuracy and precision, and between precision and resolution, but luckily "most people" here aren't the same "most people" from everywhere else). And I'll agree that dropping the last digit from pretty much any read-out is generally the best practice, as I've learned through my schooling.

I'm in agreement with you about all the goals here, as well. Getting all the meters on here to match, and *hopefully* getting them all accurate. I don't think, by doing this, we'll ever by able to get it tot he point of every person being able to say that their meter is completely accurate in whatever setting they're using it in. But, I THINK we can get to to where every person can accurately say what any given laser would put out in a certain environment (ie, the environment that the test laser was in when measured on the most accurate, reference meter). If we can get a high quality professional measurement, then we have that reference. If not, then all the ones on here will at least match.
 
Jayrob: How long does the power remain stable (as in, doesn't drop from the original number by 1mW) with a red at 250mA, and one of your massive heatsinks?

If it can keep the "exact" same power for over a minute, and we follow the suggested protocol with short measurements, the increased resolution could be beneficial.
 
pullbangdead said:
Yes, I was just making sure I understood your resolution amount.
Click to expand...

Hehe, yeah, i have to think and write in another language, and sometimes i don't find the right words.. So "percentage resolution" may sound funny, especially since the resolution of the meter is something else, but you know what i mean - the higher the power of the lasers, the better the precision of the measurements will be. ;)
 
OK, I want to play too. I have a Scientech 365 but I have a question about the testing duration time. I know for Scientech there is a time constant for measurement, for example 4 sec. with a 1" surface absorbing calorimeter and 5 to 6 sec. with a 1" volume absorbing calorimeter. I have a 2" ultra absorbing calorimeter but I don’t know what the time constant should be, any one knows? I bring this up because not all of us have the same meter so do we need a test duration time?

Now regarding the list order, wouldn't it be faster if we find out where each person is i.e. state and city that way it can shipped in an orderly manner rather than one cost to the other? I'm in Sothern California, Alhambra close to "daguin".
 
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