Power Meter Calibration and Comparison

[Zom-B]

then mind, that while adjusting, your body heat may get in the way, unless you plan on using long wires between driver and laser :-/

 

[Kenom]

Tuning is a long and lengthy process. (redundant eh!)  Meticulous.  I tweak the resistor, assemble the laser, zero my meter and test the laser output.  Once it's stabilized, I determine if the setting needs to go up or down.  Dissasemble the laser and tweak the pot once more in the desired direction, then repeat.  I continue to repeat this until I get as close as humanly possible over the desired output.  So if I'm shooting for 100mw I will not settle for 98mw.  However 101mw or 104mw is acceptable.  Ulike laser retailers that try for a specified output power and fail, my lasers are always above the specified output. The only time I've ever seen one of mine not be above spec is when the diode has degraded from pushing it too hard. My 300mw Kryton protopye is now around 289mw without having made any changes.

 

[Zom-B]

Wouldn't it be easier to plot a graph, look up the desired current for 100mW, and then set the pot to that current in one go? My experience is that these 3mm pots are so touchy (especially with rckstr and lava drives, because they are not linear and speed up in the high regions), that I have to go back and forth around the same spot because I keep overshooting, because the tiniest single change is already too much for what I want. I can't imagine doing this without direct feedback, but with trials, like you do.

I'm designing a drive right now that will fit aixiz and have a linear pot, and with an option, records ontime. I first went with a modified fusion drive concept (the electronic concept, not the marketing ), but after discussing it and stuff, I decided to go with a miniaturized version of my own precicion voltage to current converter. Parts are ordered and once the design has been tested and fine truned, I may start competing with the other driver suppliers here. (no direct competition though, it has both advantages and disadvantages over other drives, I think it is a welcome addition). My guess is that it'll be ready before this is over.

 

[Kenom]

nah. with each diode being different and needing a different current, it's just as easy to get a desired output as it would require small tweaks to get a desired current as well.

 

[jayrob]

I uploaded readings from my two meters...

pullbangdead, let me know how much I owe you for the shipping and I will PayPal you!

danq, I am shipping with signature confirmation tomorrow. (unless they are closed, then it will be Wednesday) I'm sure it will be around $10 bucks or less. I'll PM you...
Jay

P.S. Ken, I got those exact caps that you showed from Ace Hardware. They were pretty soft and I didn't have to do anything to them. There is however, the 'thick' labels that you must have put on the lasers. But if people are careful, the caps will go over the labels. About half way covering the labels is plenty. The caps don't have to be pushed all the way down...

 

[danq]

gotcha... PM received and reply sent... over 'n out...

 

[Kenom]

Weren't we shipping these insured? I know all of the times I sent them out they were.

 

[jayrob]

Yes, I will be shipping with $200 dollars insurance, plus signature confirmation. Shipping tomorrow, because the Post office is closed today...
Jay

 

[Kenom]

Yeah I was bummed myself I couldn't mail out stuff.  I've got a few drivers and one assembled Krtyon that is going to electron to ship and pulled into the empty parking lot cursing!!!  I appreciate you getting those caps for me jay.  The only reason I sand them inside is so that they go on smooth with the labels as well.  

So now that you've finally seen the Dorcy whatya think??

I'm also curious why pullbanddeads readings aren't on the spreadsheet yet. We need it for SCIENCE MAN!!! lol

 

[hydro]

Jay, on your reading did it hold steady at over 30 sec. or was the total time on was 30 sec.?

 

[jayrob]

Ken, I was surprised at just how small the Dorcy is! Very nice host indeed...

Last communication from pullbangdead, he was very busy. Hopefully he will add his readings to the spreadsheet!




hydro, it was 30 seconds total for each test. I would call it steady... maybe fluctuating one mW or less. I followed the instructions for the 'measurement phase' by Zom-B. (in the spreadsheet: http://spreadsheets.google.com/ccc?key=pW49OuYfRMm7FXsb9trxWdQ&hl=en )

You may have read in my notes what my opinion is, of the LPM-1 with blu-ray's... too much room for error because of not having the 405nm setting built in. That said, it seems very good for the wavelengths that it is calibrated for.

I am very happy to know that my Coherent PM5200 is right in there with the (now solid looking) average!
Jay

 

[IgorT]

I'm a bit concerned about the bluray laser.  Initially I was ok with the reading being 75mw as it was still pretty close to the 100mw target and would still give us a better understanding of the correction factor needed for the optical meters.  However since my initial reading it looks as if the laser has dropped in current or whatever that has resulted in dropping the power.  60mw or slightly above is almost half of what I wanted the laser at.  I'm pretty sure when I get the laser back that my meter will show the same readings that everyone else has gotten (if not then I have some tweaking to do) but I think it is barely sufficient for our needs.  Igort's initial argument was to keep it above 100mw as it was easier to determine meter efficiency over 100mw.  I know that it can still be used but not as efficiently.  Well, needless to say, the experiment is underway and changing the laser would nulify the experiment but after I get it back, I plan on replacing the rckstr driver and pushing it back over 100mw.

I'm just glad that this is finally under way and is moving smoothly.

I kinda almost forgot about the calibration lasers, as i was barelly reading the forum latelly..


Anyway, what worried me when you said that you can't set the laser above 75mW was, that that should be impossible. You put another pot on, and every pot goes to zero, regardless of value. A new pot should not cause this. It was an indication of some kind of a problem somewhere.

It's hard to say what exactly. One possibility would be the driver being out of regulation. That's the first thing that comes to mind. That's why i asked Dave to measure the PSU voltage..

Another possibility would be that something physically changed on the driver, a component moved or something, while replacing the pot.

Yet another possibility would be a blown output capacitor. It would start conducting current and less would go through the diode. The longer it was used, the more it could conduct.


What i'm trying to say is, that there is always a reason for problems like that. If it was impossible to set it higher than 75, the same problem causing this could cause it to drop further, or behave differently in every situation. Even if you find a way to fix it immediatelly, it would be better to find the cause of the problem FIRST. Sometimes you can get the desired result, even when things don't work as they should. That's why it's important to test such setups under different conditions.


A new driver would probably be the best solution. But you have to make sure, that it allows you to set it HIGHER than you want, and stays stable there, before setting it where you want it.


A higher power would give us better precision. However PHRs can and do degrade at as little as 100mW. If everyone only does the required measurements and nothing else, it shouldn't happen during the experiment tho.

 

[IgorT]

You may have read in my notes what my opinion is, of the LPM-1 with blu-ray's... too much room for error because of not having the 405nm setting built in. That said, it seems very good for the wavelengths that it is calibrated for.

I am very happy to know that my Coherent PM5200 is right in there with the (now solid looking) average!
Jay

It wouldn't help Jay.. PHRs vary too much in wavelength. If they were consistent, figuring out a multiplier for them would be easy. But they vary among each other, and then their wavelength drifts with both power and temperature.

Climbak has a $2000 ThorLabs meter with a calibrated 405nm setting, but his PHR measures in way too high, simply because it has a higher wavelength...

It would probably be possible to find a multiplier for 6x's, and it would be somewhat reliable, but for PHRs and even 4x's, optical readings will vary as much as the diodes do.



Kenom: Otherwise, after reading the spreadsheet, i don't think there is a problem with the blu ray drifting. I think you will measure it pretty much where you set it last time...

 

[Kenom]

Kenom: Otherwise, after reading the spreadsheet, i don't think there is a problem with the blu ray drifting. I think you will measure it pretty much where you set it last time...

This causes me a bit of concern then as my reading is higher than everyone elses. I don't know how to explain this as the thermal sensor in my meter is not coated for a specific wavelength I don't think. I think it's just like all the others and has a broadband coating so shouldn't be this far off in only the bluray and not in the red. I've sent a bluray to Electron and his meter read exactly what mine did so I've concluded that my initial readings are not accurate. However it's not only Electron's readings that lead me to believe this. I've shipped other blurays to others with meters and thier meters have always synched with my readings. It can only be concluded that my initial reading was not accurate or the temperature variance during my reading has cause the differential. The only way to find out for sure is wait for it to come back to me and have me do a reading again.

I've had a thought. Before shipping it out of country, we should have it shipped back to me and I can do a midway reading to verify the lasers outputs halfway through the experiment on my meter again. I'll of course pay to have it shipped to me like everyone else. What does everyone else think?

 

[danq]

That's a good idea, let's do it.

I just received the kit from Jay - nice lasers, Kenom!

I may not get to do my testing until the weekend, as I'm supposed to be leaving town for 2 days within the next few hours... but will do it as soon as I get back.

DanQ

 

[danq]

hey - looking at the data, Kenom's ambient temp was 4 degrees higher than most of the others - 80 degF vs. 75/76 degF

could that have made such a big difference??

my initial rough test shows similar to the others: generally lower than the standard.

DanQ