Power Meter Calibration and Comparison

rectumfire  ;D

I was thinking of having it hard wired to the drivers. So you plug it in, and then just flip whichever switch you want, with everything completely contained in the box with the exception of the power cord itself  

Oh and the hand thing, I was referring more to the hand temperature effecting the thermal sensor. Also I think the remote switches were also an idea to prevent movement of the whole unit when turning it on and off.

GooeyGus said:

Oh and the hand thing, I was referring more to the hand temperature effecting the thermal sensor. Also I think the remote switches were also an idea to prevent movement of the whole unit when turning it on and off.

Click to expand...

I see. Maybe we can just trust the tester to move his/her hot hand away from the box after turning it on?
Movement of the box will cease pretty quickly too - and would be negligible anyway imo.

GooeyGus said:

rectumfire  ;D

I was thinking of having it hard wired to the drivers. So you plug it in, and then just flip whichever switch you want, with everything completely contained in the box with the exception of the power cord itself

Click to expand...

yah, gud...
but watch out, that wall-wart is heavy and it may be swinging on a thin cord (the DC side), someone may dis-con it without benefit of unplugging. I'd suggest putting all but the AC cord in the box... that makes packing/shipping easier too.

If you do go with the wart outside, consider extending the DC cord so it can plug in a distance from the laser test site. Like about 8-10 feet?

rectumfire? roflmao

danq said:

[quote author=GooeyGus link=1217029972/140#144 date=1217497787]Oh and the hand thing, I was referring more to the hand temperature effecting the thermal sensor. Also I think the remote switches were also an idea to prevent movement of the whole unit when turning it on and off.

Click to expand...

I see. Maybe we can just trust the tester to move his/her hot hand away from the box after turning it on?
Movement of the box will cease pretty quickly too - and would be negligible anyway imo.[/quote]
Not only for vibrations, but also for displacement (dot should hit the same spot during each and every measurement

danq said:

[quote author=GooeyGus link=1217029972/140#144 date=1217497787]rectumfire ;D

I was thinking of having it hard wired to the drivers. So you plug it in, and then just flip whichever switch you want, with everything completely contained in the box with the exception of the power cord itself

Click to expand...

yah, gud...
but watch out, that wall-wart is heavy and it may be swinging on a thin cord (the DC side), someone may dis-con it without benefit of unplugging. I'd suggest putting all but the AC cord in the box... that makes packing/shipping easier too.

If you do go with the wart outside, consider extending the DC cord so it can plug in a distance from the laser test site. Like about 8-10 feet?[/quote]
Did you take into account the different voltages (100v/120v/230v/240v)? Harvesting a universal adapter is plausible, but using a cannibalized transformer NOT.

Y'all will NEVER remove all of the extraneous and confounding variables. Even the BEST LPM's get no better than +-3% when measuring against themselves. This is a "pass around." As soon as they leave Kenom's house, true "control" is lost.

Set it up
Send it around
Everybody promise not to screw with it
Record whatever is found at each stop

AFTER the "data" is collected, we can decide if it has any real value to us. We have enough stops to get an idea where we stand and what potential problems there were with the experiment. Does it really matter if the unit is 130mW or only 127mW; run at 73f vs. 78f; in a box vs. a tube? No. We will understand the variability between our different LPMs and MAYBE come up with a reliable conversion number for the optic sensors.

K.I.S.S.

Peace,
dave

GooeyGus said:

Oh and the hand thing, I was referring more to the hand temperature effecting the thermal sensor. Also I think the remote switches were also an idea to prevent movement of the whole unit when turning it on and off.

Click to expand...

Yeah, the idea was to eliminate the hand from the measurement, to eliminate shaking of the laser at power up and to get the exact same aim every time. All this could be achieved with a remote switch. It would result in higher consistency on the same meter, and and more precise zeroing in.

The aim definitelly matters. Maybe not as much on thermal meters.. I can get my 6x to show between 174 and 178mW depending on the aim (most of the center shows 174mW). The edges of the sensor are no good.  Jayrob mentioned he can make a red go from 250 to 270mW or so..  If a laser is 250mW, 270 will give the wrong correction factor - 8% too high.

Most people know their meter well enough by now, and know about these quirks and how to elliminate or reduce them.
But making it simple would still help reduce measurement errors further, and with everyone, regardless of their experience..

I have to zero in my meter while holding a powered down laser in front of it with my hand. As i move my other hand there, to zero it in, the reading changes, and the zero is only correct for both hands there. When i then remove the other hand, the zeroing can be off again. Then, after i get a reading, i have to power the laser down, to make sure it goes to zero again. But if i'm holding it with a hand it might not end at zero. So if i want to get a good reading, i often have to repeat it several times.

This only matters for thermal sensors of course. But the "aim" or shaking matter for all of them obviously. A remote switch would make getting precise results simple and faster.

You can achieve the same results with a pointer of course, but then the testing procedure itself is going to require more precision. If it's gonna be a pointer, then i'm just gonna use a tripod i guess.




I also noticed a belief, that the LavaDrive keeps a more constant current than a rkcstr driver. That's simply not true. If you give Rkcstr's driver the voltage it needs, the current will be just as constant as with a LavaDrive. And if you don't give the LavaDrive the voltage it needs, the current will drop faster or become more unstable, than with a linear driver under the same conditions.. Every constant current driver will keep the current constant, as long as you give it what it needs.

The only reason the LavaDrive doesn't usually drop out of regulation, is that people mostly use protected batteries with it. Protected batteries cut off before the voltage get's close to the minimum. And two 3V Li-Ions with a series diode are at the upper edge of what the lavadrive can take, so it would take very long for it to drop out of regulation. On the other hand, people try to drive PHRs with rkcsrt's driver from two Li-Ions at a very high current. But for a high current, a PHR can require almost 6V. The driver itself needs 2.25V, so the absolute minimum for regulation is 8.25V, to be sure it is working right. If you give it two Li-Ions, of course it won't regulate the current.

The only thing, that should be done differently is, that if rkcstr's driver was used, it should be kept away from the diode, and connected to it through wires, so as not to affect it with heat.



I don't care what driver get's used, as long as current regulation at all times is ensured by design. And yes, there will be errors by default. But we don't have to increase them by default.

In the end, whatever comes out of it will be better, than nothing. But how much better depends on how it's done.


Still, i'll be happy if i can finally compare my findings to other people's results and hopefully draw some conclusions.

Well, seeing how ideas are making their rounds again... I have a 9VDC wall adapater, universal voltage, could be adapted to accept an international IEC cord simply. This could then easily power a linear driver. Also, I could pretty quickly and simply make up a small "driver module" that could be remotely connected to a diode, be fully heatsinked, etc, sort of like the lab-style drivers. I thought about using one of those heatsinks from the red lab-style lasers they sell on DX as they're nice a big, but if anyone had one of those lying around, it would probably be simple enough to swap the diode and use a new driver.

Again, just throwing around ideas. I'm perfectly fine with using one of Kenom's builds as I'd actually like to see one in person ;D

Hehe, i wouldn't mind seeing his pointer build myself.

I just hope that preciselly this doesn't become one of the problems, when someone puts it in their pocket for two days and take it to school, or something. That would be the WORST thing that could happen. Especially if they then tried to demonstrate burning, and change the focus, only to later glue it back, hoping no one will notice..

This is why i said a while ago, that having both types of lasers should be one of the requirements for joining this experiment. And even in this case someone might have a box, and then they would suddenly hold a pretty pointer. It could be hard to resist the temptation.

Kenom said:

Unclear on Hydro, pullbanghead, and electron's involvement or not.

Click to expand...

I think pullbanghead should definitelly be involved. And not just because it was his idea. He doesn't have a meter of his own, but he does have access to probably some of the most accurate meters on the planet in his university lab.

If he can arrange to measure the two lasers there, the numbers would be of a great importance for this experiment, as they would provide a good baseline, i think.

daguin said:

Y'all will NEVER remove all of the extraneous and confounding variables.  Even the BEST LPM's get no better than +-3% when measuring against themselves.   This is a "pass around."  As soon as they leave Kenom's house, true "control" is lost.

Set it up
Send it around
Everybody promise not to screw with it
Record whatever is found at each stop

AFTER the "data" is collected, we can decide if it has any real value to us.  We have enough stops to get an idea where we stand and what potential problems there were with the experiment.  Does it really matter if the unit is 130mW or only 127mW; run at 73f vs. 78f;  in a box vs. a tube?  No.  We will understand the variability between our different LPMs and MAYBE come up with a reliable conversion number for the optic sensors.

Click to expand...

I agree... If you have used the FlexDrive, you know that it is very efficient. And that it will not be out of adjustment, unless someone messes with it...
Jay

I was going to include the tripod I mentioned earlier so movement wasn't going to be an issue.  The thing folds up to be not much larger than the dorcy itself and is universal.  It will hold the laser and since it's a constant on clicky, the only thing you need worry about is getting it on your sensor in the place you need and moving your hand away.  

I truly have no objection to doing a box and setting it up that way with whatever driver and whatever power source.  The big problem I see in doing so is heatsinking of the module itself.  you CANNOT drive either of these lasers in a blank module without some heat accumulation and potentially skewing readings.  Now albiet this has less of a chance of skewing the readings than a stable current source in the laser, but I'm pretty confident (99%) that if you use a new CR123 it won't even be an issue with the flexdrive.  

I agree with IgorT that we need to make sure that the laser is not messed with other than for measuring purposes.  Once I glue that lens in place, it WILL NOT move without seriously messing up the threads, and the top of the lens.  We'll know if the focus has been messed with.  My lasers also come with a dust cover that goes over the top of the pointer if you notice in this picture here.

so dust accumulating on the lens will also not be an issue.

We can back and forth all month on what would be the ultimate setup.  I will agree that the constant source of a psu as apposed to a set or single battery would be better.  but I also like the portability of a pointer in not having yet another cord in (can't speak for everyone) my already cord cluttered workspace.  We need to decide once and for all what is going to get built and build it.  If we wait much longer I'll throw the doggone lasers in a Kryton groove (way more stable heatwise) and ship that. *(also with the tripod.)

I would be voting for a laser with power cord. Even I have a chronical power cord clutted workspace, but because of that I know which cord I can plug out temporarily for other mains powered stuff I'm working with/on. I also think this is going to discourage people to take it outside, shining it at remote churches and the like.

I still would like to know how this all pans out, so I guess I'm in

Kenom said:

I was going to include the tripod I mentioned earlier so movement wasn't going to be an issue.  The thing folds up to be not much larger than the dorcy itself and is universal.  It will hold the laser and since it's a constant on clicky, the only thing you need worry about is getting it on your sensor in the place you need and moving your hand away.  

Click to expand...

Great! A tripod would definitelly reduce any errors created by aim or shaking.. The hand will have to be removed when zeroing in and after powering down, to see if the meter returns to zero.

I just got these tripods and clamps today, and they are quite nice. Not perfect quality, but good enough to remove much of the human error while meauring.


If this laser is used, you might also want to seal the threads, where the host comes appart, maybe with some kind of colored hard paint around the edges, which would break if opened and make it obvious, it was messed with..



Otherwise, one of GG's arguments for a box was better potential heatsinking, definitelly not a blank module.. But if they are not set too high, that won't be a problem in this setup either..

About the batteries, if people use protected rechargeable CR123s, the driver would not be able to drop out of regulation, as it needs 2.5-5.5V while the battery cuts off at 2.75V.

If primaries are used, the usefull battery voltage range is reduced drastically - only from 3V down to 2.5V. Even if a battery measures at 3V, the current draw can cause it to sag this much, especially since the driver needs more and more current as the voltage goes lower.
On a switching driver, when the input voltage becomes too low, the regulator can start "struggling", the noise and current ripple increase, and the current starts dropping. At a certain point the laser can even start blinking, but by then the current is already reduced by 10-20%. A protected rechargeable would not allow this to happen. The current would vary less than 1mA.

much as I would like to see Kenom's builds, I think the plug-in box idea is better, for reasons already stated by others:

• no battery issues - low voltage, wrong type, in backwards...
• no taking anything apart (to replace batteries)
• less likely to be lost or stolen
• no extra parts (tripod, remote sw) needed
• easily sealed... maybe even have a key lock? (not a flappy padlock, but like on a computer case)
• may be easier to get past customs? it's 'test equipment' not 'lasers'
• less likely to be taken outside for a walk in the rain ;-)

danq said:

[*]no extra parts (tripod, remote sw) needed[*]

Click to expand...

Actually, a remote switch was meant as one of the benefits of a box. By a remote switch i meant simply a switch on an ~0.5m cable. Either on the power supply cable, or on another cable, meant only for this, to elliminate the possibility of metering your hand or shaking or changing the aim at power ON/OFF.