Proper way to use a LPM to do a Power Test

[DTR]

Due to a recent product review on an engraver head that the reviewer could not get to cut and engrave different materials at the rates advertised. I think there was an issue with the lens being contaminated during the testing but the reviewer did correctly call out an overstated power rating due to improper testing, and during the tear down revealed use of a DC-DC voltage regulator not a constant current laser driver which will severely affect the long term reliability of the product. These are produced with the NUBM44-V2 7W diodes in modules I supply but this company even without my endorsement were calling them 8W/10W/12W.

LPM testing that does not give any useful info and even can be deceptive is something I am seeing more and more which Is one of the first things I want to address since I have been dragged into this.

So hopefully to give understanding on from a buyers perspective on what to need to see before buying a laser and for sellers how to do the proper testing for full disclosure to their customers.

Hopefully this will start to cut though some of the confusing misconceptions that the many many followers of both parties were throwing out there. For the reviewer on Youtube subscribers and for the company on their own forum hosted on their website. The real issue was the original knee jerk reaction of the company(which it was a pretty devastating review) as the way he responded to the review which was very aggressive to say the least and caused a lot of twitter.

Also as far as I know the high power MM display diodes are not designed to be pushed very high running in pulsed mode but see a lot of these 12W/15W ect... being explained by running them in pulsed mode. If not designed for it even though you can do it does not mean it won't cause failure. Maybe the AR coating on the window can't handle it and burns up and that is just an example which there are many others. Bond wires might not be able to handle it, Could deweld the wires or even the dye, the cavity could receive great shock damage ect....

To start here is the correct way to do a power test of finished laser. A picture is useless and more likely can be used to deceive and a test video where you just get to the peak and turn it off also is not very useful unless you are saying ti can only run that long before you have to turn it off to cool the laser. Here is an example of worthless as I can make a NUBM44-V2 show 9W real for a spit second so the way tests are done now this is a 9W laser.




1. A proper test should be for the duration of the duty cycle if one is being stated to show that the laser can do what is claimed and the power that is being held. If offered with a claim of continuous operation then the test should be at least from power up to the point where the unit stabilizes. The rated power of the laser can be figured based on the average over this run.

2. The laser should not be close enough to the meters sensor that there is heat radiation from the laser interfering with the optical readings. Usually 4-6 inches between the two should be enough.



Here are some examples of the proper way to power test on a LPM. There are a lot of mist calibrated LPM's out there but even more important than than the max is the stability of the laser which even a out of calibration LPM will show. Or if the laser is not holding constant current and the readings don't slowly fall but go up as it runs this is a sign of a constant voltage power source which will cause significant reliability issues.

If you are not showing the stability of the laser under normal operating conditions then it is a waste of effort.

 

[BowtieGuy]

Very informative post, DTR; this should be stickied for sure.

Your #2 point has always been a pet peeve of mine, so many people put their laser right up to the LPM sensor and then make mistaken claims on the max. output of their lasers.
Hopefully this correct procedure coming from you will convince the guys to meter their units properly.

 

[DTR]

Very informative post, DTR; this should be stickied for sure.

Your #2 point has always been a pet peeve of mine, so many people put their laser right up to the LPM sensor and then make mistaken claims on the max. output of their lasers.
Hopefully this correct procedure coming from you will convince the guys to meter their units properly.

Yep I could probably go back and find the old timers giving me the same lectures as I loved nice peak readings when I was a new and gung ho for more power and staying on the top of that 445 chart. Can still hear Laserbee correcting me on the distance from the sensor. It may have felt like he was raining on my parade when correcting me in "my own thread" but in the end he was dead on.

 

[GSS]

Are these 2W tests done with the lasers out of a tight focus?

 

[paul1598419]

I usually only tested my lasers for 60 to 90 seconds as that was the limit I would normally have them on. Unless they were lab lasers and on for much longer times, I never tested past these times. I have an M140 that does 2210 mW in an MS Envy host, but I never had it on more than 90 seconds at a time. It was the highest power one that I ever got out of over a dozen builds.

 

[DTR]

Are these 2W tests done with the lasers out of a tight focus?

Here is an old pic I used to use to explain best how to not burn your sensor and collect the most power by going past collimation.

I usually only tested my lasers for 60 to 90 seconds as that was the limit I would normally have them on. Unless they were lab lasers and on for much longer times, I never tested past these times. I have an M140 that does 2210 mW in an MS Envy host, but I never had it on more than 90 seconds at a time. It was the highest power one that I ever got out of over a dozen builds.

Hell 30 seconds would be a huge improvement over just a pic. If your units is still running pretty stable at 90 seconds sure you can probably stop there and still figure where it would go from there. Two of the biggest things you want to look for is a peak and a mass drop or like most the units above like the sirus units which had flawed drivers and instead of a nice soft drop they are increasing in power meaning the driver is not maintaining constant current. Sent that siruis to Brazil and the buyer did a test video right when they got it but they had about a 15 degree temp ambient difference since she did not use AC and it was hot there. Will try to see if I still have the video but it just ran away starting much high than my cooler test and blew. That guy made some amazing hosts but his driver design just was terrible.

 

[GSS]

Thx , iv'e been going on a power metering spree on all my units since Rich gave me a LPM..
Only the units I have that are lower than 100mw iv'e been metering at full tight focus..

 

[paul1598419]

Here is an old pic I used to use to explain best how to not burn your sensor and collect the most power by going past collimation.






Hell 30 seconds would be a huge improvement over just a pic. If your units is still running pretty stable at 90 seconds sure you can probably stop there and still figure where it would go from there. Two of the biggest things you want to look for is a peak and a mass drop or like most the units above like the sirus units which had flawed drivers and instead of a nice soft drop they are increasing in power meaning the driver is not maintaining constant current. Sent that siruis to Brazil and the buyer did a test video right when they got it but they had about a 15 degree temp ambient difference since she did not use AC and it was hot there. Will try to see if I still have the video but it just ran away starting much high than my cooler test and blew. That guy made some amazing hosts but his driver design just was terrible.

I was wondering why the Sirus lasers were continuing to increase in power the longer they were on. A bad driver design makes the most sense. They were a very pretty host, but with that driver, not worth having, IMHO. I guess I would have just removed the driver and replaced it with one of lazeerer's.

 

[DTR]

I was wondering why the Sirus lasers were continuing to increase in power the longer they were on. A bad driver design makes the most sense. They were a very pretty host, but with that driver, not worth having, IMHO. I guess I would have just removed the driver and replaced it with one of lazeerer's.

Yes, ended up rebuilding every unit that I had used that driver with. There is one build test above that used the old 1.25A Mohberg linear which also had issues holding a constant current. The driver was designed properly but the current set resistors that were underrated for the current they needed to handle which caused a little thermal runaway current rise situation. You had to sink them directly which can be tricky as to not short them out but when done they would settler. Later revisions changed them out for higher current rated ones which fixed the issue.

 

[CDBEAM777]

Thanx Jordan/BTG/GSS/Paul !! Oh yea...there are ways to....er…..ah....Skew the truth !! Put the unit in the freezer for an hour, pull it out, Take a 15 second reading.... There ya go ya go...Oh....and get that diode about 5mm from the LPM sensor !!….Sigh !!
SO....as with many industries/disciplines...there are Standard Test procedures....Perhaps such standards exist....in the Professional Laser arena.....Dunno, Will research.

CDBEAM