Anything Wrong With This LPM?

[HighPowerObsession]

Hey so before you tell me I'm posting in the wrong section, I know. This belongs in the lasers measurements section, but there's hardly anyone viewing that section so I thought I would post here where there are 2,000+ people viewing.

Anyway, I found this LPM on Ebay that can measure up to 10W continuously and up to 20W for <5 minutes. It also reads down to the .01W (10mW) which is a huge plus over the 30W continuous/60W for <5 minute LMP he sells that only reads down to .1W (100mW).

So my questions: Is there anything I should be worried about with an LMP this cheap? I was literally on the verge of buying the LaserBee 5.2W for $250 and then I found this 30W/60W one for $325. I only ask because this seems suspiciously cheap especially when compared to the professional LMPs that measure up to 10W but cost $1,000+.

 

[Euphonious Nonsense]

http://laserpointerforums.com/f51/lpm-availability-socal-99027.html

that thread has your answer.

 

[HighPowerObsession]

Is this listing a Hyperion?? And this listing doesn't have the resolution problem as is reads down to .01W.

 

[Euphonious Nonsense]

I don't mind trying to help but did you read the post? It's literally the same LPM/seller as the one you posted.

Yea, that .1 watt resolution isn't so great when using low power pointers where you want a more accurate reading...

 

[HighPowerObsession]

??? Yes I read the entire thread....did you read mine? I have said twice now that the LMP that I'm talking about reads down to .01W (all the accuracy I need and pretty much anyone else would need).

 

[Euphonious Nonsense]

So i guess if you aren't working with low power pointers it probably will be fine for you

 

[HighPowerObsession]

Ok first of all I posted this thread asking if there is anything to be worried about with this LPM (in terms of quality, accuracy, life expectancy, etc). I also stated in the original thread that it reads down to .01mW which is perfect for the testing I will be doing hence the resolution isn't a problem at all. You do realize that this LPM reads down to .01W resolution, not .1W like that one in the other thread you referred me to right?

For anyone else reading this thread, my question hasn't been answered at all so please let me know if there is anything I should be worried about before purchasing this LMP.

 

[diachi]

A stand would probably be a good idea for the sensor.

Also, from the description: "The calibration of the system is close, but not to a NIST standard." - Something to be aware of, probably not an issue for your use case. That's probably why it seems cheap, because it's not a professional LPM. A professional LPM would come properly calibrated, with more features and higher quality components, hence the $1000 price tag. Doesn't seem to have any graphing capability either, the LaserBee USB capable LPMs DO and that's a nice feature to have.

 

[HighPowerObsession]

Yeah I was thinking about getting a stand too, but I have no idea what to even search for....do you have any suggestions for a stand?

And about it not being calibrated up to NIST standards, I have no idea what that means, but I dont think it will matter much.
I am not looking to graph anything either, just to test out my high powered lasers and see how stable they are when left one for a certain period of time.
I also want to test out how long my lasers can perform at its max and what power output they will give for certain battery voltages. I already have a Nitecore D4 charger
so I can test out all my battery's voltage with ease. The one downside that does matter in my case is there is no offset control like there is on the LaserBee which is a bit of a bummer
but I can live with that for a LMP that can read 4X higher than the LaserBee 5.2W one can. I also feel pretty safe buying a 20W LPM since it seems pretty future proof.

Anyway, so in terms of accuracy this LPM should be good?

 

[diachi]

Yeah I was thinking about getting a stand too, but I have no idea what to even search for....do you have any suggestions for a stand?

And about it not being calibrated up to NIST standards, I have no idea what that means, but I dont think it will matter much.
I am not looking to graph anything either, just to test out my high powered lasers and see how stable they are when left one for a certain period of time.
I also want to test out how long my lasers can perform at its max and what power output they will give for certain battery voltages. I already have a Nitecore D4 charger
so I can test out all my battery's voltage with ease. The one downside that does matter in my case is there is no offset control like there is on the LaserBee which is a bit of a bummer
but I can live with that for a LMP that can read 4X higher than the LaserBee 5.2W one can. I also feel pretty safe buying a 20W LPM since it seems pretty future proof.

Anyway, so in terms of accuracy this LPM should be good?

NIST: https://en.wikipedia.org/wiki/National_Institute_of_Standards_and_Technology

If you're wanting to look at stability, power over time, duty cycle and so on you probably want graphing functionality with peak and average power readings...

Keep in mind, you can use a 5W sensor with a >5W laser, you just need to have an attenuator of known value in between so that you can work out the true output power.

It should be accurate enough, as long as you're taking into account the lack of an offset and using lasers where a resolution of 10mW won't be much of an issue, such as anything Class IV.

Also, LPM, LPM, LPM. Say it with me now, LPM. Not LMP... Sorry, but it bugs me.

 

[HighPowerObsession]

Haha I have been saying LPM this whole time, my bad I accidentally typed LMP once...

And I rarely leave my lasers on for more than like 2 minutes so I can just watch the power reading for 2 minutes or whatever; a graph really isn't necessary.
I can see why people who are going to be posting their results online would want/need a graphing capability, but I won't be doing anything like that.
As long as this LPM is accurate and lasts that is all good with me.

Oh and about a stand, do you know where I could get one? I have no clue what to search for.

 

[diachi]

Haha I have been saying LPM this whole time, my bad I accidentally typed LMP once...

And I rarely leave my lasers on for more than like 2 minutes so I can just watch the power reading for 2 minutes or whatever; a graph really isn't necessary.
I can see why people who are going to be posting their results online would want/need a graphing capability, but I won't be doing anything like that.
As long as this LPM is accurate and lasts that is all good with me.

Oh and about a stand, do you know where I could get one? I have no clue what to search for.

Actually, you said it 6 times... anyway...

Yep, fair enough if you don't want the graphing. Can always manually or mentally note the readings for a general idea of what's going on.

Look on Amazon for one of those tripod/gooseneck stands with the clamp on the end, that might work well. Actually, one of those small tripods designed for smartphones may work as well.

 

[HighPowerObsession]

...k bro, I think you're aware that I know its called an LPM

I'll try searching gooseneck stands and see what I get. Thanks

 

[astralist]

Personally i would buy that LPM on ebay if i had spare cash right now, the head's surface seems in a perfect condition. Only thing is, i'll just throw the display box because it's junk (for me, at least)

The head comes from molectron, and has no internal amplifier CMIIW.
That means the calibration should not drift from manufacturer's calibration value (it should be printed on the head, like "1mV/W") as long as the surface is not disturbed by any kind of chemical or mechanical stress (like humidity, touching, brushing, blowing, etc), not like those ophir head which uses internal amplifier, as the amplifier's properties (silicon) will drift over time so that the calibration needs to be renewed every year.

About the suspicious price:
AFAIK those type of molectron head (used) is indeed cheap, and the display uses cheap technology (my guess is that it contains low resolution ADC). All i can say is that selling that setup for about $300 is a bit expensive (as i know the true raw material costs)

I think the only "real" bad thing is about the offset, the worst case scenario is that it can display about >50mW without the laser being exposed to the sensor, or even the sensor outputting a negative value at first.
I can saay this because i have a similar sensor like that (only with different brand)

Here is some information for you:

• Fact: Even if the sensor is NIST calibrated, doesn't mean that it will 100% accurate when measuring laser with different wavelength compared to the laser used to calibrated that sensor at NIST.
• Reason: Because there is no single coating in this world capable of "flat" broadband response. Even for those ophir head, you won't find the specific and detailed spectral response chart because they don't want you to know (unless i'm missing something). AFAIK from their youtube, this type of coating absorbs more at wavelength below 800nm, meaning if it's NIST calibrated on YAG 1064nm with 100mW power reference, it won't give you 100mW when measuring true 100mW 447nm. Instead it'll give you readings above 100mW because of more absorption. The workaround for their product is, they are compensating the reading and user can select if want to measure <800nm or >800nm (this choice exist on their power meter interface, AFAIK). This is also the reason why some OEM design may want you to chose in which wavelength do you need your sensor to be calibrated to. This also apply for that molectron head, only we don't know the wavelength used for calibrating it.
• Conclusion: The sensor will give fairly different reading from its guaranteed calibration, if you are measuring wavelength other than what it's originally calibrated to. So "calibration is close" is acceptable i guess.

 

[Dutch67]

I think all euphonious was trying to say is that he thought you should ask there instead of making a new thread on this LMP (diachi:crackup

 

[HighPowerObsession]

haha wow that was alot of info, thank you for that.

I will be testing lasers from 405nm-650nm and I want the accuracy to be within 50mW....will this be a problem? (NOT including offset, just recorded mW vs true mW)

You said something about the calibration needing to be renewed every year; were you referring to this setup or another setup? That part was confusing.

About the quality of the parts, I don't really care about the quality much; as long as they last and they are somewhat accurate (within 50mW of so) that is all I want.