Anything Wrong With This LPM?

I don't think that is what he was saying at all; he told me that thread had all the answers and it didn't at all.
He even quoted parts of that thread that had noting to do with the question I was asking.
Even if he was saying that, it would be nice if someone could just answer my question instead of telling me where else to post it. This is why I don't like asking questions in this forum; I try to use this forum 99% of the time to find answers and if I can't find the answers I will research it myself. In this case, I couldn't find anything about molectron and no threads really explained how reliable their sensors are so I didn't really have a choice but to start a new thread.
(yeah someone finally answered my question but I'm talking about before)

HighPowerObsession said:

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)

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A good thermal sensor will vary at most only a few percent over the visible spectrum.

See graph:

.

I don't know enough about science and lasers to be able to read that graph and know what it means. I have no idea what an "um" is either.

HighPowerObsession said:

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.

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usually the accuracy is calculated within percentage of the readings, many thermal sensors stated a max accuracy of 4%, meaning if you measure a 1000mW laser, you'll get ±40mW readings. The higher power you measure, the higher the swings, but sadly i can't find the datasheet of that molectron PM10 head. All source on google is redirected or 404 not found :undecided:

About every year calibration, it's for another setup (usually for "ophir" sensor head)

diachi said:

A good thermal sensor will vary at most only a few percent over the visible spectrum.

Click to expand...

WOW.. that's a really nice spectrum response, compared to ophir thermal sensor.

So I guess most LPMs just arent that accurate when testing higher powered lasers like 2.5W+ (4% is 100mW now)

If I wanted to test a 7W blue laser its gunna read +/-300mW....

So in the OP you asked: "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+."

Astralist answered that one at the very least and he should know as he makes some very nice LPMs (I have one myself ) and most likely understands thoroughly as to how they work.

He also answered your question about accuracy on the bottom of his post. He said: "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."
So it probably wont be that .01mW that it has listed.

Edit: Woops look like Astralist finished for me. Oh well :crackup:

HighPowerObsession said:

I don't know enough about science and lasers to be able to read that graph and know what it means. I have no idea what an "um" is either.

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um = micrometers, instead of nanometers (nm). 1 micrometer is 1000 nanometers.

Oh ok so why are there 3 lines? Like whats the difference between the blue, green and red lines?

HighPowerObsession said:

So I guess most LPMs just arent that accurate when testing higher powered lasers like 2.5W+ (4% is 100mW now)

If I wanted to test a 7W blue laser its gunna read +/-300mW....

Click to expand...

Yeah, even a thousand $$$ meter will have the same characteristic.
And please remember that every measurement device has its own accuracy.

Additionally, the ADC (analog to digital converter) that convert the voltage from sensor's output, has its own accuracy specification. If all the system tolerance taken into accout, that 4% number seems too good to be true, especially if the ADC is cheap and low resolution.:shhh:

Ha this is turning into a confusing nightmare...I'm not sure if all this is even worth purchasing an LPM anymore

If you HAD TO guess how accurate that LPM on Ebay is, what would you say??

Yea.. The more we know, the more doubt we have :crackup:

FOUND IT!!


It's ±3% said the datasheet. In a new condition, NIST calibrated.

As for that LPM on ebay, i can guess about <6%

HighPowerObsession said:

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.

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Yes it could be a problem with this meter and head, because if there isn't any offset of 0 then you may have negative readings, or positive readings instead of 0. As astralist said differen wavelength calibration may throw it off further, so therefore you could be testing 50mw laser and reading 150mw; or you could read 10mw on a 50mw laser...

The smart choice here is to go for a LaserBee or one of Astralist's Hyperion LPM. I have one of Astralist's because I couldn't justify spending that much on the LaserBee when his product works for what I need.

I can get pretty good readings, graph my power to log the duty cycles (notice significant drop when the temperature of the die is to hot), and I can take graphs or log to my PC to review later if I want to; or just plug it in for 10 seconds to a battery pack, test it, and put it away..... Oh and it was only 150$ and I can test 5mw laser or a 5W laser.... I had one small quality issue so far with it, but I also saved a couple hundred bucks over a LaserBee.

Just my .02$ anyway; If testing lower power lasers (NOT CO2 or 7W+) currently then you don't need that high of a reading from your meter. This meter would be bought by someone using a CO2 laser if you ask me...

Well whatever the offset is, I will take that into consideration so that wont be a problem. The problme I have with even the highest powered LaserBee (which is 5.2W) is that its not future proof (considering lasers get more and more powerful as they have been). Even lasers out right now are over the what LaserBee can read so thats honestly not an option anymore. I don't think 10W is a ridiculous power range at all, 30W is though which is why I'm not getting that one. I'll check out the Hyperion LPM

HighPowerObsession said:

Oh ok so why are there 3 lines? Like whats the difference between the blue, green and red lines?

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They refer to the model numbers shown in the key. Those model numbers are for professional thermal sensor heads from Thorlabs.

Yeah I saw the key but had no idea what those codes meant, but ok they are sensors Thorlabs sells which are far too expensive for me.
Basically though, that graph has nothing to do with the sensor I'm looking to get.

Here is spectral response data for that LPM sensor on ebay (PM10) which is a surface absorber, just for reference and knowledge: