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Thread: Budget digital laser power meter - LPM-1 mini-review

  1. #1
    Join Date
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    Default Budget digital laser power meter - LPM-1 mini-review

    [disclosure]I worked with the designer on tweaking the specifications of this meter to fit the common laser uses and add RS232 datalogging. After completing this I have begun a group buy to get a quantity discount for us. I do not work for or have any connection other than stated to Andover Holography.[/disclosure]

    I have some good news, this meter seems to have turned out very nicely. A big thanks to Tony from Andover Holography for working with me concerning the specifications.

    The LPM-1


    It's a nice looking unit with an easy to use menu and silver buttons, but who cares how it looks? How does it WORK?

    First, you select the wavelength you want to measure from the menu, including 473, 532, 635, 660, and 808nm options. Once selected, the display is continuously updated at 2Hz with the measured value. The peak value is recorded and can be reset with the push of a button.

    The really slick feature for us experimenters that none of the other portable meters have is the serial datalogging option. Automatic power-down can be turned off in the menu for long datalogging sessions.

    Example datalogging plot made using the meter and excel:


    It's a very easy feature to use and enables the tweaker/experimenter to monitor the output of their laser over time. The datarate is 57600-8-n-1. Samples transmitted every 0.5 seconds.



    Now, I was skeptical about the accuracy claims at first when I read about this meter, is uses a monocrystalline solar cell as the sensor, and relies on I->V conversion for the measurement. After I got the temporary test unit I tested the linearity and accuracy by comparing its reading with that of my Scientech calorimeter laser meter. (I used a red diode from our group buy for the test) The results were impressive:


    Linearity test comparing calorimeter laser meter reading with the LPM-1:


    result: less than 2% error (within the accuracy of my control standard) within the specified range. So there's no problem there.


    Here's a list of features:
    Autoranging measurement of light power in 4 ranges from ~100 uW to 100mW (800mW with ND8 option)
    At least 5% accuracy over native range
    Multiple sensor calibrations for different wavelengths :473,532,635,660, and 808nm selectable in a menu.
    16 character by 2 line alphanumeric display
    3 Pushbuttons provide control of measurements & configuration using a simple menu system.
    Automatic 5-minute power down to extend battery life (can be turned off for datalogging)
    RS232 datalogging capability
    Peak hold remembers the peak reading in a series
    2Hz (2 samples/sec) update and logging rate, 400Hz internal sample rate
    Sensor at top of meter for easy, safe readings
    Rugged surface-mount component construction
    Operated on a 9V battery
    Optional features:
    Range extending ND8 neutral density filter included and calibrated
    RS232 datalogging pre-built cable OR
    RS232 datalogging DIY kit
    Backlit display

    The kit schematics for the RS232 interface will be posted free for those who can build their own.


    I'd rate this product at 90%: great value for the price ($150 base group buy price), but limited to the discrete wavelengths it is calibrated for.


    So, check out the group buy thread if you're interested.

  2. #2

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    That looks cool. At some time when I have spare money again (a fond memory, spare money...) I want one for a second opinion meter, and the data logging idea is nice.

    Got a question: why ND8? Given maximum base range of 100 mW, going beyond 800 mW to 1 watt is one factor of ten, which I was told was specifed as ND1, ND2 being hundredfold, ND3 thousand fold, etc. For example, a Lasercheck max goes from 10 mW to 1W with the ND2 filter in place, according to various Googleable references in Sam's LaserFAQ. Weirdly, Coherent don't seem to specify it as ND anything, they just call it an NG-10 glass attenuator.
    Last edited by The_Doctor; 02-16-2007 at 12:42.

  3. #3
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    Quote Originally Posted by The_Doctor View Post
    Got a question: why ND8? Given maximum base range of 100 mW, going beyond 800 mW to 1 watt is one factor of ten, which I was told was specifed as ND1, ND2 being hundredfold, ND3 thousand fold, etc. For example, a Lasercheck max goes from 10 mW to 1W with the ND2 filter in place, according to various Googleable references in Sam's LaserFAQ. Weirdly, Coherent don't seem to specify it as ND anything, they just call it an NG-10 glass attenuator.
    Different manufacturers label the filters differently. In this case, the ND8 is a widely-available photographic filter that reduces the incoming light by 3 stops in a power of two rating (2^3 = 8). ND10 filters are not as easily or cheaply available, and beyond 1 Watt there was some concern of the filter glass becoming too hot, so NDs higher than 10 weren't considered. NDx is not to be confused with ODx rating of goggles, which use a power of 10 rating.

  4. #4

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    Quote Originally Posted by drlava View Post
    Different manufacturers label the filters differently. In this case, the ND8 is a widely-available photographic filter that reduces the incoming light by 3 stops in a power of two rating (2^3 = 8).
    I thought it might be a three fold binary multiple. I never studied photography so I didn't know the conventions, so I didn't say what I thought earlier.

    ND10 filters are not as easily or cheaply available, and beyond 1 Watt there was some concern of the filter glass becoming too hot, so NDs higher than 10 weren't considered.
    NG-10. Wasn't a typo.. I think they mean a type of glass formulation, not an optical property, specifically.

    NDx is not to be confused with ODx rating of goggles, which use a power of 10 rating.
    The two things are close, even though confusion is possible. Optical density (usually given for specific thickness (http://en.wikipedia.org/wiki/Optical_density)) is specified in goggles for specific wavelength, in a way that is not specific to thickness. Neutral density is the same except that it is made equal for all wavelengths in a broad range. Whether the factors are decimal or binary is probably just a convention. Granted, it can be dangerous to pick the wrong one... Note that that Wikipedia entry specifies log to base 10, so it might be better to get a log10 ND1 and let your meter work to 1 watt. After all, I bet it autoranges in decimal, no? If Laserchecks can use an ND2 without overheating problems, you'd be ok with ND1 to go from 100 mW to 1W, even for long periods if you mounted it in something like acetal rather than ABS plastic.
    Last edited by The_Doctor; 02-16-2007 at 15:58.

  5. #5

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    I have an LPM-1 myself and the .122 plastic lensed filter that comes with it seems to be of different ND level than a true ND8 glass filter. The LPM is calibrated for 808nm ND with the stock plastic filter. using the glass nd8 would result in a markedly less power reading.

    Can someone explain or inform me on if the plastic .122 filter is incorrect or how might I go about registering a 600mw laser on the LPM-1 without burning it out with either the .122 filter or a glass ND8.... it certainly can't be merely dividing the output (without ND) on 808nm by 8....

    Quote Originally Posted by drlava View Post
    Different manufacturers label the filters differently. In this case, the ND8 is a widely-available photographic filter that reduces the incoming light by 3 stops in a power of two rating (2^3 = 8). ND10 filters are not as easily or cheaply available, and beyond 1 Watt there was some concern of the filter glass becoming too hot, so NDs higher than 10 weren't considered. NDx is not to be confused with ODx rating of goggles, which use a power of 10 rating.

  6. #6
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    Wow very nice meter, what is the aperture size of the sensor?

    A known fixed aperture and the peak hold feature will make this a perfect MPE meter.

    You still have to measure R G and B separate, or can the meter olso be tuned for a white beam?


    the link to the groupbuy does not work here, what does the meter costs?

  7. #7
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    Very nice meter, I'd like to see more common wavelengths catered eg. 445, 458, 640, 650, 660 for, but that aside, its extremely nice.

  8. #8

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    The Andover LPM-1 has been around at least since 2007..
    Judging by the date of the last Thread dates...

    Jerry
    See the LaserBee II and all other LaserBee LPM products here....
    All LaserBee Laser Power Meter Products

    New 3.2Watt RS232/USB LaserBee II LPM REVIEW


    Always in stock and ready to ship....
    Subsidary:-Pharma Electronic Solutions

  9. #9
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    Someone needs to make a basic meter for R / G / B for up to 500mw in the $75 - $100 range.

    I want to measure mine but im super cheap.

    The DMM module Jerry has for sale looks ok, but its only up to 200mw.

    It says "higher with ND filter" but how much higher? What sort of ND filter? Still accurate above 200mw?
    Regards,

    Aidan

  10. #10

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    First... I would like to get a Lamborghini Countach S for $1000.00....

    Almost any ND filter that has a linear optical ratio can be used with almost any
    optical LPM... I believe Newport sells linear optical ratio ND Filters for ~$40.00.

    For single Laser wavelengths... much less expensive Photographic ND Filters can be
    used after you test the reduction ratio using the Laser's wavelength you want to
    test... We found that Photographic ND Filters do not reduce the powerof different
    wavelengths equally...

    The amount of Laser Beam power is irrelevant (to the optical sensor) as long as the
    actual active sensor area doesn't see more than the rated specs.
    What is important is that the maximum ratings of the Sensor's surface are respected.

    The only thing that changes with an ND filter... is the resolution of the readings is
    lower (by the ratio figure).. not the accuracy..


    Jerry
    Last edited by lasersbee; 03-24-2010 at 04:31. Reason: Spelling errors
    See the LaserBee II and all other LaserBee LPM products here....
    All LaserBee Laser Power Meter Products

    New 3.2Watt RS232/USB LaserBee II LPM REVIEW


    Always in stock and ready to ship....
    Subsidary:-Pharma Electronic Solutions

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