Modding Low Power LPM

[Greenmechanic]

I just bought this LPM on e-bay for next to nothing (for a LPM). Max. measuring is 10mW. Does someone know if this meter can be modded to measure up to 250 or 300mW. Will the sensor handle higher outputs?(it's all aluminum)
I know this is a hard question to answer without schematics. But if someone knows anything about this meter, I could send pics of the circuit boards and such. Sorry if this is a noob question, but I have to start somewhere, right?

 

[lasersbee]

The only thing that I can see that you can do is use a ND filter to drop the
test laser's beam power...

You may have been better off getting one of these at 120mw....

Calibrated Laser Power Meter Sensor Module by J.BAUER Electronics (EBAYHLPM)

It also uses an optical sensor and the same ND filter trick can be used..
Maybe someone else has a better idea of how to modify yours..

Jerry

 

[Hemlock_Mike]

The name "Metrologic" is old and remonisant of earily days of HeNe lasers. The sensor is likely a photo diode and will need ND filters and calibration for different wavelengths.

Mike

 

[Greenmechanic]

Thanks to all for your help.
Thanks to Laserbee for that link. That is in my price range for right now.
I'll have to do a search for "ND filter" as I have no idea what that is.The seller did include a "optical attenuator" to use with higher power lasers. I tried it with my 5mW red, the readings were the same with or with out it. I did not want to try any higher power for fear of burning up the sensor.
I guess I will just use the Metrologic with low powered lasers. I have to use it for something now that I already bought it:yabbmad: It's all part of the learning process I guess. If anybody has any more input I'll be glad to accept it. Thanks all!!

 

[HIMNL9]

ND filters are neutral grey broadband filters that block a certain percentual of the light that pass through ..... a 90% filter, let pass only 10 % of the light (so the LPM read 10 times more), a 99% filter let pass only 1%, and so on.

Be careful with that sensor, anyway, it's a planar silicon photodiode with a limited power capacity ..... if you shoot 100 mW or more in it without a filter, you risk to burn it.

 

[lasersbee]

That is why our 120mW LPM Module is limited to 120mW.
Higher powers than that.. heat up the sensor and throw off
the readings..

Here is a link to some Glass ND Filters....

http://cgi.ebay.ca/52mm-52-Neutral-...ters?hash=item1c03f89c49&_trksid=p3911.c0.m14


Jerry

 

[Benm]

ND filters would be the best solution, at least up to a few 100 mW. Beyond that, the laser will damage the filter and possibly burn straight through, especially if its plastic.

 

[HIMNL9]

^ plastic ones, yes, try to avoid them

The ones in ebay auction are good, they're photographic ones, and usually they are optic grade glass with AR coating ..... the only problem is that they usually come in "stops" grades (2, 4, 8, 16 and so on), where instead, for our purpose, the better grades are 10 and 100 ..... anyway, also them can be used, just multiply the reading for the attenuation factor

 

[lasersbee]

^ plastic ones, yes, try to avoid them

The ones in ebay auction are good, they're photographic ones, and usually they are optic grade glass with AR coating ..... the only problem is that they usually come in "stops" grades (2, 4, 8, 16 and so on), where instead, for our purpose, the better grades are 10 and 100 ..... anyway, also them can be used, just multiply the reading for the attenuation factor

Been there.... Done that...
That's why I suggested Glass ND filters...

They are only ones we have in the shop now without any Laser damage...:crackup:


Jerry

 

[Greenmechanic]

OK, just to claify. If I get a 90% ND filter I can safely measure up to 100mW?
And if I use a 99% ND(if they are avaliable) I can measure up to 1W? Is this correct? What about [2] 90% ND's one in front of the other, would that let me measure up to 1W? I am saving up to buy a Laserbee I , so this is just a stop-gap measure untill I have enough saved. Thanks again for all your help.

 

[HIMNL9]

They are only ones we have in the shop now without any Laser damage...:crackup:

Uhm, think i can guess why ..... you tried to measure a 5 mW keychain pointer through the plastic one ..... or was 500 mW ? :thinking: ..... (LOL )



@ Greenmechanic: basically yes ..... anyway, cause is more easy to find the photographic ones, you can just get a pair of 3stop, or 8X, and multiply the reading for 64 (or have a full scale reading at 640 mW, if you prefer), or a 3stop and a 4stop, and multiply the reading for 128 (with a full scale reading at 1,28 W), if you can't find the decimal ones (decimal ones are used mainly in labs, and with the excuse that are for professional use, they usually rise the prices absurdly ..... perhaps that any time that you write "professional" on something, one or more zeroes appears magically, alone, at the end of the price ..... instead, is more easy to find old models of photographic ND filters more cheap, like as examples the ones for old cameras with small diameter objectives)

 

[Greenmechanic]

Uhm, think i can guess why ..... you tried to measure a 5 mW keychain pointer through the plastic one ..... or was 500 mW ? ..... (LOL )

It was only 5mW. But holding the filter up to the light ,you can barely see the gray. It must be a 5% or something like that

 

[HIMNL9]

^ ROTFL ..... sorry, this part was referred to the post from lasersbee, about glass filters ..... sorry

 

[Bionic-Badger]

Unless you have it calibrated to a known source you're not going to know how your ND actually affects the power levels on your meter. Half of owning the laser meter is the calibration. All you'll know is that the power level has dropped down somewhat; it may not even be a linear change. Furthermore, do you even know if the meter itself is still accurate? With that age, it's probably not.

 

[lasersbee]

Since it is a "Photometer" it is an optical LPM.

If you don't have an optical correction chart for the detector and
you don't know which wavelength of laser was used to calibrate it..
you will never know hoe accurate it is over different wavelengths
without a known calibrated stable laser source or Cailbrated LPM.

as BB said... without all that... the best you can do is say this laser
is stronger than that laser of the same wavelengh..


Jerry

 

[daguin]

All of the above is WHY it was "next to nothing"

Peace,
dave