Laser MPE meters, but is there any point?

[mccarrot]

Laserbee, you called me Troll but I still think i'm right.

If you look closely at Docs graph you see the laserbee is 20% off in the range below the 30mW.

[drlava]

For clarity, you will want to use an aperture for the laserbee and not just rely on calculating irradiance based on the sensor area. The reason is that the TEC sensor is differential in nature and so illumination of the surrounding heatsink may affect the reading a small amount.

[lasersbee]

In case anyone needs to know...

The size of the active area of our New Thermopile's sensor is 8mm X 8mm
I'm not sure if it help in the calculations required but I thought I would put it
out there..

The sensitivity is linear all over the surface... we've test it with a 2mm Laser
beam in all locations on it's surface...

But as drlave states.. the Heat Sink non active area should be isolated...


@mccarrot.... of course you are right again.... 20% at 10mw is a staggering 2mw
even at 30mW on that graph I still see only 2mW off... now that's only 7%
(and we are assuming thsat the Scientec meter is 100% accurate)

As I stated in the PM when I replied to yours...

You need to remember that the LaserBee I is not a $1000.00 to $4000.00
commercial LPM...

and sells in the neighborhood of $220.00 you can't expect the accuracy of a commercial
LPM for that price... That's a given...
Even the LaserCheck startes an accuracy of +/- 5% that's a total of 10% accuracy..


Jerry

[mccarrot]

Yes the fixed size of the sensor (0,64cm2) is very easy for MPE calculation IF the sensor was sensitive en accurate enough in the range between 1-10mW

You could use it as a rough indication, if you measure a the closest point in the audiance and the whole sensor is covered in light you should measure 6mW (or less) to be within MPE

If you use a 7mm aperture in front of the sensor you should measure 3.6mW and this is not in the range of the meter.

Again I'm talking about the simplified approach.

[Doc]

I think the Laserbee is a great tool and I use mine all of the time as it stabilizes very quickly and is accurate enough for most duties i.e. tech tuning DPSS, angle tuning cubes and dichros.

I think the sensitivity in the lower range could never be as accurate as a pro LPM because the head design has an exposed sensor, which is obviously going to pick up extraneous radiation if the gain was high (you only have to put your hand on axis with a standard calorimeter and you get a considerable reading from the heat of your hand).

However, so long as the reading is optimistic on the particular Laserbee being used (which could always be verified); the MPE calculation is going to be safe.

Ian

[Pangolin]

Since this "Making shows safe and enjoyable" article has been referenced several times, I should point out that the article referenced so far in this thread has been the really old one that appeared in The Laserist magazine back in fall of 1997, and then again in 2001. That article has gone through several revisions over the years, and the latest one is here:
http://www.pangolin.com/resguide09a.htm

The latest one at least alludes to a simplified method which can be used to evaluate shows.

Bill

[drlava]

very helpful and clear, thanks for posting.

[dzodzo]

Hello, from what i read about estimating MPE levels based on various factors, is it possible to create some table with "safe" values? I mean like the maximal safe laser diodes power, at the minimal safe distance with minimal safe scanspeed? And does the MPE level count differently for each wavelength or can you count with combined power? Sorry for noob questions i'm just curious.

[mccarrot]

Hello, from what i read about estimating MPE levels based on various factors, is it possible to create some table with "safe" values? I mean like the maximal safe laser diodes power, at the minimal safe distance with minimal safe scanspeed? And does the MPE level count differently for each wavelength or can you count with combined power? Sorry for noob questions i'm just curious.

Sure you can make a table, but for this you need to know the beam size, power an DIVRIGENCE etc. becouse those values are different for all lasers you cannot make a universal table for all lasers.

You could make a table with worst case values (eg. 1,5mm beam and 0,6mRad) and use this for your projectors. then you are always ok.