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Thread: QS Safety Check Request

  1. #11
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    It's easier than the old method, which was to measure every point in the frame!

    Cross-over points can be avoided easily: Don't bend or morph a line through itself, or if you must, then blank out some of the points at the crossover point. It's only necessary for the portion of the scan-field that goes down into the audience, so it's not that restrictive.

    Adam

  2. #12
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    Reading back at the simplified approach, I can't see any assumptions about scan speed. It simply involves measuring a static beam and ensuring that it doesn't exceed 10mW/cm2.

    Nothing about exposure time.

  3. #13
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    I think a pragmatic approach is what's needed here...

    - There is no such word as "can't" -
    - 60% of the time it works every time -

  4. #14
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    Quote Originally Posted by norty303 View Post
    Reading back at the simplified approach, I can't see any assumptions about scan speed. It simply involves measuring a static beam and ensuring that it doesn't exceed 10mW/cm2.
    This is the dirty little secret about audience scanning. Lots of people read this simplified approach and assume that 10mw/cm^2 is all you need to be safe. Unfortunately, that's not the case. (And I agree that even here on PL, it's hard to find a good discussion of the rest of the calculation.)

    The 10mw/cm^2 irradiance limit assumes a single pulse with a duration of .001 seconds. That's it. If you have multiple exposures (which you almost certainly will, since the frame will be scanning for several seconds), then the calculation is more involved. But few operators go that far. (One assumption people make is that the frame will always be moving, so in theory an audience member will only get flashed once. But it's obvious that this short-cut does not apply in all cases.)

    Remember, it's the multiple-pulse MPE that is the most restrictive. Patric Murphy gave an excellent presentation on these calculations at SELEM 2008, but I can't seem to find the video at the moment. (I thought Aaron had uploaded it to youtube, but I could be mistaken.) His lecture was nearly 90 minutes long, and he *flew* through the slides. There's a lot to learn.

    @daniel: Yes, I agree that a pragmatic approach would be nice, if not for the legal threat. And in principle I also freely admit that 10mw/cm^2 is ridiculously low. I routinely expose my own eyes to a lot more than that, and I *have* had my retinas examined by a corneal surgeon - twice. No observable changes. But even so, I won't chance an audience-scanning show here in the US. It's not worth the risk, at least not here.

    Adam
    Last edited by buffo; 12-12-2010 at 09:32.

  5. #15
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    From Greg Markov's Paper on Audience Scanning p.12:

    Show measurement is vastly simplified. The show operator only needs to measure the accessible exposure at the point of closest audience access. If the operator sets the power to about 10 mW/cm2 (four times the 2.5 mW/cm2 average power MPE), this will approximate the single-pulse MPE limit for the audience-scanning portion of the show.

    This simplification assumes the show has been designed so effects are kept moving, and
    the scanned shapes are smooth with no “hot spots”.
    I also do not claim to be an expert at this. In fact I readily state I know next to nothing!

    I've attached the full Safety Document written by Greg Markov and Patrick Murphy for anyone who would like to use it for reference.

    (BTW Norty indirectly, safety is also one reason why I was trying to steer you away from Fiesta instead of Pangolin - so far as I'm aware in my short play with the demo, there is no Beam Attenuation Mapping in Fiesta, which if true makes it far more difficult to control powers at the closest point whilst maintaining visible beams overhead. Fiesta can of couse be operated perfectly safely, no manufacturer would release anything unsafe, but without BAM's and depending on your laser power, you may need reduced power overall whereas BAM's allow you to step the powers).
    Attached Thumbnails Attached Thumbnails audience-scanning_overview_2pt1.pdf  


  6. #16
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    safety is also one reason why I was trying to steer you away from Fiesta instead of Pangolin
    I didn't mention it in the other thread because I didn't want to junk it up further, but you may have the wrong impression of why I was posting in that thread. It certainly wasn't because I'm in the market for a new controller.

    I am unlikely to be steered in any buying decisions by a thread of that nature - and I am a happy user of FB3 and LivePro for a year or 2 now.

    However, it is interesting to see what other companies are doing, and thats not to say I wouldn't consider them i the future.

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