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Thread: What (should) 10K/20K/40K mean?

  1. #1
    Join Date
    Aug 2007
    Location
    Indianapolis, IN
    Posts
    196

    Default What (should) 10K/20K/40K mean?

    How do you work out the rating of a scanner set?

    If I buy a 40K scanner set does that mean it can render 40,000 points per second? Or does that mean the the mirrors can oscillate at a maximum speed of 40,000 Hz?

    ...and how do you compare the rating with the speed control in something like Mamba?

  2. #2
    Join Date
    Nov 2005
    Location
    Melbourne, Australia
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    Hey,

    Usually the ratings indicate the speed in points per second they can correctly display the ILDA at.
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  3. #3
    Join Date
    Jan 2006
    Location
    Charleston, SC
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    2,147,488,500

    Cool

    To expand on what Dave said, 40Kpps *should* mean that they can display the ILDA test pattern at 40,000 points per second AT A SCAN ANGLE OF AT LEAST 8 DEGREES.

    However, in practice there is a lot of variation in the marketplace. And, to be perfectly truthfull, ILDA has never agreed on a standard for 40K, or 45K, or even 50K. There is a standard for 30K and one for 60K. That's it.

    To convert point speed to hz of actual movement is difficult. However, if you consider that the scanners are moving as fast as they can when they draw the central circle in the ILDA test pattern, and you further consider that the circle is actually made up of 12 points that lie outside the square, then you can see that point speed divided by 12 equals the speed (in herz) that the scanners can reach when drawiing that circle.

    But remember too that there is considerable error in the *position* of the scanners when drawing that circle. If they were 100% accurate, you would see a 12-sided closed figure, not a circle. Still, it's about as close of an estimate that you'll ever get, and it's consistent across all speeds. Thus 30Kpps = roughly 2.5 Khz for very small steps. Larger movements will, of course, have much lower absolute maximum frequencies.

    As for the speed setting in Mamba (or whatever software you use), that setting should be set at the same speed that you tune your galvos at. For example, I've got a set of DT-40 scanenrs (which are supposed to be capable of 40Kpps speeds). I tuned them at a speed of 30Kpps, and I run them at 30Kpss. This means that I can scan the ILDA test pattern at around 14 degrees optical while still keeping the circle right on the square, and everything is nice and clean.

    If I were to increase the display speed to 40Kpps, the circle would end up smaller, and way inside the square. Likewise, if I were to reduce the display speed to 20Kpps, the circle would be outside the square.

    If I decided to re-tune the galvos for a speed of 40Kpps, I could do that, but my scan angle would be smaller. I like to run at 30Kpps because all the artwork (and all the shows) I have are designed to run at that speed, and I like having the wider scan angle.

    Adam
    Last edited by buffo; 01-25-2008 at 05:21.

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