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Thread: Best way to mesure real output from projector?

  1. #1
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    Default Best way to mesure real output from projector?

    I got my new Laserbee USB 3,7W yesterday. Big thank you to Mr. Jerry Bauer for beeing patient and generous.
    Now i can get the real readings from my builds, but I`m not shure what is the best way to get be most accurate result.
    Ripping out the modules from the projectors are something i really hope to avoid, and what i really want to know is the output after the optics.

    Did som initial testing yesterday, and hooked up one Projector with Beyond and FB3. Tried to do a small cone in one frame and shoot it at 100%. It actually did not produce the same power as the ILDA testframe i used to align the beam towards the receiver.

    So main question is: How to produce a 100% module output for measurement with beyond or QS?
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    Basically, you can't, but you can get very close.

    Best thing is just to use a 5V source or something like Stanwax LaserGem.

    If you must use an FB3, then display the LaserMedia test pattern with zero size. You'll get at least 95-98% of your max output this way (having done the testing vs 5V and various frames) which should be good enough for almost all scenarios. The Laserbee will have about as much variation anyway.

    I tend to measure pre-scanner, but post optics as there's usually a space in there to get the meter head, and you're dealing with a static beam so don't need to worry about zero size.
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    Best way IMHO is to tie colour input ILDA lines up to +5vdc remove scan-amp supply and input signal (to eliminate any scan wobble) and measure after the output window!.

    Any scanned output figure will give much higher apparent power reading ...so not surprising that small cone not same as test pattern. (bigger more complicated scan = higher power).... wobble can be checked at far field (long distance).

    However judging by other posts here seems that most people in the US ignore scan wobble as "irrelevant" (don't think most even bother to short scan input signals), any wobble will give a higher reading than a truly static beam

    Obviously this method is popular with manufacturers.

    If I can't get to the signal lines, I often leave output in "white" and intercept beam just before scanners with a pick-off mirror to redirect beam thru output window just to get an idea of scan mirror losses,.... if this measurement gives lower power reading than thru scanners it means scan wobble is causing significant over-reading!

    Also bare in mind that losses on scanner mirrors will depend on output beam direction to a certain extent (usually right angles give less losses)

    Cheers

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    I'm not sure what you mean by scan wobble, or actually why you think a scanned pattern, or even one more complex will give any more total energy than is present in the beam?

    I'm also curious how you even manage to get a scanned image on the sensor? Most I've seen are just not that big, certainly he isn't going to get a scanned image on his Laserbee.

    Regardless, the only thing that should count is the amount of 'on' time that the laser has in the given pattern. In that regard, the LaserMedia test wins. A complex pattern shouldn't matter providing it has no blanking. the reason why the LaserMedia wins is because it is all redraw lines, where another pattern might perform blanked jumps.

    I've never seen a case of a scanned image giving more power than a CW static beam - I'm not even sure how that is possible given the heating energy is the same, just spread over an area (assuming we're talking about thermal heats here, which the Laserbee is). Got any examples?
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  5. #5
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    Catalanjo: Me neither have a clue what scanner wobble is. Some explaining would be appreciated.

    Norty: No problem getting a scanned image to fit the laserbee sensor, just a question about sizing down the scan angle in the projector setting page in QS and Beyond.

    The challenge seems to be a safetything build into the software. I seem to recall a thread where the topic were discussed regarding sizing down vs output power in pangolin sw. Not shure, but if it is so, then the setup with the testframe as Norty suggest will not work.

    Using a bouncing mirror to intercept might work and som of my projetors certainly will have the space available after dichros. I`ll give that one a shot.

    Setting 5v for the respective color module is also a possibility, and will give a good indication to what loss is produced through the galvo mirrors when the data are harvested before and after.

    Thanks for good answers.
    __________________________________________________ __________

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    Hi,.. first off ..apologies ! ....I had no idea that so few people were aware of this characteristic of broadband PMeters !
    I suppose it maybe just us old GAS heads with years of adjusting resonator mirrors for max power, that have noticed this!

    Anyone with a bit of experience optimizing resonators will automatically allow for this when adjusting optics, and be able to reach a higher power level, in a shorter time, than someone doing it for the first time, almost entirely due to this phenomenon.

    To clarify further ...Bband PMeters do NOT measure heat...they measure the temperature gradient across a known thermal bridge.! (usually the perimeter of a disk).
    This is an integrated measurement (over time) and any change either in the position of beam OR it's intensity will for a short time give a notably increased reading. To see this, one just has to hold a meter in front of a fixed beam (without any table support) and move the head a bit. The reading will increase ...then settle once meter is stationary.
    The same effect can be achieved by modulating power slightly with erratic pulses.

    Scan wobble is just that! (the wobble on a scanner)
    If one feeds a fixed coordinate to a scanning system the beam appears stationary in the near field.
    At a distance (>100M) however it will appear to "wobble" due to slight hunting or input noise or just ripple on the PSU.
    At 10km for example this is incredibly noticeable (gas lasers again) result is over reading on a Bband Pmeter.
    The more "erratic" (acceleration) in the wobble the greater the effect in question.
    A few years ago (well perhaps maybe a bit more than a few,) when illuminating the clock tower in Ibiza town from KU in San Raphael (approx 8km), thru scanners, I couldn't even hit the tower, let alone the clock, however straight out of the laser I had no problem at all!

    I hope this helps to clarify my earlier comments !
    Cheers

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    Thanks for the explanation Lari! I have to say, my scanners seem pretty solid on a single beam so it's never even come up as an issue. As I said too, I measure pre-scanners anyway. Unless I was specifically trying to identify bad mirrors I don't see the point, when I have a nice stable optical plate to rest my meter head on

    Regarding QS and power reduction with size, that only applies to the live control tab sizing.
    If you reduce the size in the projector settings or better in the zone geometric settings you'll get full power.
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  8. #8
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    Catalanjo is correct
    .
    Most meters have an input circuit with a phase lead characteristic to speed settling time. A good thermal meter overshoots slightly and settles. This "anticipation" circuit helps with human factors in tuning as well. So when scanning, the phase lead circuit will have a high gain at low frequency alternating currents, and you'll possibly see an artifact. If you've never tuned a laser cavity mirror for best power, you probably would not notice this part of the power meter.
    .
    Good Analog meter movements also have a "damping" circuit to keep the needle steady during tuning and when centering the beam on the detector.
    .
    .
    These circuit features are often missing in low cost hobbyist meters...
    ..
    ..
    And my meters , like Catalanjo's, all have 25 mm or larger Active Areas, you can scan on them.
    ..
    Usually scan mirror coatings have a widely variable reflectance with respect to angle, because of mirror coating physics issues*, so it helps to measure with the inputs grounded so the beam exits perpendicular to the scan head, at zero degrees of scan. That will be the "best" power position.

    ..
    *Reflected power is typically a quasi-cosine function with respect to input beam angle, and is very polarization sensitive on wideband mirrors..."

    .

    Steve
    Last edited by mixedgas; 09-17-2015 at 10:12.
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    Quote Originally Posted by mixedgas View Post
    Most meters have a circuit with a phase lead characteristic to speed settling time. A good thermal meter overshoots slightly and settles. The "anticipation" circuit helps with tuning as well. So when scanning, the phase lead circuit will have a high gain at low alternating currents, and you'll see an artifact. If you've never tuned a laser cavity mirror for best power, you probably would not notice this part of the power meter.

    Steve
    Hi Mixedgas
    That might be english to you, but pure latin to me.
    I have no clue to what an Laserbee is anticipating, and just want to feed it with the beam at highest possible power. Just to know what i am dealing with.

    So far i have learned that using the testpattern might give the most accurate result without opening the box or removing the modules. If possible, open case and use a bouncemirror to redirect the beam prior to the galvos and shoot an image without blanking.

    This helps a lot.

    Will have time next weekend to do some testing in my workshop.

    Thanks guys
    __________________________________________________ __________

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    the best way to get an accurate meter reading is to apply 5v to each color modulation pin on the ilda input and measure the static beam coming out of the projector.

    pin 5 (red+) and pin 18 (red ground)
    pin 6 (green+) and pin 19 (green ground)
    pin 7 (blue+) and pin 20 (blue ground)

    and ground

    Quote Originally Posted by Datsurb View Post
    I got my new Laserbee USB 3,7W yesterday. Big thank you to Mr. Jerry Bauer for beeing patient and generous.
    Now i can get the real readings from my builds, but I`m not shure what is the best way to get be most accurate result.
    Ripping out the modules from the projectors are something i really hope to avoid, and what i really want to know is the output after the optics.

    Did som initial testing yesterday, and hooked up one Projector with Beyond and FB3. Tried to do a small cone in one frame and shoot it at 100%. It actually did not produce the same power as the ILDA testframe i used to align the beam towards the receiver.

    So main question is: How to produce a 100% module output for measurement with beyond or QS?
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

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