Last update: 2021/04/27 20:10
safety:pass
https://wiki.pangolin.com/doku.php?id=safety:pass
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Printed on 2022/07/28 09:15
Once the photodiode is prepared as described above, use a function generator or software’s built-in
ability to project a circle. The circle should preferably be continuous, and non-modulated. In LD2000 this
is easily accomplished using the Abstract Generator. (Just go to SFX/Abstract Generator, and click OK.)
The size of the circle should be such that it scans within the area where the audience will reside.
As with some of the tests above, during these tests, it is important to use the lowest amount
of laser power possible. This will avoid overloading the photodiode and also reduce the
chance of illuminating personnel who might be in the room during these tests.
Move the tripod and photodetector such that the circle scans across the 7m aperture – AT THE CLOSEST
POINT OF AUDIENCE ACCESS – and look at the output on the oscilloscope. Preferably, the photodiode is
positioned roughly in the center of the beam path as it scans past the detector. This should also be the
brightest part of the beam. You should be careful, and be aware that photodiodes have shiny surfaces
which can create mirror-like back-reflections. Therefore you must be very careful while placing the
photodiode into the beam path, that the reflected stray beam will not accidentally wind up targeting
personnel or an undesired location.
Adjust the voltage input and time setting on the oscilloscope so that you can measure the height (i.e.
maximum voltage) of the pulses. During this part of the test, it is very important to make sure that the
photodiode is not overloaded with light, and merely delivering a “saturated” maximum voltage to the
oscilloscope, as this will artificially lengthen the pulse width. The PDA100A photodiode has an attenuator
dial on the side to adjust the gain. Make sure that this gain setting is adjusted properly, so that the
photodiode is not overloaded.
Step 5: Adjust the Minimum Velocity potentiometer
Once you have a reliable voltage measurement, the pulse width is determined at the “full width at half
maximum” points on the waveform. For example, if the voltage waveform slopes from 0 volts upward to
4 volts, and then downward to 0 volts, essentially this means that the pulse width is the amount of time
that the pulse is greater than 2 volts.
Since laser industry best practices are that audience scanning shows are done using the assumption of a
1-millisecond maximum pulse width, you should compare this against the pulse width seen on the
oscilloscope. If the pulse width is shorter than 1 millisecond, then you will need to slow down the function
generator (or Pangolin software abstract generator) until you get to a pulse width of 1 millisecond.
Generally, PASS should be adjusted to extinguish the laser beam for pulse widths greater than 1
millisecond. If you are able to slow down the function generator to obtain longer pulses, then this means
that the MINIMUM VELOCITY adjustment on PASS must be increased (turned clockwise).
Step 6: Adjust the Maximum Dwell Time potentiometer
Now that the Minimum Velocity adjustment has been setup, you can move to the next part of the test,
which ensures that the Maximum Dwell Time is adjusted properly. To do this, change the test pattern
from a circle to a Quadrature Squarewave. (A Quadrature Squarewave is a pattern where the beam stops
in four places, and jumps very quickly from place to place. The Abstract Generator in LD2000 has a drop-