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PASS
Complete Help Docs - https://wiki.pangolin.com/
down list box where you can select the waveform that will be used.)
Move the photodiode and tripod into one of the corners of the quadrature squarewave, taking all of the
precautions mentioned above. Adjust the voltage level on the oscilloscope, and adjust the attenuator dial
on the photodiode to ensure that you have a reliable voltage measurement.
As described above, determine the pulse width at the “full width half maximum” points on the waveform.
If the pulse width exceeds 1 millisecond, adjust the MAXIMUM DWELL TIME potentiometer
counterclockwise.
Using PASS with a light sensor
When PASS is used with the “LIGHT SENSOR USED” switch setting, then a light sensor must be connected
to J803 Pin 1, Pin2, and Pin 3.
When a light sensor is not used, J803 Pin 2 should be connected to Pin 1. Note: it should be
understood that using PASS without a light sensor should only be allowed if you are using
the PASS hardware as a simple scan-fail safeguard AND if the laser power is low enough to
justify this AND if you implement additional safety-related systems down-stream from the
PASS hardware. Contact Pangolin for more information if you are interested in using PASS
without a light sensor.
When used, a light sensor must be installed within the beam path of the projector. Generally we
recommend that the light sensor be placed before the final shutter, but it may also be placed after, as
long as the final shutter opens faster than around 1/20th of a second.
Generally the light sensor is fashioned as a glass window that is used to “sample” the outgoing laser
beam at a 45-degree (or so) angle, and direct a small portion of the laser beam to light-sensitive
material.
The light sensor used with PASS must be a relatively fast sensor – one that is able to react as quickly as
the light can be modulated. Generally this means that the light-sensor must be based on silicon
photodiode or silicon PIN photodiode type technology.
If the projector is a multi-wavelength projector (e.g. an RGB projector), and a single light sensor is used in
the combined beam path, then the light sensor must have an additional “spectral flattening” filter to
make the light sensor provide the same output for all wavelengths. This is because the safety standards
treat all visible wavelengths the same. Since silicon detectors have a peak response in the near infrared
and since their response tends to trail off toward the visible blue spectrum, this filter appears to the
naked eye as a bluish piece of glass – allowing light in the blue end of the spectrum to pass freely, while
attenuating longer wavelengths more progressively. These tend to be specialized filters, generally
matched to a particular photodiode, and therefore we have not found a place that sells just the filter by
itself.
An alternative to using a single sensor in the combined beam path would be to put individual light
sensors after each separate- wavelength laser, and sum the output of all of the light sensors so that the
total output voltage sent to PASS corresponds linearly with wattage (i.e. delivers the same amount of