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Low Noise Particle Sensor with Improved Particle Size Classification

IP.com Disclosure Number: IPCOM000115529D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Brunsch, A: AUTHOR [+3]

Abstract

A dual beam particle detector is described, which will result in lower noise level and higher accuracy in size determination than conventional single beam laser light scattering detectors.

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Low Noise Particle Sensor with Improved Particle Size Classification

      A dual beam particle detector is described, which will result
in lower noise level and higher accuracy in size determination than
conventional single beam laser light scattering detectors.

      Laser light will be spreadened into a light band by means of
cylindrically shaped lenses.  After passing the particle detecting
area, the light band will be reflected twice by a prisma and will
pass the detecting area in some distance a second time.  Between both
passes the scattering light detectors are mounted.  A particle
falling through this sensor will scatter light twice with a time
difference depending on the travelling speed and the distance between
the two light bands.  The travelling speed for small particles at
pressures of some millitorr is strongly dependent on the size of the
particle.  There is also a size dependency on the amount of scattered
light (Figs. 1 and 2).

      Since the travelling speed and the amount of scattered light
can be determined independently, the system will have a strongly
improved accuracy for size determination compared to standard
particle counters.  The noise level will be drastically reduced
because light coming from outside the detector will result only in a
onetime detection.  Since particles have a preferred scatter
direction (small ones in forward direction) there will be additional
information from the difference of signals coming from detec...