Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1990-09-21
1992-01-28
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250574, 356336, H01J 516, H01J 4014
Patent
active
050846140
ABSTRACT:
An instrument for detecting single airborne particles, and measuring their concentration, includes a transmitting optical fiber optically connected to a light source at one end, and a collecting optical fiber connected to a photodiode at one of its ends. The respective opposite ends of the optical fibers are potted into a rigid probe head with their exposed ends polished smooth and flat, facing each other and separated by an air gap of about one-tenth of an inch. At least some of the light from the source crosses the gap between the optical fibers and reaches the detector, such portion of the light defining a particle sensing volume. Particles passing through this volume are detected by optical extinction as they reduce the amount of light reaching the detector. The device has simple optics, requiring no lenses or mirrors. The transmitting and collecting fibers, and the air gap, form a well defined and repeatable sensing volume so that individual devie calibration is not required. The probe is small and rugged, allowing it to be inserted directly in a fluid flow for in-situ measurements even in hostile environments. Associated signal processing electronics account for fluid stream velocity, so that the device measures true aerosol concentration in a fluid stream, regardless of changes in the stream velocity. The particle size threshold in the electronics is a percentage of the light to the detector which allows to remain in calibration when the amount of light through the probe changes.
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Allen S.
Nelms David C.
TSI Incorporated
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