Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-05-19
1991-02-19
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250902, 73293, G01N 1506
Patent
active
049946820
ABSTRACT:
A fibre optic sensor, particularly for ascertaining fluid levels, utilizes two cylindrical lightguides with regular perturbations to emit and/or accept light in a radial direction. Each waveguide is coupled to one (or more) light source and/or to one (or more) light detector. A light source such as a light emitting diode or laser diode is coupled to the lightguide which emits radially, illuminating a planar dielectric surface, which in the presence of a fluid with a low index of refraction, e.g. air, behaves as a mirror, coupling light via total internal reflection to the lightguide which accepts this light radially and channels the light to a light detector. In the presence of a fluid with a high index of refraction, for example water, at the planar dielectric surface the fluid dielectric interface becomes primarily transmissive, with relatively little light being coupled to the lightguide which accepts light radially. The optical signal received at the light detector is thus related to the depth of the planar dielectric surface which is immersed in liquid. Several different embodiments to achieve liquid level sensing, as well as a scheme for eliminating sensitivity to optical signal changes induced in the lead fibre, are disclosed.
REFERENCES:
patent: 3192392 (1965-06-01), Reed
patent: 4164077 (1979-08-01), Thomas
patent: 4870292 (1989-09-01), Alpert et al.
patent: 4878383 (1989-11-01), Wiegand, Jr. et al.
"Fiber Optic Fluid Level Sensor", Belkerdid and Ghandeharioun & Brennan, SPIE, vol. 566, Fiber Optic and Laser Sensors III (1985), pp. 153-158.
"Experimental Investigations on Fiber Optic Liquid Level Sensors and Refractometers", Spenner et al., pp. 96-99.
Focal Technologies Incorporated
Le Que Tan
Nelms David C.
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