Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1986-10-01
1987-08-25
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250577, 356 5, G01N 2186
Patent
active
046894896
ABSTRACT:
A method and apparatus are provided for measuring the level of a surface of a material in a tank. The apparatus and method modulate an optical radiation beam at a radio frequency. The radiation beam is transmitted to the surface and the reflected beam received. The modulation frequency is changed until the phase of the received beam is the same as that from an optical reference path. The optical reference path is any fixed length path that allows the beam to pass from the source of the beam to the receiver that receives the reflected beam. An optical switch determines whether the receiver receives the reflected beam or the reference beam. The change in modulation frequency may then be correlated with the level on the material's surface in the tank.
REFERENCES:
patent: 3649123 (1972-03-01), Ulicki
patent: 3900260 (1975-08-01), Wendt
patent: 4210023 (1980-07-01), Sacamoto et al.
patent: 4236819 (1980-12-01), Green
patent: 4274736 (1981-06-01), Balmer
patent: 4297030 (1981-10-01), Chaborski
patent: 4359902 (1982-11-01), Lawless
patent: 4458530 (1984-07-01), Bastida
patent: 4498764 (1985-02-01), Bolkow
Nelms David C.
Shell Oil Company
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