Liquid level gauge comparing moldulations of incident and reflec

Details Liquid level gauge comparing moldulations of incident and reflec Liquid level gauge comparing moldulations of incident and reflec

1991-10-21

1993-03-16

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

356 5, 340619, G01N 1506, G01C 308

Patent

active

051947471

ABSTRACT:
A laser liquid level gauge for detecting the level of the surface of a fluid in a vessel includes an optical unit in the top wall of the vessel and a remotely located control unit. A laser diode at the control unit is amplitude modulated with a frequency tone to produce an incident beam which is carried by a fiber optic cable to the optical unit where it is directed through collimating optics to the fluid boundary. Reflections of the incident beam from the fluid boundary are focused by receiver optics to a photodiode at the optical unit, the output of which is coupled by a cable to the control unit, which includes a phase detector for comparing the phase of the modulation tone with that of the detection signal to produce a level indicating signal for display.

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