Liquid-level sensor with optical fibers

A liquid-level sensor, consisting of three optical fibers, is described. A light is projected onto an oil surface through a transmitting fiber. A receiving fiber picks up the light reflected from the oil surface. A reference fiber transmits the light from a light-emitting diode back and forth along the same path as that of the transmitting fiber and the receiving fiber. Division is accomplished by using the reflected signal and the reference signal, so it becomes possible to eliminate apparent distance variations that are due to the variations in light intensity, which may be caused by external forces and temperature changes. The distance range is 100 mm.