Image Number 3 for United States Patent #3995169.
An optical liquid level gauge is described for sensing and indicating the height of a liquid within a container, such as within a fuel tank. The gauge includes an optical liquid probe that has a plurality of U-shaped light pipes to be inserted into a tank. Each of the light pipes terminates in a U bend with the U bends of such light pipes being staggered in position relative to one another so as to be positioned at different liquid height indication levels within the tank. A source of light is provided for transmitting light into a first arm of each of the light pipes, and sensors are provided at the end of the second arm of each of such light pipes for detecting the amount of light transmitted from one end of the pipe to the other. The U bend of each pipe has a geometrical design which assures that when liquid is not present in the tank it transmits substantially all of the light received by it from the first arm of the light pipe into the second arm thereof for sensing by the sensor associated therewith. The design of the U bend is such, though, that when the liquid within the tank is at a height submerging the U bend, light received by the U bend from the first arm of the light pipe will be refracted out of such light pipe, rather than passed to the second arm thereof. The sensor associated with the end of the second arm of each light pipe is connected with a display providing a visual indication of whether or not liquid is present at the U bend and, hence, at the liquid level in the container represented by such U bend.