Ultrasonic fuel level sensing device

An apparatus for measuring the height of liquid contained in a storage tank, the storage tank having a top, a bottom and a vertical axis extending from the tank bottom to the tank top:

• a tube having opposed ends, an interior diameter, ID, and an inner and outer surface, and being disposed inside the tank coaxial with the vertical axis, one end of the tube being mounted to the tank bottom and the other end being disposed adjacent the tank top;
• a float having a top portion and a bottom portion being separated by a cylindrical portion and being disposed inside and closely spaced to the inner surface of the tube, the bottom portion of the float defining a spherical surface, wherein the cylindrical portion of the float has a height, H, the spherical surface has a predetermined radius, R, which is at least a function of the interior diameter of the tube and the height of the cylindrical portion of the float, and the float is buoyed on the surface of the liquid;
• an ultrasonic transducer being disposed inside the tube and axially aligned with the vertical axis, the ultrasonic transducer being mounted to the tank bottom and adapted to emit ultrasonic pulses toward the bottom portion of the float, receive the reflected ultrasonic pulses, and responsively produce an echo signal;
• a temperature sensor being disposed adjacent the tank and adapted to monitor the temperature of the liquid, the temperature sensor producing a thermometric signal in response to the liquid temperature;
• and
• processing means for receiving the echo and thermometric signals, determining the speed of the ultrasonic pulse traveling in the liquid, and responsively determining the height of the liquid in the tank, the processing means producing a liquid level signal representing the liquid height.