1994-03-01

A Universal and Cost-Effective Fuel Gauge Sensor Based on Wave Propagation Effects in Solid Metal Rods 940628

In recognition of safety considerations, modern fuel tanks are frequently extremely irregular in shape. This places limits on the application of conventional potentiometric sensors. Required are more universal sensors without mechanically-moving parts. These sensors should also be characterized by especially good resolution and precision in the residual-quantity range, that is, the zero point precision should be of a high order.One type of metal rod can be bent into any of a variety of shapes to provide an effective means of monitoring the fuel level. In this metal rod, the propagation characteristics of a certain type of sound wave, known as bending waves, display major variations according to the level of the surrounding medium: The waves spread more rapidly through the exposed section of the rod than through the area which remains submerged. Thus the rod's characteristic oscillation frequency varies as a function of immersion depth. For electric processing, electromagnetic excitation is employed to induce ultrasonic oscillations in the rod. The phase at the exposed end of the rod is regulated to a constant value in order to maintain the rod at a characteristic natural frequency corresponding to the instantaneous fuel level. It is possible to maintain temperature-induced fluctuations in both zero-point stability and sensitivity at minimal levels through careful selection of suitable rod material and an appropriate operating frequency. Suitable profiles can be employed to optimize other operating parameters and adapt the sensor for use with specific measurement ranges.The present treatise reports on the basic principles of the process - the theory of which is simple to describe and simulate - as well as initial research results.

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