An ultrasonic level sensor of novel design continuously measures the level of a liquid subjected to a high pressure (up to 6000 psi or sim;4times;107Pa), as is sometimes required for the effective transfer of the liquid. The sensor operates as a composite resonator, fabricated from a standard highhyphen;pressure plug. A flathyphen;bottom hole is machined into the plug along its center line. An ultrasonic transducer is bonded rigidly to the interior surface of the bottom wall, while the exterior surface is in contact with the liquid. Although the bottom wall is designed to satisfy the pressure code, it is still sufficiently thin to permit ready excitation of the axisymmetric plate modes of vibration. The liquid level is measured by a conventional pulsehyphen;echo technique. A prototype sensor was tested successfully in a 600hyphen;gal (sim;2300hyphen;l) water vessel at pressures up to 5500 psi. A spectral analysis of the transmitted pulse reveals that the flexural, extensional, thicknesshyphen;shear, and radial plate modes are excited into vibration, but none of these appears to be significantly affected by pressurization of the liquid.
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