Non-intrusive pressure and level sensor for sealed containers

Abstract

A method and apparatus for determining the internal pressure of a sealed container are disclosed. The method involves: exciting a lid of the container so as to create at least two modes of vibration having separate frequencies, wherein said frequencies are fundamental, f1, and a second frequency, preferably the second axisymmetric mode, f2; detecting the vibration resulting from said exciting to determine f1, and f2; using f2, which is indicative of internal pressure, to calculate a first value for internal pressure using a first mathematical model that is calibrated to the lid on the sealed container; using f1, which is indicative of volume of contents, to calculate the volume of contents in the sealed container using a second mathematical model that is calibrated to the lid on the sealed container, wherein a natural frequency of said lid is a function of said internal pressure and said volume of contents; and compensating for said volume of contents to determine a second value for internal pressure, wherein said second value for internal pressure is more reliable than said first value for internal pressure. The apparatus for determining the internal pressure of a sealed container of the invention includes: means for exciting a lid of the container so as to create at least two modes of vibration having separate frequencies, wherein said frequencies are fundamental, f1, and a second frequency, preferably the second axisymmetric mode, f2; detecting means for detecting vibration resulting from the exciting of said container to determine f1, and f2; calculating means for calculating a first value for internal pressure of said container using f2; calculating means for calculating the volume of contents of said container using f1; wherein a natural frequency of said lid is a function of said internal pressure and said volume of contents; and calculating means for compensating for said volume of contents to determine a second value for internal pressure, wherein said second value for internal pressure is more reliable than said first value for internal pressure.

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