Measuring and testing – Fluid pressure gauge – Vibration type
Reexamination Certificate
2001-03-07
2003-04-01
Williams, Hezron (Department: 2855)
Measuring and testing
Fluid pressure gauge
Vibration type
C073S715000, C073S728000
Reexamination Certificate
active
06539806
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to liquid-load measurements and in particular to sensors of the vibrating-diaphragm type.
2. Background Information
Many approaches have been taken to making liquid-load measurements. One approach particularly well suited to some applications is that of determining the loading on a vibrating diaphragm that has been placed in contact with the liquid. The mass of liquid that loads the diaphragm affects the diaphragm's response to flexural excitation. The loading inferred from the diaphragm's vibration can be used to determine the depth of a liquid of known density or the density of a liquid of known depth.
U.S. Pat. No. 5,035,140 to Daniels et al., for instance, describes a sensor arrangement in which a member potentially loaded by liquid in a tank is caused to vibrate, and the resultant vibration is measured to determined whether it is consistent with the member's being loaded by the liquid. Such a sensor is employed to determine whether liquid in a tank has reached a level at which the sensor is mounted.
Although the Daniels et al. sensor presumably performs adequately for the intended purpose, it is not well suited to providing a relatively accurate liquid-load measurement throughout a continuous load range. For that purpose, U.S. Pat. No. 5,345,811 to Alexandrovich et al. describes an approach that can be used to measure the density of fuel in an aircraft tank. The Alexandrovich et al. arrangement infers the density from the natural vibration frequency of a diaphragm as loaded by the fuel, with which the diaphragm is in contact. To achieve the desired accuracy, Alexandrovich et al. employ processor-based calibrations to determine coefficients in an equation relating the density to the natural frequency. With these coefficients, a processor calculates the density of the tested fluid from the observed frequency.
To minimize the effects that ambient-pressure variations would have on the measurement, Alexandrovich et al. mount and excite the diaphragm in a special fashion. Specifically, the diaphragm extends through a sealed slit in the tank wall, and the diaphragm is so excited as to assume vibration in a mode that has a node at the wall location. This allows both faces of the diaphragm to be exposed to the fuel so as to cancel out pressure effects.
My previous U.S. Pat. No. 6,079,266 describes an arrangement that eliminates the need for complex mounting of the type that Alexandrovich et al. use to minimize pressure effects. That arrangement simply takes a static-flexure measurement along with the measurement of the diaphragm's response to flexural excitation. By using calibration data taken for different pressures, it uses the static measurement in the liquid-loading calculation to eliminate any pressure effects. And it employs a common strain gauge both for the static-flexure measurement and for the measurement of the response to flexural excitation.
SUMMARY OF THE INVENTION
I have now developed an effective way to make the necessary static and dynamic measurements without a strain gauge, simply by using signals developed in the coil used to excite the diaphragm. I so mount a permanent magnet on the flexible diaphragm that diaphragm flexure displaces it, and I provide the coil with a saturable magnetic circuit so positioned with respect to the magnet that its degree of saturation significantly depends on the permanent magnet's displacement. This makes the coil's inductance relatively sensitive to the diaphragm's flexure, so the static pressure can be determined from the coil inductance. Moreover, the diaphragm's response to flexural excitation can be determined from the coil signal induced by the moving permanent magnet's field.
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Born, Esq. Joseph H.
Cesari and McKenna LLP
Jenkins Jermaine
Starr-Johnson
Williams Hezron
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