Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1999-07-15
2001-12-04
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06324914
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to pressure sensors and transducers and in particular to glass-ceramic components of such sensors.
BACKGROUND OF THE INVENTION
Ohnesorge et al, U.S. Pat. No. 4,422,335 discloses a pressure transducer made using quartz plates and Bernot, U.S. Pat. No. 5,189,591 discloses a pressure transducer using alumino-silicate glass plates. Whether glass or quartz, these sensors have generally been mounted to headers made of aluminum or stainless steel. Besides being expensive to machine, another disadvantage to these aluminum and stainless steel headers is that it is difficult to hermetically seal the electrical connections to these sensors. Without a hermetic seal, liquid and gas contaminants in the sensing medium can enter and ruin the sensor. As a result these types of sensors can only be used where the pressure medium is contaminant free such as dry gasses.
A further advance in sensor technology is disclosed in Bernot et al, U.S. patent application Ser. No. 08/986,253, filed Dec. 5, 1997, entitled, (as amended), “Capacitive Pressure Sensor Housing Having a Ceramic Base” which is assigned to the assignee of this application. This application discloses a sensor in which the prior art aluminum or stainless steel headers, (also referred to as bases), are replaced with a ceramic header and a cover that is either ceramic or metallic. The cover and header are sealed together with glass frit to define an interior chamber. A capacitive pressure sensor with alumino-silicate glass plates is mounted within the chamber.
Referring to
FIGS. 1-5
, in the fabrication of low-cost pressure sensor a critical component is the sensor base or header
36
that supports the housing
24
and the sensor
10
which is frit bonded to the top surface of pillar
50
. The base can be fabricated by a number low cost ceramic process which form the base from a glass powder. Because of the relatively small dimensions of the pillars
50
, it is difficult with these processes to achieve the required surface flatness of the top surfaces of the pillars
50
without the additional steps machining and grinding the surface. These steps of course increase manufacturing cost and reduce yield. They also cause a wide variation in tolerance that reduces sensor accuracy.
Accordingly, there is a need for base or header design that eliminates the flatness problem associated with the pillars.
SUMMARY OF THE INVENTION
An object of the present invention is to a sensor that has a base or header design that eliminates the flatness problem associated with the pillars.
The present invention accomplishes this object by providing a capacitive pressure sensor with a cavity is provided. The capsule includes a housing having a ceramic cover sealingly attached to a ceramic base to define an interior chamber. The base has a cavity facing this interior chamber and at least one hole adjacent the cavity that extends through said base. A glass sensor comprising a first diaphragm with a first electrode thereon and a second diaphragm with a second electrode thereon bonded together to form a capacitor is mounted in the chamber so that one of the diaphragms is received within the cavity and the other diaphragm lies on the surface of said base and covers the hole. A conducting member extends from said sensor, through the hole to electronic circuitry mounted to the capsule. The cavity also has a land for supporting the diaphragm disposed in therein.
Because the area of the top surface of the base is much larger than the area of the top surface of the pillar, its flatness is no longer a concern and in making these bases the steps of machining and grinding are no longer necessary.
These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings.
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Bernot Anthony J.
Xue Liang A.
Allied-Signal Inc.
Newburry, Esq. Keith
Oen William
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