Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1999-10-20
2001-08-14
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06272927
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to condition responsive sensors and more particularly to fluid pressure responsive capacitive transducers.
BACKGROUND OF THE INVENTION
A known pressure sensor as shown in U.S. Pat. No. 4,875,135, assigned to the assignee of the present invention, the subject matter of which is included herein by this reference, comprises a capacitive pressure transducer having a thin ceramic diaphragm mounted in closely spaced, sealed, overlying relation to a ceramic base and having metal coatings deposited on respective opposing surfaces of the diaphragm and base to serve as capacitor plates arranged in predetermined closely spaced relation to each other to form a capacitor. Transducer terminals connected to the capacitor plates are arranged at an opposite surface of the transducer base and a signal conditioning electrical circuit connected to the transducer terminals is mounted on the transducer. A connector body of electrical insulating material is fitted over the electrical circuit and is secured to a metal housing having a cavity in which the transducer is received. The metal housing is formed with a port for connection to a fluid pressure source to be monitored and a flexible O-ring seated in the metal housing around the port with the transducer biased against the O-ring to form a fluid seal and to define a fluid receiving recess with the diaphragm exposed to fluid in the recess. In that arrangement, the diaphragm is movable in response to variation in pressure applied to the diaphragm to vary the capacitance of the capacitor in accordance with the changes in applied pressure and the electrical circuit provides an electrical output signal corresponding to the applied pressure.
Although sensors of the type described have been very successful, there are certain fluids which are corrosive relative to elastomers used for the O-ring seals. By way of example, fluids having ammonia and automotive fluids having certain additives are incompatible with typical elastomers.
It is conventional to place a sensing element in a chamber and to seal the chamber with a flexible diaphragm with the chamber filled with relatively incompressible oil to serve as a pressure transfer fluid. This approach could be used in sensing a condition, such as pressure, of a fluid to be sensed, which fluid is corrosive to the sensing element. However, this represents a relatively expensive solution in manufacturing a suitable package requiring a number of processing steps including evacuation of a chamber and back filling with oil and providing a seal compatible with the pressure of the sensed fluids.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a fluid pressure sensor free of the above noted prior art limitations. Another object of the invention is to provide a fluid pressure sensor which has a hermetic fluid receiving chamber with a pressure transmitting surface for transferring pressure to the sensor which is accurate with little or no hysteresis and which is reliable and long lasting.
Briefly described, according to the invention, a metal housing having a fluid receiving port leading to a cavity in which a pressure sensing element is received has a flexible metal diaphragm extending over a portion of the cavity which includes the port. The metal diaphragm is hermetically attached to the housing as by welding or brazing. The pressure sensing element having a ceramic pressure sensing diaphragm is placed in the cavity with the ceramic diaphragm disposed against the metal diaphragm but with a thin intermediate layer of plastic material, preferably somewhat resilient, such as elastomeric material, therebetween. The fluid pressure is transferred to the ceramic diaphragm through the flexible metal diaphragm and intermediate layer with the intermediate layer effectively mitigating hysteresis. According to a first preferred embodiment the metal diaphragm and intermediate layer are essentially flat while in a second preferred embodiment both the metal diaphragm and the intermediate layer are formed with a plurality of corrugations to enhance engagement and compliance with the pressure sensing ceramic diaphragm.
REFERENCES:
patent: 4617607 (1986-10-01), Park et al.
patent: 4716492 (1987-12-01), Charboneau et al.
patent: 4774626 (1988-09-01), Charboneau et al.
patent: 4875135 (1989-10-01), Bishop et al.
patent: 5329819 (1994-07-01), Park et al.
Abrahamson Karl R.
Amatruda Andrew A.
Beringhause Steven
Aw-Musse Abdullahi
Baumann Russell E.
Fuller Benjamin R.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
LandOfFree
Hermetically sealed pressure sensing device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hermetically sealed pressure sensing device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hermetically sealed pressure sensing device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2522069