Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1998-09-17
2001-04-03
Felber, Joseph L. (Department: 2732)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S718000
Reexamination Certificate
active
06209398
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to fluid pressure transducers and packaging therefor and more particularly to low pressure sensing transducers and to transducers adapted for use in environments containing electromagnetic radiation such as in automotive, industrial and wireless communication environments.
BACKGROUND OF THE INVENTION
Pressure transducers of the type which comprise a thin, relatively flexible diaphragm portion of suitable material, such as silicon or ceramic, on which either a selected resistive element or a capacitive plate is printed whereby exposure to a fluid pressure source causes deflection of the diaphragm will cause a change in the resistive value of the resistive element or a change in the spacing of the capacitive plate with a mating capacitive plate and concomitantly a change in capacitance are well known in the art.
When used as a low pressure sensor, economical packaging of the transducer in a housing so that an effective seal is obtained while at the same time preventing stress related to the mounting and sealing of the transducer from influencing the output becomes problematic. This is caused, at least in part, by the significant difference in thermal expansion between the material used to form the transducer, e.g., silicon, ceramic or the like, and the housing of plastic or the like. A conventional sealing arrangement involves placement of a ring of sealing material around an inlet pressure port in a housing and mounting the transducer so that the pressure sensitive diaphragm is precisely aligned with the pressure port. This conventional arrangement not only involves stress isolation issues, it also limits flexibility in design choices in defining the location of the transducer within the package.
Another problem involved with liquid pressure transducer designs whether for use in monitoring high or low fluid pressure sources relates to their use in environments, such as automotive, industrial and communication, which contain electromagnetic radiation which cause interference (EMI) with the transducer signal. Typically, an outer electrically conductive metallic housing electrically tied to ground is used in which to mount the transducer package in order to shield the assembly from such EMI. This approach, however, not only adds to the expense of the product by adding to the part count of the assembly but it is also cumbersome and adds to the physical size of the package which is undesirable since such transducers are typically located in areas in which space is at a premium.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus and a method which overcome the above noted prior art limitations. Another object of the invention is to provide a fluid pressure transducer particularly suitable for use with relatively low pressure levels which is inexpensive to manufacture yet has improved yield and reliability. Yet another object of the invention is to provide a pressure transducer having improved means for isolating the transducer from EMI.
Briefly stated, a fluid pressure transducer made in accordance with a first feature of the invention comprises a housing formed of suitable material such as plastic having a cavity defined by a bottom wall circumscribed by a raised seating platform,the top surface of which lies in a first plane, and enclosing sidewalls extending upwardly from the platform. A plurality of height control pins extend upwardly from the bottom wall to a position which lie in a second plane spaced above the first plane by a specific, defined dimension or gap. A bead of flexible adhesive sealing material, such as RTV, is placed on the platform circumscribing the bottom wall and extending to some height above the second plane. A fluid pressure transducer formed of silicon, ceramic or the like and having a diaphragm formed in the bottom surface thereof spaced inwardly of the outer perimeter of the transducer is mounted on a circuit board formed of ceramic or other suitable material and sealed thereto by a bead of suitable sealant material, such as RTV, around the outer perimeter of the transducer. A suitable bore is formed through the circuit board at any desired location with the transducer aligned with the bore so that the diaphragm of the transducer is exposed to fluid pressure received through the bore. The circuit board is configured and sized to be received on the platform and to completely enclose the bottom wall of the housing. The circuit board is placed on the adhesive sealing bead on the platform prior to curing of the bead material and pressed downwardly into engagement with the height control pins so that a pressure seal comprising a bead of uniform, controlled height is formed all around the periphery of the circuit board. A first pressure port is formed in the bottom wall of the housing at any convenient location on one side of the circuit board and a second pressure port may be formed in the sidewall of the housing at any convenient location at a height above the location of the sealing bead on the other side of the circuit board.
The provision of the height control pins used in conjunction with the platform to form a sealing bead of uniform height greatly facilitates automated assembly as well as providing complete flexibility in locating the transducer at any desired location of the circuit board.
According to another feature of the invention, the top surface of the circuit board on which the transducer is received, as well as the top surface of the transducer body itself, are metallized to form EMI shielding surfaces. These surfaces are electrically connected together by means of suitable wire bond connections with another electrical connection being made from one of the metallized surfaces to a ground. This results in EMI protection without adding to the physical size of the device as well as without adding to the parts count and with minimal effect on cost.
REFERENCES:
patent: 5763787 (1998-06-01), Gravel et al.
patent: 5920015 (1999-07-01), Hallberg et al.
Davis Gerald F.
Fowler, Jr. John R.
Tomlinson James L.
Baumann Russell E.
Felber Joseph L.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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