Pressure sensor apparatus

This invention relates generally to pressure sensors and more particularly to apparatus for housing pressure responsive, variable, parallel plate capacitive transducers having, in plan view, a rectangular configuration and associated conditioning electronics.

Sensors comprising pressure responsive, variable, parallel plate capacitive transducers having a generally circular disc shaped configuration are well known. An example of such sensors is shown and described in U.S. Pat. No. 4,716,492, assigned to the assignee of the present invention. In that patent a capacitive transducer is shown having a thin, generally cylindrical ceramic diaphragm mounted in closely spaced, sealed, overlying relation to a generally cylindrical ceramic base with metal layers on respective facing 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 cup-shaped connector body of electrical insulating material is fitted over the electrical circuit and is secured to the transducer by a port fitting which has a port for exposing the transducer diaphragm to an applied fluid pressure. The diaphragm is movable in response to variations in fluid 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.

In copending U.S. Pat. No. 5,880,371, rectangular (in plan view) pressure sensing capacitive transducer elements are disclosed and claimed. The present invention relates to apparatus for housing such rectangular transducer elements.

It is an object of the present invention to provide a suitable package for housing a generally rectangular, in plan view, fluid pressure sensing capacitive transducer. Yet another object is the provision of a housing for receiving rectangular-shaped (in plan view) transducer elements which has essentially the same outer shape and dimensions as housings used for receiving cylindrical fluid pressure sensing capacitive transducers already in the market place so that the packages can be interchanged in a common application. Yet another object of the invention is the provision of a package having a cylindrical port fitting for interfacing with a fluid pressure source whose pressure is to be monitored having a rectangular-shaped (in plan view) sensing element mounted therein in which a circular sealing element is reliably received between the port fitting and the sensing element. Yet another object of the invention is the provision of connector means for electrically interconnecting a generally thin, rectangular (in plan view) sensing element to an electrical circuit mounted in the package and for providing a suitable interconnection between a ground conductor of the electrical circuit and the port fitting.

Briefly, in accordance with the invention, a base assembly has a first base member formed of electrically insulating material mounting a plurality of elongated terminal members in spaced apart, parallel relationship with an end of the terminal members received in an electronics chamber formed at one end of the first base member. A flexible circuit bent generally in a U-shaped configuration with one lobe portion overlying a second lobe portion is received in the chamber for attachment of terminal pads of the circuit on one, the first, lobe portion with the terminal members. A ground portion extends from the flexible circuit out of the chamber through a slot formed in the first base member. A pressure sensing capacitive transducer element has a rectangular configuration in plan view and is composed of a substrate having a diaphragm thereon with the contact pads on an outer surface along an edge of the element. The transducer element is butted up against an upstanding lip extending from the outer end of the other, the second, lobe portion of the flexible circuit. Generally U-shaped edge connectors are received over the edge of the transducer element and outer end of the second lobe portion to electrically join the contact pads and electrical circuitry of the flexible circuit.

A cover, or second base member, is receivable over the top of the base member and is formed with a wall having a circular fluid pressure receiving opening and with a first sealing gasket seat and a second sensing element seat coaxially formed in the wall with the circular opening. A generally circular, annular sealing gasket is received in the circular opening of the cover and is provided with outwardly extending tabs received on the first gasket seat and the sensing element is received in the second sensing element seat. The cover is provided with opposing leg members having an outer lip which are received in slots formed in the first base member and snap into transversely extending openings or notches to attach the cover to the first base member with the corner portions of the rectangular transducer element received on the end face of the first base member. A port fitting of suitable material, such as aluminum, is then received over the cover and is clamped to a circumferential flange of the first base member and with the ground portion of the flexible circuit pressed against the port fitting.

Other objects, advantages and details of the novel and improved capacitive pressure sensor of the invention appear in the following detailed description of the preferred embodiment of the invention, the detailed description referring to the drawings in which:

FIG. 1 is an exploded perspective of a pressure sensor made in accordance with the preferred embodiment of the invention;

FIG. 2 is a bottom plan view of the FIG. 1 sensor;

FIG. 3 is a cross sectional view taken on line 3 — 3 of FIG. 2;

FIG. 4 is a cross sectional view taken on line 4 — 4 of FIG. 2;

FIG. 5 is a perspective view of the first base member of the FIG. 1 sensor;

FIG. 6 is a top plan view of flexible circuit prior to being bent into a U-shaped configuration for receipt in the FIG. 1 sensor with the end portion of one lobe portion bent to form an outwardly extending lip;

FIG. 7 is a front view of the FIG. 6 flexible circuit;

FIG. 8 is a schematic diagram of the FIG. 1 sensor;

FIG. 9 is a perspective view of a capacitive sensing element used in the FIG. 1 sensor;

FIGS. 9 a and 9 b are respective plan views of the diaphragm and the substrate of the FIG. 9 capacitive sensing element;

FIG. 10 is a side view of an edge clip attached to a frame element;

FIG. 11 is a top plan view of a sealing element or gasket used in the FIG. 1 sensor;

FIG. 12 is a cross sectional view taken on line 12 — 12 of FIG. 11;

FIG. 13 is a side elevational view of the FIG. 11 gasket;

FIG. 14 is a perspective view of the second base member, or cover, taken from above;

FIG. 15 is a perspective view of the cover of FIG. 13 but taken from below; and

FIG. 16 is a cross sectional view taken through a port fitting used in the FIG. 1 sensor.

With reference to FIG. 1, a fluid pressure capacitive transducer 10 is shown comprising a first base member 12 , a flexible circuit 16 , a generally parallelepiped configured capacitive sensor 18 , edge clips 20 , a gasket seal member 22 , a second base member or cover 24 and a port fitting 26 .

First base member 12 , best seen in FIGS. 2-5, is generally formed of suitable electrically insulative, moldable material, such as Noryl, and mounts therein a plurality of elongated terminal members 14 in spaced apart relation with a distal end 14 a of each terminal received in an electronics receiving recess 12 a formed at one end of the base member. The opposite end 12 g of base member 12 forms a shroud for terminal members 14 . Sidewall 12 b extending around the periphery of recess 12 a is formed with a ground tab receiving slot 12 c , to be discussed, and with opposed notches 12 d having an inclined lead in surface 12 e for facilitating mounting of interfitting leg members of a second base member to be discussed. The thickness of wall 12 b is selected so that the end face 12 f of base member 12 will receive therein corner portions of the generally rectangular (in top plan view) shaped sensing element, to be discussed.

Flexible circuit 16 , formed of copper traces 16 d on a suitable substrate such as a polyimide and preferably having a cover layer of polyimide, has first and second lobe portions 16 a , 16 b joined by an intermediate central portion 16 c . Solder pad portion 16 e at one end is bent generally 90° along line 16f to form a fold or downwardly extending lip to facilitate installation of edge clips 20 , to be discussed. The outer cover of polyimide is etched away to expose ground layer 16 g and ground tails 16 h are formed in central portion 16 c by slitting the flexible circuit along lines 16 k.

The schematic circuit of FIG. 8, including integrated circuit U 1 , resistors and capacitors use the circuit paths of FIG. 6 and serves as conditioning electronics.

Lobe portion 16 b is placed in electronic chamber 12 a with terminal end portions 14 a received through apertures VO, VS and GND and soldered to solder pads surround the respective apertures. Flexible circuit 16 , at this point, extends out beyond chamber 12 a with central portions 16 c received in slot 12 c of wall 12 b of first base member 12 .

Capacitive transducer 18 , generally rectangularly shaped in top plan view, see FIGS. 9, 9 a , 9 b , has a relatively thin diaphragm 18 a received on a relatively thick substrate portion 18 b with terminal solder pads 18 c adjacent edge 18 d of the substrate left exposed or uncovered by the diaphragm. Capacitor plates 18 e and 18 f are deposited on opposed faces of the diaphragm 18 a and substrate 18 b respectively which are disposed in spaced apart relation by glass separation material 18 g . End 18 d of transducer 18 is butted up against the fold or lip in the solder pad portion 16 e of the flexible circuit with the solder pads of the transducer and the flexible circuit in alignment and edge clips 20 (FIGS. 1 and 10) are then pushed over the edge of the substrate and flexible circuit with an interference fit. Edge clips 20 are generally U-shaped having first and second legs 20 a , 20 b preferably with each leg having a solder pad 20 c . Legs 20 a and 20 b are preferably spaced apart a distance selected to form an interference fit with the transducer and flexible circuit layer thereon. An edge clip 20 is shown in FIG. 10 with a leader 20 used for handling purposes and which is broken off at score 20 e . After the edge clips are installed a reflow soldering operation is performed to form a good electrical connection between each solder pad of transducer 18 with a respective solder pad of flexible circuit 16 . The folded portion 16 e of the flexible circuit not only serves as a reference point for positioning the transducer but also allows the placement of the edge clips preventing movement of the flexible circuit substrate as the edge clips are forced onto the transducer and layer of the flexible circuit substrate.

The second base member, or cover 24 , best seen in FIGS. 14, 15 , is a generally circular member having a circular opening 24 a formed through top wall 24 b . The lower surface of wall 24 b is formed with a sealing gasket seat having four tab receiving portions 24 c . A second co-aligned, generally rectangular recessed seat 24 d , complimentary to the shape of transducer 18 , is also formed in the lower surface of wall 24 b for receiving transducer 18 in nesting relation thereon. Seat 24 d is elongated at one end (see 24 e ) and recessed further at 24 f to provide clearance for edge clips 20 . Circular opening 24 a is aligned with the center of diaphragm 18 a and offset from the center of cover 24 essentially by the elongated portion 24 e.

Cover 24 is provided with opposed, downwardly extending legs 24 h each having an outwardly extending lip 24 k at the distal end thereof for engagement in notches 12 d of base member 12 . It will be noted that inclined lead in surfaces 12 e of base member 12 are provided to facilitate placement of cover 24 by camming the distal ends of legs 24 h inwardly as the cover is pushed onto base 12 until lips 24 k are received in notches 12 d.

After transducer 18 is attached to flexible circuit 16 , lobe portion 16 a to which transducer 18 is attached, is bent back over lobe portion 16 b with its movement limited by engagement of the corners of transducer 18 with end face 12 f of base member 12 and with ground tails 16 h projecting through slot 12 c of base member 12 . Cover 24 is provided with a third downwardly depending leg 24 m which is slidably received in slot 12 c with projections 24 n on the end face of leg 24 m providing a back-up surface for positioning ground tails 16 h.

Annular sealing gasket 22 (FIGS. 11-13) is a generally circular element formed of suitable flexible material and is provided with a plurality of outwardly extending tabs 22 a . Although four such tabs are shown, the particular number of tabs provided is a matter of choice. The tabs serve as positioning and handling members to facilitate placement in seat 24 c with the circular element disposed in opening 24 a . With sealing gasket 22 in place, base member 12 with the flexible circuit and transducer mounted thereon, can be inverted and placed onto cover 24 with leg 24 m received in slot 12 c and opposed legs 24 h cammed inwardly until lips 24 k are received in notches 12 d.

Hexport 26 formed of suitable material, such as aluminum, has a threaded fluid coupling tubular portion 26 a shown with an internal thread; although it will be appreciated that an external thread could be employed, if desired, and a cup shaped portion 26 b formed with a sidewall having an attenuated outer portion 26 c . The base assembly of base member 12 and cover 24 is inserted into the cup shaped portion 26 b and the distal free end of the attenuated sidewall is crimped over flange 12 h of base member 12 at 26 d (see FIGS. 3, 4 ).

According to the invention, the second base member or cover provides a back-up for the internal pressure seal, a geometric relation between the sensing element and the internal seal, a support for the flex tail connection to the hexport, electrical insulation between the edge clips and the floor of the hexport, a hard stop to control compression of the sealing gasket, a means for retention of the internal seal for manufacturing assembly and for retention of the flexible circuit/transducer element prior to final assembly, a means for locating the transducer element on structural supports and for protecting the corners of the transducer element from damage during assembly while a reduced access depth to the terminal pins facilitate manual soldering of the flex circuit to the terminals. Features of the first base member includes interlocking retention with the second base member (cover) and a tail window flush with the terminal pins for allowing flex circuit optimization. The lip of the flexible circuit provides a positive stop for location of the flexible circuit relative to the transducer element with the edge clips providing connection to parallel, opposite surfaces of the flexible circuit and transducer element. Forming the hexport connection tails from within the overall circuit profile minimizes scrap material. The tabs on the sealing gasket facilitates retention of the gasket by the second base member (cover) for manufacturing assembly and the flat bottom of the gasket allows greater height to width ratio without causing bucking of the cross-section thereby increasing structural stability.

It should be understood that although the preferred embodiment of the invention has been described by way of illustrating the invention, various modifications can be made within the purview of the invention. For example, the U-shaped edge clips 20 used with transducer 18 and flexible circuit 16 facilitated by butting the transducer against the fold in solder pad portion 16 e can be used with other condition responsive sensor elements such as strain gauge sensors. It is intended to include all modifications and equivalents of the described embodiment falling within the scope of the appended claims.