High pressure package for pressure transducers

Abstract: The disclosure relates to a pressure transducer for use in measurement of pressures in the range of 3000 to 5000 psi and above wherein the pressure sensing module (7) is physically separated from the electrical connector (13) by a barrier formed from a material which is less readily deformable under high pressure than the connector. This is accomplished in one embodiment by separating the electrical connector (13) from the pressure sensing element (7) by a metal support ring (31) against which the pressure sensing element bears. In accordance with a second embodiment, the electrical connector is disposd externally of the housing with the pressure sensing element being disposed within the housing and bearing against an interior wall thereof. In accordance with a third embodiment, the housing is formed of two inexpensive members, one crimped within the other, with the pressure sensing module (7) bearing against an interior wall of the inner housing member and the connector being crimped to the system by a flange (15) on the outer housing member. Preferably, a conductor, which is connected to the circuit ground of the electronic circuitry (11) is also coupled to the system ground by crimping it between the housing and the electrical connector during the crimping of the connector to the remainder of the transducer.

Description: This application is related to our European Patent Application No. 89312263.0, filed 27th November 1989 for Pressure Sensor (Robert P. Bishop et al. Inventors) the contents of which are incorporated herein by reference. This invention relates to a packaging technique for pressure transducers and, more specifically, to such packaging for pressure transducers capable of measuring high pressures in the range of up to about 35 MPa (5000 psi). Pressure sensors containing pressure transducers are well known, typical such systems being described in United States Patents Nos. 4,716,492 and 4,774,626. Pressure transducers of the prior art have generally been fabricated by providing a pressure sensing module in the form of a variable capacitor responsive to pressure which abutted an electronic circuit. The electronic circuit sensed the capacitance of the capacitor and provided an output through a plastic electrical connector indicative of the sensed pressure. The transducer elements were arranged such that a metal cup assembly having an opening or pressure inlet at one end thereof to receive the fluid under pressure to be measured also included therein the pressure sensing module which was separated from the inlet by a gasket, the electronic circuit and connector also being contained within the metal cup. The parts were held together within the metal cup by crimping the metal cup over the plastic connector, the latter being used as a support member. Such pressure transducers are disclosed in US-A-4,716,492 and US-A-4,774,626 as mentioned above. The above described pressure transducer provided highly satisfactory results when operated in the low to moderate pressure ranges of up to 3.5 to 4.2 MPa (500 to 600 psi). However, when subjected to pressures at the pressure inlet in the range of about 21 to 35 MPa (3000 to 5000 psi) and up, the above described pressure transducers tended to fail. There were several points of failure, these arising from the inability of the plastic connector to support the high pressures to which it was being subjected. More specifically, the crimp at the metal cup was unable to retain the electrical connector crimped thereunder with the result that the connector was moved out of the cup and caused a failure of the transducer. A further point of failure was the plastic connector itself which would tend to shear or compress and release the gasket under the high pressure and release the gas under pressure. It is therefore clear that the prior art pressure transducer of the type described hereinabove was incapable of reliable operation in the high pressure environment. In accordance with the present invention, the above noted problem of the prior art is minimized and possibly overcome and there is provided a pressure transducer which is capable of withstanding operating, proof and burst pressures in the high pressure ranges of up to about 35 MPa (5000 psi) and possibly greater. According to the present invention there is provided a pressure transducer comprising metallic housing means enclosing a closed chamber having a front wall and a back wall and joined to a high pressure fluid inlet, a pressure sensing element having a pressure responsive surface and being supported in said closed chamber so as to abut the back wall of said chamber opposite said high pressure fluid inlet, sealing means between the pressure responsive surface of said pressure sensing element and the front wall of said chamber so that the sealing means, the pressure responsive surface of said pressure sensing element and the front wall of said chamber form the boundaries of a pressure cavity connected to said high pressure fluid inlet, and electrical connector means connected to said pressure sensing element and secured to said housing means so as to be physically isolated from said pressure sensing element by the back wall of said chamber. An advantage of a transducer according to the present invention is that the pressure sensing element is isolated from the connector by being disposed in an all metal surrounded cavity whereby the plastic connector is separated from the pressure sensing element and is not bearing the loads produced by the high pressure fluid. This is accomplished by means of a metal member disposed between the pressure sensing element and the plastic connector whereby the high pressures encountered by the pressure transducer are never applied to the plastic connector. In accordance with a first embodiment of the invention, a support ring is disposed within the metal cup or can and between the pressure sensing element and the plastic connector with the electronic circuit being disposed in the open portion of the ring between the connector and the pressure sensing element. In this arrangement, the metal cup or can is crimped over both the metal support ring and the plastic connector disposed therein to hold them in place, fixturing the pressure sensing module securely within the can. The gasket and pressure sensing module are as in the above noted prior art with the pressure sensing element abutting the metal support ring which provides the required support. The support ring may be open at its center region as above discussed or solid with holes or slots for the electrical feed from the pressure sensing element to the electronic circuitry. The can is in one piece with a threaded fitting to mate to the pressure port on the system with which the transducer is used. A hex configuration is formed on the part to allow the use of a wrench on the body of the device. The use of one piece as opposed to a separate can and port fitting has several advantages. For example, there are fewer parts and assembly operations and a potential leak path that would result from the joining of two parts is eliminated. The use of this assembly configuration fixtures the pressure sensing element independently of the connector, yet allows for component loading from one end during assembly, this being advantageous from both cost and complexity standpoints. In accordance with a second embodiment of the invention, the independent fixturing of the pressure sensing element is maintained. Here a can is used to enclose the pressure sensing element. The can is crimped over a hexport which allows mounting to the system being sensed. The other end of the can has a raised wall which crimps over the plastic connector, holding the connector in place and enclosing the electronic circuitry. Holes or slots are used in the can as required for electrical feedthroughs and gaskets and/or seals are used, where necessary, to protect the internal components. In accordance with a third embodiment, two inexpensive metal cans are used in place of the single can used in the second embodiment. The first can is used to fixture the pressure sensing element and crimp over a hexport. The second can is used to crimp over the first can at one end and over the plastic connector at the other end to enclose the electronic circuitry and hold the assembly together. Preferably, the embodiments use a flexible circuit as the mounting surface for the electronic circuitry. This allows for fold-up assembly during manufacture of the device. In addition, the flexible circuit allows for direct connections to the pins on the ceramic sensing element and the connector without the addition of wires and the connections required to attach them. The flexible circuit also allows for a direct connection from the circuit module to the can. This is done to couple the transducer ground pin to the metal can (system ground) to improve the device's electromagnetic compatibility (EMC) This is accomplished by folding a conductive "tail" from the flexible circuit over the edge of the connector and crimping the can thereover to make electrical contact. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1a is a cross sectional view of a prior art pressure transducer; Figure 1b is a view taken along the line 1b-1b of FIGURE 1a; FIGURE 2 is a cross sectional view of a pressure transducer in accordance with a first embodiment of the present invention; FIGURE 3 is a cross sectional view of a pressure transducer in accordance with a second embodiment of the present invention; FIGURE 4 is a cross sectional view of a pressure transducer in accordance with a third embodiment of the present invention; and FIGURE 5 is a cross sectional view of a pressure transducer in accordance with a fourth embodiment of the present invention. Referring first to FIGURES 1a and 1b, there is shown a pressure transducer 1 in accordance with the prior art. The transducer includes an outer metal can or cap 3 having a pressure inlet 5 at one surface thereof and a pressure sensing module 7 within the can separated from the inlet by a gasket or O-ring 9. Electronic circuitry 11 is positioned in contact with the module 7 and is otherwise surrounded by a plastic electrical connector 13 having a flange portion 15 over which the can 3 is crimped. An environmental sealant 17 is positioned at the junction of the can 3 and the connector 13 to prevent contaminants from travelling between the can and connector to the electronic circuitry 11. Three terminals 23, 24 and 25 extend outwardly at the rear of the connector and are connected to the electronic circuitry to provide an output therefrom. The pressure sensing module 7 is composed of a pair of ceramic layers 19 and 21 which are spaced from each other, each layer having an electrically conductive coating thereon on opposing surfaces to form a capacitor. The layer 19 receives the force of fluid entering the pressure inlet 5 thereon and, operating as a diaphragm, varies the distance between electrically conductive coatings to vary the capacitance of the capacitor as a function of applied pressure. As stated above, the above described pressure transducer provides excellent results with pressures at the pressure inlet of up to about 4.2 MPa (600 psi). However, at high pressures, such as in the range of 21 MPa (3000 psi) and higher, failures occur due to movement of the crimp over the connector and release of the connector. Also, failures occur due to compression of the connector and movement of the gasket between the can and the connector to permit inlet fluid to escape through the rear of the transducer due to leakage. Referring now to FIGURE 2, wherein all structure similar to that of FIGURE 1 bears the same reference character, there is shown a first embodiment in accordance with the present invention. This embodiment is similar to that described with respect to FIGURES 1a and 1b except that a metal support ring 31 capable of withstanding pressures in the range of up to about 35 MPa (5000 psi) is disposed between the pressure sensing module 7 and the electrical connector 13 to isolate the electrical connector and the electronic circuitry 11 from the high pressure applied at the pressure inlet 5. In this embodiment, the can 3 is shown to be crimped over both the support ring 31 as well as the flange 15 of the connector 13. Also, an O-ring 9 is used in conjunction with a rigid back-up ring 33, preferably of polytetrafluoroethylene (Teflon) to prevent the O-ring from movement between the sensing element 7 and the can 3. It should be noted that seating systems other than an O-ring, such as, for example, gaskets, lip seals, metal seals and the like, can be used. The result is that metal has been crimped over metal to provide an ability to withstand the high pressures to be encountered with transducer failure. The exterior surface of the pressure inlet 5 can be threaded to receive a mating threaded member (not shown). Referring now to FIGURE 3, wherein all structure similar to that of FIGURES 1a, 1b and 2 bears the same reference character, there is shown a second embodiment in accordance with the present invention. In accordance with this embodiment the metal can 41 comprises a set of crimping flanges 43 and 45 at opposite ends thereof, the crimping flanges 43 being crimped over a metallic hexport 47 capable of withstanding pressures of at least 21 to 35 MPa (3000 to 5000 psi). The hexport 47 includes a central pressure inlet passage 5 for entry into the transducer of the high pressure fluid to be measured. A gasket 9 or O-ring and back-up ring 33 (not shown) is positioned within the can 41 and spaces the pressure sensing element 7 from the hexport 47, the other surface of the element 7 resting against an interior wall of the can. The electronic circuitry 11 is positioned external of the can 41 on the wall against which the pressure sensing element 7 rests. The plastic electrical connector 13 is disposed over the electronic circuitry 11 with the crimping flange 45 being crimped over the flange 15 of the connector to form the completed pressure transducer. It can be seen that the pressure sensing element as well as all high pressure containing locations have been physically separated from the electronic circuitry as well as the electrical connector by a metal member capable of withstanding the pressures to be encountered. Referring now to FIGURE 4 wherein all character references corresponding to those previously used represent the same or similar structure, there is shown a third embodiment in accordance with the present invention. This embodiment includes a first interior metal can 61 which includes a flange 63, similar to the flange 43, for crimping over the hexport 47 with pressure inlet 5. Again, the pressure sensing module 7 is spaced from the inlet 5 by means of a gasket 9 with the module 7 resting against the interior wall of the can 61 remote from the pressure inlet. A second metal can 65 is disposed over the can 61 and includes crimping flanges 67 and 69 at opposite edges thereof. The crimping flange 67 is crimped over the can 61 and the crimping flange 63 thereof. The electronic circuitry 11 is positioned against the exterior of the can wall supporting the pressure sensing module 7 and is surrounded by the plastic electrical connector 13. The flange 69 is crimped over the flange 15 of the connector to provide the completed pressure transducer. Again, it can be seen that the electronic circuitry as well as the electrical connector are isolated from regions of high pressure by a metal member capable of withstanding the pressures to be encountered. Referring now to FIGURE 5 wherein all character references corresponding to those previously used represent the same or similar structure, there is shown a fourth embodiment in which provision is made for direct connection between the electronic circuitry 11 and the metal can. This is done to provide a direct connection between the circuit module and the can so that the transducer ground pin (circuit ground) can be coupled to the metal can (system ground). This improves the electromagnetic compatibility (EMC) of the transducer. This is accomplished by folding an electrically conductive tail 71 in the form of a flexible conductor and connected to electronic circuit ground over the flange 15 of the connector 13 and then crimping the metal can over the flange and the tail or flexible conductor 71 which is positioned between the flange and the can. As can be seen, this provides a simple interconnection between system ground and circuit ground, as desired. Though the invention has been described with respect to specific preferred embodiment thereof, many variations and modifications will immediately become apparent to those skilled in the art. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.

Claims: A pressure transducer comprising metallic housing means (3,31;41,47) enclosing a closed chamber having a front wall and a back wall and joined to a high pressure fluid inlet (5) at the front wall of said chamber, a pressure sensing element (7) having a pressure responsive surface and being supported in said closed chamber so as to abut the back wall of said chamber opposite said high pressure fluid inlet (5), sealing means (9,33) between the pressure responsive surface of said pressure sensing element (7) and the front wall of said chamber so that the sealing means, the pressure responsive surface of said pressure sensing element (7) and the front wall of said chamber form the boundaries of a pressure cavity connected to said high pressure fluid inlet (5), and electrical connector means (11,23,24) connected to said pressure sensing element (7) and secured to said housing means (3,31;41,47) so as to be physically isolated from said pressure sensing element (7) by the back wall of said chamber. A pressure transducer according to claim 1 wherein the sealing means (9,33) comprises a relatively rigid ring member (33) contacting said pressure responsive surface of said pressure sensing element (7) and said front wall of said chamber and a relatively less rigid O-ring (9) located inside said relatively rigid ring member (33) and contacting said pressure responsive surface of said pressure sensing element (7) and said front wall of said chamber, so as to form a boundary defining said pressure cavity, and wherein said relatively rigid ring member (33) prevents movement of said O-ring (9) between said pressure responsive surface and said front wall. A pressure transducer as set forth in claim 2 wherein said front wall is substantially parallel to said pressure responsive surface. A pressure transducer as set forth in claim 2 or 3 wherein said rigid member (33) is formed from polytetrafluoroethylene and said O-ring (9) is formed from a relatively softer material. A pressure transducer according to any one of claims 1 to 4 wherein said housing means comprises a cup-shaped part (3) with the high pressure fluid inlet (5) and a support member (31) secured within said cup-shaped part and defining said back wall of said chamber. A pressure transducer according to any one of claims 1 to 4 wherein said housing means comprises a cup-shaped part (41) defining said back wall of said chamber and a port (47) member with the high pressure fluid inlet (5) and defining the front wall of said chamber secured within said cup-shaped part (41). A pressure transducer according to claim 5 wherein said support member (31) includes a hollow central region and the electrical connector means includes an electronic circuit module (11) disposed in said hollow central region. A pressure transducer according to claim 7 including an electrically conductive member (71) secured between a ground connection of said electronic module (11) and said housing. A pressure transducer according to claim 5 including an electronic circuit module (11) disposed on said support member (31) remote from said pressure sensing element. A pressure transducer according to claim 6 in which there is provided a flange member (45) integral with the cup-shaped part (41) and extending externally thereof; and said electrical connector means is secured to said flange member (45). A pressure transducer according to claim 6 or 10 wherein said port (47) member is a hexport having a central bore forming said high pressure fluid inlet (6).

Inventors: BISHOP ROBERT P, BISHOP, ROBERT P.
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1989
Main classification: G01L9
IPC codes: G01L9, G01L19