FLUID PRESSURE TRANSMITTER

Abstract: A fluid differential pressure transmitter assembly in­ cludes a housing (2, 10) having a spacer (34) within the housing to minimize the internal fill fluid used to conduct fluid pressure from a fluid inlet port (4) to a pressure responsive diaphragm (26). Input pressures are applied to respective sides of the diaphragm (26) to produce an electrical signal output representative of the differential pressure from piezoresistive elements deposited on the diaphragm. The sensor (26) is electrically connected by flexible wires (30) to electrically conductive paths (32′) supported on an end surface (32) of the spacer (34). The conductive paths are, in turn, electrically connected to electrode wires (38) at electrically conductive support junc­ tions (48) between the spacer (34) and the electrode wires (38). However, the spacer (34) is supported on the electrode wires (38) at the support junctions (48) in a free floating arrangement without any other physical contact to either adjacent elements within the housing or the interior wall of the housing. Thus, physical changes to the spacer such as those occasioned by temperature changes are not transmit­ ted to the fluid seals (42). The electrode wires (38) are arranged to pass through fluid-tight seals (42) in the transmitter housing to provide external electrical connect­ ions to the sensor while supporting the spacer within the housing.

Description: The present invention is directed to fluid pressure transmitters. DE-A1 27 18 931 describes a differential pressure transmitter and shows in Figure 3 a version of the transmitter in which a disk-shaped support for the sensor is carried by a pressure supply tube which projects through one of the walls of the housing. An ion migration shield or Farraday shield is located in front of the sensor within the cavity and is supported by several studs fixed to said wall. This wall furthermore holds within hermetic seals a plurality of electrically conducting wires whose one end extends out of the housing and whose other end by means of a flexible wire is electrically connected to the sensor. Another known pressure transmitter shown in Electronic Engineering, November 1981, page 169, includes a sensor consisting of a silicon diaphragm supporting four piezoresistors with two located along the diaphragm radius and two others implanted tangentially to the diaphragm radius. As pressure is applied to one side of the diaphragm, two of the resistors increase in value while the other two decrease. The sensor chip together with a sensor support and a thick film circuit are clamped between a base portion of the housing and its cover. O-ring seals are provided between the housing and the sensor on the one side and the ceramic thickfilm circuit and the cover on the other side. The sensor is electrically connected to the thickfilm circuit by resilient wire bonds. US-A 43 42 231 shows in Figures 2a and 2b the sensor unit of a differential pressure transmitter including a semiconductor sensor supported on a support member carried by the housing. The semiconductor sensor is surrounded by a ring-shaped ceramic substrate, also fixed to the housing but spaced apart from the sensor and its support. This ceramic substrate carries the wiring for the sensor and is electrically connected to the sensor by a plurality of wire-bonded lead wires. A protective cover is positioned in front of the sensor and is also fixed to the housing. Lead wires transmit the electrical signal from the ceramic substrate to the outside of the housing. These lead wires extend through passages in the wall of the housing and said passages are filled with a hermetic seal extending along the entire passage. An objet of the present invention to provide an improved fluid pressure transmitter assembly, where the seals of the electrical connections of the sensor to the outside of the housing are relieved from mechanical stress caused by changes in temperature of the fluid and the parts inside the housing. A further object of the invention is to minimize the volume of the fluid fill in the housing. In accomplishing these and other objects, there has been provided the invention, as described in claim 1. Further features and improvements are described in the dependent claims. A better understanding of the present invention may be had when the following detailed description is read in connection with the accompanying drawing, in which the single figure is a cross section illustration of a fluid pressure transmitter assembly embodying an example of the present invention. Referring to the single figure in more detail, there is shown a fluid differential pressure transmitter having an outer cup shaped housing 2. A first fluid inlet port 4 is provided in an end wall 6 of the housing 2 to enable a first input pressure to be admitted into an interior volume or cavity 8 defined by the housing 2. A cover 10 for an open end 12 of the housing 2 is attached thereto by any suitable means providing a fluid-tight seal, e.g., an electron beam weld 14. A second fluid inlet port 16 is provided in the cover 10 to allow the admission of a second input fluid pressure into the housing 2. The cover 10 is provided with a circular recess 18 coaxial with the second fluid inlet port 16. A hollow support tube 24 has a first end 20 coaxially mounted within the recess 18 and is bonded to the adjacent side wall of the recess 18 by any suitable means, e.g. an adhesive, to provide a fluid-tight seal thereto. A fluid conduit 22 within the tube 24 is aligned with the second fluid port 16 to conduct a fluid admitted by the second port 16. A second end of the tube 24 is used to support a pressure sensor in the form of a diaphragm 26 which is secured at its peripheral edge 28 to the second end of the tube 24. The attachment of the diaphragm 26 to the tube 24 is arranged to provide a fluid-tight seal between the diaphragm 26 and the tube 24. The diaphragm 26 has a pressure sensitive coating thereon which may be in the form of piezo-resistive elements, in a manner well-known in the art. These diaphragm elements are attached to one end of respective ones of a plurality of flexible wires 30 which provide electrical connections thereto. The other ends of the wires 30 are connected to respective ones of electrically conductive paths 32′ supported on a first end surface 32 of a spacer 34 located within the interior volume 8 defined by the housing. The spacer 34 is preferably in the form of a cylindrical element coaxial with the tube 24 and having an axial aperture 36 spaced from the tube 24. A plurality of electrically conductive and relatively rigid electrode wires 38 are arranged to pass through holes 40 in the cover 10. Hermetic seals 42 are located between the wires 38 and the surfaces of the cover 10 surrounding the holes 40 to provide fluid-tight connections thereto. The wires 38 extend into the housing cavity 8 and pass through respective ones of a plurality of bores 44 in the spacer 34 which coaxially surround each of the corresponding ones of the electrode wires 38 while being spaced therefrom. The free ends 46 of the electrode wires 38 within the housing 2 are rigidly attached to the first end surface 32 of the spacer 34 by any suitable means to provide mechanical and electrical connections 48 thereto, e.g., or soldering. The connections 48 are arranged to provide a support junction for the spacer 34 and to provide a current path between the electrode wires 38 and the aforesaid electrically conducting paths 32′ on the end surface 32 of the spacer 34 which, in turn, as previously described, are connected to the wires 30 leading to the diaphragm pressure sensor 26. The spacer 34 is arranged to be a free floating element within the cavity 8 of the housing 2 and is, accordingly, spaced from the interior walls of the housing 6, the cover 10, the electrode wires 38, the support tube 24 and the diaphragm 26. Thus, the spacer 34 is suspended from the connections 48 to the electrode wires 38 whereby temperature changes in the environment of the pressure transmitter, which can produce physical changes in the spacer 34 based on the coefficient of temperature expansion of the spacer 34, do not affect the hermetic seals 40, i.e., the hermetic seals 40 are not stressed by temperature induced expansions and contractions of the spacer 34. The spacer 34 is used to reduce the volume within the housing 2 to minimize the amount of a fill fluid (not shown) needed for transmitting the first input pressure to one side of the sensor diaphragm 26. A first fill fluid would be arranged to fill the cavity 8 within the housing 2 while a second fill fluid (not shown) would be arranged to fill the fluid conduit 22 within the tube 24 to transmit a second input pressure to the other side of the sensor diaphragm 26. Concurrently, the spacer 34 provides a support for the electrical connections 32′ between the flexible wires 30 and the electrode wires 38. The illustrated size relative and shape of the spacer 34 is only intended to provide an example of the present invention since the size and shape thereof may be modified to conform the spacer 34 to the operating requirements of the transmitter. Accordingly, it may be seen that there has been provided, in accordance with the present invention an improved fluid pressure transmitter assembly.

Claims: 1. A pressure transmitter comprising: a) a housing (2, 6, 10) for being filled with a fill fluid and having at least one pressure inlet port (4, 16); b) pressure sensing means (24, 26) mounted within said housing and including a pressure sensor in the form of a diaphragm (26) and a mounting tube (24) for said sensor (26); c) electrically conducting wires (38) held in a wall (10) of said housing (2, 6, 10) by hermetic seals (42) with one end of said wires extending out of said housing and the other end being electrically connected to said pressure sensor (26); d) a spacer (34) provided within the cavity (8) of said housing for minimizing the free volume therein; e) bores (44) extending through said spacer (34) in the direction of said wires (38); f) said wires (38) extending freely through said bores (44) and being mechanically fixed to said spacer (34) at the end of said bores remote from said wall (10), such that g) said spacer (34) is suspended as a free floating body within said housing (2, 6, 10) and is spaced from the interior walls of said housing and from said sensing means (24, 26). 2. The transmitter according to claim 1, characterized electrical connection means (30, 32′) electrically connected to said wires (38) and supported on that surface (32) of said spacer (34). 3. The transmitter according to claim 2, characterized in that the connection means (30, 32′) includes at least one electrical conductor (32′) mounted on said surface (32) of the spacer (34) and at least one flexible wire (30) connecting said conductor (32′) to said sensor (26). 4. The transmitter according to claim 3, characterized in that said spacer (34) is coaxial with said tube (24) while being spaced therefrom. 5. The transmitter according to claim 4, characterized in that a) pressure supply ports (4, 16) are provided in opposite wall portions (6, 10) of the housing (2, 6, 10); b) the sensor mounting tube (24) is positioned with one end (20) in a recess (18) of one of said wall portions (10) and with its internal fluid conduit (22) communicating with one of said ports (16); c) the sensor mounting tube (24) is sealed within said recess (18); d) the sensor (26) is fixed to the free end of said tube (24) closing said fluid conduit (22); e) the spacer (34) is ring-shaped and surrounds said tube (24) without touching said tube or parts of the housing; f) said bores (44) are open at that side of the spacer (34) which faces said one wall portion (10).

Inventors: WAMSTAD, DAVID B., WILDA, DOUGLAS W.
Applicants: HONEYWELL INC.
Application year: 1984
Main classification: G01L9
IPC codes: G01L9, G01L19, G01L13