Abstract:
A pressure transducer assembly includes a transducer member supporting a transducer element for measuring pressure within an environment. The transducer member has a sealing surface surrounding the transducer element. A housing having an integral resilient member resiliently supports the transducer member and exerts a sealing force on the transducer member against a mating member secured to the housing.

Description:
BACKGROUND 
     Pressure transducers, for example a Pirani gauge or equivalent, are commonly used to measure gas pressure within enclosed environments (for example, processing chambers, areas between the pump and the process chamber, or load locks). Typically, the pressure transducer is contained within a housing that is positioned externally relative to the enclosure or chamber surrounding the environment. The pressure transducer housing is in communication with the enclosure by a conduit sealed therebetween. Consequently, the environment within the enclosure is extended to the pressure transducer via the conduit. The connecting conduit usually consists of a first fitting, secured to the pressure transducer housing, and a mating second fitting connected to the enclosure. Common methods of forming a gas tight seal between the pressure transducer housing and the fitting secured thereto include welding, soldering, brazing, bolting and the use of adhesives. Most of these methods require trained or skilled labor, as well as the use of tools for assembly. 
     SUMMARY 
     The present invention provides a transducer assembly where a gas tight seal can be formed against a fitting without employing skilled labor or the use of tools. The transducer assembly includes a transducer member supporting a transducer element for measuring properties of an environment. The transducer member has a sealing surface surrounding the transducer element. A housing is included which has an integral resilient member for resiliently supporting the transducer member and for exerting a sealing force on the transducer member against a mating member secured to the housing. 
     In preferred embodiments, the transducer assembly is a pressure transducer assembly for measuring pressure. The transducer assembly further includes the mating member which consists of a fitting having a circular cavity therethrough for sealing against the sealing surface of the transducer member and for surrounding the transducer element. The fitting facilitates coupling of the transducer assembly to the environment. A locking arrangement on the housing locks the fitting to the housing. The locking arrangement includes an angled circular groove formed in the housing near the opening of the housing for engaging an angled circular locking flange extending from the fitting. A filter element is positioned within the fitting for protecting the transducer element from contaminants. The housing has an interior with a circular opening thereto and a resilient rear wall forming the resilient member. A protrusion extends from the resilient rear wall towards the opening of the housing and into contact with the transducer member for exerting the sealing force on the transducer member in an axial direction. The transducer member includes a rigid circular plate having first and second sides. The transducer element and an annular flange forming at least a portion of the sealing surface, extend along the first side of the plate. An “O” ring is positioned on the annular flange to provide further sealing between the transducer member and the fitting. A circuit board facing the second side of the plate is electrically connected to the transducer element. The circuit board has an opening therethrough so that the protrusion from the resilient rear wall is able to extend through the opening before contacting the rigid circular plate. 
     The present invention allows a fitting to be sealed to a pressure transducer member in a gas tight manner merely by pushing the fitting by hand into the opening of the housing which surrounds the pressure transducer member until the fitting locks to the housing. This saves labor and time during assembly which results in cost benefits as well as flexibility for inventory. For example, the pressure transducer assembly may be offered with a choice of fittings. The customer is able to request a particular fitting which is secured to the housing prior to shipment. Alternatively, since the assembly procedure is simple and easily conducted, this can also be performed by the customer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIG. 1 is a side view of an embodiment of the present invention pressure transducer assembly positioned for securement to an enclosure. 
     FIG. 2 is a side sectional view of the pressure transducer assembly depicted in FIG.  1 . 
     FIG. 3 is a side sectional exploded view of the pressure transducer assembly depicted in FIG.  1 . 
     FIG. 4 is a top view of the pressure transducer plate depicting the transducer element wires. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, pressure transducer assembly  10  includes a housing  20  containing a pressure transducer plate  14  (FIG. 4) having pressure transducer elements  16  for measuring gas pressure within an enclosed environment, such as the interior  44   a  of an enclosure  44  (for example, a process chamber, areas between the pump and the chamber, or a load lock). A fitting, for example fitting  12 , is secured to housing  20  and sealed against transducer plate  14  around pressure transducer elements  16 . Fitting  12  is engaged with a mating fitting, for example fitting  42 , which is secured to the wall  46  of the enclosure  44  and is in communication with the interior  44   a  thereof. Typical methods of engaging fitting  12  with fitting  42  include clamping with an external annular shaped clamp or with bolts. Alternative methods include the use of threaded fittings. Pressure transducer elements  16  preferably consist of two resistive wires (FIG. 4) which extend above the surface of pressure transducer plate  14 . The wires of pressure transducer elements  16  are connected to a circuit contained within a circuit board  18  (FIG.  2 ). Typically, one wire is heated relative to the other wire. The unheated wire is connected in series with a temperature compensating resistor which is not exposed to the measured environment. The current through the heated wire is controlled such that the resistance of the heated wire is equal to the combined resistance of the unheated wire and the temperature compensating resistor. The current and voltage passing through the heated wire is measured and correlated to the appropriate pressure of the measured environment. Pressure transducer elements  16  operate in a manner similar to that described in U.S. patent application Ser. No. 09/583,339, filed May 31, 2000, which describes Pirani type and related gauges, the contents of which is incorporated herein in its entirety by reference. 
     Referring to FIGS. 2-4, the pressure transducer elements  16  of pressure transducer plate  14  are electrically connected to circuit board  18  by a series of pins  14   a  extending therebetween (FIGS.  2  and  3 ). Both the pressure transducer plate  14  and circuit board  18  are circular in shape and are housed within the interior  20   a  of housing  20 . Housing  20  has a circular cup shape and is formed of resilient material. A cable  26  extends through an opening  24  within the circular side wall  23  of housing  20  and is electrically connected to circuit board  18  by leads  26   a . Housing  20  includes a deflectable resilient rear wall  40  with a circular post  22  extending from the center of rear wall. Post  22  extends through an opening  18   a  within circuit board  18  to contact the rear surface of pressure transducer plate  14 . Pressure transducer plate  14  is sealed to fitting  12 , which facilitates coupling to enclosure  44  for pressure. Fitting  12  has an external angled annular flange  32  which engages or snaps into an internal angled annular groove  34  in the housing  20  near the opening  31  for locking fitting  12  to housing  20 . The resilient rear wall  40  behaves as a spring and exerts a sealing force on pressure transducer plate  14  thereby forcing pressure transducer plate  14  against fitting  12  for sealing therebetween. An “O” ring  30  is positioned between fitting  12  and pressure transducer plate  14  to improve sealing and ensure that the seal is gas tight. 
     During assembly, circuit board  18 , cable  26  and pressure transducer plate  14  are first preassembled together. Cable  26  is perpendicular to circuit board  18 , so that the leads  26   a  are cut at staggered lengths (FIG. 3) and then bent at right angles (FIG. 2) before soldering within corresponding holes  18   b  of circuit board  18 . The pins  14   a  of transducer elements  16  extending from pressure transducer plate  14  are also soldered into corresponding holes  18   b  of circuit board  18 . Pressure transducer plate  14  is spaced apart from circuit board  18  so that leads  26   a  are positioned therebetween. The “O” ring  30  is slid over diameter  28   a  of pressure transducer plate  14  and positioned on the annular flange  28  (FIG. 3) which extends around the perimeter of plate  14 . The circuit board  18 /cable  26 /pressure transducer plate  14  preassembly is then inserted into housing  20 . The circuit board  18  is slid over post  22  through opening  18   a  (FIGS. 2 and 3) in circuit board  18  and cable  26  is slid into housing  20  through the opening  24  in the side wall  23 . The preassembly is advanced into the housing  20  until pressure transducer plate  14  abuts against the flat end  22   a  of post  22 . 
     Pressure transducer assembly  10  may be kept in stock at the manufacturing plant or distributor&#39;s warehouse without fitting  12  assembled thereto to provide flexibility in meeting customer&#39;s needs. For example, fitting  12  is one of the many different fittings which may be assembled with housing  20  before shipping to the customer. The reason for this is that there are many different types of mating fittings which are commonly secured to enclosed environments. Therefore, prior to shipping, the manufacturer (or distributor) may secure the particular type of fitting requested by the customer (for example fitting  12 ) to the housing  20 . Alternatively, the customer can perform the assembly task. 
     Engagement of the fitting, for example, fitting  12 , with housing  20  is easily and quickly performed without tools or skilled labor. A filter screen  36  for protecting transducer elements  16  from contaminants is first inserted into the bore  21  of fitting  12  against shoulder  38  of counterbore  38   a  (FIGS.  2  and  3 ). Next, the end  12   a  of fitting  12  is inserted by hand into the opening  31  of housing  20 . The outwardly angled surface of the external annular flange  32  of fitting  12  progressively expands portion  33  of the resilient housing  20  outwardly, thereby allowing the passage of flange  32  therethrough. As the flange  32  passes through portion  33 , the end  12   a  of fitting  12  engages pressure transducer plate  14 , pushing plate  14  against post  22  backwardly and causing rear wall  40  to bow or deflect backwardly or outwardly in a curved manner. The central area of rear wall  40  experiences the greatest amount of deflection while the perimeter of rear wall  40  near the side wall  23  experiences the least amount of deflection. Deflection of rear wall  40  provides an axial sealing force between fitting  12  and pressure transducer plate  14 . Axial forces exerted by the outward deflection of rear wall  40  are transferred by post  22  to pressure transducer plate  14  which in turn presses against fitting  12 . Consequently, pressure transducer plate  14  is resiliently supported by the rear wall  40  of housing  20  via post  22 . After passing portion  33 , the external angled annular flange  32  of fitting  12  enters the internal annular angled groove  34  which is shaped to mate with flange  32  and snaps in place. The angled portions  34   b / 32   b  of groove  34  and flange  32  angle inwardly moving towards rear wall  40 . Vertical shoulder  32   a  of flange  32  abuts the vertical shoulder  34   a  of groove  34  and prevents the flange  32  from being pushed out of groove  34  by the sealing force provided by rear wall  40 . The resilient nature of housing  20  allows portion  33  to spring back to resume its original size and shape after flange  32  passes therethrough. 
     Once fitting  12  is locked to housing  20 , a constant axial sealing force is maintained between fitting  12  and pressure transducer plate  14 . The end  12   a  of fitting  12  presses axially against annular flange  28  of pressure transducer plate  14  and the counterbore  38   a  of fitting  12  radially engages diameter  28   a  (FIG.  3 ). The end  12   a  of fitting  12  includes a counterbore  17  for engaging and trapping “O” ring  30  between both annular flange  28  and diameter  28   a  of pressure transducer plate  14 . The depth of counterbore  17  is slightly less than the width of “O” ring  30  which allows the “O” ring  30  to compress under the axial sealing force and provides axial sealing between annular flange  28  and the end  12   a  of fitting  12 . Axial compression of “O” ring  30  also makes the “O” ring  30  widen or flatten and thereby presses the inner surface of “O” ring  30  radially inwardly against diameter  28   a  to provide radial sealing between counterbore  17  of fitting  12  and diameter  28   a  of pressure transducer plate  14 . The mating sealing surfaces of pressure transducer plate  14  and fitting  12  along with “O” ring  30  provide a gas tight seal between the plate  14  and fitting  12  which encircles pressure transducer elements  16 . Not only is the end  12   a  of fitting  12  tightly pressed against annular flange  28  of pressure transducer plate  14 , but “O” ring  30  is compressed against both the annular flange  28  and diameter  28   a  thereby providing annular sealing over a perpendicular region. Since the pressure transducer plate  14  is formed of rigid material, the sealing surfaces of plate  14  remain stable, thereby providing reliable or consistent sealing. 
     The pressure transducer assembly  10  depicted in FIGS. 1-3 is typically connected to an enclosed environment, such as enclosure  44 , in the following manner. Fitting  12  includes an external annular flange  15  which enables fitting  12  to be clamped to a mating fitting such as fitting  42  which is in communication with the interior  44   a  of enclosure  44  (FIG.  1 ). The mating fitting  42  is commonly mounted directly to the enclosure  44 , but alternatively, may be connected by a hose or tubing. A counterbore  19  allows clearance for an “O” ring which is included with the mating fitting  42 . Once fitting  12  is coupled to the mating fitting  42 , pressure transducer elements  16  are in communication with the interior  44   a  of enclosure  44  by way of fittings  12  and  42 , which form a conduit to the enclosed environment. Consequently, the enclosed environment is extended by this conduit from the enclosure  44  to the pressure transducer plate  14  thereby positioning the pressure transducer elements  16  in the same conditions as within the enclosure  44 . This enables the pressure transducer elements  16  to accurately measure the pressure within the enclosure while being positioned remotely relative to the enclosure  44 . Since the fitting  12  is sealed to the pressure transducer plate  14 , it can be seen that the region behind plate  14  within the interior  20   a  of housing  20  is external to the conditions surrounding transducer elements  16 . It is understood that fitting  12  is just one of many different fittings that can be assembled to pressure transducer assembly  10 . The particular fitting for engagement with pressure transducer assembly  10  is determined by the mating fitting (such as fitting  42 ) attached to the enclosure  44 . Typically, in most cases, any differences between fittings occurs at the end which engages the mating fitting. Therefore, it is apparent that different configurations and methods of securing the two mating fittings together are common. Although a fitting, for example, fitting  12 , has been described to be part of pressure transducer assembly  10 , pressure transducer assembly  10  in particular circumstances may be considered complete without such a fitting. 
     In one embodiment of pressure transducer assembly  10 , housing  20  is formed of a resilient polymer such as delrin and is about 0.875 inches in diameter and 0.55 inches wide. The wall thickness of housing  20  is about 0.05-0.06 inches thick and post  22  is about 0.2 inches in diameter. Post  22  extends to a position just below groove  34 , about 0.18 inches below opening  31 . Diameter portion  33  is about 0.757 inches in diameter. Groove  34  begins about 0.072 inches from the opening  31  and is 0.8 inches in diameter at that point. Groove  34  angles inwardly moving toward rear wall  40  at about a 17 degree angle. Opening  24  in sidewall  23  is about 0.2 inches wide and is sized to pinch cable  26  so that any pulling on cable  26  does not pull leads  26   a  from circuit board  18 . Rear wall  40  provides about 2.5 lbs. of sealing force for about 0.025-0.030 inches of deflection. 
     The pressure transducer plate  14  in this embodiment is about 0.6 inches in diameter and 0.06 inches thick. Flange  28  is about 0.037 inches wide and 0.015 inches thick. Transducer plate  14  is rigid such that virtually all the sealing force for sealing fitting  12  to transducer plate  14  is provided by the resilient rear wall  40  of housing  20 . Transducer plate  14  is formed of gold plated Kovar and has  12  pins  14   a  extending therefrom such as that used in integrated circuit packaging and available from Reeves-Hoffman (a division of the Dynamics Corporation of America). A portion of the pins  14   a  extend above the surface of transducer plate  14  on the side facing fitting  12 . Referring to FIG. 4, the wires of pressure transducer elements  16  are each supported by a pair of pins  14   a  above transducer plate  14  and face fitting  12  as shown. The resistive wires are about 0.0005 inches in diameter and 0.425 inches long. The unused pins  14   a  which extend to circuit board  18  may be employed for providing support for circuit board  18 . 
     In this embodiment, the outer diameter  13  of fitting  12  is about 0.75 inches in diameter with flange  15  being about 1.18 inches in diameter. When engaged, the combined axial length of housing  20  and fitting  12  is about 1.06 inches long. Angled flange  32  has an outer diameter of 0.797 inches resulting in a clearance of about 0.003 inches with groove  34 . Flange  32  is about 0.078 inches long in the axial direction and is angled outwardly at about 17 degrees starting at end  12   a . Counterbore  17  is about 0.585 inches in diameter and 0.024 inches deep. Counterbore  38  is about 0.53 inches in diameter and 0.135 inches deep. Bore  21  is about 0.42 inches in diameter. Fitting  12  is preferably formed of metal, such as aluminum. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. 
     For example, although particular dimensions and materials have been described for housing  20 , pressure transducer plate  14  and fitting  12 , such dimensions and materials may vary depending upon the application at hand. Housing  20  may be formed from more than one piece, may have metallic or composite parts, and may be formed of suitable polymers other than delrin. In addition, fitting  12  may be formed of other suitable metals such as brass, bronze or stainless steel, or may be formed of a polymer or composite material. Although flange  32  and groove  34  have been shown to be angled and engage on the interior of housing  20 , alternatively, flange  32  and groove  34  may have curved or square surfaces and engage on the exterior of housing  20 . In such a case, the fitting  12  and housing  20  are configured appropriately. Also, other suitable locking configurations may be employed such as threaded members, etc. The material of housing  20 , the thickness and diameter of rear wall  40 , the position of the flat end  22   a  of post  22  relative to groove  34 , and the thickness of flange  28  of pressure transducer plate  14  may be controlled to provide different sealing forces as required. Although rear wall  40  has been described to provide all the sealing force, alternatively, plate  14  may be configured to provide some or all the sealing force. The sealing force may be provided by other means such as with resilient tabs, a resilient intermediate annular wall, or a centrally located spring such as a coil spring. The spring may be a separate component or integrally formed with the housing. The particular “O” ring sealing configuration depicted in FIGS. 2 and 3 may be varied to suit the situation at hand. For example, “O” ring  30  may be arranged to seal between flange  28  and the end  12   a  of fitting without radially engaging diameter  28   a . Although pressure transducer assembly  10  has been shown to include a circuit board  18  positioned apart from pressure transducer plate  14 , alternatively, circuit board  18  may be omitted, with circuitry being positioned on the back side of plate  14 . In such a case, leads  26   a  of cable  26  would be connected to the back side of plate  14 . Although pressure transducer assembly  10  is typically connected to an enclosed environment, alternatively, pressure transducer  10  may be physically positioned within the environment to be measured. Also, although particular pressure transducer elements  16  have been described above, other suitable pressure transducer elements may be employed. Finally, the present invention may provide a sealed arrangement for transducer elements other than pressure transducer elements, or for other electronic elements or devices such as light emitting devices.