Abstract:
There is disclosed a high pressure sensing header which is relatively insensitive to mounting torque. The header comprises an outer torque isolating shell which surrounds an inner “H” section header. The inner “H” section header has a thick diaphragm and is surrounded by the torque isolating shell which is secured to the “H” section header at a peripheral flange of the “H” section header. In this manner when the header is installed, the installation force is absorbed by the outer shell and there is no installation force or torque exhibited by the inner “H” section which will respond only to stress due to pressure. The torque isolating shell also contains a top surface which has a counterbore that accommodates a crush ring. When the unit is installed, the crush ring is crushed against an installation wall to enable the inner header to receive pressure without experiencing significant installation force.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application is a continuation application claiming priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 13/010,837, entitled “TORQUE INSENSITIVE HEADER ASSEMBLY,” filed 21 Jan. 2011, which is a continuation application claiming priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 12/387,548, entitled “TORQUE INSENSITIVE HEADER ASSEMBLY,” filed 4 May 2009, both of which are hereby incorporated by reference in their entirety as if fully set forth below. 
         [0002]    Further, the following applications are generally related to this application. See application entitled “HIGH PRESSURE TRANSDUCER HAVING AN H-SHAPED CROSS-SECTION” filed on Mar. 19, 2008 as Ser. No. 12/077,637 which is a continuation in part (CIP) of application Ser. No. 11/825,089 filed on Jul. 3, 2007 with the same title, both applications are assigned to Kulite Semiconductor Products, Inc., the assignee herein, and incorporated by reference as if fully set forth below. 
     
    
     FIELD OF THE INVENTION 
       [0003]    This invention relates to high pressure transducers and more particularly to an “H” shaped cross sectional transducer header which is relatively insensitive to mounting torque. 
       BACKGROUND OF THE INVENTION 
       [0004]    If one refers to the above-noted co-pending applications cited under related applications, one will ascertain that there is disclosed high pressure transducers which basically have an “H” shaped cross section. As indicated in the co-pending applications, these devices can operate at pressures in excess of 60,000 psi. Thus as one can ascertain, the pressures are extremely high. The applications, as indicated above, disclose a transducer having an “H” shaped cross section. Essentially the diaphragm is thick in order to obtain high pressure operation. In any event, the above noted applications describe such a diaphragm which has a step or flange portion, which essentially surrounds the active a diaphragm area. Thus the active area is smaller than the active area of prior art devices. By including the step resulting in a smaller diameter active area, one can now obtain negative stresses at the edges of the diaphragm. This enables a full Wheatstone bridge configuration to be employed. As one can ascertain from the above noted applications, most high pressure sensing headers employ front faced sealing. Such techniques utilize a crush ring or a metal to metal seal. In any event, the force to make this seal is applied by installing a threaded element behind a header. The header and seal are then placed in compression. Based on experimental data, there is a high zero shift and a torque sensitivity when employing this installation technique. The finite element analysis indicates that the face sealing header is placed in compression, which in turn compresses or pinches the outer periphery of the thick sensing diaphragm in the “H” section. This pinch causes radial strain in the diaphragm and affects the linearity and zero shift of the pressure sensor. It is therefore an object of the present invention to provide a header assembly which is insensitive to installation torque. The header assembly, as will be described, is insensitive to the mounting torque and therefore enables high pressure sensing headers to be utilized in a reliable and efficient manner. 
       SUMMARY OF THE INVENTION 
       [0005]    A pressure transducer assembly, comprising: a diaphragm member having an “H” shaped cross section with a central diaphragm area having two upper extending arms and two lower extending arms forming an “H” shaped cross section, an outer cylindrical shell surrounding said “H” shaped diaphragm member, said shell secured to said diaphragm member, said shell having a top surface with an aperture communicating with said central diaphragm area of said member, said shell positioned to enclose said diaphragm member operating to absorb installation torque applied to said assembly during installation whereby said diaphragm member receives a relatively insignificant installation torque. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]      FIG. 1  is a cross sectional view of a prior art “H” shaped diaphragm which employs face sealing. 
           [0007]      FIG. 2  is a cross sectional view of a prior art transducer utilizing the diaphragm of FIG. 
           [0008]      FIG. 3  is a cross sectional view of an improved torque insensitive header assembly according to this invention. 
           [0009]      FIG. 4  is a graph depicting test data of a torque insensitive unit as compared to a torque sensitive unit without employing this invention. 
           [0010]      FIG. 5  is a cross sectional view of a transducer assembly which employs a torque isolation shell according to this invention. 
           [0011]      FIG. 6  is a cross sectional view showing the installation of a transducer fabricated according to this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring to  FIG. 1  there is shown a cross sectional view of a prior art “H” shaped transducer as the type utilized in the prior art.  FIG. 1  essentially corresponds to  FIG. 3  of the co-pending applications designated as Ser. Nos. 12/077,637 and 11/825,089. Thus, there is shown in  FIG. 1  the “H” shaped transducer as indicated in the above noted applications. The transducer configuration  19  includes a step or flange portion  21  which essentially surrounds the active area or diaphragm area  24 . Thus the active area  24  is smaller than the active area of prior art devices. By including the step  21  and the smaller diameter active area  24 , one now obtains negative stresses at the edges of the diaphragm area  24 . Thus the step section  21  enables negative stresses to be provided at the periphery of the diaphragm area  24 . By measuring the strain, one can obtain an electrical output proportional to the high pressures experienced by the diaphragm. Thus as seen in  FIG. 1 , sensors which are piezoresistive gauges are positioned on the diaphragm  24  as sensors  30 ,  31 ,  32  and  33 . The sensors are arranged into a full Wheatstone bridge which therefore increases the output and accuracy. Thus there are two gauges as  30  and  31  which are positioned about the center of the active area  24  and on the gauge side  23 . Gauges  30  and  31  are both positive operating strain gauges. Overlying the step portion  21 , which surrounds the active area  24 , are gauges  32  and  33 . These gauges are negative strain gauges. Thus gauges  30 ,  31 ,  32  and  33  are wired as a conventional Wheatstone bridge to enable one to obtain greater output as well as greater accuracy. The full Wheatstone bridge on the transducer responds to pressures up to 60,000 psi with a large and accurate output. 
         [0013]    Referring to  FIG. 2  there is shown a cross sectional view of a typical transducer utilizing the “H” shaped cross sectional unit of  FIG. 1 . Thus as seen in  FIG. 2 , the transducer configuration which is the “H” shaped transducer  19  is welded to the front end of a pressure sensor. The front end of the pressure sensor or pressure transducer has a passageway  52  which allows wires from the gauges on the section  19  to be directed. There is also a threaded portion  53  which mates with a sealing housing section  54 . The housing section  54  is coupled to a body  56  or shell which has an internal hollow  55  where compensation/electronics are positioned. There is shown a connector  57  as well. Thus the device in depicted in  FIG. 2  is mounted as follows: An aperture is provided into which a threaded section  53  is directed. The aperture is also threaded and the “H” section  19  is then inserted in the aperture while the device is placed in position by means of the thread  53 . There would be a compression ring which would co-act with the front edge of the “H” section header and abuts against the bottom of the aperture to enable a tight seal to be formed between the face of the header  24  and the wall of the aperture. The crush ring or a metal to metal is provided the installing the threaded element  53  behind the sealing header  54 . In this manner, a tight seal is provided to prevent leakage. The force required to mate the seal is supplied by installing the threaded element  53  behind the header section as  19 . Thus the header and seal are placed in compression. Experimental data indicates a high zero shift in torque sensitivity which results from this installation technique. The analysis indicates that the face sealing header  19  is placed in compression which in turn compresses or pinches the outer periphery of the thick sensing diaphragm  24  in the “H” section  19 . This pinch causes radial strain in the diaphragm  24  and affects the linearity and zero shift of the pressure sensor. 
         [0014]    Referring to  FIG. 3  there is shown a cross sectional view of a “H” shaped header  61  and a torque isolating outer shell  60 . As seen in  FIG. 3 , there is shown an isolation shell  60 . The shell  60  essentially is of a “C” shaped cross section and has extending arms  72  and  73 . The shell has a sealing surface  67 , which surface will be pressed against the wall into which the header will be placed, as will be shown and explained. Essentially the shell contains an aperture  69  which allows media passage and contains a counterbore  68  which will accommodate a crush ring so that when the unit is placed on a surface or wall, a crush ring which is situated in aperture or depression  68  is forced against the wall in which the transducer is inserted and forms a tight metal seal. Essentially the media passage aperture  69  communicates with aperture  65  which is the top aperture in the “H” shaped header  61 . The “H” shaped header has thick diaphragm  74 , the underside of the diaphragm has secured or fixed thereto strain gauges as  63 , which strain gauges are conventionally formed in a Wheatstone bridge array. Essentially the header, which is “H” shaped, has top arms  75  and  76 , which are shorter than the bottom extending arms  78  and  77 . As one can see, the “H” shaped header has a peripheral flange  70  which encircles the top portion of the header. The peripheral flange  70  has a peripheral face  62  which will be welded to the main transducer body. Thus as can be seen from  FIG. 3 , the torque isolation shell  60  surrounds and encloses the “H” shaped header  61 . The walls  73  and  72  of the isolation shell have their ends welded to the peripheral flange  70  associated with the “H” shaped header  61 . As one can ascertain, there is a space  71  between the surfaces of the “H” shaped header and the top portion. In this manner, the torque isolation shell  60  encloses the pressure sensing “H” shaped diaphragm member  61  while isolating the section  71  from the installation stresses caused by the face sealing feature. As seen in  FIG. 3 , the outer shell  60  consists of a cylindrical wall which encloses the “H” section unit  61 . The surface  67  of the shell  60  has a counterbore  68  which will enclose a crush ring. The outer shell  60  acts as a bypass element for the compressive load. The passage  69  through the center allows the sense media to reach the “H” section diaphragm  74 . Thus as one can ascertain upon installation, only the crush ring, which is positioned in counterbore  68  and the outer shell  60  experiences compression. There is no installation load on the interior “H” section  61 . Accordingly, the installation torque will compress the outer section  60  and the crush ring, and the crush ring forming the high pressure metal to metal seal. The interior “H” section  61  only experiences stress due to pressure which is directed to the diaphragm via the inlet  69 . Thus, the unit which is the “H” shaped configuration  61  will not be affected by the installation torque. 
         [0015]    Referring to  FIG. 4  there is shown the torque versus the change in zero shift of the new units as depicted in  FIG. 3  by curves  92  and  93  as compared to prior art units as shown as curves  90  and  91 . The prior art units, being the unit depicted in  FIG. 2 . It is seen that the “H” shaped section shown in  FIG. 3  also contains the step concentric flange or rim which essentially is depicted in the above noted co-pending applications and which step portions surrounds the active area of the diaphragm  74 . The step of course functions as described in the prior art. 
         [0016]    Referring to  FIG. 5  there is shown the composite structure depicted in  FIG. 3  consisting of the outer torque isolating shell  60  which is welded at its ends to the “H” section header portion  61 . The ends of the “H” section header, such as surfaces  62  are welded to a main body  80 , which has a threaded portion  84 . The main body has a central aperture  81  which accommodates leads and also accommodates the extending pins  64 . There is a hex shaped section  82 , which hex shaped section enables placement with a wrench. Extending from section  82  is a hollowed area which contains the circuit board  83 , which is contiguous with a cable release section  86  and cable  85 . Thus the entire transducer, which contains the isolation shell  60  and the “H” shaped header  61  is secured to the body  80 , which body  80  is threaded by means of a thread portion  84 . In this manner, the hex portion  82  is accommodated by suitable wrench, where the entire transducer unit is now placed in a threaded aperture via the threads  84 . The aperture communicates with a force transmitting media which essentially passes through the diaphragm  74  of the “H” section via passageway  69 . The same reference numerals have been employed in  FIG. 5  to designate corresponding parts as used in  FIG. 4 . Thus as shown, because of the isolation shell  60 , the “H” shaped header  61  experiences no installation load and therefore will only experience stress due to pressure as directed through aperture  69  and not in any manner be affected by the installation torque. As seen in  FIG. 4 , zero shift is negligible in units which have the header configuration depicted in  FIG. 3 . 
         [0017]    Referring to  FIG. 6  there is shown a typical installation. In  FIG. 6 , numeral  101  depicts a wall which may be the wall of a combustion engine and so on. The wall has formed therein an aperture  102  which is threaded, and which also has an inlet aperture  106  to allow pressure to enter. The pressure environment  110  may be oil pressure or some other pressure. In any event, the entire transducer assembly as depicted in  FIG. 5 , is inserted into the aperture  102 . It is inserted into the aperture  102  by the thread  84  co-acting with the thread of the aperture and by turning or exerting a torque on the installation hex portion  82  via a tool such as a wrench. As seen by the arrow, the entire unit is rotated by means of the hex wrench or other device so that it is screwed into the aperture  102 . The counterbore  68  contains a crush ring  100 . As the unit is turned and therefore proceeds to enter the aperture  102 , the crush ring  100  is pushed against the inner face of the wall, thus allowing the passageway  106  to communicate with the passageway  69  in the transducer assembly. The torque isolation shell  60  bears the force imparted as the crush ring  100  is pushed against the wall associated with the aperture  106 . Thus the majority of the torque is experienced by the shell  60  and there is virtually no torque transmitted to the “H” section header  61 . As shown in  FIG. 6 , only the crush ring  100  and the outer shell  60  experience compression, thus there is no installation load on section  61 . The shell  60  is separated from the header  61  by the space  71  and only the flange  70  experiences torque. The crush ring and the outer section form the high pressure metal to metal seal. The wall  101  is conventionally a metal wall and the entire body of the transducer including the isolation shell, the header and so on are also fabricated from metal. Thus there is described a torque insensitive header assembly which may be utilized in conjunction with high pressure measurements using “H” shaped devices having relatively thick diaphragms. It should be apparent to one skilled in the art that there are many alternative embodiments which may be discerned from the Figures and descriptions given above and all of which are deemed to be encompassed within the spirit and the scope of the claims appended hereto.