Abstract:
A connector has conductive pins extending from outside the device to within the device and an electrically conductive wall surrounding a portion of the pins. The conductive wall abuts a printed wiring board containing EMI protective circuitry and contacts a ground plane within the printed wiring board. A selected pin is brazed to the connector and holds the printed wiring board in compression to assure a low impedance connection to the ground plane.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS (IF ANY) 
     Not applicable. 
     U.S. GOVERNMENT RIGHTS (IF ANY) 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to the control of electromagnetic interference (EMI) and specifically to an apparatus for making electrical connection to a device containing electronics requiring EMI protection. Electromagnetic interference is said to exist when unwanted voltages or currents are present so that they adversely affect the performance of a device or system. These voltages or currents may reach the victim circuit by conduction or by radiation. Electrical filters may be designed to offer little opposition to the passage of certain frequencies or direct current (dc) while blocking the passage of other frequencies. Filters play a significant role in the reduction of conducted interference. A metal barrier may be imposed between sources of electrical noise and their victims to reduce or eliminate the electrical interference due to radiated interference. 
     The present invention is described in the environment of a pressure sensor or pressure transducer application. However, it is to be understood that this is only an illustrative environment and the present invention applies to other applications as well. 
     A transducer transforms one form of energy into another form. For example, a transducer can covert the measure or value of some physical property such as pressure or temperature into a corresponding value of an electrical parameter such as voltage. Transducers typically include extensive electronics to reliably manipulate or process very low level electrical signals. Therefore, it is necessary to take precautions in the design to minimize the effects of EMI on the transducer electronics. Transducers, for example precision pressure transducers, are applied in a wide variety of industrial and other applications in which the associated wiring or cabling is routinely exposed to EMI from many sources. In the past, electrical filtering arrangements including electrical components provided on a separate board specifically designed to reduce EMI have been employed in pressure transducers. In the past, EMI shielding of the EMI board circuitry has been provided by using additional parts for shielding. The extra parts add both piece part and labor costs. Thus, there is a need for an improved apparatus for making electrical connections to a device containing electronics requiring EMI protection. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention solves these and other needs by providing an apparatus for making electrical connections to a device requiring EMI protection. The apparatus includes a connector having conductive pins extending from outside the device to within the device and an electrically conductive wall surrounding a portion of the pins. A printed wiring board includes EMI protective circuitry and a ground plane. The conductive wall abuts the circuit board making electrical contact with the ground plane and forming a cavity of conductive material. 
     In another aspect of the present invention a selected pin is brazed to the connector and secured to the printed wiring board so that the printed wiring board is in compression. the compressive force holds the printed wiring board against the connector wall assuring a low impedance connection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross sectional perspective view of the present invention applied to a pressure sensing device with portions of the pressure sensing device also being shown. 
     FIG. 2 shows an enlarged cross sectional perspective view of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An apparatus for making electrical connections to a device containing electronics requiring EMI protection is shown in the drawings and generally designated  10 . FIG. 1 shows a pressure sensing device or pressure transducer assembly  12  including pressure interface  14 , sensor header  16 , housing  18  and apparatus  10 . Sensor header  16  includes diaphragm  20 , sensor die  22  and conductive pins  24  which provide for communication between sensor die  22  and electronics located within housing  18 . Housing  18  contains electronics such as printed wiring board  26  and connector  28  for communication between board  26  and a board that is not shown. Pressure interface  14 , sensor header  16 , housing  18  and apparatus  10  are joined together by welding. Apparatus  10  includes a connector body  40  which has an outwardly extending connector coupling arrangement  42  such as the 6 pin military connector type that is shown. Connector body  40  includes a generally planar portion  44  which has a shoulder  46  for being received on end  32  of housing  18 . Connector body  40  further includes a downwardly extending wall or shell  48  which in the preferred embodiment is shaped or beveled so that it presents a small surface or a sharp edge  50 . Conductive pins  52  are accessible outside pressure transducer  12  and extend through glass insulators  54  located in planar portion  44 . Apparatus  10  further includes an EMI board  60 . The purpose of EMI board  60  is to provide electrical filtering of the power or signals that are coming into the electronics of pressure transducer  12  and of signals coming from pressure transducer  12 . EMI board  60  has a surface  62  on which electrical filtering components (not shown) are typically mounted and a surface  64 . EMI board  60  may be referred to herein as second printed wiring board  60 . Components found on the EMI board  60  may include, for example, AVX transguards to protect against incoming transients (ESD, etc.), capacitors to filter out high frequency noise, both incoming and outgoing, and ferrite beads to act as high impedance to high frequency noise, both incoming and outgoing. EMI board  60  includes a low impedance shielding plane  66  which may also be referred to as an internal ground plane or chassis plane. Plane  66  is brought to surface  62  by equally spaced vias  68 . At surface  62  a circumferential conductive surface  70  is provided. 
     In the preferred embodiment pin  72 , is not insulated from connector body  40 , but rather is brazed to connector body  40  and is therefore at the potential of connector body  40 . In the manufacturing process, EMI board  60  is located as shown and a tool is used to apply a force to surface  64  of EMI board  60  so that it is deflected toward connector body  40 . While EMI board  60  is in this compressed position, pin  72  is soldered to EMI board  60  at  74  to take the stress of the compression once the force is removed. When the tool is removed, pin  72  will continue to hold EMI board  60  in compression so that a low impedance connection between edge  50  of wall  48  and circumferential conductive surface  70  is assured, through all environmental changes such as temperature variations. Electrical circuitry on EMI board  60  is connected through connector  76  to electronics located in housing  18 . 
     In the present invention, having the internal EMI ground plane  66  attached to the chassis at both the chassis pin  72  and the entire circumference of the EMI board allows the ground plane  66  to be both very low impedance and low inductance. The low impedance and low inductance ground connection at circumferential conductive surface  70  allows the capacitors to more effectively filter out the incoming (coupled into the cabling) and outgoing (generated by the electronics) high frequency signals. In addition, the ground plane and the connection at the circumference of the EMI board acts like a faraday cage, eliminating possible internally-radiated high frequency signals from going further in the housing. A significant benefit from the invention is the very low impedance and low inductance chassis connection. 
     The present invention has been described in the environment of a ruggedized pressure transducer where the material used for connector body  40  is stainless steel and it is of single piece construction. In other environments other materials and construction may be used. Means other than the use of pin  72  to hold printed wiring board  60  in compression may be used. For example, a threaded type of fastener could be used. 
     Thus since the invention disclosed herein may be embodied in other specific forms without departing from the spirit or general characteristics thereof, some of which forms have been indicated, the embodiments described herein are to be considered in all respects illustrative and not restrictive. The scope of the invention is to be indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.