Patent Publication Number: US-6902414-B2

Title: Harsh environment rotatable connector

Description:
FIELD OF THE INVENTION 
     This invention relates to electrical connections, and more particularly to apparatus for the safe electrical connection of electrical components in harsh environments such as in oil well drill strings. 
     BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART 
     In oilfield and gas drilling operations, electronic equipment such as pressure probes, directional sensing probes, and the like are typically all located together down-hole in a well-bore and co-axially within one drill pipe of a multi-pipe drill string. The probes each have multiple electrical contacts which require electrical mating connection to be made with a mating electrical connection in an up-well segment of another drill pipe/collar. The up-well drill pipe typically contains additional electronic equipment such as a battery power supply as well as transmitting equipment powered by such battery power supply, for powering such sensors in said down-hole pipe and for powering transmitters for transmitting information received from such sensors via the mating electrical connection up-well to surface receptors and data recorders. 
     More particularly, in an underground drilling environment, measurement or logging instruments are often employed to provide information regarding the drilling status, performance or environment. This information may be stored in memory or telemetered to surface in real time. The measurement and/or telemetry tools are typically battery or generator powered and both the electronics and batteries are contained in pressure resistant housings mounted concentrically along the central axis of the drill collars forming an annulus within the drill pipe through which high-pressure drilling fluid is passed. 
     The measurement/telemetry tools of the type described above must withstand extremes of pressure, vibration and temperature. Depending on the combination of measurement/telemetry tools chosen, they may exceed the approximate 30′ length of standard drill pipe/collars, or specific sensors may be rigidly fixed to shorter sections of modified drill collars. In this case, electrical tools must span more than one drill collar. Difficulty occurs with the need to simultaneously mate and unmate both the drill collars and the internal electrical housings, yet do so in a manner in which the electrical connections are shielded from the environment to not only protect the electrical connections from a corrosive, potentially explosive, and/or wet environment which would be detrimental to establishing electrical connection, but also from physical damage or deformation to the electrical connectors during the mating and un-mating connection of drill strings and the associate required mating and un-mating connection of electrical connectors axially situate within respective adjacent drill pipe/collars. 
     In addition, a further problem arises where mating connection between co-axial male plug and mating female socket connections are required to establish such electrical connection. In particular, where electrical connection is required between a coaxial male plug, having multiple circumferential spaced apart electrical contacts thereon, and a female socket connector having a mating diameter and a corresponding number of electrical contacts thereon. Specifically, the procedure of engaging a male plug having a plurality of circumferential electrical connections thereon within a coaxial female socket aperture so as to form the electrical connection with the multiple electrical contacts thereon will cause many of the contacts in the male plug to “wipe” past those of the female socket during insertion, generally in an electrically inappropriate manner, that may damage the electronic circuits associated with such contacts before the contacts are each fully and appropriately engaged with the responding electrical contact. In addition, a further problem arises in that the preferred method of making such electrical connections is typically to insert by rotationally screwing one tubular housing containing the male plug into a similar tubular housing containing the female socket. The environment in which this occurs could also be hazardous—for instance, on the floor of an oil-drilling rig where flammable gases may be present. In such circumstances it is advisable to make certain that no potentially live electrical contacts are capable of causing a spark or thermal effect that could ignite flammable gas, dust or vapor during rotatable insertion of the male plug into the female socket. 
     Accordingly, a means and apparatus to allow for the joining of the internal electrical connections is desired, and in particular in a down-hole drilling application to allow electrical connection between electronic componentry located in two or more separable drill pipes to be accomplished. 
     Referencing U.S. Pat. Nos. 6,123,561, 6,392,317, and 5,334,801, prior methods for drill collar electrical connections have included electrical connectors integral to the drill collars. This arrangement requires specialized drill collars, and makes required recutting of the mating threads an additional step and expense, and also requires a method to transfer the electrical leads back and forth between drill collars and internal electrical components. 
     Additional patents such as U.S. Pat. Nos. 5,389,003, 6,439,932, and 5,358,418 teach a class of connectors referred to as “wet connects”. These connectors, while primarily employed to make electrical connections downhole between a wireline cable and probe, have also been employed in an attempt to make interconnections between probes mounted in drill collars. The art is not well suited for this application, as the wet connects tend to be elongated to the point that they extend out of the drill collar connections, making them subject to damage. Further, the unconnected contacts are generally exposed, and this makes safety a concern in hazardous environments, where the exposed contacts could create a spark. 
     SUMMARY OF THE INVENTION 
     In order to overcome certain of the disadvantages of the prior art, the present invention in a broad aspect thereof provides two connector halves matingly engageable in co-axial arrangement, where the electrical contacts on each of the connector halves are physically covered in order to protect electrical contacts on each of said connector halves from environmental damage. The first connector half (which includes a male member on the plug means) is protected by a resiliently-biased outer insulating sleeve or sheath. The sheath contains one or more seals and acts to shield electrical contacts on the male member from dirt, corrosion, or the like. 
     The second connector half (the socket means) has a female receptacle, the inner periphery of which possesses a plurality of electrical contacts (corresponding to the number of electrical contacts on the male member). The electrical contacts within the female receptacle are protected by a resiliently-biased movable member, which in a preferred embodiment is a sliding piston member. The piston member and/or female receptacle includes one or more seals to shield electrical contacts within the female receptacle from the environment. 
     In a preferred embodiment, such as where the connector halves are installed respectively in mating drill pipes, the two connector halves are each contained in pressure-resistant housings which support and centrally locate the connector halves within the respective drill pipe, and are capable of withstanding external pressure. 
     During the connection of the two connector halves, namely the plug and socket means, the male member on the plug means displaces the resiliently-biased piston member while the socket member displaces the resiliently-biased sheath member. The connector halves each continue to displace the protective shields on the mutually opposite connector half until mating engagement is complete, at which time the male member should be fully inserted in the female receptacle means, and each of the electrical contacts on each of the male member and the female receptacle means are properly aligned. This fully-engaged position may also be determined when the respective pressure-resistant housings containing each connector half shoulder against one other at which time the connectors have reached proper alignment of all respective co-axial conductors. 
     In the preferred embodiment where each of such connector halves are fixedly installed respectively within the interior of mating drill pipes which are then threadably coupled together, a third resiliently biasing means, such as a spring, may further be provided. Such further resilient biasing member functions, during threading of the drill members together and thereafter, to exert a force to ensure that the connectors remain fully mated while allowing for some variation in the length of the threaded members. 
     In a further aspect to the present invention, when such plug and socket means are each contained in respective mating pressure housings [which assist in preventing exterior liquids and gases from coming into contact with electrical contacts of such plug and socket means as is necessary when such plug and socket means are installed respectively in mating drill pipes], at least one of the pressure housings may be configured in such a way so as to utilize the ambient pressures surrounding such housings and within such drill pipe to exert a force which assists in maintaining the pressure housings containing such plug and socket means in mating engagement. 
     In a preferred embodiment, electrical switching circuits are connected to the electrical contacts situate on one or both of said male member and female receptacle means. Such electrical switching circuits serve to prevent the flow of electrical power to respective electrical contacts in either or both the male member or female receptacle means until the connecting halves are fully mated. Through the electrical switches, the multiple electrical contacts of the male and female connectors are electrically isolated (ie “switched off”) as they slide past one another, and are only electrically powered after mating engagement of the plug means with the socket means is complete. 
     During unmating, the electrical switches cut power prior to the conductors sliding past each other. The resiliently-biased sheath and piston member move back over the electrical contacts so as to again cover and thus protect the electrical contacts from the environment. Reference is to be had to pending U.S. patent application Ser. No. 10/655,028 filed Sep. 4, 2003 assigned to the same entity as this within application, the entity of the subject matter of which is incorporated herein by reference. 
     Accordingly, in one of its broad embodiments the present invention is to a plug and socket means adapted for mating engagement, for establishing electrical communication there between in a hazardous environment. The plug means comprises: 
     a) an elongate male member, having a plurability of electrical contacts about an outer periphery thereof; 
     b) a resiliently-biased sheath member, slidably biased over said male member so as to substantially cover said electrical contacts on said male member, which upon application of force thereto may be slidably moved so as to uncover said electrical contacts; and 
     c) biasing means for biasing said slidable sheath member over said male member. 
     The socket means comprises: 
     a) elongate receptacle means having disposed about an inner periphery thereof a plurality of electrical contacts, said electrical contacts adapted to contact said electrical contacts respectively on said male member when said male member is inserted in said receptacle means; 
     b) resiliently-biased protective means displaceable from said receptacle means so as to permit insertion of said male member within said receptacle means; and 
     c) biasing means, biasing said protective means so as to prevent ingress of any foreign material into said receptacle means when said male member is not yet inserted in said receptacle means. 
     The male member is adapted for insertion in the receptacle means upon mating engagement of the plug means with said socket means. 
     In a preferred embodiment the resiliently-biased protective means comprises a piston member, slidably-biased within said receptacle means, adapted to substantially cover said electrical contacts disposed on said inner periphery of said female receptacle means when said male member is not yet inserted in said female receptacle means. The piston member is displaceable from within said receptacle means by the male member upon insertion of said the member in said receptacle means. 
     In yet a further refinement, the socket means further comprises means for contacting the sheath member upon mating engagement of said plug means with said socket means, so as to cause said sheath member to be slidably displaced from a position covering said male member as said male member is inserted in said receptacle means. 
     In a preferred embodiment, the plug means and socket means is contemplated for use in two separate drill pipes which are desired to be matingly engaged to one another during drilling, typically by threadable engagement, and more particularly is contemplated as providing apparatus for establishing electrical connection between a plug means and associated electrical componentry in one drill pipe, and a socket means and its associated electrical componentry located within another drill pipe which will be connected to one another during drilling. In such embodiment the plug means is adapted for positioning within an interior of a first drill pipe proximate an end thereof, said end of said drill pipe adapted for mating engagement with a mating end of another drill pipe, and said socket means is adapted for positioning within an interior of said another drill pipe proximate said mating end thereof; wherein said male member is adapted for insertion in said receptacle means upon said first drill pipe being fitted in mating engagement with said another drill pipe. 
     More particularly, in an embodiment of the invention contemplated for use in drill pipe, for establishing electrical connection between electrical componentry in each of two respective drill pipes, the present invention comprises plug and socket means adapted for respective positioning within two separate drill pipes and adapted to permit electrical communication between components situated in each of said two separate drill pipes and further adapted for mating engagement upon rotatable engagement of said two separate drill pipes with each other; said plug means comprising: 
     a) an elongate male member, having a plurality of electrical contacts about an outer periphery thereof; 
     b) a resiliently-biased sheath member, slidably biased over said male member so as to substantially cover said electrical contacts on said male member, which upon application of force thereto may be slidably moved so as to uncover said electrical contacts; and 
     c) biasing means for biasing said slidable sheath member over said male member; 
     said socket means comprising: 
     a) elongate receptacle means having disposed about an inner periphery thereof a plurality of electrical contacts, said electrical contacts adapted to contact said electrical contacts respectively on said male member when said male member is inserted in said receptacle means; 
     b) resiliently-biased protective means displaceable from said receptacle means so as to permit insertion of said male member within said receptacle means; and 
     c) biasing means, biasing said protective means so as to substantially prevent ingress of foreign material into said receptacle means when said male member is not yet inserted in said receptacle means; 
     wherein said male member is adapted for insertion in said receptacle means upon mating engagement of said plug means with said socket means. 
     In yet a further preferred embodiment, particularly suited where the plug means and the socket means are contemplated each for location in two separate drill pipe which are to be rotatably engaged with each other during drilling, the plug means is rotatable relative to said socket means to permit said socket means to rotate relative to said plug means during rotatable mating engagement of said two separate drill pipes with each other. 
     In a further refinement of the embodiment of the invention contemplated for use in association with two separate drill pipes, said plug means is adapted for positioning within an interior of a first of said two separate drill pipes proximate an end thereof adapted for mating engagement with a mating end of a second of said two separate drill pipes, and said socket means is adapted for positioning within an interior of said second of said two separate drill pipes proximate said mating end thereof; and said male member is inserted in said receptacle means upon said first drill pipe being fitted in mating engagement with said second drill pipe. 
     In a further embodiment, due to a problem that when the male member is inserted within the female member there may temporarily be inappropriate electrical contact made due to electrical contacts on the male member “wiping” past the electrical contacts on the elongate receptacle means until full engagement of the male member within the female receptacle means, in a preferred embodiment means is further provided to avoid such inadvertent and inappropriate connections being temporarily made which would otherwise possibly result in damage to associated electrical circuitry. 
     Accordingly, in a further preferred embodiment, said plurality of electrical contacts disposed about said periphery of said male member comprise first and second plug contacts, electrically coupled to each other via plug-side current direction-limiting means; said plurality of electrical contacts disposed about said inner periphery of said receptacle means comprising first and second socket contacts, situate in said receptacle means and adapted to correspondingly come into electrical contact respectively with said plug contacts when said plug means is properly and fully matingly engaged with said socket means, said first and second socket contacts electrically coupled to each other via socket-side current direction-limiting means; at least one additional plug contact and socket contact on each of said plug and socket means, respectively, each similarly adapted to come into electrical contact with each other when said plug means is fully matingly engaged with said socket means; wherein said plug and socket means are each adapted to be used with circuit isolation means capable of only permitting flow of electrical current through said at least one additional plug and socket contact when current flow through at least one of said plug side and socket side current direction-limiting means is detected. Reference is to be had to U.S. patent application Ser. No. 10/655,028 filed Sep. 4, 2003 assigned to the same entity as the written application, the entire contents of which are incorporated herein by reference. 
     In yet a further embodiment, third biasing means (in addition to the biasing means possessed by each of the plug means and socket means) is further provided. Such third biasing means is adapted, when said plug means and said socket means are in mated engagement, to exert a force so as to maintain said plug means in mating engagement with said socket means. This feature is particularly advantageous where the plug and socket connectors are subjected to vibrations and jarring, typical of the types of environmental stresses subjected to drill strings during drilling. 
     In a preferred embodiment, were the plug and socket are intended to be used in respective mating drill pipes, the socket means is contained in a first pressure housing, said first pressure housing attachable to an interior of said first drill pipe. The plug means is contained in a second pressure housing, said second pressure housing positionable within an interior of said second drill pipe; a portion of the second pressure housing being slidably moveable within a third pressure housing, said third pressure housing attachable to an interior of said second drill pipe; and the second pressure housing is matingly engageable with said first pressure housing along a common longitudinal axis. 
     In a further refinement of the invention where the plug and socket means are contained in pressure housings, the second pressure housing is provided with an area of reduced cross-sectional area so as to present a surface area normal to said longitudinal axis of said first and second pressure housing so that ambient pressure within said first and second drill pipes acts on said surface area so as to cause said second housing to be biased in mating engagement with said first housing. 
     Likewise, instead of locating the socket means within the first pressure housing member and the plug means within the second pressure member, the order may be reversed. Accordingly, in such embodiment, the plug means is contained in the first pressure housing, said first pressure housing attachable to an interior of said first drill pipe; the socket means is contained in the second pressure housing, said second pressure housing positionable within an interior of said second drill pipe; a portion of the second pressure housing is slidably moveable within a third pressure housing, said third pressure housing attachable to an interior of said second drill pipe; and the second pressure housing is matingly engageable with said first pressure housing along a common longitudinal axis. 
     Likewise, in a further refinement of the above embodiment where the plug and socket are intended to be used in respective mating drill pipes, the second pressure housing is provided with an area of reduced cross-sectional area so as to present a surface area normal to said longitudinal axis of said first and second pressure housing so that ambient pressure within said first and second drill pipes acts on said surface area so as to cause said second housing to be biased in mating engagement with said first housing. 
     Lastly, in yet another aspect of the present invention, such invention provides for a method for establishing electrical communication between a plug means in a first drill pipe and a socket means in a second drill pipe, comprising the steps of: 
     i) positioning said plug means within an interior of said first drill pipe, proximate to a first end thereof; 
     ii) positioning said socket means within an interior of said second drill pipe proximate a first end thereof, said first end of said first drill pipe adapted for rotatable engagement with said first end of said second drill pipe; 
     iii) rotatably securing said first end of said first drill pipe to said first end of said second drill pipe, while at the same time simultaneously: 
     a) inserting a male member having a plurality of electrical contacts thereon arranged about an outer periphery and situate within said first drill pipe, into a receptacle means on said socket means having a plurality of mating electrical contacts thereon arranged about an inner periphery thereof so that each respective electrical contacts on said male member come into respective contact with said electrical contacts within said receptacle means; 
     b) displacing, with said male member, a resiliently-biased piston member situate in said receptacle means; and 
     c) displacing, with said socket means, a sheath member covering said male member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and permutations will appear from the following detailed description of various non-limiting embodiments of the invention, taken together with the accompanying drawings, in which: 
         FIG. 1  is a cross section of two separate drill pipes, each containing a respective connector half, with the left-hand drill pipe and associated connector half comprising the socket means and possessing a female receptacle means having a plurality of electrical contacts disposed about an inner periphery thereof, and the right-hand drill pipe and associated connector comprising the plug means and possessing a male member having electrical contacts disposed about an outer periphery thereof; 
         FIG. 2  shows an enlarged cross section of the plug means and associated pressure housing therefore shown in  FIG. 1 ; 
         FIG. 3  shows an enlarged cross section of the socket means and associated pressure housing therefore shown in  FIG. 1 ; 
         FIG. 4  is a cross section of the two drill pipe members in mated threadably-engaged position, showing the electrical contacts and pressure housings also mated; 
         FIG. 5  is a simplified diagram demonstrating the principle of projected surface area; 
         FIG. 6  is a schematic showing a general form of the coaxial plug and socket electrical. connections of the present invention; 
         FIG. 7  is a more detailed schematic diagram of isolation circuit for the plug isolation circuit shown in  FIG. 6 ; 
         FIG. 8  is a more detailed schematic diagram of the isolation circuit for the socket side isolation circuit shown in  FIG. 6 ; 
         FIG. 9  shows schematically a sensor circuit of the type used in the isolation circuits shown in  FIG. 6 , where both plug and socket have associated circuits and are each electrically powered; 
         FIG. 10  is a sensor circuit similar to that shown in  FIG. 9 , but modified slightly to form an alternate embodiment; 
         FIG. 11  shows schematically a sensor circuit, where only the plug side has associated isolation circuits and is electrically powered; 
         FIG. 12  shows schematically a sensor circuit, where only the socket side has associated circuits and is electrically powered; and 
         FIG. 13  is a schematic drawing showing a typical plug and socket connector which may be used in the present invention, further showing wiring connections which correspond to the associated wiring of the respective plug and socket electrical isolation circuits where the plug side only has electrical circuits which require isolation. 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     The description will be made in reference to the invention being used to connect electrical equipment mounted concentrically within drill collars or drill pipes, for drilling boreholes in the earth, although the invention has application in electrically connecting any mating members. 
     Referencing  FIG. 1 , the plug and socket assembly  10  of the present invention consists of two matingly engageable half-members, namely a plug means  12  and a socket means  14 . Plug means  12  contains a male member  16 , having a plurality of electrical contacts  18  thereon, circumferentially disposed about a periphery of said male member  16 . Plug means  12  is disposed in pressure housing  33   a,  which in turn is matingly engaged to pressure housing  33   b,  a portion of which is slidable in pressure housing  41 . Socket means  14  comprises a female receptacle  20 , having a plurality of circumferential electrical contacts  22  disposed about an inner periphery  24  of said receptacle  20 . 
     In a preferred embodiment, socket means  14  and associated receptacle  20  and pressure housings  15  are positionable in a first drill pipe  26 , and plug means  12  and associated male member  16  are positionable within a second drill pipe  28 , as shown in FIG.  1 . Socket means  14  is situated within a pressure housing  15 , and plug means  12  is situated within pressure housing  33   a,  as more fully explained below. 
     In typical drilling rig operating conditions, the female end  27  drill pipe  26  faces upward, and the male end  29  of drill pipe  28  is lowered down to it by using a winch or similar system, and thereafter rotated so as to permit mating engagement of drill pipes  26 , 28  together. However, in lowering pipe  28  onto pipe  26 , it is typical that the male end  29  of the drill pipe  28  will on occasion swing across the female end  27  of drill pipe  26 , and would severely damage plug means  12  if it were to protrude from male end  29  of drill pipe  28 . Similarly, socket means  14  could be similarly damaged if it were to protrude from female end  27  of drill pipe  26  by male end  29  of drill pipe  28 . Accordingly, in a preferred embodiment, each of plug means  12  and socket means  14  are recessed from the respective male and female ends  29 ,  27  of drill pipes  28 ,  26  respectively, in order that plug means  12  and male member  16  thereon as well as socket means  14  and receptacle  20  thereon are protected from inadvertent contact with and potential damage during handling of the drill pipes  26 ,  28 . 
       FIG. 2  is an enlarged view of the plug means  12  and male member  16 , housed in a pressure housing  33   a,  pressure housing  33   b  and pressure housing  41  all shown in FIG.  1 . Male connector  16  and electrical contacts  18  thereon are shrouded by a non-conductive sheath or sleeve  34 , which is slidable along male member  16  and biased by compression spring  35  to a position as shown in  FIG. 2  covering male member  16  and electrical contacts  18  thereon. Sleeve  34  possesses elastomeric seal  36  adapted to surround male member  16  and to prevent ingress of potentially harmful fluids or gases which might otherwise come into contact with electrical contacts  18  on male member  16 . Additional seals  37 , 38  interposed between pressure housing  33   a  and sleeve  34  prevents ingress of liquids or gases which would otherwise gain access to the plenum  39  rearward of sleeve  34  and thence to electrical contacts  18  on male member  16 . 
     In a preferred embodiment, an electronic switch  40  (identified in  FIG. 6  as item  202  for the purposes as explained later herein) is contained within the pressure housing  33   b.  A further pressure housing  41  is provided, slidably mounted on a portion of pressure housing  33   b,  as shown in FIG.  2 . Such pressure housing  41  is adapted to be fixedly mounted to an interior of drill pipe  28 , as shown in FIG.  1 . Pressure housing  41  contains a compression spring  43  of much higher stiffness relative to the compression spring  35  and which, when such plug means  12  and pressure housings  33   a, b  and  41  are situated in the interior of a drill pipe  28  as shown in FIG.  1  and matingly engaged with a socket means  14  and associated pressure housing  15 , is adapted to bias pressure housings  33   a,b  in contact with pressure housing  15  so as to form a slidable assembly  10  and assist in maintaining the socket means  14  and associated receptacle means  20  in mating engagement with the plug means  12  and male member  16  during high axial shocks, typical of the drilling environment. 
     While pressure housing  15  and associated socket means  14  may rotate relative to plug means  12  and associated housing  33   a,b,  relative rotation between the pressure housings  33   a,b  and  41  is prevented with a splined, anti-rotation sleeve  42 , which is fixed at a first location  42   a  to pressure housing  41 , and splined at a second location  42   b  to pressure housing  33   b.  The heavy compression spring  43  allows the slidable assembly to compensate for axial mis-alignment of the two pressure housings  33   a,b  and  15 . Axial mis-alignment may be of some reasonable amount, within a quarter of an inch, for instance, which results when the socket means  14  and associated drill pipe  26  is mated to plug means  12  and associated drill pipe  28 . (see  FIG. 4 ) 
     The male member  16  mounts to plug means  12  via mounting rod  43 , which is held in place by a washer  44  and a snap ring  45  (See FIG.  2 ). The mounting rod  92  and electronic switch  40  are supported by impact-absorbing, elastomeric washers  46   a, b.  O-ring  46   a  seals pressure housing  33   a  to pressure housing  33   b.  Pressure housing  33   b,  in a reduced area portion  31 , is slidably mounted within pressure housing  41  (see FIG.  2 ). Pressure housing  41 , in order to permit that portion of pressure housing  33   b  to be slidably mounted within it, is lined with sliding bearings  47  and elastomeric seals  48 . Pressure housing  33   b,  at least in its reduced area portion which is slidably mounted in pressure housing  41 , is retained and is held inside pressure housing  33   b  with two split bushings  32  and a threaded cap  49 . O-rings  50  and back-up rings  51  in conjunction with thread  52  allow a sealed connection between that portion of pressure housing  33   b  and pressure housing  41 . Such scaling permits pressure housing  41  to further contain therewithin, or further upwell therefrom additional sensors, telemetry modules, power supplies, or other electrical equipment. Insulated wires  53   a, b  from the end of the male member  16  pass through the mounting rod  92 , and attach to switching electronic switch  40 . The switched lines  54  are then carried through pressure housing  33   b,  anti-rotation sleeve  42 , and pressure housing  41  to aforementioned electrical equipment located up-well. 
       FIG. 3  shows a cross section of socket means  14 , pressure housing  15 , and receptacle  20 . Receptacle  20 , when not engaged by male member  16 , possesses therewithin a slidable piston  55  as shown in  FIG. 3 , which is resiliently biased into said receptacle  20  by compression spring  56 . Seal  57  within receptacle  20  operates in conjunction with slidable, non-conductive piston  55  to sealingly protect receptacle  20  from ingress of dirt or other foreign material, which may otherwise harm or prevent good electrical connection being made between circumferential electrical contacts  22  disposed about an inner periphery  24  of receptacle  20 , and electrical contacts  18  disposed about outer periphery of male member  16  when such male member  16  is placed in receptacle  20  during mating engagement of plug means  12  with socket means  14  during mating engagement of the two drill pipes  26 , 28 . 
     Outer pressure housing  15  houses an inner housing  61 , which encloses compression spring  56 , non-conductive piston  55 , and an electronics carrier  62 . Electronics carrier  62  may contain such things as a battery power supply and/or radio frequency transmitter, and/or one or more sensors, all of which are typically located in downhole members such as aforesaid drill pipe  26 , and which require electrical connection via plug means  12  and wires  52   a, b  to up-well electronic equipment. 
     Receptacle  20  mounts onto the end of an inner housing  61 . An elastomeric shock absorber/seal  64  is mounted between at the interface between the inner surface of pressure housing  15  and the outer periphery of the receptacle  20  to prevent contaminents and foreign matter from entering pressure housing  15  and inner housing  61 . A threaded mount  65  supports electronics carrier  62  and retains the compression spring  56 . A coupling  66  in turn supports threaded mount  65 , and permits passage of wires  90  from electronics carrier  62  down-pipe within pipe  26 . An off-the-shelf electrical connector  67 , such as an ITT-Canon MDM connector, mounts on the coupling  66  to provide electrical connection to the down-pipe mating components, which may consist of additional sensors, telemetry modules, power supplies, or other electrical equipment (not shown). 
     As may be seen from  FIG. 4 , during mating engagement of drill pipe  26  with drill pipe  28 , wherein the male end  29  of drill pipe  28  is threadably inserted in the female end  27  on drill pipe  26 , such results in rotating and helical travel of male member  16  into the female receptacle  20 . Slidable piston  55  is slidably displaced from within receptacle  20  by the insertion of male member  16 . Simultaneously, sleeve  34  is slidably displaced from covering male member  16  upon socket means  14 , and in particular receptacle  20 , coming into contact with plug means  12  and in particular sleeve  34 . The leading faces of the receptacle  20  and male member  16  push on sleeve  34  and piston  55 , respectively, causing them to slidably retract against the spring force exerted by springs  56  and  35 , respectively. In a preferred embodiment, as the electrical conductors  18  on male member  16  slide past the circumferential contacts within receptacle  20  remain switched off (ie electrically isolated) by means of an electrical switch  40 , as more fully described below. The electrical switch  40  only connects the electrical contacts of the receptacle  20  and/or the male member  16  to electrical power only when male member  16  is substantially inserted within receptacle  20  and after the electrical contacts  18 ,  22  are each in the desired and intended alignment. 
     Advantageously, as the joining of the drill pipe  26 ,  28  continues past the full mating of the plug means  12  and socket means  14 , namely past the full mating engagement of male member  16  within receptacle  20 , additional axial travel compresses the stiffer compression spring  43 . Spring  43  provides continual clamping force on the plug  12  and socket  14  means while allowing for variation in the threaded length of the joining members, namely drill pipes  26  and  28 . 
     With reference to  FIG. 5 , an additional benefit of the invention may be seen when fluid pressure is acting on the exterior of the pressure housings  15 ,  33   a,b  and  41 . When proper consideration of the projected area of the external surfaces of the pressure housings  15  and  33  is made, it is possible to cause the housings  15  and  33   a,b  to be held together by external pressure. The housings  15 ,  33   a,b  are thus less likely to be affected by shock and vibration, which if allowed to go unchecked may cause separation of the plug  12  and socket  14  means, and eventually an electrical discontinuity. 
     For the purpose of demonstrating the above principle, a simplified diagram is used as shown in FIG.  5 . Slidable member  70  represents pressure housings  33   a,b.  Fixed member  71  represents pressure housing  15 , and fixed member  73  represents pressure housing  41 . Slidable member  70  is sealed between fixed members  71  and  72 . The projected surface area  80  in the axial direction on the first face of slideable member  70  is less than the projected surface area  78  on the second face of slideable member  70 . A difference in projected surface area between the first and second face of approximately 1 square inch is easily achieved. Should the external pressure acting on these faces be, for instance, 15,000 psi (pounds per square inch), the clamping force holding slideable member  70  to fixed member  71  due to the external pressure is 15,000 lbs. 
     While there are many methods of connecting two electronic circuits together, in one aspect the invention contemplates use of a coaxial plug and socket pair  212  and  226  respectively, as indicated in  FIG. 6 , each having a plurality of coaxially situate, concentric electrical contacts  211 ,  213  respectively thereon. The advantage of using such a coaxial multi-contact system is that the plug  212  and socket  226  can be housed in tubular containers (eg. pressure housings  15  and  33   a, b ) and the housings matingly engaged such as by screwing them together, thereby engaging the coaxial plug  212  into socket  226 . The mechanical advantage of this method of engagement brings a disadvantage—the majority of the contacts  211 ,  213  wipe past each other during insertion of plug  212  into socket  226  before the plug  212  and socket  226  become fully engaged. This may cause damage to attached electronic components if they are activated by some power source. Accordingly, the invention provides for interposing specific isolation circuits  202  and/or  216  to isolate and protect such components during the engagement process. We accomplish this by connecting plug  212  via wire harness  210  to switching circuit  202 . This circuit  202  isolates a variety of input/output lines (I/O)  200  from I/O lines  208 . A pair of lines is dedicated to use as sensor lines (Sensor Line  1   204  and Sensor Line  2   206 ) contacts  286  and  284  which are preferably but not necessarily at the distal end  207  of plug  212 . Similarly we connect socket  226  via wire harness  224  to an isolation circuit  216 . Circuit  216  isolates a variety of input/output lines (I/O)  214  from I/O lines  222 . A pair of lines is dedicated for use as sensor lines (Sensor Line  1   218  and Sensor Line  2   220 ). For simplicity of deployment we have designed circuit  202  to be identical to circuit  216  (ref. FIGS.  7  &amp;  8 ), though this feature is not a required aspect of this invention. Although we indicate seven sets of corresponding electrical contacts  211 ,  213  associated respectively with plug  212  and socket  226 , it is obvious that the number of sets of contacts  211  and  213  applicable to this application can be any reasonable number greater than two, and the depiction of seven contacts is merely arbitrary and illustrative of the principals to be employed. 
       FIG. 7  is a more detailed schematic diagram of the isolation circuit  202  in respect of the plug contacts  211 , as shown in FIG.  6 . The I/O lines comprise a Power Line  235  monitored by Current Sensor  242  and controlled by Power Switch  244 , digital lines  233 ,  234  controlled by Digital Switches  246 , an unswitched line  248 , a Ground Line  250 , two Sensor Lines  280  and  282  controlled by Sensor Circuit  256  and Timer Circuit  258 , the Timer  258  providing an Interrupt Line  260  to control Power Switch  244  and Digital Switches  246 . 
       FIG. 8  is a more detailed schematic diagram of the isolation circuit  216  in respect of the socket contacts  213 , as shown in FIG.  6 . The I/O lines comprise a Power Line  235  monitored by current sensor  242  and controlled by Power Switch  243 , digital lines  232 ,  232  controlled by digital switches  245 , unswitched  248 , a ground line  250 , two sensor lines  292  and  294  controlled by a sensor circuit  257  and Timer Circuit  259 , the Timer  259  providing an Interrupt Line  260  to control Power Switch  243  and digital switches  243 . 
       FIG. 9  shows plug sensor circuit  256  and socket sensor circuit  257  shown generally in  FIGS. 7 &amp; 8  respectively and how the sensor lines  292 ,  294  and  280 ,  282  are activated only by the full engagement of the plug  212  and socket  226 . A positive potential +V on the plug sensor circuit side  256  is connected to a resistor R 1   272 , then to a forward-biased diode  274 , then to diode  276  that acts to block this current, and finally to another resistor  278 . Sensor Line  1  ( 280 ) is connected at the junction of  274  and  276  to plug contact  284 . Sensor line  2  ( 282 ) is connected at the junction of  276  and  278  to plug contact  286  and also to the plug sensor circuit  256  output. Similarly, a positive potential +V on the socket circuit side  257  is connected to a resistor R 1   298 , then to a forward biased diode  300  then to a diode  302  that acts to block this current, and finally to another resistor  304 . Sensor Line  1   292  is connected at the junction of  300  and  302  to socket contact  290 . Sensor line  2  ( 294 ) is connected at the junction of  302  and  304  to plug contact  288  and also to the socket sensor circuit  257  output. 
     It will be noted that the sensor lines  292 ,  294  on the socket sensor circuit  257  are crossed with respect to the sensor lines  280 ,  282  on the plug circuit  256 ; apart from this circuits and wiring for both plug and socket sensor circuits  256 ,  257  are identical. The plug-side and socket side sensor circuits  256 ,  257  may alternatively be arranged as shown in  FIG. 10 , wherein sensor lines  280 ,  282  are crossed with respect to sensor lines  292 ,  294 . 
     To clarify how the units sense that the plug/socket combination has achieved full engagement, we proceed by explaining various embodiments. 
     Embodiment 1 
       FIG. 11  denotes an arrangement where active powered electronic circuits are incorporated only on the plug side, and electronic access to the plug side circuits does not require socket side isolation circuitry, the socket side being essentially passive. For illustrative purposes we set the power line +V at 15 volts, resistor R 1   272  is 50,000 ohms and resistor R 2   278  is 100,000 ohms. 
     As may be seen with reference to  FIG. 11 , the determination of the full engagement of plug  212  and socket  216  (whereby electronic circuitry which requires isolation occurs on the plug side) is achieved as follows. Current from supply line  235  flows through resistor R 1  ( 272 ), through forward-biased diode  274  and is blocked from the plug sensor circuit output by diode  276 . A current pathway is available across the plug/socket junctions  284  and  288 , through diode  302  that now acts as a sensor diode, back through plug/socket junctions  290  and  286 , and finally through resistor R 2  ( 278 ) to Ground  250 . The potential across resistor  278  is sensed by the plug Sensor Circuit  256  to be approximately ⅔ times 15V (set by the potential divider R 1 /R 2  i.e. ˜10V. This value is chosen to be comfortably greater than a threshold voltage input to the plug Sensor Circuit  256 . Diode  302  is forward biased because of the crossed sensor lines  292  and  294  on the socket side. Were this not the case the required voltage potential at the plug sensor circuit  256  would not be available. Thus only when plug  212  and socket  216  are fully engaged is the plug sensor circuit  256  activated and the remaining switched lines  233 ,  234  (ref.  FIG. 13 ) connected to corresponding plug contacts  211  then available at the plug electrically powered for use by the circuit(s) attached to the socket  216 . 
     It will be obvious to one reasonably skilled in the art that there should be no electrical circuits associated with socket  226  such as digital switches  245  that are in electrical communication with any of the non-sensor contacts  213  that would be electrically mistaken for the action of diode  302 , so as to otherwise initiate a “triggering” of the power switch  244 . To further guard against such a possibility, in a preferred embodiment of this aspect of the invention the output of sensor circuit  256  in respect of the plug sensor circuitry is passed through timer  259  (FIG.  7 ). The function of timer circuit  259  is to delay activation of Interrupt Line  260  controlling Power Switch  244  and Digital Switches  246  (ref.  FIG. 7  ) until the full engagement of plug  212  and socket  226  can be reasonably expected (typically one to two minutes). 
     The only significant requirements on the passive socket side is a diode  302  that is forward biased by crossed sensor lines  292 ,  294  in order that the sensed circuit  256  is correctly activated. 
     Embodiment 2 
     The complementary circuit of Embodiment 1 is depicted in FIG.  12  and denotes an arrangement where active powered electronic circuits are incorporated only on the socket side, and furthermore that electronic access to the socket side circuits does not require plug side isolation circuitry because the plug side is essentially passive. For illustrative purposes we set the power line +V at 15 volts, resistor R 1 ( 298 ) is 50,000 ohms and resistor R 2  ( 304 ) is 100,000 ohms. 
     As may be seen with reference to  FIG. 12 , the determination of the full engagement of plug  212  and socket  216  (whereby electronic circuitry which requires isolation occurs on the plug side) is achieved as follows. Current from supply line  236  flows through resistor R 1  ( 298 ), through forward-biased diode  300  and is blocked from the plug sensor circuit output by diode  302 . A current pathway is available across the plug/socket junctions  290  and  286 , through diode  276  that now acts as a sensor activation element by passing current back through plug/socket junctions  284  and  288 , and finally through resistor R 2  ( 304 ) to Ground  250 . The potential across resistor R 2  ( 304 ) with respect to Ground  250  is sensed by the socket Sensor Circuit  257  to be approximately ⅔ times 15V (set by the potential divider R 1 /R 2  i.e. ˜10V.) The threshold voltage necessary to activate the socket Sensor Circuit ( 257 ) could be set at 6 or 7 volts, greater than typical logic levels of 5V. Thus the activation voltage of ˜10V is comfortably greater than the threshold, and false activations are minimized. Diode  276  is forwarded biased because of the crossed Sensor Lines  292  and  294  on the socket side. Were this not the case the required voltage potential at the socket Sensor Circuit  257  would not be available because no current could flow through resistor R 2 ( 304 ), causing the appropriate activating voltage to be absent. Thus only when plug  212  and socket  216  are fully engaged is the socket Sensor Circuit  257  activated, and the switched lines forming part of the I/O bus  214  are then electrically connected to the I/O bus  222 . Hence the switched (and also the unswitched) lines are correctly available at the socket via the fully engaged plug. 
     It will be obvious to one reasonably skilled in the art that there should be no electrical circuits associated with plug  216  such a Digital Switches  246  that are in electrical communication with any of the non-sensor contacts  213  that would be electrically mistaken for the action of diode  276 , so as to otherwise initiate a “triggering” of the Power Switch  243 . To further guard against such a possibility, in a preferred embodiment of this aspect of the invention the output of Sensor Circuit  257  in respect of the socket sensor circuitry is passed through Timer Circuit  259  (ref. FIG.  8 ). The function of Timer Circuit  259  is to delay activation of Interrupt Line  261  controlling power Switch  243  and Digital Switches  245  until the full engagement of plug  212  and socket  226  can be reasonably expected (typically one to two minutes). 
     The only significant requirements on the passive plug side is a diode  276  that is forwarded biased by crossed sensor lines  292 ,  294  in order that the Sensor Circuit  257  is correctly activated. 
     Embodiment 3 
     The discussion of Embodiment 1 and Embodiment 2 above now makes the understanding of Embodiment 3 as exemplified by  FIG. 9  straightforward. Both plug sensor circuit  256  and socket sensor circuits  257  are powered independently by +V(plug)  235  and +V(socket)  236 . The voltage potential at Sensor Circuit  256  (plug) output is available in either of two routes: 
     a) current from line  235  via resistor R 1 ( 272 ) and diode  274  passes along sensor line  1  ( 280 ) to contacts  284  and  288 , then via sensor line  2  ( 294 ) through diode  302 , Sensor Line  1  ( 292 ), contacts  290  and  286 ; or 
     b) current from line  236  through resistor R 1  ( 298 ) and diode  300 , along Sensor Line  1  ( 292 ), through from contacts  290  and  286  to sensor line ( 282 ). 
     The choice of routes a) or b) is determined solely by whether +V(plug)  235  is greater than +V(socket)  236  by more than one diode drop (typically 0.6V). In either case the significant issue is that the plug Sensor Circuit  256  is activated by an adequate +V(socket)  235  potential or by the presence of diode  300 —both are associated with the full engagement of the plug and socket, and either will suffice. 
     Likewise, the potential at sensor circuit  257  (socket) is available in either of two means: 
     c) current from line  236  via resistor R 1  ( 298 ) and diode  300  passes along sensor line  1  ( 292 ) to contacts  290  and  286 , then via Sensor Line  2  ( 282 ) through diode  276 , sensor line  1  ( 280 ), and contacts  284  and  288 ; or 
     d) current from line  235  through resistor R 1  ( 272 ) and diode  274 , along sensor line  1  ( 280 ), through from contacts  284  and  288  to sensor line  2  ( 294 ). 
     The choice of routes c) or d) is determined solely by whether +V(socket)  236  is greater than +V(plug)  235  by more than one diode drop (typically 0.6V). In either case the significant issue is that the plug Sensor Circuit  256  is activated by an adequate +V(plug)  235  potential or by the presence of diode  276 —both are associated with the full engagement of the plug arid socket, and either will suffice. Diodes  274  and  300  ensure that there can be no unintended reverse flow into their associated power supplies. 
     This embodiment illustrates usefulness of the symmetry of the circuit operations attached to either plug or socket—fabrication of the switching circuits is simplified in that both assemblies can be identical. The only necessary modification is that the lines must be crossed between contacts  288 ,  290  and sensor lines  292  and  294 . 
     With reference to the embodiment shown in  FIG. 11 , it is clearly apparent to a person reasonably skilled in the art that the sensing of full engagement of the plus  212  and socket  226  is facilitated by presence diode  276  in the case of the sensor circuit  256 . With reference to the embodiment shown in  FIG. 12 , it is likewise apparent that the sensing of full engagement is facilitated by the presence of diode  302 . 
     From  FIG. 11  it may be clearly seen that where there is electrical circuitry on digital lines  231 ,  232  and  233 ,  234  that require isolation to prevent damage, it is apparent that the sensing of full engagement of the plug  212  and socket  226  is facilitated by the inclusion of a diode  302  and  276  on each side of the multi-point connectors  284 / 288  and  286 / 290 . [It is noted that in such a case, both the plug  212  and socket  226  would need 10 contacts and not 7 (i.e. ground line  250 ,  284 / 288 ,  290 / 286 , separate switched power connections  235  and  236 , switched digital lines  231 ,  232 ,  233  and  234 , and the unswitched line  248 .) 
     Importantly, with respect to each of the embodiments shown in  FIGS. 11 ,  12 , &amp;  13 , the present invention is not limited to a sensory circuit using only a simple diode as a sensing means. In particular, it is possible and is contemplated within the scope of the present invention to replace each diode  276  and/or  302  by other electrical circuitry, including current direction-limiting circuitry, so as to permit the sensor circuit to produce a particular electronic signal when specifically sensed at full engagement of the plug  212  and socket  226 . The present invention is not to be limited to circuitry implementing only diodes  276  and  302 . 
     Although the disclosure described and illustrates preferred embodiments of the invention, it is to be understood that the invention is not limited to these particular embodiments. Many variations and modifications will now occur to those skilled in the art. For definition of the invention, reference is to be made to the appended claims.