Abstract:
A connector interconnect two coaxial cables each having a central conductor surrounded by an outer conductor. A respective connector piece is assigned to each coaxial cable. The invention ensures the easy and rapid use of the connector, while reliably guaranteeing the electrical contact between the interconnected coaxial cables. To achieve this, each connector piece has one connection region that is electrically connected to the respective central conductor of the corresponding coaxial cable, a connection head of the second connector piece being supported on the connection region of said piece by means of a spring element, in order to make electrical contact with the connection region of the first connector piece.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This is a continuing application, under 35 U.S.C. § 120, of copending international application No. PCT/EP2003/009316, filed Aug. 22, 2003, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German patent application No. 102 40 563.8, filed Aug. 29, 2002; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Field of the Invention  
         [0003]     The invention relates to a coupling for coaxial cables. Each of the two coaxial cables to be coupled to one another has a central conductor, which is surrounded by an outer conductor. Each coaxial cable has a coupling piece associated therewith, each of which has a connecting area which is electrically connected to the central conductor of the coaxial cable associated with it. A connection head, which is provided in order to produce an electrical contact with the connecting area of the first coupling piece and is mounted on it such that it can move, of the second coupling piece is supported on its connecting area via a spring element.  
         [0004]     A coupling such as this is disclosed, for example, in European published patent application EP 0 314 299 A1. Couplings for coaxial cables with spring-mounted connection elements are also disclosed in the prior U.S. Pat. Nos. 3,416,125, 4,012,105, and 6,053,777.  
         [0005]     A coupling such as this may be important in many industrial applications wherein coaxial cables must be disconnected from one another and reconnected quickly and easily, for example for maintenance work. In particular, a coupling such as this may be used with rigid coaxial conductors, such as those used for the transmission of electrical signals or pulses in a nuclear installation or in a nuclear power station installation.  
         [0006]     In nuclear power station installations, the filling level of an operating or cooling medium in a container which cannot be looked into directly must be monitored and, if required, readjusted, for example the filling level of the primary coolant in the reactor pressure vessel. The so-called TDR (time domain reflectometry) measurement principle may be used for this purpose, as is known, by way of example from German patent DE 199 58 584 C1 (corresponding to U.S. Patent Application Publication No. 2002/0186025). The TDR measurement principle makes use of the effect that an electromagnetic pulse which is carried in an antenna system is partially reflected when the impedance between, for example, a central conductor of the antenna and an outer conductor which surrounds it in the form of a coaxial cable changes abruptly.  
         [0007]     An abrupt change in the impedance such as this occurs, for example, where the antenna that is formed in this way enters a liquid from a gaseous environment, since the impedance depends on the capacitance between the central conductor and the outer conductor, and thus on the dielectric constants of the medium filling the space between the central conductor and the outer conductor. An electromagnetic pulse which is passed to an antenna such as this that is immersed in the medium to be monitored is thus partially reflected on the surface of the medium. A further reflection occurs at the normally short-circuited antenna end. Since, apart from this, the propagation speed of the electromagnetic pulse in the antenna is known, the propagation time difference between the pulse reflected on the boundary layer and the pulse reflected at the antenna end can be used as a measure of the position of the boundary layer, and thus as a means for determination of a position value which is characteristic of the position of the boundary layer, wherein case it can be assumed that there is an essentially proportional relationship between the propagation time difference and the characteristic position value.  
         [0008]     In order to make it possible to use this method for diagnosis and for monitoring of, for example, a medium in a closed container, it is thus necessary to transmit electromagnetic pulses from an external area into the interior of the container, and vice versa. On the other hand, however, depending on the nature and characteristics of the medium stored in the container, it may be absolutely essential or at least of major importance to ensure that the container is sealed particularly well. Depending on the operating parameters in the container by virtue of the design, such as the pressure and temperature of the medium stored there, the electrical bushing which is used to pass electromagnetic pulses in and out is thus subject to particularly stringent requirements in some specific cases. This also applies to the transmission of an electromagnetic pulse from the containment surrounding the reactor pressure vessel to a pulse generator and to an evaluation and control unit, and vice versa.  
         [0009]     In this case, by way of example, rigid coaxial conductors may be used to transmit electromagnetic pulses between the containment wall and the reactor pressure vessel, in particular in order to ensure the high signal quality which is required to ensure that reliable measured values are obtained. Nevertheless, however, it may be necessary to make the reactor pressure vessel accessible, for example for maintenance work. In order to allow this with only little effort even using rigid coaxial conductors, a coupling apparatus is desirable which allows segments of the coaxial conductor to be disconnected from one another and to be reconnected quickly and without any complications between the two bushings that have been mentioned.  
         [0010]     In order to keep the interference with and the attenuation of the electromagnetic pulse as low as possible even at the coupling point in a system such as this, the coupling should satisfy stringent requirements. In particular, the impedances should be kept constant over the length of the conductor, or at least should not change with any discontinuities, so that disturbing reflections at sudden impedance changes are avoided as well as possible for the measurement. A high-quality electrical contact between conductors that are connected by means of the coupling is particularly important for reliable transmission of the electromagnetic pulse.  
       SUMMARY OF THE INVENTION  
       [0011]     It is accordingly an object of the invention to provide a coupling for coaxial cables which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a coupling that, on the one hand, can be operated easily and quickly and, on the other hand, ensures the electrical contact between the coupled coaxial conductors with high reliability.  
         [0012]     With the foregoing and other objects in view there is provided, in accordance with the invention, a coupling for connecting two coaxial cables to one another, each of the coaxial cables having a central conductor surrounded by an outer conductor.  
         [0000]     The Coupling Comprises:  
         [0000]    
       
         
           
              first and second coupling pieces each associated with a respective coaxial cable and each having a connecting area electrically connected to the central conductor of the respective coaxial cable;  
              a connection head movably mounted on the second coupling piece for producing electrical contact with the connecting area of the first coupling piece, and a spring element supporting the connection head on the connecting area of the second coupling piece;  
              the connection head ending in a number of contact fingers which are inserted into recesses formed in the connecting area of the second coupling piece, the connecting area of the second coupling piece being provided with a contact piece having an associated connecting surface for at least one of the contact fingers.  
           
         
       
     
         [0016]     In other words, the objects of the invention are achieved in that the end of the connection head which faces the connecting area of the second coupling piece is provided with contact fingers which are inserted into recesses, that are provided for this purpose, in the connecting area of the second coupling piece, with the connecting area of the second coupling piece being provided with a contact piece which has an associated connecting surface for the or each contact finger.  
         [0017]     The invention is in this case based on the concept that a coupling mechanism for coaxial cables should be easily operable, that is to say should allow the cables to be coupled and decoupled quickly and easily. At the same time, however, the electrical contact between coaxial conductors which are connected via the coupling should also be particularly intensive during operation of the installation. In order to satisfy these two fundamentally mutually contradictory conditions, the coupling is provided with an apparatus which reinforces the contact between the conductors to be coupled, to a particular extent. In this case, the deliberate use of the restoring force of a spring element is provided, with the spring being loaded while the two coaxial conductors are being coupled, and thus continuously exerting a force, which assists the electrical contact, on the two conductors.  
         [0018]     In order to make it possible to ensure that there is a particularly close contact between the connection head and the connecting area of the first coupling piece, the connection head is in this case mounted on the connecting area of the first coupling piece such that it can move. In this case, the connection head is expediently positioned with the coupling open in such a way that, during mating of the coupling, the connecting area of the first coupling piece moves the connection head towards the connecting area of the second coupling piece, and thus loads the spring element. The spring element restoring force produced in this way in consequence leads to the connection head being permanently pressed against the first coupling piece, and thus to a particularly reliable electrical connection. The contact fingers result both in centering of the connection head with respect to the longitudinal axis of the coupling and in the production of the electrical contact between the connection head and the connecting area. The interaction of the contact fingers with the associated recesses and in particular with contact surfaces arranged in them ensure an adequate contact with the connecting area fitted to it at all times even when the connection head is moved in the longitudinal direction.  
         [0019]     The contact fingers on the connection head surround a contact piece which is fitted to the connecting area of the second coupling piece and is used to ensure the electrical contact between the connection head and the connecting area. Depending on the load on the spring element associated with the connection head, the contact fingers rest on a larger or smaller area of the contact piece. The contact piece thus additionally has the task of reliably maintaining the electrical contact between the connection head and the connecting area of the second coupling piece even if the length of the spring varies.  
         [0020]     The connection head is advantageously inserted into a recess which is formed in the connecting area of the first coupling piece in such a way that it in consequence centers itself with respect to the longitudinal axis of the coupling. In this case, the shape of the connection head may, in particular, be convex and may be inserted into a corresponding concave recess in the connecting area of the first coupling piece, with both the connection head and the recess being rotationally symmetrical about the longitudinal axis of the coupling. This ensures that the connection head can be attached to the second coupling piece particularly easily and that the center axes of both coupling pieces cannot move with respect to one another while being coupled, which can lead to undesirable interference with the electromagnetic pulse and, furthermore, can make it impossible to connect the outer conductors to one another.  
         [0021]     For manufacturing reasons, a conical recess in the connecting area of the first coupling piece is particularly advantageous in this case, with a corresponding connection head in the form of a truncated cone.  
         [0022]     In accordance with an added feature of the invention, a retaining screw is advantageously anchored on the connecting area of the second coupling piece, holds the connection head on the connecting area and prevents the connection head from being completely loosened when the coupling is open. The outer conductor of each coupling piece is expediently equipped with a mounting flange which allows the coupling pieces to be connected to one another. In this case a circumferential seal is advantageously fitted between the mounting flanges and allows the coupling to be closed such that it is sealed.  
         [0023]     In accordance with an additional feature of the invention, the two coupling pieces are expediently securely connected via a closure element which allows the two coupling pieces to be held together firmly. The shape and contours of a closure element such as this are matched to those of the mounting flanges, and it surrounds the mounting flanges in the mated state.  
         [0024]     In an advantageous embodiment of the invention, the closure element is a clamping ring with a spring clip. This allows the coupling to be operated particularly easily and quickly.  
         [0025]     Undesirable attenuation of the electromagnetic pulse can be precluded, or at least kept to a minor level, since the impedances do not change, or change only slightly, over the length of the coupling point. The appropriate components, that is to say in particular the connecting areas and the outer conductors surrounding them, are advantageously suitably designed to ensure this.  
         [0026]     The advantages which are achieved by the invention are, in particular, that the use of a spring element for production of an electrical connection between the central conductors of the coaxial cables results in a coupling which can be operated particularly easily and quickly and ensures a particularly high-quality electrical connection between the coaxial conductors. This allows the coupling to be used even for sensitive measurements which require a high signal quality. The coupling is thus particularly suitable for use with coaxial conductors which transmit signals for TDR measurements in nuclear power stations.  
         [0027]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0028]     Although the invention is illustrated and described herein as embodied in a coupling for coaxial cables, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0029]     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]      FIG. 1  is a schematic view of a system for monitoring the filling level in a closed reactor pressure vessel;  
         [0031]      FIG. 2  is a cross section taken through a coupling for coaxial cables according to the invention;  
         [0032]      FIG. 3  is a cross section through the outer conductors of the coaxial cables with a closure element; and  
         [0033]      FIG. 4  is a cross section through the same outer conductors of the coaxial cables with a closure element and a seal.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a system  1  for monitoring a medium M within the connected reactor pressure vessel  2  of a nuclear installation. The reactor pressure vessel  2  is disposed within closed containment  4 , an wall of which is indicated schematically in the figure. In order to transfer signals S in a suitable form, the reactor pressure vessel  2  is connected to a communication interface  10  for the system  1  via a signal line  6  which is passed via a bushing  8  through the containment  4 .  
         [0035]     Water W is stored as the medium M in the reactor pressure vessel  2  in the exemplary embodiment and is used as the primary coolant for the nuclear installation. The water W is in the so-called undercooled state in a lower area. In contrast, there is a phase mixture W,D between the water W and the vapor bubbles D which are formed in an area above this, wherein the nuclear fuel elements which are arranged in the reactor pressure vessel  2  are heated. In contrast, an area even farther above this contains exclusively vaporized primary coolant, that is to say exclusively steam D. The medium M which is stored in the container  2  thus has a first boundary layer  12  between water W and the phase mixture W,D, and a second boundary layer  14  between the phase mixture W,D and the steam D.  
         [0036]     A large number of operating parameters must be monitored during the operation of the nuclear installation. In this case, inter alia, it may be desirable or necessary to monitor the position of the boundary layers  12 ,  14 . For example, in this case, a filling level measurement can be used for the position of the boundary layer  14 .  
         [0037]     The system  1  is intended for real-time determination and the monitoring of position characteristic values for the boundary layers  12 ,  14 . For this purpose, the system  1  is designed to use the so-called TDR measurement principle (time domain reflectometry). A substantially vertically arranged coaxial cable  16 , which is used as an antenna, is provided within the reactor pressure vessel  2  for a TDR measurement such as this. The coaxial cable  16  is passed out of the reactor pressure vessel via an electrical bushing  18 , and is connected to the signal line  6 . The communication interface  10 , which is connected to the signal line  6 , is itself connected to a pulse generator  20 , which produces the electromagnetic pulses, and to an evaluation and control unit  22  with an output module  24  and a memory module  26 . The evaluation and control unit  22  is, of course, also connected to other components that are required for correct operation, such as an input apparatus.  
         [0038]     The system  1  together with its components is specifically designed for use of the TDR measurement principle. Inter alia, particularly high-quality signal transport is desirable for this purpose in the lines provided for this purpose, in particular such as the signal line  6 . In order to particularly assist this, the signal line  6  is itself in the form of a rigid coaxial cable.  
         [0039]     However, in order to allow maintenance work to be carried out on the reactor pressure vessel  2 , it may be necessary to break down the signal line  6  into individual pieces as required, to join them together again and, for example, decouple them from one another at various points between the bushing  8  and the bushing  18 , and to recouple them together quickly and easily once the maintenance work has been carried out. For this purpose, the signal line  6  is composed of two or more coaxial cables  30 ,  32 , which are detachably connected to one another via a coupling  33 .  
         [0040]     In order to comply with the transmission quality requirements, which are stringent overall, the coupling  33  is also specifically configured for this object. In this case, provision is made in particular for the coupling  33  to produce a particularly close electrical contact between the central conductors  34  and  35  in the coaxial cables  30 ,  32  to be connected, while being simple to operate overall.  
         [0041]     As is illustrated in  FIG. 2 , the coaxial cable  30  and the coaxial cable  32  have a respective outer conductor  36  or  37  and a respective central conductor  34  or  35 . The coupling  33  which is provided in order to connect the coaxial cables  30 ,  32  to one another accordingly comprises a first coupling piece  38  and a second coupling piece  39 , with the coaxial cable  30  being firmly connected to the first coupling piece  38 , and the coaxial cable  32  being firmly connected to the second coupling piece  39 . The first coupling piece  38  has a connecting area  40  which is connected to the central conductor  34 . The second coupling piece  39  likewise has a connecting area  41 , which is connected in a corresponding manner to the central conductor  35  of the second coupling piece  39 . In order to produce a particularly close contact, the connecting area  41  is equipped with the connection head  42  which can be brought into contact with the connecting area  40  and is supported in a sprung manner on the actual connecting area  41  via a spring element  43 . The spring of the spring element  43  is loaded while the coupling  33  is being closed, and its resetting force presses the connection head  42  continuously against a corresponding contact surface of the connecting area  40  in the first coupling piece  38 , thus ensuring a particularly reliable electrical connection. Suitable springs are, for example, spiral springs, plate springs, leaf springs or helical springs, as in the exemplary embodiment.  
         [0042]     In order to allow the connection head  42  and the connecting area  40  to be joined together particularly easily and to allow the connection head  42  to be self-centering, the connection head  42  is equipped with, for example, a convex tip  44  which in the exemplary embodiment is in the form of a truncated cone and is inserted into, for example, a concave recess  45  which is provided for this purpose in the connecting area  40 . The recess  45  in the exemplary embodiment is conical, and its contours are thus matched to the tip  44  of the connection head  42 . Contact fingers  46  which are fitted to the connection head  42  allow a high-quality electrical contact to be made between the connection head  42 , and the connecting area  41 , which supports it, in the second coupling piece  39 . These contact fingers  46  surround a contact piece  47  which is fitted to the connecting area  41  and, depending on the load on the spring element  43 , rest on a larger or smaller area of the contact piece  47 . The contact fingers  46  can slide along the contact piece  47 , with the electrical contact between the connection head  42  and the connecting area  41  of the second coupling piece  39  being ensured in every position of the contact fingers  46 . This ensures that there is a high-quality electrical contact between the connection head  42  and the connecting area  41  even if the spring has a variable length.  
         [0043]     The connection head  42  is held on the connecting area  41  by means of a retaining screw  50 . This reliably prevents the connection head  42  from being completely loosened even when the coupling  33  is open.  
         [0044]     The outer conductors  36  and  37  which surround the respective connecting areas  40  and  41  of the respective coupling pieces  38  and  39  are each provided with a mounting flange  52  which allows the coupling pieces  38  and  39  to be connected to one another.  
         [0045]      FIG. 3  shows a cross section through the outer conductors  36  and  37 , respectively, of the coupling pieces  38  and  39  with a closure element  54  (for example a clamping ring which is held together by a non-illustrated spring clip) which surrounds the flanges  52  and thus connects the coupling pieces  38  and  39  to one another.  
         [0046]      FIG. 4  likewise shows a cross section through the outer conductors  28  of the coupling pieces  38  and  39  with a closure element  54  which surrounds the mounting flanges  52 , and thus connects the coupling pieces  38  and  39 , and which is equipped with a circumferential seal  56 . The seal  56  allows the closure element  54  to close the coupling  33  in a particularly sealed and secure manner.