Patent Publication Number: US-6220891-B1

Title: Probe connector

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to remote nondestructive sensors and, more particularly, to a connector capable of disconnecting a probe from a probe drive shaft while insulating a data line from a drive line when the probe is connected to the shaft. 
     2. Prior Art 
     It is known in the art to have a remote sensor, or probe, traveling in small tubes as small as ½ inch inside diameter such as are found in steam generators and heat exchangers to inspect the integrity of such tubes or to deliver the probe to a remote location. Generally, a testing probe is urged through a tube by means of a positioning, or drive, shaft to which it is attached. During operation, the probe sensor is driven by a drive line voltage and transmits responsive measurement data, both through cables carried within the shaft. An Eddy current probe is one such remote sensor commonly employed in the inspection of tubes. 
     Cracks and bubbles and other material nonuniformities produce variations in conductivity and permeability. Induction of Eddy currents in the material is a commonly-used technique for nondestructively detecting such defects near the surface of materials by sensing changes in material conductivity or permeability at a material nonuniformity by detecting changes in Eddy currents. Eddy currents are induced in the test material by a drive coil in an Eddy current probe. An oscillating electrical current in the coil generates an alternating primary electromagnetic field that is propagated into the test material. It is this primary field that induces the Eddy currents in the measured material. The Eddy currents in turn generate a secondary electromagnetic field that is propagated back to a sense coil in the probe where an electric current and voltage is induced. The sense coil voltage is therefore a function of the magnitude of Eddy current flow in the test piece. Discontinuities and nonuniformities in the material being tested with inherent change in permeability and conductivity cause a reduction in the magnitude of the Eddy currents and thus a change in the voltage in the sense coil which is analyzed as an indicator of the causing defect in the test material. 
     The voltage to the drive coil, which might be 400 volts at 4-5 watts, is typically carried in a coaxial drive cable within the drive shaft to the eddy current probe coil. The voltage induced in the sense coil at perhaps 1% of the drive voltage is carried from the probe in a different data cable, well insulated and separated from the drive cable so the drive voltage does not induce a voltage in the data cable that overwhelms the data voltage. When multiple drive coils and multiple sense coils are employed in the probe, a plurality of drive cables are employed, all spaced apart and insulated from multiple data cables. 
     It is often desirable to disconnect the probe head from the shaft for probe replacement or repair. This requires that the power drive lines and data communication cables be broken. At the break, without other precautions, loss of insulation between the power and communication cables induces cross-talk into the data lines that masks the data signals. Available large coaxial connectors designed to prevent this cross-talk are not suitable because their size prevents their use in small, ½ inch tubes. Thus, previously detachment of an Eddy current probe from the shaft has been ill-advised. 
     SUMMARY 
     It is the primary object of the present invention to provide a cable connector useful to connect and disconnect an Eddy current probe from a drive shaft including power and communication cables passing through the shaft to the probe. A second object is to maintain electromagnetic insulation between the power and communication cables at the connector break to avoid electromagnetic leakage from the power cable that might induce a voltage in the communication cable. Another object is that the connector be sufficiently small so that it can be employed in tubes with an inside diameter of about ½ inch. 
     These objects are achieved in a connector comprising a union with connectable shaft and probe sections of electromagnetically insulative material mating at matching transverse surfaces. The connector includes upper and lower portions with power line connecting pins and matching sockets in the upper portions of the sections and communication line connecting pins and matching sockets in the lower portions of the sections. Each section upper portion transverse surface is separated, or staggered, longitudinally from its lower section transverse surface by a planar ledge surface. The two ledges and the section upper and lower matching surfaces are in face to contact when the union is connected. A trepan may also be provided at inner comers formed between ledge and transverse surfaces. Matching plugs at outer comers formed between ledge and transverse surfaces then slide into and fill the trepans when the connector is closed. Thus, any electromagnetic radiation that may leak from the connection of the matching surfaces at the power line upper portion is effectively prevented from conducting to the connection of the matching surfaces at the communication line lower portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the shaft and probe sections of the connector, side by side. 
     FIG. 2 is an exploded view of the connector of FIG.  1 . 
     FIG. 3 shows top, end and side views of the shaft section showing insert bores 
     FIG. 4 shows end and side views of the probe section showing insert bores. 
     FIG. 5 shows end and side views of a three-pin probe insert. 
     FIG. 6 shows end and side views of a four-pin shaft insert. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The probe connector of the present invention comprises a cylindrical union  10  having a shaft section  11  intended to be connected to a drive shaft  12 . The shaft section is disconnectable at a break  13  from a probe section  14  intended to be connected to a remote probe such as an eddy current probe  15 . 
     A union lower portion including a probe section lower portion  16  and a shaft section lower portion  17  houses a plurality of power lines  18  between union ends  19  and  20  for providing a drive voltage to a probe. The power lines are shown in FIG. 2 to comprise four power connector pins  21  in the shaft section  11  and four power connector sockets  22  matching and in alignment with the pins  21  for receiving the pins in electrical contact in the probe section. 
     An upper portion including a probe section upper portion  24  and a shaft section upper portion  25  similarly houses a plurality of data communication lines  26  between union ends  19  and  20  for communicating a data signal from at least one probe. The data communication lines are shown in FIG. 2 to comprise two sets of three data connector pins  27  in the probe section and two sets of three data connector sockets  28  or pins  27  (typically one set of sockets and one set of pins) matching and in alignment with the pins for receiving the pins in electrical contact. Clearly, it is equivalent to reverse the pin and socket locations with the pins in the pins in the shaft section and the sockets in the probe section. It is to be understood for both the power lines and the data communication lines that the number of connector pins and connector sockets are given as an example, and another number of pins and sockets is to be deemed included in the definition of the connector. 
     The shaft and probe sections include matching upper portion transverse contact surfaces  29  and  30  that come into face to face contact when the union is connected. Matching lower portion transverse contact surfaces  31  and  32  are similarly in face to face contact along with the upper surfaces when the union is closed. The contact surfaces of the upper portion are spaced apart, or staggered, from the contact surfaces of the lower portion. Necessarily, the shaft section upper portion extends substantially beyond the shaft section lower portion, and the probe section lower portion extends likewise beyond the probe section upper portion. A longitudinal planar ledge  33  runs between the staggered upper and lower contact surfaces. Thus, the upper portion of the shaft section overlaps the lower portion of the probe section on matching sliding planar ledges  33  and  34  also in face to face contact to form an integral union body with effectively no airspace between contacting ledges. With the union formed of an electromagnetically insulative material, there is effectively no electromagnetic leak between the power lines and the data communication lines due to the union break. 
     In a first embodiment the transverse contact surfaces  29 ,  30 ,  31 , and  32  are planar. In an alternative embodiment, they are nonplanar so that propagation of an electromagnetic field along the surface is further impeded as shown in FIG.  3  and FIG.  4 . 
     As a further impediment to electromagnetic field propagation from the power lines along the longitudinal planar ledge, a trepan  35  may be provided in the probe section at one or both inside comer intersections  36  of the transverse contact surface and the longitudinal planar ledge extending across the transverse contact surface. A plug  37  closely matching the trepan or trepans in size and shape extend from one or both outside comers  38 , respectively, of the shaft section at the intersection of its transverse contact surface and its longitudinal planar ledge also extending across its transverse contact surface such that with the transverse surfaces in face to face contact, the plug or plugs fit closely within the trepan or trepans. Thus, for an electromagnet field to propagate from the power lines along the transverse surfaces and the longitudinal planar ledge, it must also propagate and change directions along each plug and trepan pair or jump the plug. Because a change of direction dampens an electromagnetic field as it is absorbed by the insulative material of the connector, and because the plug leaves virtually no open air space within the trepan in which the field may propagate, field propagation is effectively eliminated. Also, because the plug is a strongly insulative material, a field is effectively unable to propagate through it 
     The probe section upper portion has longitudinal bores  40  therethrough in each of which is secured a probe section insert  41 . Typically, one insert contains connector pins  27  and one insert contains connector sockets  28 . Correspondingly, the shaft section upper portion has longitudinal bores  42  therethrough in each of which is secured a shaft section insert  43  containing the connector sockets  22 . Similarly, the probe section lower portion has a longitudinal bore with inserts containing its connector sockets  22  and the shaft section lower portion has a longitudinal bore  46  with inserts containing its connector pins  27 . Probe section insert  41  and shaft section insert  43  both are electrically nonconductive with permeabilities less than that of the probe section and shaft section such that propagation of electromagnetic waves through the inserts is impeded.