Abstract:
The present device relates to a sensor capable of detecting changes in the electromagnetic field it generates when in proximity to either conductive or nonconductive materials. This occurs by way of oscillating a transmit coil with an electro motive force at a resonant frequency thus creating an electromagnetic field. The magnetic field passes through a target of either conductive or nonconductive material and is then intercepted by a receive coil which likewise oscillates at a resonant frequency, which when in proximity to the transmit coil and transmit coils resonant frequency produces an enhanced signal by way of the interaction of the respective resonant frequencies and receive coil output.

Description:
RELATED APPLICATION DATA 
       [0001]    This application is a continuation-in-part of co-pending U.S. application Ser. No. 13/396,378 filed on Feb. 14, 2012, which, in turn, claims the priority date of Provisional Application for Patent No. 61/442,742 filed on Feb. 14, 2011. 
     
    
     BACKGROUND 
       [0002]    The present device relates to a sensor capable of detecting changes in the electromagnetic field it generates when in proximity to either conductive or nonconductive materials and a device for orbiting about the joint between two tubular components for inspecting the welded or joined joint. 
         [0003]    There has been a persistent need to inspect both conductive and nonconductive items for consistency and for the presence of flaws with a single technology capable of overcoming deficiencies associated with traditional x-ray, eddy current, ultrasonic and other nondestructive inspection methods currently employed. The problem with x-ray has been the dangerous nature of the high energy electromagnetic wave and the hazards to biological organisms are well understood, given this and the need for elaborate shielding, x-ray can be very undesirable. Also, while x-ray is useful for detecting volumetric anomalies such as voids or the presence of foreign objects, flaws such as cracks where the adjoining faces of the cracks may be in intimate contact and having no appreciable volume, are very difficult to detect. 
         [0004]    Standard eddy current inspection is useful in detecting discontinuities in metal and other conductive materials, but do not work well when inspecting nonconductive materials. The inability to inspect nonconductive materials has limited eddy current applications. Eddy current inspection may also employ design features which allow the effects of signal output due to changes in liftoff (the distance between the sensor and the item) to be inspected to be mitigated. These design features are permanent and may not be changed on the fly during inspection, thus limiting its ability to instantaneously determine liftoff. 
         [0005]    Ultrasonic inspection can be difficult to employ, given the need to provide a coupling fluid or gel to transmit the ultrasonic frequency from a transducer to a target being inspected. It is often impractical to use such coupling fluids and gels on many structures as well as completed structures such as can be expected in the air frame of a finished aircraft, especially when constructed of composite. Also, it is not possible to use ultrasonic inspection technologies when there is an air gap separating otherwise inspectable walls, as air lacks the necessary transmissive qualities associated with a coupling fluid. 
         [0006]    Furthermore, the problem of inspecting small orbitally welded systems comprised of at least two components, each having at least one tubular extension meant to convey fluid with the extensions being orbitally welded one to the other, has been one of accessibility and motion control. Orbitally welded assemblies are generally comprised of at least two components, each component having at least one tubular element extending from the component for conveying fluid. The tubular elements of at least two components are connected one to the other by way of orbital welding such as the orbital welding method described in McGushion U.S. Pat. No. 5,196,664. 
         [0007]    Motion control is required to precisely place a sensing means over a weld joint and move the sensing means rotatably, and at times translationally, around the central axis of the weld joint in order to accomplish a complete inspection of the joint, areas adjacent to the joint, and areas in transition with the joint (known as the heat affected zone) in the smallest envelope possible. 
         [0008]    To inspect the above type of joint, a motion control system must also be able to transport a sensing means around a joint while avoiding impact or other mechanical interference with other components in the orbitally welded assembly. Orbitally welded components are often in close proximity to the joint being inspected as might be expected in the tight confines of a propulsion system of a satellite, rocket, or the hydraulic system of a fighter or commercial jet. In these tight applications, densely configured fluid control systems are often made with the prerequisite need to economize both size and weight. It is also necessary to transmit the data collected with such an inspection means to a computer controlled processing means and graphical interface so that the sensing means signal output may be correlated to a precise location on the welded joint in graphical form which can then be easily interpreted. 
         [0009]    Previous attempts to image these sorts of orbital welds have almost exclusively been done with an x-ray means, either with the use of film, computer tomography (CT), digital real-time radiography (digital RTR). The use of x-rays creates a safety hazard, where the work area must be evacuated and lead shielding employed. While x-ray inspection is well suited to discovering volumetric flaws such as porosity or inclusions of foreign objects in the weld, they are ill suited for discovering flaws, such as cracks which have very little volume. Additionally, x-ray inspection is time consuming, often requiring the orbital weld assembly to be removed from manufacture and brought to an x-ray booth. X-ray inspection often requires secondary methods to be used in order to effectively detect cracks which may not have been otherwise visible. The secondary method of inspection is generally a dye penetrant inspection, where fluorescing liquid is applied to the surface of the weld causing any existing surface cracks or imperfections to be filled with minute quantities of the liquid, which when illuminated by a type of light source, reveals the surface cracks or imperfections. The penetrant method requires a time consuming post inspection cleaning to remove the liquid. For these reasons, both x-ray and dye penetrant are inadequate to the task. 
         [0010]    Other inspection technologies, such as eddy current sensors, eddy current sensor arrays, ultrasonic sensors, ultrasonic sensor arrays, and thermographic inspection, are capable of inspecting orbitally welded joints for evidence of surface and subsurface defects, and possess the necessary miniaturization of the sensor technology itself to inspect tightly configured orbital welds. However, each of the above inspection methods lack the combination of sufficient miniaturization and sophistication in motion control, to transport the sensor precisely and repeatedly in order to inspect a weld in the confined space of a fluid assembly that has been orbitally welded. 
         [0011]    Accordingly, there is a need for a sensor which does not produce harmful radiation, which can inspect conductors and nonconductors alike and can inspect through walls of various materials and air gap transitions. Such a sensor should be very compact to allow easy access to confined spaces and should also allow for inspection of small features and anomalies which may be critical to the performance of the item or system being inspected. The sensor should provide an output that has signal variation relative to varying features or anomalies of a target and which may be located in the item being inspected. The sensor should have the ability to control for variables such as liftoff or material changes without the need to make permanent physical changes to the sensor. 
         [0012]    Furthermore, there is a need for a system with a sensing means capable of inspecting cracks, volumetric flaws and other defects on and in orbital tube welds which can be rotatably transported around the central axis of a weld joint and adjacent areas, so that a complete analysis of the weld area may be made, revealing defects and cracks. Additionally, a motion control system capable of transporting a sensing means is needed, that is suitably compact to allow placement and use in areas of tight configuration within an orbitally welded assembly, where other components of that assembly may be present and in close proximity to the area being inspected. This motion control system must lend itself to rapid installation onto and removal from the joint being inspected. Such a system must also communicate its sensing means output or data to a computerized controller for graphical presentation and interpretation of data. 
       SUMMARY 
       [0013]    The present resonant electromagnetic sensor provides an enhanced signal output by utilizing a transmit coil which resonates at a fixed or series of resonant frequencies. When an electro motive force (EMF) at resonant frequency or frequencies is induced to the transmit coil, it generates an electromagnetic field which oscillates relative to the frequency applied. This electromagnetic field passes through a target of either conductive or nonconductive material; and is then intercepted by a receive coil which also resonates at a frequency or series of frequencies in strategic proximity to the resonant frequency or frequencies of the transmit coil. The receive coil, by way of Lenz&#39;s Law converts the intercepted oscillating magnetic field and converts it to a signal which can be analyzed to reveal subtle and gross changes in the material being inspected. The proximity of the frequencies of the transmit and receive coils is meant to maximize sensor output by way of high ‘Q’ or quality factor and of high output signal which occurs when the transmit and receive coils have been tuned and brought into proximity to one another. 
         [0014]    The present sensor also provides frequencies at which the effects of liftoff and/or target material change may be mitigated if the transmit and receive coils have been appropriately tuned. Because of its high ‘Q’ and output signal, the present sensor is very sensitive to not only the subtle changes that may exist in a target of conductive material, but nonconductive material as well, so that it may scan from one type of material to the next without the need for sensor changes. Because of its unique “tuning” ability by way of adjusting resonant frequencies of transmit and receive coils, the present sensor may neglect the effects of liftoff and or changing materials under the sensor in order to generate a more complete image of the material being inspected. The present sensor is also capable of scanning through multiple walls of materials, with air and other materials at the transition boundary between the walls, and resolve characteristics not only of the intermediate walls but of the wall on the far side as well. 
         [0015]    Additionally, an orbital weld inspection system provides a motion control system with eddy current type sensing means and accurately controls both rotational motion around a joint and axial motion across the joint when necessary in order to generate a coordinate based output of data, where rotation may be represented as the ‘x’ axis or polar axis and where the axial distance across the joint may be represented as the ‘y’ axis and in a Cartesian or polar coordinate system where the signal output may be represented as a third or ‘z’ axis. This coordinate matched data is communicated to a computerized controller for graphical display and interpretation of said data. The present system also incorporates a means for quickly installing and uninstalling itself on the joint in space with limited clearance. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0016]      FIG. 1  is an isometric view of the orbital tube weld inspection head constructed in accordance with this specification; 
           [0017]      FIG. 2  is an isometric view of the head with the fixturing means open; 
           [0018]      FIG. 3  is an isometric view of the head and fixturing means with a weld joint assembly ready to be inserted in the head and fixturing means; 
           [0019]      FIG. 4  is an isometric view of the head with a weld joint assembly inserted into the head and locked in place by the fixturing means; 
           [0020]      FIG. 5  is an isometric projection of a portion of the head showing the sensing means aligned adjacent to a weld joint; 
           [0021]      FIG. 6  is a side projection of the head and fixture means; 
           [0022]      FIG. 7  is a top cross sectional view along line AA of the sensing means, weld joint assembly and fixturing means; 
           [0023]      FIG. 8  is a front projection of the head; 
           [0024]      FIG. 9  is a side cross sectional view along line BB of the fixturing means, motion control means and a weld joint assembly; 
           [0025]      FIG. 10  is an isometric view of a portion of the motion control assembly showing the cable management system and constant force spring return system; 
           [0026]      FIG. 11  is a front projection of the head with the cover removed showing the tandem gear drive system; 
           [0027]      FIG. 12  is a front projection of the head with the cover removed showing the tandem gear system transitioning past the open portion of the rotatable gear; 
           [0028]      FIG. 13  is a front projection of a portion of the head with the cover removed and gear portion of the rotor removed revealing a holder for the sensing means; 
           [0029]      FIG. 14  is an isometric view of the head and computer control system; 
           [0030]      FIG. 15  is a view of an x, y or Cartesian coordinate data representation with sensing means data output as the z axis; 
           [0031]      FIG. 16  is a view of a polar coordinate data representation with sensing means data output as the z or radial axis; 
           [0032]      FIG. 17  is a perspective view of the resonant electromagnetic sensor constructed in accordance with this specification; 
           [0033]      FIG. 18  is an orthographic end view of the sensor; 
           [0034]      FIG. 19  is an orthographic side view of the sensor; 
           [0035]      FIG. 20  is a perspective view of the sensor with a target material positioned in proximal to the sensor; 
           [0036]      FIG. 21  is a schematic of transmit coil; 
           [0037]      FIG. 22  is a frequency response graph of the transmit coil; 
           [0038]      FIG. 23  is a schematic of the transmit coil and receive coil; 
           [0039]      FIG. 24  is a frequency response graph of the transmit and receive coil; 
           [0040]      FIG. 25  is a frequency response graph showing sympathetic resonance; 
           [0041]      FIG. 26  is a schematic of the transmit and receive coils where the transmit capacitance is variable; 
           [0042]      FIG. 27  is a schematic of the transmit and receive coils where the receive capacitance is variable; 
           [0043]      FIG. 28  is a schematic of the transmit and receive coils where both receive and transmit capacitance are variable; 
           [0044]      FIG. 29  is a frequency response graph showing an air gap control frequency; 
           [0045]      FIG. 30  is a frequency response graph showing a wall control frequency; and 
           [0046]      FIG. 31  is a schematic showing rectification and amplification of the receive coil output. 
       
    
    
     LISTING OF REFERENCE NUMERALS OF DESCRIBED EMBODIMENTS 
       [0000]    
       
         
           
             Weld Joint Assembly  1   
             Arrow  5   
             Arrow  7   
             Fixture Means  9   
             Opening  10   
             Pin  11   
             Hook  12   
             Open Portion of the Rotatable Gear  13   
             Thumb Cam  14   
             Front Main Housing  16   
             Pedestal  18   
             Motor Housing  20   
             Back Main Housing  21   
             Fixture Bottom  22   
             Changeable Collet Type Insert Bottom  24   
             Fixture Top Hinge Point  25   
             Changeable Collet Type Insert Top  26   
             Fixture Top  28   
             First Component  30   
             First Path  31   
             Orbital Weld Joint  32   
             Second Path  33   
             Second Component  34   
             Sensor  36   
             Rotatable Gear  40   
             Translation Table Track  41   
             First Wire Spool  42   
             Rotor Assembly  43   
             Linear Glide Bearing  44   
             Rotor Assembly Groove  45   
             Combination Rotation and Translation Stepper Motor  46   
             First Constant Force Spring Spool  48   
             Slip Ring Capsule  50   
             Second Wire Spool  52   
             Rail for Linear Glide Bearing  54   
             Drive Gear  56   
             Drive Coupler  58   
             Translation Table  59   
             First Set of Tandem Gears  60   
             Second Set of Tandem Gears  62   
             Arrow  64   
             Arrow  66   
             Constant Force Spring  68   
             Input and Output Signal and Power Lines  70   
             Arrow  72   
             Signal and Power Cable  74   
             Arrow  76   
             Arrow  78   
             Second Constant Force Spring Spool  79   
             Cable Groove  80   
             Port for Main Power Signal and Control Cable  82   
             Strain Relief Toe-Clamp  84   
             Torsional Spring  86   
             Sensing Means Pivot Point  87   
             Arrow  88   
             Orbital Weld Inspection Head  90   
             Main Power and Signal Control Cable  92   
             Controller with Computer and Graphical Display  94   
             Sensor Assembly  220   
             First Lead of the Transmit Coil  222   
             First Lead of the Receive Coil  224   
             Receive Coil  226   
             Transmit Coil  228   
             Core  230   
             Second Lead of the Receive Coil  232   
             Second Lead of the Transmit Coil  234   
             Oscillating Magnetic Field  236   
             Discontinuity in Target Material  238   
             Target Material  240   
             Transmit Coil Circuit  241   
             Source of Oscillating EMF  242   
             Receive Coil Circuit  243   
             Transmit Coil Capacitor  244   
             Transmit Coil Resistor  246   
             Resonant Peak  248   
             Voltage Level at −3 dB  250   
             Upslope Side of Curve  252   
             Frequency  1   254   
             Resonant Frequency  256   
             Frequency  2   258   
             Bandwidth  259   
             Downslope Side of Curve  260   
             Peak Voltage at Resonant Frequency  262   
             Receive Coil Resistor  264   
             Signal Monitoring and/or Conditioning Device  266   
             Receive Coil Capacitor  268   
             Transmit Coil Resonant Peak  270   
             Trough  272   
             Receive Coil Resonant Peak  274   
             Transmit Coil Variable Capacitor  276   
             Transmit Coil First Resonant Peak  278   
             Transmit Coil Second Resonant Peak  280   
             Sympathetic Resonant Peak  282   
             Transmit Coil Fourth Resonant Peak  284   
             Transmit Coil Fifth Resonant Peak  288   
             Transmit Coil Sixth Resonant Peak  290   
             Receive Coil Variable Capacitor  292   
             Wall Control Frequency  294   
             Resonant Frequency Shift for Air Gap  296   
             Air Gap Control Frequency  298   
             Resonant Frequency Shift for Wall  300   
             Rectifier Portion of Circuit  302   
             Amplifier First Stage  304   
             Amplifier Second Stage  306   
             Signal Output  308   
             Offset Input  310   
             Gain Resistor  312   
           
         
       
     
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0154]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views. The following description of the resonant electromagnetic sensor is the preferred embodiment when said system is reduced to practice however, it is not intended to be the only embodiment as features and practices may be altered while still remaining within the intent and scope of this specification. 
         [0155]      FIGS. 1-4  illustrates the fixturing action of the orbital weld inspection head  90 , where a tube is inserted and in clamped in place.  FIG. 1  shows the fixture portion in its closed position with changeable collet type inserts  24  and  26  accommodating various diameters of assemblies to be inspected. Insert  24  are rigidly affixed to the fixture bottom  22  and insert  26  are affixed to the movable fixture top  28  which is hinged at point  25  to allow easy opening and closing, fixture bottom  22  is made as an integral part of head housing  21  for ease of manufacture and fixture top  28  is brought into compressive load by way of hook  12  being engaged in pin  11  and being downwardly loaded toward fixture bottom  22  by the action of thumb cam  14 ; collectively these elements are referred to as the fixture means  9 . The inspection head  90  is mounted on a pedestal  18  for ease of use on a table however, this pedestal may be removed in order to make the head more mobile and allow insertion into complex welded assemblies which may be inspected. 
         [0156]      FIG. 2  illustrates the fixture in its open position, having pivoted hook  12  off pin  11  and out of groove  13  in the direction of arrow  5  by releasing thumb cam  14 , fixture top  28  is free to open in the direction of arrow  7  carrying with it insert  26 .  FIG. 3  illustrates a welded joint assembly  1  having been orbitally welded, joining components with at least a tubular end meant to convey fluid and comprised of at a minimum a first component  30  and a second component  34  joined by orbital weld  32 . This welded joint assembly  1  is ready to be inserted into the inspection head  90  and said assembly may be inserted axially in along first path  31  or if the assembly were more complex and attached to other components it may be inserted along second path  33 , passing through opening  10  clearing all internal working components of inspection head  90  until it comes to rest on lower insert  24  of fixture means  9 . 
         [0157]      FIG. 4  illustrates the clamping action of fixture top  28  as it is pivoted downward at pivot point  25  carrying with it insert  26  which is applied against tube  30  and in opposition to insert  24 . Hook  12  is reinserted into groove  13  and engages pin  11 , then thumb cam  14  is engaged pulling hook  12  downward bringing load to bear on fixture top  28  and insert  26  securely holding the weld joint assembly by clamping tube  30  between inserts  24  and  26 .  FIG. 5  illustrates the weld joint assembly securely being held by the fixture means  9  such that the sensing means  36  is allowed to be positioned at a point where inspection is to begin. In this embodiment is an eddy current type sensor is used however, other types of sensors may just as easily be substituted for instance an eddy current array, ultrasonic sensor or an ultrasonic array collectively these types of sensor are referred to as the sensing means  36 . In some cases the inspection will begin adjacent to the orbital weld joint  32  so as to allow inspection of the heat affected zone or HAZ which is an area of changed metallurgy being brought about by the extreme heat of welding and adjacent to the actual orbital weld joint  32 . In other cases the HAZ may not be inspected and the point at which inspection begins may be on the orbital weld joint  32 . 
         [0158]      FIG. 6  illustrates orbital weld inspection head  90  in side view and with weld joint assembly  1  secured in the fixture.  FIG. 7  is a sectional view along the line AA illustrating weld joint assembly  1  being held securely by fixturing means  9  with sensing means  36  positioned to inspect the joint assembly and being held by rotor assembly  43  being comprised of a rotatable gear  40  first wire spool  42  and sensing means  36 .  FIG. 8  is an illustration of orbital weld inspection head  90  in front view. 
         [0159]      FIG. 9  is a sectional view along the line B-B of orbital weld inspection head  90  illustrating a motion control system comprised of a translation table  59  combination rotation and translation stepper motor  46  drive coupler  58  drive gear  56  first set of tandem gears  60  second set of tandem gears  62  linear glide bearings  44  rails for linear glide bearings  54  second wire spool  52  first constant force spring spool  48  and slip ring capsule  50  where said motor  46  transmits rotational motion to the rotor assembly  43  in discrete steps or at a constant speed by way of driving the main drive gear  56  which then drives first set of tandem gears  60  which then drives second set of tandem gears  62  and where said motor  46  being able to drive both rotatably and translatably also transmits translational motion to the rotor assembly  43  by moving said drive coupler  58  in an axial manner causing translation table  59  which carries said rotor assembly to move translatably. 
         [0160]      FIG. 10  illustrates the internal motion control of the orbital weld inspection head  90  where drive coupler  58  having been rotated by combination rotation and translation motor  46  (not shown in this view) and passing through translation table  59  engages drive gear  56  which is best viewed in  FIG. 11 . The drive gear  56  having been rotated a prescribed amount or at a fixed speed, first set of tandem gears  60  are driven in turn driving second set of tandem gears  62  which in turn drive rotatable gear  40  of the rotor assembly  43  causing the sensing means  36  to be rotatably moved around weld joint assembly  1  being conducted and restrained by the translation table track  41  being contained in a slip fit fashion by the rotor assembly groove  45 . 
         [0161]    As the previously described rotation takes place it can be appreciated in  FIG. 10  that the signal and power cable  74  is allowed to remain in constant connection with the rotating sensing means  36  and the rotationally stationary portion of the translation table  59  where input and output signal and power lines  70  are located by way of a cable management system comprised of a first wire spool  42  signal and power cable  74  second wire spool  52  second constant force spring spool  79  constant force spring  68  first constant force spring spool  48  and slip ring capsule  50  where as rotor assembly  43  rotates in direction  78  signal and power cable  74  is allowed to wind-up on rotor assembly  43  with signal and power cable  74  lying in cable groove  80 . Signal and power cable  74  being donated to the rotational motion of rotor assembly  43  second wire spool  52  serves as a wound reservoir of said signal and power cable  74  sufficient in length to accommodate any expected rotation of the rotor assembly  40 . Some tensile pull being required to manage signal and power cable  74  a constant force spring  68  applies a tension load to signal and power cable  74  in the direction of the second wire spool  52  by said constant force spring  68  being wound onto second constant force spring spool  79  and first constant force spring spool  48 . Given the natural reaction of the constant force spring  68  to resist extension or being unwound, a constant tension force is applied to the signal and power cable  74  through counter rotation being applied to the second constant force spring spool  79  and the second wire spool  52  respectively. As the rotor assembly  43  rotates back to its original start position the signal and power cable  74  is donated from the first wire spool  42  back to the second wire spool  52  and kept in constant tension to allow organized rewinding by the pulling action of the constant force spring  68 . The wound signal and power cable  74  is communicated to the central axis of the second wire spool  52  where it is connected to leads of the slip ring capsule  50  where a brush type contact in the slip ring capsule  50  translates the rotary motion of the second wire spool  52  and signal and power wire  74  to a fixed position at input and output signal and power lines  70  said rotation being given by this action to said sensing means  36  sufficient to rotate past the whole of or a desired portion of the weld joint assembly  1 . 
         [0162]    The combination rotation and translation stepper motor  46  being capable of linear translation in discrete steps or a constant velocity said motion is connected to the translation table  59  by way connection to the motor with the drive coupler  58  said translation being guided and restrained within the back main housing  21  by linear glide bearings  44  and rails for linear glide bearings  54  with relative motion of the combination rotation and translation motor  46  restrained by being affixed to said back main housing  21  said translation being given by this action to sensing means  36  sufficient to traverse the desired distance across the weld joint assembly  1  and in desired increments or at a constant velocity. 
         [0163]      FIG. 12  illustrates the constant drive feature of the tandem gear sets  60  and  62  whereas the rotor assembly  43  rotates and the open portion of the rotatable gear  13  approaches tandem gear  62 -A the rotatable gear  40  remains in constant drive contact with tandem gear  62 -B during the transition of open portion of the rotatable gear  13  past tandem gear  62 -A when the open portion of the rotatable gear  13  has sufficiently traveled, tandem gear  62 -A reengages rotatable gear  40  of rotor assembly  43 . This action will take place alternately for the second set tandem gears  62  to accommodate any number of full rotations of the rotor assembly  43 . The rotation and translation actions having thus been described any combination of these actions may be employed in any increment or series of increments or velocity or velocities and in conjunction with the sensing means output delivered to input and output signal lines  70 , sensing means signal output may be correlated so as to match a particular rotational or translational location or series of locations. 
         [0164]      FIG. 13  illustrates the sensing means  36  with rotatable gear  40  removed and being held against weld joint assembly  1  by the rotating action of torsional spring  86  about sensing means pivot point  87  said action causing said sensing means to remain in compliant contact with said weld joint assembly. Signal and power cable  74  within first wire spool  42  being restrained by strain relief toe-clamp  84  against the tensile action of the previously described constant force spring  68  applied to the signal and power cable  74  said tension having been restrained constituent wire of the signal and power cable  74  may be hooked-up to said sensing means for power and signal delivery and transmission. 
         [0165]      FIG. 14  illustrates the orbital weld inspection system being comprised of an orbital weld inspection head  90  a main power and signal control cable  92  and a controller with computer and graphical display  94 .  FIG. 15  illustrates a method of graphical display where previously described sensing means signal output may be correlated so as to match a particular rotational or translational location of orbital weld inspection head  90  or a series of locations such that ‘x’ axis  96  representing rotational movement of the orbital weld inspection head  90  with output data from said sensor collected at known intervals and being placed on the ‘x’ axis at intervals which match the distance traveled by said head over said interval and ‘y’ axis  98  representing the translational movement of the orbital weld inspection head  90  with output data from said sensor collected at known intervals being placed on the ‘y’ axis at intervals which match the distance traveled by said head having traveled over said interval and sensing means signal output  100  being displayed as the ‘z’ axis of the graphical display such that a topographical map of the weld joint assembly  1  is created. 
         [0166]      FIG. 16  illustrates a method of graphical display where previously described sensing means signal output may be correlated so as to match a particular rotational or translational location of orbital weld inspection head  90  or a series of locations such that rotational axis  102  representing rotational movement of the orbital weld inspection head  90  with output data from said sensor collected at known intervals and being placed on the rotational axis of the graph at intervals which match the distance traveled by said head over said interval and ‘y’ axis  98  representing the translational movement of the orbital weld inspection head  90  with output data from said sensor collected at known intervals and being placed on the ‘y’ axis of the graph at intervals which match the distance traveled by said head having traveled over said interval and sensing means signal output  100  being displayed as the radial axis of the graphical display such that a curvilinear topographical map of the weld joint assembly  1  is created. 
         [0167]      FIG. 17  is a preferred embodiment of the sensor assembly  220 , comprised of a transmit coil  228  and a receive coil  226  concentrically arranged and with the receive coil  226  within the transmit coil  228 . Within the receive coil is an optional core  230  made of material with high magnetic permeability and suitable for concentrating a magnetic field. This core serves to direct a greater amount of magnetic field to be generated by the transmit coil  228  into the area within the receive coil  226  so as to provide greater magnetic field to the receive coil  226 . This magnetic field once concentrated within the receive coil  226  by way of the core  230  can be converted to an oscillating electromotive force or EMF in accordance with Lenz&#39;s Law. Also shown in this figure are the leads of the coils. The first lead of the transmit coil  222  and the second lead of the transmit coil  234  are to be energized with an oscillating electromotive force or EMF. The first lead of the receive coil  224  and the second lead of the receive coil  232  provide a signal output by converting an induced magnetic field to an EMF. 
         [0168]      FIG. 18  is an end view of the sensor assembly showing the transmit coil  228  wound outside and concentric to the receive coil  226 . There is a gap shown between the two coils as illustrated, but this gap can be very small or the two coils may be in contact with one another. There may even be materials used to separate the coils or a bobbin used to wind the transmit coil, which then becomes interposed between the two coils. Also visible in this figure is the core  230  of high permeability material meant to concentrate the magnetic field to be generated by the transmit coil  228 . 
         [0169]      FIG. 19  shows the side view of the sensor and how the various components may be arranged within it. While the coils and the core are all of equal length, these lengths may be varied for ease of construction or to enhance performance. Also the number of turns on the transmit  228  and receive coil  226  may vary greatly. The number of turns selected for each will depend on several factors, such as the desired operating frequency, the desired energy transfer, and the desired amount of parasitic characteristics, or characteristics such as resistance, capacitance and inductance inherent in the winding itself. 
         [0170]      FIG. 20  shows the oscillating magnetic field  236  which has been generated by providing and oscillating EMF to the transmit coil  228 . This magnetic field oscillates at a frequency which matches the oscillation applied to the leads  222  and  234  of the transmit coil  228 . Placed in front of the sensor assembly  220 , or in sensing proximity, is the target material  240 , which may be made of conductive or nonconductive matter or a compound of materials. This matter or compound may be solid, liquid or gas as the sensor assembly  220  is capable of discerning characteristics for all of these states. For the sake of this explanation however, we will assume that this target material  240  is solid. Within or on the target material  240  is a discontinuity  238 , which may be a flaw or a desired feature of either the same material of the target or different material. This discontinuity may be present on the surface closest to the sensor, within the target or on the side of the target farthest from the sensor assembly  220 . 
         [0171]      FIG. 21  is a schematic of the basic transmit coil circuit  241  and is shown to better understand the details of the sensor assembly  220 . In this schematic, the source of oscillating EMF  242  can be seen as well as a classic LRC circuit taught in basic electronics. In this circuit there is a resistor  246 , an inductor or transmit coil  226  and a capacitor  244 . Transmit coil  226  having leads  224  and  232  connecting it to the circuit. It is well understood that in such a circuit the resonant frequency can be known by the formula f=½π (LC) 1/2 . Where f is the resonant frequency of the transmit coil circuit  241  and L is the inductance of the transmit coil  228  and C is the transmit coil capacitor  244 . It is important to note that while there is a resistor and capacitor shown, a contributing resistance and capacitance in the circuit can also be by way parasitic resistance and capacitance in the transmit coil  226 . Also, while the resistance, inductance and capacitance in this circuit is shown in series, one or more of these elements could be in parallel arrangement. It is also useful to recognize that resonance is reached when inductive reactance X L  is equal to and opposite capacitive reactance X C  and since XL=2πfL and XC=½πfC, it is easy to see how the formula for resonant frequency is derived. 
         [0172]    While resistance is not shown in these formulas, it is an important component in the overall amplitude of the magnetic field  236  being created by the transmit coil  228 . Altering either capacitance by way of changing the transmit coil capacitor  244  or the inductance of the transmit coil  228  has a dramatic effect on the resonant frequency of the circuit. Although it is not shown, inductance can be varied by adding an additional inductor or a variable inductor. However, the preferred embodiment is to vary the transmit coil capacitor  244  to tune resonant frequency as you might a radio receiver. 
         [0173]      FIG. 22  shows the frequency response of a simple LRC circuit as with the transmit coil circuit  241  where there is a clear resonant peak  248  where X L  is equal to X C . It is clear that at frequencies below and above resonant frequency  256  the reactance increases and efficiency drops as is shown by the upslope side of the curve  252  as well as the downslope side of the curve  260 . An important way to measure the quality of a resonating circuit or ‘Q’ is to divide the resonant frequency  256  by the bandwidth  259 . Bandwidth  259  is given by measuring 3 dB down from the peak voltage at resonant frequency  262  to arrive at the voltage level at −3 dB  50 . At that voltage level a horizontal line can be drawn  250  and where it intersects the frequency response curve two vertical lines can be drawn  254  and  258  where  254  is frequency  1  and  258  is frequency  2 . By subtracting frequency  2 ,  258  from frequency  1 ,  254  bandwidth  259  can be known, or bandwidth=f 2 −f 1 . To calculate ‘Q’ the resonant frequency  256  is divided by the bandwidth  259 . ‘Q’ will be used later in describing preferred operating frequencies of the sensor assembly  220 . 
         [0174]      FIG. 23  shows a schematic of the transmit coil circuit  241  and the receive coil circuit  243 . The receive coil  226 , as mentioned, is collocated concentrically with and inside the transmit coil  228 . Its purpose is to intercept the magnetic field  236  generated by the transmit coil  228  after having passed through the target material  240 . It is preferred not to simply intercept the magnetic field  236 , but rather to first tune the resonant frequency of the receive coil  226  to in some cases exactly match or have parity with the resonant frequency  256  of the transmit coil  226  and in other cases to be close to, or have approximate parity to the resonant frequency  256  of the transmit coil  226 . This is done by again tuning receive coil circuit  243  by varying either inductance or the receive coil capacitor  268 . In the preferred embodiment it is desirable to adjust or tune capacitance by varying the receive coil capacitor  268 . As before variations in the receive coil resistor  264  serves to affect amplitude of the signal output. By tuning both the transmit circuit  241  and the receive coil circuit  243  to either parity or approximate parity, depending on the particulars of the circuit, an enhanced transmission of power can be realized from the transmit coil circuit  241  to the receive coil circuit  243 . 
         [0175]    The energy transferred to the receive coil circuit  243  is monitored with signal monitoring and or conditioning device  266 . This device may monitor the oscillating signal from the receive coil circuit with a display, commonly referred to as an impedance plane display, where impedance is given on an oscilloscope type device, where one axis of the display represents resistance of the circuit and the other axis represents inductive reactance. The preferred method of conditioning and monitoring in this embodiment which will be explained in  FIG. 31  is rectification and then amplification of the DC signal. It is this preferred method that was used in the collecting of data for the frequency response curves in this specification. 
         [0176]      FIG. 24  shows a frequency response of the circuit in  FIG. 23  where the transmit coil circuit  241  has a resonant peak  270  which is at approximately 99 KHz and the receive coil circuit  243  has a receive coil resonant peak  274  which is approximately at 195 KHZ. While each of these peaks are at resonance and each is capable of detecting variations in material  240 , this circuit has not been optimized. It can be seen that there is a trough  272  between the transmit coil resonant peak  270  and the receive coil resonant peak  274 . This trough  272  is indicative of poor energy transfer from transmit coil circuit  241  and receive coil circuit  243  by way of transmit coil  226  and receive coil  228 . It is desirable to minimize this trough  272  to enhance performance of the circuit of  FIG. 23  and of the sensor assembly  220 . This trough  272  can be minimized by proper tuning of the circuit of  FIG. 23 . 
         [0177]      FIG. 25  shows the frequency response of multiple variations of the circuit of  FIG. 23 , where the receive coil capacitor  268  has been set and held at 519 pfd (pico farads) giving a receive coil resonant peak  274  of about 195 KHz. It can be seen that as the transmit coil capacitor  244  of the transmit coil circuit  241  is changed to different values there is a dramatic effect on frequency response. It can be seen that a transmit coil first resonant peak  278  with a transmit coil capacitor  244  of 1052 pfd is far removed from the receive coil resonant peak  274  and transfers a low amount of energy from the transmit coil circuit  241  to the receive coil circuit  243  and that the trough  272  is quite wide. The transmit coil second resonant peak  280  has greatly improved in amplitude by using a transmit coil capacitor  244  of 519 pfd. This has brought its resonant peak  280  closer to the receive coil resonant peak  274  and in so doing has boosted energy transfer by improving “sympathetic resonance”, where the resonant frequency of the transmit coil is either in parity with or in approximate parity to the resonant frequency of the receive coil such that output is increased beyond the output of the constituent resonant peaks. Maximum output of this particular circuit of  FIG. 23  reaches its maximum when the transmit coil capacitor  244  is set at 237 pfd, yielding sympathetic resonant peak  282 . At this frequency of about 142 KHz, the circuit will be most sensitive to changes in target material  240  and will be most able to detect variations such as discontinuities in target material  238 . In this case, this peak occurred at an approximate parity frequency which does not match the receive coil resonant peak  274 . This is due to a wide variety of reasons from the construction of the sensor assembly  220  to the particular tuning of the circuit of  FIG. 23 . Depending on construction and tuning, the sympathetic resonant peak could be at frequencies lower than, greater than or equal to the receive coil resonant peak  274 . Transmit coil fourth, fifth and sixth resonant peaks  284 ,  288  and  290 , respectively, occur at different frequencies but are not optimized. 
         [0178]      FIGS. 26 ,  27  and  28  show the addition of variable capacitors to either the transmit coil circuit  241  or the receive coil circuit  243  or both.  FIG. 26  shows transmit coil capacitor  244  being replace with transmit coil variable capacitor  276 .  FIG. 27  shows receive coil capacitor  268  being replaced by receive coil variable capacitor  292  and  FIG. 28  shows both the transmit coil capacitor  244  and the receive coil capacitor  268  being replace by transmit coil variable capacitor  276  and receive coil variable capacitor  292  respectively. These aforementioned variable capacitors may be manually variable or variable by electronic signal. The purpose of these variable capacitors is to allow rapid switching to other desired resonant peaks or sympathetic resonant peaks in order to more thoroughly inspect the target material  240 . 
         [0179]      FIG. 29  shows a circuit tuned to a resonant frequency which may or may not be the sympathetic resonant frequency, where desirable characteristics other than maximum power transfer or maximum output occur. This tuning may be achieved by adjusting one or more variable capacitors such as in the circuits of  FIG. 26 ,  27  or  28 . 
         [0180]    It is often a desirable feature of a sensor to be able to control for variables such as liftoff, the gap or distance from the sensor assembly  220  to the target material  240 , or changes in material configuration such as the wall thickness of that material.  FIG. 29  shows how the control of gap may be accomplished by monitoring the output of the circuit at the air gap control frequency  298  of 75 KHz as opposed to the resonant peak. In doing this, it can be seen that the effects of gap are greatly mitigated relative to other frequencies. 
         [0181]    The same circuit is shown in  FIG. 30 , but instead of varying gap, the wall thickness of the material is varied. It can be seen that the air gap control frequency  298 , which mitigates changes in gap, is sensitive to changes in wall. This means that even though there are changes in the distance from the sensor to the target, those changes are mitigated while the effects of varying wall can be clearly seen. 
         [0182]    Similarly, at the wall control frequency  294  of 63 KHz, as wall is varied the signal is mitigated, but as gap is varied, the signal output changes appreciably. In this manner the sensor assembly  220  may be tuned to control variables and or tuned to provide maximum output and frequencies may be switched as desired to achieve maximum signal or mitigated signal. While the control signals for wall and gap have been shown, other control frequencies exist to mitigate change in material or change in temperature which are found by similar tuning methods. 
         [0183]    Further studying the frequency response curve of  FIG. 29 , it can be appreciated that the compression of curves at and about the air gap control frequency  298  and the subsequent expansion of curves at the wall control frequency  294  occurs as a result of a resonant frequency shift for air gap  296 . It can be seen that as air gap increase the signal amplitude rises while the resonant frequencies shift lower. This is true of this particular tuning setting and the phenomena may be reversed if tuned differently where the resonant frequency shift for air gap may be to higher frequencies, causing a reversal in the compression and expansion of the curves and or causing a reduction in signal due to increased air gap. 
         [0184]    Conversely, in  FIG. 30  as wall thickness changes the resonant frequency shift for wall  300  is to higher frequencies as wall thickness increases and signal increases as wall increases. This causes a compression of the curves at the wall control frequency  294  and an expansion of the curve at the air gap control frequency  298 . Again, depending on tuning, these compression and expansion areas may be reversed and signal may diminish relative to wall. 
         [0185]      FIG. 31  shows a preferred embodiment of the signal monitoring and or conditioning device  266 , where the output of the receive coil circuit  243  is fed into a rectifier circuit  302  to convert the oscillating signal to a DC or direct current output. The DC signal is then fed into an amplifier first stage  304  where the signal is amplified. The amplified signal is then sent to the amplifier second stage  306 , where additional amplification may be accomplished by setting or adjusting gain resistor  312 . Often, there is a computer which will receive the output  108  of the signal monitoring and or conditioning device  266  and  FIG. 31 , as many computers can tolerate a relatively narrow voltage input of perhaps+/−10 volts. Should the signal become too large due to amplification, resonant tuning or high voltage being delivered by source of oscillating EMF  242 , an offset input  310  may be applied. In so doing the output voltage is shifted to a lower voltage which can be received by the computer while preserving any effects that may have come about by monitoring variations in target material  240 .