Continuity detecting apparatus
FIELD OF THE INVENTION 
     This invention relates to an electrical continuity testing apparatus. 
     BACKGROUND OF THE INVENTION 
     There are numerous situations in which there is a need for an electrical continuity testing apparatus for use in repairing damaged electrical cables having a multiplicity of conductors. The repair of damaged electrical cables involves correlating the severed or damaged ends of the conductors of the cable with their opposite ends and restoring continuity. This process is relatively simple when the damaged cable is relatively short and readily accessible and where technicians can communicate with one another by voice contact. However, the task is rather difficult when the cable is long, relatively inaccessible, must be repaired in situ and there is a high environmental noise level. Such may be the case, for example, in aircraft and ships where cables may have a length of 100 feet or more, the ends and damaged portions of the cables are located in different compartments, and other structural repairs are concurrently in the process of being effected, thereby resulting in a high noise environment. 
     SUMMARY OF THE INVENTION 
     It is therefore the primary object of the present invention to provide an apparatus which facilitates the tracing and restoring of the continuity of damaged cables in situ. 
     In accordance with one aspect of the invention, there is provided an apparatus having an electrical circuit including a continuity detector and indicator and at least two test cables. Each cable has a proximal end adapted to be connected to the electrical circuit and a distal end employed by a technician at an appropriate location with respect to the damaged cable such as at the ends and the point of severance of the damaged cable. The distal ends of the cables are provided with probes for making electrical contact with the ends of the conductors of the damaged cable. The electrical circuit includes means adapted to connect the test probe of any one of the test cables to a signal source and the probe of any of the remaining test cables to the detector. 
     Thus, when the probe of one test cable is placed in electrical contact with the end of one conductor and the probe of the other test cable is placed in electrical contact with the other end of that conductor, the circuit is completed and current flows from one test cable and probe, through the conductor and the other probe and test cable to the detector. The detector activates the indicator which signals to the technicians that the opposite ends of the conductor have been identified. 
     The preferred form of the invention includes three test cables; one test cable is employed by one technician at the point of severance of the damaged cable and the other two are employed by two other technicians at the ends of the damaged cable. The electrical circuit includes a switch for selectively activating any two of the three test cables and connecting them to the signal source and detector in the manner mentioned above. 
     In use, the switch is positioned so as to activate the test cables associated with the center technician and one end technician. These two technicians identify the opposite ends of one conductor by the end technician placing his probe in contact with the end of one conductor and the center technician sequentially placing his probe in contact with the end conductor at the point of severance until the indicator is activated. The switch is then positioned to activate the test cables associated with the center technician and the other end technician. These technicians proceed to locate the mate of the identified conductor. When that is achieved, the conductor is repaired and the switch is positioned to activate the test cables associated with the end technicians and deactivate the center technician&#39;s test cable. The end technicians place their probes in contact with the ends of the repaired conductor to confirm that the conductor has been properly identified and repaired. The procedure is repeated for each of the remaining conductors. 
     Where voice contact is insufficient to provide adequate communication between technicians, the apparatus provides continuous communication between each technician by means of headsets, including earphones and microphones, connected to the distal ends of the test cables and in communication with one another via the test cables and electrical circuit. The electrical circuit amplifies microphone signals and feeds them together with continuity indicator signals to the earphones of each headset. 
     In accordance with a still further aspect of the present invention, there is provided a novel test probe which facilitates the continuity identification task. The test probe is particularly useful for use at the damaged portion of the cable. The probe has one end adapted to be connected to a jack at the distal end of a test cable and the other end adapted to be placed in electrical contact with and secured to the wrist of a technician so that the technician&#39;s hand functions as the probe. 
     These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a circuit tester carrying case in an opened condition illustrating the front panel of the circuit tester; 
     FIG. 2 illustrates one of the test cables and a test lead extending from a distal end thereof; 
     FIG. 3 illustrates a test lead for use in attachment to a portion of the skin, such as that of the wrist, of a technician; and 
     FIG. 4 is a circuit schematic of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates various components of the continuity testing apparatus 10 of the present invention. In general, the apparatus includes a carrying case 12, in which an electrical circuit 14 (FIG. 4), a d.c. source of power 16 (FIG. 4) and a control panel 18 are disposed, in addition to three test cables 20, 22 and 24. The carrying case is formed with a lid 26 which is shown in an opened position exposing the control panel. 
     Mounted on control panel 18 are three jacks 30, 32 and 34, each of which is adapted to be connected to a plug 35 at the proximal end 36 of the test cables 20, 22 and 24 respectively, and external power jack 38 for connection to an external source of power if so desired, a selector switch 40 for activating, in a manner to be explained later, any two of the three test cables, a visual continuity indicator 42 for providing a visual indication of continuity, and a gain control switch 44 for adjusting the gain of a tone signal which provides an audible indication of continuity. 
     With reference to FIG. 2, the distal end 46 of each test cable is provided with a jack 48 for removable attachment thereto of a plug 50 of a headset 52, which includes at least one earphone 54 and a microphone 56. The distal end 46 of each test cable is also provided with a test lead terminal or jack 58 for connection to a test lead 60, the free end of which is provided with a probe 62, such as an alligator clip, for use in making electrical contact with an end of a conductor to be tested. Advantageously, the distal end 46 of each cable is provided with a clip 64 arranged to be attached to the belt, or the like, of a technician. The control cable 22 is for use by a technician, hereinafter referred to as MAN 2, at the point of severance of the damaged cable. MAN 2 operates the apparatus and, accordingly, cable 22 need not be very lengthy. A length in the order of 10 feet is sufficient. Cables 20 and 24 are for use by technicians, hereinafter referred to as MAN 1 and MAN 3, respectively, at the remote ends of the damaged cable and thus should be relatively lengthy. A length in the order of 75 feet is considered adequate. 
     FIG. 3 illustrates a test lead assembly 70 for use by MAN 2 stationed at the location of severance of the cable to be repaired. Test lead assembly 70 includes a fork terminal 72 adapted to be connected to terminal 58 of test cable 22. The bared opposite end 74 of the test lead 70 is secured to a strip of electrically conductive foam 76 by means of a tie wrap 78. Strips of a hook and loop type detachable adhesive 80, known as Velcro®, are secured to opposite sides and at the ends of strip 76 for attachment of the strip to the technician&#39;s wrist so that the technician&#39;s hand serves as a test probe. The hand is used to make electrical connection between the damaged central cable and test lead which connects to the circuit of FIG. 4. 
     FIG. 4 is a schematic of the electrical components and circuitry disposed within carrying case 12. The electrical circuitry 14 includes a circuit board 82, indicated by chain-dotted line 83, on which a number of the components are mounted as will be described. 
     Each of jacks 30, 32 and 34 includes a pair of terminals 84 and 85 which are adapted to be connected to the microphone terminals of each of headsets 52 via a test cable. The common inputs from the microphones are connected via terminals 84 and 85 to the input of an audio amplifier 86 having a potential divider 88 for adjusting the gain of the audio signal to a desired level. The output of amplifier 86, together with a tone input received from a multivibrator 90 via tone gain control switch 44, is applied to a second audio amplifier 92. The output of amplifier 92 is fed to each of three buffers, each of which is comprised of a pair of operational amplifiers 94 and a transformer 96 and associated with one of the three headsets 52. The buffers are provided to avoid impedance matching problems when only two headsets are connected to the circuit. The output of each transformer 96 is connected to a terminal 98 of an associated jack 30, 32 or 34 as shown. 
     Each jack 30, 32 and 34 further includes a terminal 100 connected to appropriate terminals of a three position selector switch 40 as shown and for connection, via plugs 35, to terminals 58 of cables 20, 22 and 24. Switch 40 serves to connect in pairs the test probe of the three test cables to the circuit. Position 1-2 of the switch, shown externally in FIG. 1, activates the test probes associated with cables 20 and 22, position 2-3 activates those associated with cables 22 and 24 while position 1-3 activates those associated with cables 20 and 24. One terminal 102 of switch 40 is connected to a signal source 103 while another terminal 104 of switch 40 is connected to a threshold detection circuit 106. 
     Circuit 106 includes a resistor 108 and diodes 110 and 112 to protect the circuitry against external voltages accidentally applied to its sensor lead. Resistor 108 is connected to the base of a transistor 114 whose emitter voltage is applied to the pin 3 of an operational amplifier 109 functioning as a level detector. A threshold level potential is applied to pin 2 of detector 109, the threshold level being selectively adjustable by a potentiometer 116. 
     As previously mentioned, resistors 108 and diodes 110 and 112 protect the circuitry against external voltages accidentally applied at the sensor leads. Should the input be raised to +117 volts, resistor 108 allows approximately 2 ma to flow via diode 110 into a positive supply terminal. Should the input be lowered to -117 volts, resistor 108 allows approximately 2 ma to flow via diode 112 from a negative supply terminal. 
     The output of detector 109 is applied to visual indicator 42, which is of the form of a light emitting diode (LED), an audio indicator or buzzer 115, and multivibrator 90. In response to an output signal from detector 109, multivibrator 90 generates a square wave train which is applied to a terminal 44b of switch 44 which, in turn, as previously mentioned, applies a tone signal to the input of amplifier 92. The frequency of the tone signal generated by multivibrator 90 may be adjusted internally by potentiometer 118. 
     Power is normally supplied to the circuit by an internal battery pack 120 comprised of four D cells providing a nominal 6 vdc. In addition, an external source of power of 12 to 30 vdc may be supplied via jack 38. This potential is regulated to 8 vdc by a voltage regulator 122 which is protected against reverse polarity by diode 124. The output of regulator 122 is applied to terminal 44a of switch 44 via fuse 126. A pair of diodes 128 and 130 are provided to avoid the need of manual switching. When 8 vdc is present, diode 128 is back biased resulting in no current drain from battery pack 120. Fuse 126 is provided to protect the power supply against both external shorts from damaged cables and application of unwanted external voltages through the test cables. 
     It will be understood that when plugs 35 of the test cables 20, 22 and 24 are connected to jacks 30, 32 and 34 respectively and the headsets are connected to jacks 48 (FIG. 2) of the test cables, three technicians are enabled to test the continuity of conductors and communicate with one another. 
     When is is desired to test the continuity of conductors in a severed cable, MAN 2, employing cable 22 and case 12, is located at the point of severance of the cable while MAN 1 and MAN 3 are located at the opposite ends of the cable to be tested. MAN 2 first positions switch 40 to its 1-2 position so as to activate probes 60 associated with cables 20 and 22. After MAN 1 connects his test probe to the end of a conductor at his end of the damaged cable, MAN 2 sequentially touches or makes electrical contact with, depending upon the test probe used, the end of each of the conductors leading to MAN 1. When contact is made with the end of the conductor to which MAN 1&#39;s probe is connected, continuity is established and sufficient voltage is routed to the base of transistor 114 so as to bias it &#34;on&#34;. The voltage developed across resistor 108 is compared by detector 109 with the threshold determined by sensitivity adjustment potentiometer 116. When this threshold is broken, detector 109 triggers LED 42, buzzer 115 and multivibrator 90. Multivibrator 90, in turn, applies a tone signal to the input of amplifier 92 via switch 44, which signal is heard by each of the three technicians via their headsets. 
     As one conductor on one side of the cable has been identified, MAN 2 then positions switch 40 to the 2-3 position so as to deactivate cable 20 and activate cable 24. The above described procedure is repeated until the mate of the identified conductor has been located. After repair of the conductor, MAN 2 positions switch 40 to 1-3 and MAN 1 and MAN 3 connect their test probes to their respective ends of the conductor just identified. A tone signal should be detected over the headsets if the conductor was properly identified and repaired. The procedure is repeated for each of the remaining conductors of the damaged cable. 
     It will be understood that various changes and modifications may be made to the aforedescribed invention without departing from the spirit of the appended claims.