Abstract:
An apparatus is disclosed for testing the integrity of inductive coils such as yokes, flyback transformers, and the like. The apparatus includes a compact housing which makes it portable and convenient for field use. The apparatus includes circuitry disposed in the housing for inducing current through the inductive coil being tested. An array of LED&#39;s is provided to give the operator a visual display which is indicative of the condition of the inductive coil. The apparatus also includes means for connecting a meter or oscilloscope to the circuit in order to examine the electrical signature from the inductive coil being tested.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part application of Ser. No. 08/463,342 filed Jun. 5, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for testing the electrical integrity of an inductive coil, solenoid, or core and coil assembly. The invention specifically relates to such apparatuses which are compact and capable of providing visual displays corresponding to the test results. 
     2. Description of the Prior Art 
     It is well known that devices employing electrical coils are subject to numerous defects and failure during operation. Electrical coils are used to develop magnetic fields which can be used to perform functions such as counting the number of revolutions of a rotating member and actuating hydraulic cylinders. Additionally, electrical coils are often used to perform various functions in solid state devices such as television sets and display monitors. 
     In many of these applications, a failure of the coil or solenoid is often undetected, thereby leading to serious consequences. For example, if a magnetic sensor coil becomes short circuited or electrically open, it will not respond to the passage of the metal segment to induce a voltage pulse accordingly. The absence of this voltage pulse is often likely to go undetected. In a hydraulic cylinder, the solenoid may be short-circuited. This will result in the failure to actuate or deactuate a cylinder, thus leading to mechanical damage in the machine or to the product which it is producing. In such applications, the output voltage from the electrical system may vary from the nominal 12 volts depending on the electrical load on the system. The variable voltage being supplied to the solenoid makes it extremely difficult to design a test circuit for on-line testing of the solenoid&#39;s electrical integrity. Additional complications arise due to the fact that an on-line test must be such that it does not actuate the solenoid. 
     Defects may also occur during the manufacture of coils, the most common of which is that of a shorted turn or turns. Such a defect is relatively difficult to identify in a manner compatible with high volume production. One reason for this is that many apparatus lack the sensitivity to quickly isolate a single shorted turn within a coil containing several hundred turns. Another defect which may occur is that of corona discharge between high and low potential components. 
     With the advent of solid state television sets and cathode ray tube (crt) monitors, a need has arisen for a small, portable field instrument for testing inductive coils, including yokes and flyback transformers. In order to isolate or detect the cause of a problem in the sweep circuits of a television, it was common to substitute the inductive coil of a test instrument for the yoke of the television set or crt monitor, and subsequently measuring the amount of power delivered to the substitute inductive coil. If the problem were fixed, then it would be apparent that the yoke was defective. However, modern solid state televisions and crt monitors employ complex circuitry which make it difficult to provide a universal substitute inductive coil which will not overload the sweep circuits. 
     One method which has been reliably used to test yoke coils and transformer windings is a ringing test. Using this testing method, a narrow voltage pulse is applied to the inductive coil to cause it to ring, or resonate, thereby producing a dampened sine wave. Any defects in the inductive coil may be determined by analyzing the dampened sine wave on an oscilloscope. This test however is highly sophisticated and requires a skilled operator to properly adjust the oscilloscope. Furthermore, it is impractical for field operators to transport an oscilloscope to each test site. 
     The prior art makes many attempts at providing various apparatus and circuitry for testing inductive coils, solenoids, and the like. For example, U.S. Pat. No. 3,659,197 issued on Apr. 25, 1972 to Alley et al. discloses an apparatus for electrically testing an electrical coil. The apparatus includes a primary inductive coil and core assembly adapted to be magnetically coupled to the coil being tested. A pick-up coil is magnetically coupled to the core and coil assembly. A limited source of high voltage direct current is provided along with switching means in order to repetitively apply the current to the primary coil of the core and coil assembly. Detection means are electrically connected to the pick-up coil so that any defects in the coil being tested will be reflected back to the detection means via the pick-up coil. 
     U.S. Pat. No. 3,990,002 issued on Nov. 2, 1976 to Baum discloses a method and apparatus for testing television yokes and flyback windings. The apparatus includes a number of capacitors which are successively connected across a coil while a train of driving pulses is applied. The pulses cause the coil to ring after each driving pulse. The number of cycles which occur in the ringing signal between the two voltage levels thereof are counted to indicate whether or not the coil is defective. 
     U.S. Pat. No. 4,547,723 issued on Oct. 15, 1985 to McLellan discloses a device for detecting shorted turns in the windings of electromagnetic coils or transformers. The device utilizes the inductive kick voltage that is developed when the current through a coil is quickly interrupted. Rectified alternating current provides power while a high speed switch controls the current flow through the coil being tested. The device is also capable of measuring the voltage developed by the inductive kick. 
     U.S. Pat. No. 4,746,869 issued on May 24, 1988 to Schrag et al. discloses a circuit for detecting shorted turns in inductive coils and solenoids. The circuit includes a computer activated device for selectively imposing a direct current voltage on a coil. A detector is used to detect current flow through the coil induced by the voltage and for producing a current flow signal indicative of the magnitude of the current flow. A comparator compares the instantaneous signal with the reference signal and a computer determines whether the respective first and second comparison signals are produced during a first or second point in time, thus indicating the integrity of the coil. 
     U.S. Pat. No. 5,296,818 issued on Mar. 22, 1994 to Vrablec discloses an electrical tester for the control yoke of an oil-filled, electrically powered switch. The tester includes connectors which are adapted to be interfitted into electrical contact with the yoke. Indicators which are electrically connected to the connectors are used to indicate the flow of electrical current through the yoke. The apparatus may also be used to isolate the source of a fault in the transfer of control signals between the yoke and the electrical switch of the power distribution system. 
     None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of the invention to provide an apparatus capable of easily determining the integrity of the windings in an inductive coil. 
     It is another object of the invention to provide an apparatus which includes output means for operatively coupling a meter or an oscilloscope. 
     It is a further object of the invention to provide an apparatus capable of visually alerting an operator of the integrity of the windings of an inductive coil under test. 
     Still another object of the invention is to provide an apparatus which allows an operator to vary the impedance through the inductive coil being tested. 
     It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes. 
     In accordance with the objects of the invention, an apparatus is provided for testing the integrity of the windings in an inductive coil. The apparatus includes a housing which has a front panel. The housing contains circuitry which is used to test the integrity of the inductive coil. A power supply is also disposed within the housing. The power supply is used to impose direct current on the circuitry, thereby inducing a current flow through the circuitry. 
     In accordance with another object of the invention, the apparatus includes a housing which has a front panel. Circuitry is disposed within the housing in order to test the windings of the inductive coil, while a power supply is disposed within the housing in order to impose direct current on the circuitry. The circuitry also includes means for generating a waveform and creating a control signal for switching current through the inductive coil. The apparatus also includes output means which is disposed on the front panel of the housing and electrically coupled to the circuitry. The output means includes a connection for operatively coupling an oscilloscope or a meter to the apparatus in order to examine the operation of the circuit. 
     In accordance with another object of the invention, the apparatus is provided with visual display means disposed on the front panel of the housing. The visual display means is operatively coupled to the circuitry. The visual display means informs the operator of the integrity of the windings of the inductive coil under test. The visual display means includes a number of light emitting diodes which are illuminated responsive to a reference signal which is indicative of the integrity of the windings of the inductive coil. 
     In accordance with another object of the invention, the apparatus is provided with means for allowing the operator to vary the impedance through the inductive coil being tested. An impedance switch is disposed on the front panel of the housing and electrically coupled to the circuitry. The impedance switch allows better results on the visual display by matching the impedance for vertical or horizontal yoke windings. 
     These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B together make up a schematic of the circuitry of the apparatus of the present invention. 
     FIG. 2 is a front elevational view of the housing of the apparatus of the present invention. 
     FIG.  3 . is a flyback transformer being tested by the apparatus of the present invention. 
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings and initially to FIGS. 1A and 1B, a circuit  10  is shown for testing the integrity of the windings of inductive coils. The circuit  10  includes a power supply  12 , a waveform generator  42 , a voltage multiplier  78 , an amplifier  94 , a test portion  110 , a comparator portion  140 , and a display  178 . The circuit is capable of testing the windings of any inductive coil, including yokes, flyback transformers, stator windings, etc.. The circuit  10  is disposed in a housing  252 , which may be seen more particularly with reference to FIG.  2 . 
     The power supply  12  consists of a direct current power source. In the preferred embodiment of the invention, the direct current power source is in the form of a first and second battery  14 ,  16  which are serially disposed. The first battery  14  is grounded at the negative end while its positive end is coupled to the negative end of the second battery  16  via line  15 . The positive end of the second battery  16  is coupled to a single pole, single throw (S.P.S.T.) switch  20  via line  18 . The first and second batteries  14 ,  16  each provide  9  volts of direct current. By coupling the first and second batteries  14 ,  16  in series, 18 volts of direct current is passed through line  18 . 
     The S.P.S.T. switch  20  occupies only an open or closed position, thereby selectively providing direct current to the circuit  10 . When the S.P.S.T. switch  20  is closed, it couples line  18  to line  22 . Resistor  24  has one of its ends coupled to line  22  while the other end is coupled to line  26 . Line  26  is also coupled to the positive plate of capacitor  28 . Capacitor  28  has its negative plate coupled to the system ground. Capacitor  28  and resistor  24  function as an L-filter to control the current flowing from the first and second batteries  14 ,  16 . 
     Line  26  directs the voltage from the first and second batteries  14 ,  16  to pin  3  of a voltage regulator  30 . Pin  2  of the voltage regulator  30  is coupled to the system ground via line  32 . The voltage regulator  30  produces a constant 12 volt direct current through pin  1 . Line  34  is coupled to pin  1  in order to direct the voltage from the voltage regulator  30  to the circuit  10 . Line  34  is also coupled to the positive plate of capacitor  36  and to one end of resistor  38 . The negative plate of capacitor  36  is coupled to the system ground. Capacitor  36  functions to filter the signal from the voltage regulator  30 . The opposite end of resistor  38  is coupled to the anode of diode  40 . The cathode of diode  40  is coupled to the system ground. Diode  40  is a light emitting diode which, when illuminated, provides the user with visual confirmation that power is being provided to circuit  10 . 
     The waveform generator  42  of the circuit  10  receives power from the power supply  12  via line  46 . Line  46  is also coupled to one end of resistor  48 . The opposite end of resistor  48  is coupled via line  50  to pin  8  of an integrated circuit (i.c.) chip  44  and to one end of resistor  54 . In a preferred embodiment of the invention, a  555  timer circuit chip is selected to be used as i.c. chip  44 . The opposite end of resistor  54  is coupled via line  56  to pin  7  of the i.c. chip  44  and to one end of resistor  58 . The opposite end of resistor  58  is coupled via line  60  to pin  6  of the i.c. chip  44  and to the positive plate of capacitor  62 . The negative plate of capacitor  62  is coupled to ground as illustrated. Line  50  is coupled to pin  4  of the i.c. chip  44  and the positive plate of capacitor  70  via line  68 . The negative plate of capacitor  70  is coupled to the system ground. Line  60  is also coupled to pin  2  of the i.c. chip  44  via line  72 . Pin  1  of the i.c. chip  44  is coupled to the system ground by line  73 . Pin  3  of the i.c. chip  44  directs the output of the i.c. chip  44  to one end of resistor  76  via line  74 . The opposite end of resistor  76  is coupled to the voltage multiplier  78  via line  77 . The output from the i.c. chip  44  is a square wave having a frequency of approximately 15,750 Hz. 
     The voltage multiplier  78  of the circuit  10  includes a transformer  86  and a transistor  82 . Line  77  couples one end of resistor  76  to the base of transistor  82 . The emitter of transistor  82  is coupled to the system ground. The collector of transistor  82  is coupled via line  84  to the transformer  86  and the  10  amplifier  94 . The transformer  86  receives 12 volts direct current from the power supply  12  via line  80 . Line  80  is coupled to one end of the primary winding  88  and one end of the secondary winding  90  in the transformer  86 . The opposite ends of the primary and secondary windings  88 ,  90  of the transformer  86  are coupled to the collector of transistor  82  via line  84 . 
     Line  84  is coupled to the positive plate of capacitor  92 . The negative plate of capacitor  92  is coupled to the base of transistor  96  via line  20   93 . The emitter of transistor  96  is coupled to the anode of diode  100 . The cathode of diode  100  is coupled to the collector of transistor  96  via line  102 . 
     Referring to FIG. 18, line  102  couples the amplifier  94  to a capacitor  104 . The positive plate of capacitor  104  is coupled to line  102  while the negative plate is coupled to the system ground. Line  102  also couples the amplifier  94  to the test portion  110  and the comparator portion  140  via lines  106  and  108 , respectively. 
     As seen in FIG. 1B, the test portion  110  includes a double pole, triple throw (D.P.D.T.) switch  120  and a plurality of plug receptors  260 ,  262 ,  264 . Plug receptor  260  is coupled to the system ground as illustrated. Line  106  is coupled to plug receptor  262  as is line  116 . A 12 volt direct current is provided to the test portion  110  via line  112 . Line  112  is coupled to pin  2  of D.P.T.T. switch  120 , plug receptor  264 , and the positive plate of capacitor  118 . The negative plate of capacitor  118  is coupled to line  116 . Line  116  is further coupled to pin  5  of D.P.T.T. switch  120 . Pin  1  of D.P.T.T. switch  120  is coupled to the positive plate of capacitor  124  via line  122 . The negative plate of capacitor  124  is coupled to pin  6  of D.P.T.T. switch  120  via line  126 . Similarly, pin  3  of D.P.T.T. switch  120  is coupled to the positive plate of capacitor  132  via line  134 . The negative plate of capacitor  132  is coupled to pin  4  of D.P.T.T. switch  120  via line  130 . 
     The inductive coil  114  to be tested is coupled to the circuit  10  at two of the plug receptors. One end of inductive coil  114  is coupled to plug receptor  262  via line  274  while the opposite end of inductive coil  114  is coupled to plug receptor  264  via line  276 . D.P.T.T. switch  120  is used for impedance matching and allows the operator to test inductive coils for shorted windings above 760 μH. 
     The comparator portion  140  includes an operational amplifier  158 , a plurality of filters, and a zener diode  156 . The comparator portion  140  is coupled, in part, to the test portion  110  via line  108 . Line  108  is coupled to the positive plate of capacitor  142 . The negative plate of capacitor  142  is coupled to one end of resistor  146  via line  144 . The opposite end of resistor  146  is coupled to one end of variable resistor  150  via line  148 . The opposite end of variable resistor  150  coupled to ground and is also adjustably coupled to line  152  as illustrated in FIG.  1 B. 
     Line  152  couples variable resistor  150  to a capacitor  154 , the zener diode  156 , and the operational amplifier  158 . Capacitor  154  has its positive plate coupled to line  152  while its negative plate is coupled to the system ground. Line  152  is coupled to the cathode of zener diode  156  and the anode of zener diode  156  is coupled to the system ground. Zener diode  156  allows an  18  volt direct current to pass to the operational amplifier  158 . Line  152  is further coupled to the normal input of the operational amplifier  158 . The operational amplifier  158  receives a 12 volt direct current from the power supply  12  via line  160 . The output of the operational amplifier  158  is coupled to the anode of diode  170  and one end of resistor  164  via line  162 . The opposite end of resistor  164  is coupled to one end of resistor  168  and fed back to the operational amplifier  158  via line  166 . The opposite end of resistor  168  is coupled to the system ground. The cathode of diode  170  couples the comparator portion  140  to the display  178  via line  172 . The operational amplifier  158  provides a signal which is indicative of the state of the inductive coil being tested. 
     When the amplifier  94  is activated, it induces current into the inductive coil  114  which is being tested. The resulting current is passed to the non-inverting input of the comparator stage  140  and into the amplifier  94 . The portion of the current received by the amplifier  94  is passed directly to ground. Capacitor  142  blocks current from passing from the comparator stage  140  to the amplifier  94 . A negative feedback loop is created between the output and inverting input of operational amplifier  158 , so that operational amplifier  158  continuously compares the current signal being received to the previous signal, at the frequency established by the waveform generator. 
     The display  178  includes an LED driver  179  and a plurality of LED&#39;s. The LED driver  179  is coupled at pin  8  to a resistor  176 , a capacitor  174 , and the cathode of diode  170  via line  172 . The LED driver  179  receives the analog output signal from the operational amplifier  158  and converts it to a digital signal capable of driving the LED display  179 . Capacitor  174  has its positive plate coupled at line  172  while its negative plate is coupled to the system ground. Resistor  176  has one of its ends coupled to line  172  and the other end coupled to the system ground. A 12 volt direct current is provided to the display system  178  via line  180 , which is coupled to a resistor  182  and a plurality of LED&#39;s. Resistor  182  has one of its ends coupled to line  180  and the other end is coupled to the positive plate of capacitor  186  and pin  9  of the LED driver  179  via line  184 . The negative plate of capacitor  186  is coupled to the system ground. 
     LED  238  has its anode coupled to line  180  and its cathode coupled to one end of resistor  242  via line  240 . The opposite end of resistor  242  is coupled to pin  1  of the LED driver  179  via line  244 . LED  230  has its anode coupled to line  180  and its cathode coupled to one end of resistor  234  via line  232 . The opposite end of resistor  234  is coupled to pin  2  of the LED driver  179  via line  236 . LED  222  has its anode coupled to line  180  and its cathode coupled to one end of resistor  226  via line  224 . The opposite end of resistor  226  is coupled to pin  3  of the LED driver  179  via line  228 . LED  214  has its anode coupled to line  180  and its cathode coupled to one end of resistor  218  via line  216 . The opposite end of resistor  218  is coupled to pin  4  of the LED driver  179  via line  220 . LED  188  has its anode coupled to line  180  and its cathode coupled to one end of resistor  210  via line  200 . The opposite end of resistor  210  is coupled to pin  6  of the LED driver  179  via line  212 . Pin  5  of LED driver  179  is coupled to the system ground via line  246 , as shown. Pin  7  of LED driver  179  is coupled to one end of resistor  250  via line  248 . The opposite end of resistor  250  is coupled to the system ground. 
     During the testing phase, the circuit  10  creates a waveform which is very similar to that present in a television set or crt monitor. The waveform created by the circuit, however, has approximately {fraction (1/10)}th of the peak to peak voltage present in a television set or crt monitor. If the inductive coil under test contains no shorted windings, then a continuous waveform will be produced. However, if the inductive coil contains a shorted turn, then the waveform produced will have the same amplitude but will contain oscillations. These oscillations may be detected by the operational amplifier  158  by comparing the current signal being received with the signal in the feedback loop. The output signal of the operational amplifier  158  is indicative of the condition of the inductive coil being tested. When the LED driver  179  receives this signal, it interprets the signal and converts it to digital form in order to drive the LED&#39;s and visually inform the operator of the integrity of the inductive coil. 
     FIG. 2 illustrates the housing  252  within which the circuit  10  may be disposed. The housing  252  includes a power button  254  which is in communication with S.P.S.T. switch  20 . When power button  254  is activated, it closes S.P.S.T. switch  20  and allows current from batteries  14  and  16  to flow through the circuit. Actuation of power button  254  also induces current through LED  40 . LED  40  responsively illuminates to indicate to the operator that current is flowing through the circuit  10 . The housing also includes a visual indicator  258  which is in communication with the LED&#39;s of the display  178 . The visual indicator  258  may include filters of multiple colors so that when the LED&#39;s of display  178  are activated in response to the condition of the coil, predetermined patterns of light will be provided to the operator. Equivalently, the LED&#39;s of display  178  may be selected in varying colors and arranged in such a manner as to visually represent the integrity of the inductive coil under test, thus eliminating the need for filters. Knob  266  corresponds to the mechanical portion of D.P.T.T. switch  120 . Knob  266  is illustrated as being rotatably capable of occupying three distinct positions. Each position operable by D.P.T.T. switch  120  corresponds to a predetermined impedance which may be placed across the inductive coil being tested. 
     While it may not be readily apparent, it should be appreciated that the housing  252  is relatively small thereby making the apparatus portable and extremely convenient for use by field operators. The apparatus is also convenient for use in a lab settings where an oscilloscope may be readily attached to it in order to examine the signature of the coil being tested. 
     Referring additionally to FIG. 3, a flyback transformer  268  is illustrated. The flyback transformer includes a plurality of accesses  270  to its primary windings. In order to test the integrity of the windings of flyback transformer  268 , lines  274  and  276  are attached to two of the accesses  270  and placed in communication with the circuit  10  of the present invention. The connection is accomplished via the housing  252  wherein plug receptor  264  receives line  276  while plug receptor  262  receives line  274 . When the power button  254  is actuated, current is induced through the windings of the flyback transformer  268 . The operator may additionally connect a meter or oscilloscope to plug receptors  260  and  262  in order to examine the electrical signature from the inductive coil being tested. 
     While the ratings of the various components may vary based on specific application, a preferred embodiment of the invention may incorporate the values suggested in table 1 for testing a variety of windings. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Reference No. 
                 Value or Part No. 
               
               
                   
                   
               
             
             
               
                   
                 Resistor 24 
                 2.2 Ohms ½W 
               
               
                   
                 Resistor 38 
                 1K Ohms ¼W 
               
               
                   
                 Resistor 58 
                 18K Ohms ¼W 
               
               
                   
                 Resistor 54 
                 3.9K Ohms ¼W 
               
               
                   
                 Resistor 48 
                 330 Ohms ¼W 
               
               
                   
                 Resistor 76 
                 470 Ohms ¼W 
               
               
                   
                 Resistor 146 
                 100K Ohms ¼W 
               
               
                   
                 Resistor 150 
                 50K POT 
               
               
                   
                 Resistors 218, 226, 234, 242 
                 1K Ohms ¼W 
               
               
                   
                 Resistor 168 
                 100 Qhms ¼W 
               
               
                   
                 Resistor 164 
                 4.7K Ohms ¼W 
               
               
                   
                 Resistor 182 
                 470 Ohms ¼W 
               
               
                   
                 Resistor 250 
                 33K Ohms ¼W 
               
               
                   
                 Resistor 176 
                 100 Ohms ¼W 
               
               
                   
                 Voltage Regulator 30 
                 7812 
               
               
                   
                 Timer 44 
                 NE555N 
               
               
                   
                 Qperational Amplifier 158 
                 LM324N 
               
               
                   
                 LED Driver 179 
                 AN6884 
               
               
                   
                 Capacitor 28 
                 1000 μFd 35V 
               
               
                   
                 Capacitor 36 
                 1000 μFd 25V 
               
               
                   
                 Capacitor 64 
                 .01 μFd 50V 
               
               
                   
                 Capacitor 62 
                 .0022 μFd 50V 
               
               
                   
                 Capacitor 70 
                 47 μFd 25V 
               
               
                   
                 Capacitor 92 
                 1000 μFd 25V 
               
               
                   
                 Capacitor 142 
                 .001 μFd 200V 
               
               
                   
                 Capacitor 154 
                 .068 μFd 25V 
               
               
                   
                 Capacitor 174 
                 1 μFd 25V 
               
               
                   
                 Capacitor 132 
                 8200 Pica Fd 200V 
               
               
                   
                 Capacitor 124 
                 18000 Pica Fd 200V 
               
               
                   
                 Capacitor 118 
                 .001 μFd 200V 
               
               
                   
                 Capacitor 104 
                 .001 μFd 200V 
               
               
                   
                 Capacitor 186 
                 100 μFd 25V 
               
               
                   
                 Transistor 82 
                 MPS-A05 
               
               
                   
                 Transistor 96 
                 ECG-171 
               
               
                   
                 Diode 40 
                 ECG-3007 
               
               
                   
                 Diode 100 
                 ECG-558 
               
               
                   
                 Diode 156 
                 ECG-5012A, 18V 
               
               
                   
                 Diode 188 
                 ECG-3007 
               
               
                   
                 Diode 214, 222,  230, 238 
                 ECG-3010 
               
               
                   
                 Diode 170 
                 1N4149 
               
               
                   
                 Primary 88 
                 750 mH 
               
               
                   
                 Secondary 90 
                 750 mH 
               
               
                   
                 Switch 20 
                 Momentary S.P.S.T 
               
               
                   
                 Switch 120 
                 Three position (D.D.D.T) 
               
               
                   
                   
               
             
          
         
       
     
     It is to be understood that the present invention is not limited to the sole embodiment described above, but encompasses any and all embodiments within the scope of the following claims.