Patent Publication Number: US-6222358-B1

Title: Automatic circuit locator

Description:
RELATED APPLICATIONS 
     This Application claims the benefit of U.S. Provisional Application No. 60/053,757, filed on Aug. 25, 1997. 
    
    
     DESCRIPTION 
     Technical Field 
     The present invention relates generally to AC power line testing equipment and, more particularly, to an AC power circuit identifying device. Specifically, the present invention is used to identify the circuit interrupter device associated with a particular power outlet receptacle, thereby performing a calibration process automatically. 
     BACKGROUND OF THE INVENTION 
     When work is performed on an electrical system in a building or facility, it is necessary to trace and identify which circuit interrupter device (e.g., circuit breaker or fuse) is supplying power to a particular power outlet receptacle or electrical component. Manual identification of the fuse or circuit breaker can be accomplished by removing each fuse or opening each circuit breaker, thereby disrupting the power flow through the circuit. Each outlet must subsequently be examined to determine whether the power to the outlet has been disconnected. This method is not only time consuming, but also may not be feasible in situations where it would be hazardous to interrupt the power flow to certain outlets, e.g., in a hospital or in an environment where computers are in use with no backup power. 
     Alternatively, a variety of circuit testers are available for identifying the fuse or circuit breaker that is supplying power to a particular outlet receptacle. These testers employ an assortment of techniques to distinguish one circuit breaker from the rest. For example, the testers disclosed in U.S. Pat. Nos. 4,906,93 8 and 5,497,094 use a relaxation oscillator to apply an identification signal comprising a large amplitude current pulse of very short duration to the circuit. A schematic diagram of the transmitter  10  disclosed in U.S. Pat. No. 4,906,938 is shown in FIG.  1 . The terminals  12 ,  14  of transmitter  10  are connected to the outlet or light fixture to be tested. Diode  16  acts as a half-wave rectifier. Specifically, if the voltage across diode  16  is positive, diode  16  acts as a short circuit, and if the voltage across diode  16  is negative, diode  16  acts as an open circuit. Sidac  18  is a short circuit when the voltage thereacross reaches its threshold value of 120-135 volts, and is an open circuit when the current through sidac  18  drops below the minimum holding current of the device. Thus, in this arrangement, sidac  18  acts as a trigger switch. 
     If a conventional power line voltage is applied to transmitter  10 , sidac  18  will initially go into conduction when the line voltage reaches approximately 120 volts. This causes capacitor  20  to immediately charge to the line voltage, resulting in a large amplitude current pulse which is used to identify the circuit. Sidac  18  will continue conducting until the current approaches 0 amps, i.e., approximately 50-150 milliamps, which occurs near the peak of the power line voltage. When sidac  18  is switched off, capacitor  20  will be charged at a voltage level close to the peak voltage, i.e., approximately 150 volts, and can only discharge through resistor  22 . Due to the relatively large resistance of resistor  22 , the discharge of capacitor  20  will be slow. 
     Because capacitor  20  remains charged at approximately 150 volts, as the line voltage decreases from 150 volts to 0 volts and continues through its negative cycle, the voltage across diode  16  is negative. Thus, diode  16  remains an open circuit and capacitor  20  continues to discharge slowly through resistor  22 . 
     During the next cycle, diode  16  becomes a short circuit when the line voltage surpasses the charge on the capacitor  20 . Sidac  18  will remain an open circuit, however, because the voltage across sidac  18 , which is the difference between the line voltage and the voltage across capacitor  20 , will not reach its threshold value. Thus, transmitter  10  will not conduct any current until the voltage across capacitor  20  has time to discharge through resistor  22 , which does not occur for a number of cycles. This results in a frequency of current spikes less than the power line frequency of 60 hertz. 
     The identification signal develops a strong magnetic field that will likely be sensed in the vicinity of a number of circuit interrupter devices, including the one that is actually connected to the transmitter. In order to isolate the specific circuit interrupter device, the end user must manually adjust the gain or amplifier of the receiver, and re-scan the circuit interrupter devices with the receiver. This procedure is repeated until only one circuit breaker triggers a response by the receiver. The circuit interrupter device connected to the transmitter may also be identified by monitoring a signal strength meter or bar-graph display. These devices require the user to select the circuit interrupter device with the strongest magnetic field. Receivers which require manual adjustment of the gain or amplifier of the receiver, and signal strength meters having analog or digital readouts can be quite difficult to use, especially if the end user has no prior experience with such instruments. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an electronic system for identifying the associated dedicated circuit interrupting device. Particularly, a transmitting device is plugged into the power outlet receptacle in question, and an identification signal is transmitted over the circuit wiring from the electrical panel. 
     Unlike most existing circuit identifiers currently on the market, the automatic circuit locator of the present invention does not require input from the end user to identify the correct circuit interrupting device. The automatic circuit locator performs the calibration process, thereby eliminating the need for the end user to do so. 
     According to a first aspect of the present invention, an identification signal is transmitted from an outlet to produce a magnetic field around a plurality of power lines. A receiver senses the strength of the magnetic fields around the power lines, and stores the largest value. The user is alerted when the receiver senses the stored value. 
     Other features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a conventional transmitting device; 
     FIG. 2 is a block diagram of a first embodiment of a receiving device in accordance with the present invention; 
     FIG. 3 is a schematic diagram of the receiving device of FIG. 2; 
     FIG. 4 is a schematic diagram of a second embodiment of a receiving device in accordance with the present invention; and 
     FIG. 5 illustrates an example of an AC wiring system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiments in many different forms, there will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as exemplifications of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiments illustrated. 
     FIG. 2 is a block diagram of a receiving device  24  in accordance with the present invention. The first section of the receiving device  24  is a parallel tuned tank  26 . The parallel tank  26  is broadly tuned to the resonance frequency of the magnetic field created by the identification signal on the power line. The identification signal is formed on the power line by the transmitter or signal feeder  10 . The signal measured by the parallel tank  26  is relatively small, in the millivolt range. After a signal is measured, it is amplified by a transistor preamplifier  28 , which is a high gain preamplifier. 
     Although the parallel tank is tuned to the frequency of the identification signal, it will pick up other signals if they appear as a sharply rising short duration pulse, e.g. noise, that may be present on the line. These other signals will be amplified by the preamplifier  28 . To avoid further processing, the amplified signal from the preamplifier  28  is passed through a narrow band-pass filter  30 . The frequency band of the narrow band-pass filter  30  corresponds to the frequency of the magnetic field on the power line. Thus, any extraneous noise at frequencies outside the range of the filter  30  will be removed. 
     The filtered signal is AC coupled to a booster amplifier  32 . This amplifier  32  is configured as a high impedance, closed-loop AC follower. To achieve the high input impedance, a bootstrap technique is incorporated. 
     The resulting signal is an outcome of the strength of the magnetic field. Because the strength of the magnetic field will fluctuate, the signal from the booster amplifier  32  is applied to a peak detector  34  to provide a consistent measurement for the strength of the magnetic field. 
     Comparator  40  compares a signal from the buffer  38  with the reference signal stored by the receiving device  24 . If the incoming signal is greater or equal to the stored reference value, display  42  generates an alerting signal. If the incoming signal exceeds the reference value, the incoming signal replaces the reference value. A reset  44  shown in the receiving device  24  of FIG. 2 resets the initial reference voltage to begin a new scan. 
     FIG. 3 is a schematic diagram of the receiving device  24  of FIG.  2 . As shown in FIG. 3, the parallel tuned tank  26  comprises a pick-up coil  46  and a capacitor  48 . The signal is AC coupled from the parallel tuned tank  26  through capacitor  50 , to the transistor preamplifier  28 . The transistor preamplifier  28  is built around a general purpose NPN transistor  52 , which is configured in association with its supporting component resistors  54 ,  56 ,  58  and capacitor  60  as a common emitter preamplifier with AC and DC feedback for biasing the transistor  52 . Emitter resistor  58  and its capacitor  60  stabilize the preamplifier  28 . 
     The narrow band-pass filter  30  comprises operational amplifier  62 , resistors  64 ,  66  and capacitors  68 ,  70 . The filtered signal is AC coupled by capacitor  72  to the booster amplifier  32 . The booster amplifier  32  comprises operational amplifier  74 , resistors  76 , 78  and capacitor  80 . The peak voltage detector  34  comprises operational amplifier  82 , diode  84 , capacitor  86  and resistor  88 . This stage is in many respects similar to a “sample and hold” circuit  36 . Diode  84  conducts whenever the input voltage is greater than the output voltage, thus making the output voltage equal to the peak value of the input voltage. The sample and hold  36  holds the output voltage by charging the holding capacitor  86  to the level of the output voltage. Resistor  88  shunts capacitor  86  to signal-ground, and is thus, the only discharge path for capacitor  86 . The newly produced DC signal, which represents the amplitude of the magnetic field is further stored in a large storage capacitor  90 . Since a low impedance current source is needed to charge the storage capacitor  90 , an additional transistor  92  is added to the output. When the output of the peak voltage detector  34  rises, current is passed to the base of transistor  92 , thereby forcing the collector-emitter path of the transistor  92  into conduction and charging capacitor  90  rapidly. Resistor  94  helps transistor  92  to bias on. Transistor  92 , resistor  94 , resistor  96 , capacitor  90  and operational amplifier  98  comprise the buffer  38  of the circuit. Operational amplifier  98  is configured as a high impedance follower to avoid loading the storage capacitor  90  and giving low drift along with a low output resistance. 
     Since storage capacitor  90  is relatively large, resistor  96  is an isolation resistor between the capacitor  90  and the input of the follower  98 . This will insure that the operational amplifier  98  will not be damaged by shorting the output or abruptly shutting down the supplies when the capacitor  90  is charging. 
     Comparator  40  is a two stage comparator comprising operational amplifiers  100 ,  102 . Resistors  104 ,  106  serve as current limiters, while resistor  108  is part of a feedback loop. The output signal obtained from the buffer  38  serves as a reference signal and is fed into the inverting input of the first comparator stage  100 , while the output of the peak voltage detector  34  is fed through the non-inverting input of the first comparator stage  100  and is thus the instantaneous DC equivalent for the measured strength of the magnetic field. As soon as this signal equals or exceeds the reference voltage, the output of the first comparator stage  100  goes high, thereby forcing the second comparator stage  102 , which serves as a buffer, to go high as well. 
     The display subcircuit  42  is built around a timer  110 , such as a  555  timer, which is arranged as a free running or astable multi-vibrator whose frequency is determined by resistors  112 ,  114  and capacitor  116 . If the output of the second comparator  102  goes high, it pulls the reset pin of the timer  110  to the positive supply voltage, supported by resistor  118 , which acts as a pull-up resistor. Capacitor  120  connected to the modulation pin of the timer  110  provides this subcircuit  42  with somewhat more stability. If the reset pin is pulled-up to the positive supply voltage, the oscillator operates with its pre-determined frequency. This causes piezo  122  to sound and LED  124  to fire an intermitting pattern equal to the multi-vibrator frequency. Since LED  124  serves as a power-on indicator as well, it will dim as soon as voltage is supplied to the circuit. Resistor  126  allows only a very small amount of current to flow to LED  124 . Thus, LED  124  does not shine very brightly. Diode  128  prevents current from feeding back to the output of timer  110 . 
     If both the “NEUTRAL” and the “GROUND” terminals of the transmitter are not connected, but the “HOT” terminal is connected, no current will flow through the transmitter. Thus, one may incorrectly assume that the outlet is not energized, and therefore, believe it is safe to work on the outlet. The addition of an AC voltage sensor  130  in the receiving device  24 , as shown in FIG. 4, will allow a user to detect this situation. 
     The circuit is built around a CMOS hex invertor. The resonance tank of the receiver is connected through capacitor  132  to the first input stage  134  of the AC voltage sensor  130 . While capacitor  32  ensures that the relatively strong 60 Hz magnetic field of the AC power itself is rejected from further travel, capacitor  132  only passes the 60 Hz signal. Operational amplifier  136 , resistors  138 ,  140  and capacitor  142  comprise an oscillator circuit which is triggered when a sufficient voltage level is applied to the input of this stage. 
     The oscillating output signal is fed to the second stage  144  of the AC voltage sensor  130  and resistor  146  integrates the oscillating signal so that it appears as a logical “LOW” level. The third stage  148  of the AC voltage sensor  130  inverts this signal, resulting in a logical “HIGH” level of the output when a 60 Hz field is sensed. The output of the AC voltage sensor  130  is connected to the reset pin of the timer  110  through diode  150 , which isolates the branch circuit from the rest of the arrangement. If the signal goes “HIGH,” the timer circuit  110  will be activated and thus, the LED will be illuminated and the buzzer will sound. The switch  152  has been changed to a DPDT part with three positions. The center position switches the unit off and resets the storing capacitor  90  in the same manner as before, while the first position switches the circuit identifier on, and the third, momentary contact position activates the voltage sensor. 
     The identification signal typically travels from the specific circuit breaker to a connecting bus-bar and onto other circuit breakers within the load center. The strength of the magnetic fields, however, diminishes due to additional transition resistance rising on the mechanical connections between the breakers and the busbar. Thus, the specific circuit breaker that provides power to the branch circuit to which a transmitter or signal feeder  10  is connected has the strongest magnetic field. 
     The basic operation of the automatic circuit locator of the present invention requires the transmitter to be plugged into a receptacle outlet. An LED on the transmitter will indicate whether the transmitter is reading voltage from the outlet. To identify the circuit breaker or fuse supplying the power to the receptacle, two scans of all circuit breakers will be necessary. During the initial scan, the receiver will measure the strengths of the magnetic fields associated with each of the interrupter devices, and store the value of the largest strength measured. During the second scan, the receiver will alert the user when it measures the value stored. 
     The initial reference voltage stored in the receiver is approximately 100 mV (0.1 V). Every value measured from the interrupter devices is compared to the reference signal. If the incoming signal is equal to or greater than the stored reference signal, an alert signal will be generated. If the incoming signal exceeds the reference value, the incoming signal becomes the reference value. After all circuit interrupter devices are scanned, the value stored in the receiver will contain the highest value measured during the scanning procedure. The circuit breaker possessing the highest value is the circuit breaker supplying power to the transmitter or signal feeder. During the second scan, all of the signals will be below the stored reference value, except for the signal originating from the circuit breaker supplying power to the transmitter or signal feeder. 
     For example, if a transmitter is connected to branch circuit  3  of FIG. 5, the first scan from branch 1 to branch 6 will result in the following readings: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 Branch 
                 V in   
                 V stored   
                 Result 
                 Action 
               
               
                   
               
             
            
               
                 1 
                 0.2 V 
                 0.1 V 
                 V in  &gt; V stored   
                 Alert user; 
               
               
                   
                   
                   
                   
                 update V stored   
               
               
                 2 
                 2.2 V 
                 0.2 V 
                 V in  &gt; V stored   
                 Alert user; 
               
               
                   
                   
                   
                   
                 update V stored   
               
               
                 3 
                 3.8 V 
                 2.2 V 
                 V in  &gt; V stored   
                 Alert user; 
               
               
                   
                   
                   
                   
                 update V stored   
               
               
                 4 
                 1.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 5 
                 0.8 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 6 
                 3.4 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                   
               
            
           
         
       
     
     The second scan from branch 1 to branch 6 will result in the following readings: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 Branch 
                 V in   
                 V stored   
                 Result 
                 Action 
               
               
                   
               
             
            
               
                 1 
                 0.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 2 
                 2.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 3 
                 3.8 V 
                 3.8 V 
                 V in  = V stored   
                 Alert 
               
               
                 4 
                 1.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 5 
                 0.8 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 6 
                 3.4 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                   
               
            
           
         
       
     
     After the first scan, the receiver will only generate an alert signal when the receiver is measuring the magnetic field of branch 3. The value of the reference voltage must be reset for all subsequent scans. Because the receiver includes “power on reset,” the reference voltage may be reset by simply switching the receiving device off and on. 
     In the following example, the transmitter remains connected to branch circuit  3  of FIG.  5 . The branch circuits, however, will be scanned from branch 6 to branch 1, resulting in the following readings: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 Branch 
                 V in   
                 V stored   
                 Result 
                 Action 
               
               
                   
               
             
            
               
                 6 
                 3.4 V 
                 0.1 V 
                 V in  &gt; V stored   
                 Alert user; 
               
               
                   
                   
                   
                   
                 update V stored   
               
               
                 5 
                 0.8 V 
                 3.4 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 4 
                 1.2 V 
                 3.4 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 3 
                 3.8 V 
                 3.8 V 
                 V in  &gt; V stored   
                 Alert user; 
               
               
                   
                   
                   
                   
                 update V stored   
               
               
                 2 
                 2.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 1 
                 0.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                   
               
            
           
         
       
     
     The second scan from branch 6 to branch 1 would result in the following readings: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 Branch 
                 V in   
                 V stored   
                 Result 
                 Action 
               
               
                   
               
             
            
               
                 6 
                 3.4 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 5 
                 0.8 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 4 
                 1.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 3 
                 3.8 V 
                 3.8 V 
                 V in  = V stored   
                 Alert 
               
               
                 2 
                 2.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                 1 
                 0.2 V 
                 3.8 V 
                 V in  &lt; V stored   
                 No Action 
               
               
                   
               
            
           
         
       
     
     Thus, both of the above examples result in the identification of the correct branch. 
     It will be understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.