Abstract:
The transmitter of the circuit breaker locator draws large amplitude, short duration, phase locked unipolar pulses of current from the power source at a frequency lower than that of the AC line frequency. The audible and visual indicators of the transmitter are triggered at the rate of the current pulses drawn from the AC line. The receiver of the circuit breaker locator has a pick-up coil that responds to magnetic field surrounding the circuit breaker, an amplifier for boosting the signal from the pick-up coil, and a single shot pulse stretcher triggered by the amplifier. The pulse stretcher drives both audible and visual signals, and at the same time charges a memory capacitor in a staircase generator fashion. The magnitude of the memory capacitor voltage in turn controls the gain of the amplifier. A switch controls the voltage applied to the amplifier, which increases by a predetermined amount when released.

Description:
FIELD OF THE INVENTION 
   The present invention relates to power line testing equipment and more particularly to the identification of the circuit breakers supplying power to a particular branch circuit and AC outlets. 
   BACKGROUND OF THE INVENTION 
   When working on the electrical wiring of a home or building, it is desirable, and necessary for safety purposes to shut off the circuit breaker supplying power to a particular electrical outlet. Circuit breaker panels typically have a plurality of circuit breakers supplying power to many areas of the home. Many times, the branches these circuit breakers control are not clearly marked, and often the markings are only general in nature. Because of the marking system employed on almost all circuit breaker panels, the person desiring to remove power to a particular branch circuit or AC power outlet usually turns off many circuit breakers in the process of trying to locate the correct one. During this trial and error period, power could be removed to other locations in the home or building not related to the branch circuit the person is trying to disable. Since the AC outlet is remotely located from the breaker panel it is difficult to know for sure that the correct circuit breaker has indeed been shut-off. It then becomes necessary to go to the remote location and check to be certain that power to the AC outlet has been removed. A test or measuring device is then required to verify that the outlet power has been properly shut off, and if it is found that the incorrect circuit breaker was selected, then another trip to the breaker panel is required. It becomes obvious that a low cost easy to use device that would allow the user to identify the correct circuit breaker from the many others in the panel would be a desirable product in the marketplace. 
   In the past, many methods for generating the AC line signal have been devised. A very efficient, low cost transmitter and receiver is shown in U.S. Pat. No. 4,906,938. This patent shows a simple four-component transmitter that draws short duration, fast rise time pulses of high current from the AC line. Since then many others have employed variations of this circuit to generate similar signals on the AC line. These circuit variations produce signals equal to or higher than that of the AC line frequency, and are similar to signals produced by light dimmers, which also draw fast rise time current pulses from the AC line. In some cases, these light dimmers, depending on their load, can generate signals approaching the levels of those generated by the transmitter and can be difficult to distinguish from the desired transmitter signal. In fact, most of the circuit breaker receivers developed by others will respond to the signal produced by a light dimmer even when their transmitter is not plugged into an AC outlet. 
   U.S. Pat. No. 4,906,938 patent also shows a simple receiver for detecting the current pulses flowing through the circuit breaker. The gain of this receiver is controlled with a user adjustable potentiometer. In order to identify the correct circuit breaker the user adjusts this potentiometer, thereby reducing the gain of the receiver amplifier, until only one circuit breaker produces a response in the receiver. Although this method of adjusting the sensitivity works quite well, first time users sometimes find it difficult to adjust this control in a timely manner. 
   Therefore, there is a need of a power line testing equipment that allows proper detection of signals generated by the transmitter to eliminate confusion with signals produced by other sources and facilities adjustment to the sensitivity of the receiver. 
   SUMMARY OF THE INVENTION 
   Transmitter 
   By injecting fast rise time current pulses that have a repetition rate significantly lower than that of the line frequency, it becomes possible to distinguish the difference between a light dimmer and the transmitter. This is due to the lower frequency of the transmitted current pulses and consequently the lower repetition rate produced by the receivers audible and visual signal indicators. In addition to having transmitter current pulses lower than the AC line frequency it is also important to have unipolar pulses of current. The importance of generating current pulses during both the positive and negative portion of the AC line cycle is due to the nature of the pick-up coil and amplifier combination in the receiver. When the pick-up coil of the receiver is placed at a right angle to the circuit breaker it will produce a ring wave, this ring wave will produce slightly different positive and negative peak values when detecting a fast rise time current pulse. Due to the nature of the magnetic field produced by the current pulse in the circuit breaker, the output of the pick-up coil will be inverted by the direction of the current flowing through the breaker. Since the circuit breakers in a panel are typicality comprised of two rows with the power bus between these two rows, the circuit breakers on the left side of the panel will have current flowing from right to left, and the breakers on the right side will have current flowing from left to right. Because it would be inconvenient for the user to rotate the receiver 180 degrees, the signal developed across the pick-up coil should be the same regardless of whether the circuit breakers on the left side or the right side of the panel are being scanned. Because the receiver&#39;s amplifier responds only to the positive going peaks from the pick-up coil, the transmitter needs to generate unipolar current pulses so that the peak signal value will be the same regardless of the which side of the panel the circuit breaker is located on. 
   A simple, cost effective, way to generate these unipolar current pulses is with two relaxation oscillators, each controlled by a common voltage breakdown device. The first oscillator generates a current pulse only when the line voltage is positive and the second generates a current pulse only when the line voltage is negative. Because these oscillators are free running, and independent of each other, they need to be locked together. The result of locking the oscillators together insures that the signal produced by the transmitter will not cause the signal received at the circuit breaker panel to be higher than the desired six to seven pulses per second. 
   Since safety is extremely important, there should be no doubt, as to whether the outlet has had the power removed. Previous transmitters have a built in light that indicates that the AC outlet is receiving power, but this light is sometimes difficult to see depending on ambient lighting conditions. Additional features have been incorporated into the new transmitter that will alert the user as to whether power to the electrical outlet has, or has not, been removed. The L.E.D. used as a visual voltage indicator will now flash at the same rate as the current pulses drawn from the AC line. Additionally an audible device has been incorporated into the transmitter; this device will produce a beeping sound that will further alert the user to the fact that the AC outlet has power in the event that power has not been removed from the outlet. 
   Receiver 
   Drawing fast rise time pulses of current from the AC line will cause a signal to be present on more than one of the circuit breakers in the panel. Since many factors will effect the strength of the signal at the circuit breaker panel, the gain of the receiver must be high enough to respond to the lowest signal level anticipated. Consequently, the gain of the receiver is usually higher than necessary, and needs to be reduced in order to identify the correct circuit breaker. Since the circuit breaker supplying power to the transmitter will always have the strongest signal, reducing the receiver gain until only one breaker produces a response in the receiver is sufficient to identify the correct circuit breaker. To eliminate the need for adjusting a manual gain control, an automatic reduction in amplifier gain is accomplished using a voltage step generator. When locating a circuit breaker the user presses and holds a momentary button or switch, this allows the pulse stretching output stage of the receiver to charge a memory capacitor in a step fashion every time the receiver output stage is triggered from signals produced from the circuit breakers. The magnitude of charge on this capacitor controls a field effect transistor that in turn reduces the gain of the amplifier by a predetermined amount each time the pulse stretching output stage is triggered. In this manner, the receiver becomes less and less sensitive every time it is triggered by a signal from the circuit breakers. 
   The nature of the amplifier to the stepped reduction of sensitivity is such that after the output stage has been triggered five to ten times (depending on signal strength) the amplifier will no longer respond to these signals. When the amplifier stops responding to all signals emanating from the panel the user then releases the momentary button or switch they had been previously holding. Releasing the switch causes a predetermined amount of reduction, in the voltage applied to the gate of the gain controlling field effect transistor. This change in voltage then increases the gain of the receiver amplifier. This increase in gain now allows the circuit breaker having the largest signal to resume triggering the receiver. In addition to applying the gain controlling step voltage to the memory capacitor, the pulse stretching output stage of the receiver also drives a flashing light and audible beeper. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention have been chosen for purposes of illustration and description and are shown in the accompanying drawings forming a part of the specification wherein: 
       FIG. 1  shows a schematic of the preferred transmitter. 
       FIG. 2  shows the line current waveforms produced by the transmitter of  FIG. 1 . 
       FIG. 3  shows the relationship of the positive and negative transmitter pulses. 
       FIG. 4  shows the transmitter timing waveforms of  FIG. 1 . 
       FIG. 5  shows a schematic of the preferred receiver. 
       FIG. 6  shows the step voltage controlling the gain of the receiver amplifier of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to the drawings, wherein the same reference number indicates the same element throughout, there is shown in  FIG. 1  a schematic of the pulse-generating transmitter  10 . Transmitter  10  is adapted for use with a standard AC receptacle powered from one of the branch circuits supplied by a circuit breaker panel. 
   Transmitter  10   
   AC line voltage is applied to fuse F 1 , the junction of F 1 , S 1  and D 1  have Hot AC line voltage present with respect to the AC Neutral return connection. The series combination of D 1  and R 1  form a half wave current limited source for charging capacitor C 1 , the magnitude of this voltage is limited by zener diode D 2 . The resulting voltage at the junction of R 1 , C 1 , and D 2  produces a DC supply for powering beeper B 1  and light emitting diode (LED) D 3 , current through LED D 3  is further limited by resistor R 2 . Transistor Q 1  is configured as a voltage controlled switch, when this switch is in conduction its collector emitter creates a path to circuit common, that turns on beeper B 1  and LED D 3 . The combination of S 1 , D 4 , C 2 , R 3 , and R 4  form a first relaxation oscillator that draws positive going pulses of current from the AC line at approximately 7 Hz. The combination of S 1 , D 5 , C 4 , and R 5  form a second relaxation oscillator that draws negative going pulses of current from the AC line at approximately 7 Hz. Because these two relaxation oscillators are free running, it becomes necessary to synchronized them to each other. The result of this synchronization is that within one-half of a line cycle after one of the relaxation oscillators has generated a pulse the other oscillator will also generate a pulse of the opposite polarity. This synchronization is accomplished by coupling the two oscillators together with capacitor C 3 . 
   Sidac S 1  is a bi-directional voltage breakdown device, when the voltage across it exceeds its breakdown rating it becomes conductive, and remains conductive until the current flowing through it drops below the rating of its holding current. Referring to  FIG. 4 , during the positive portion of the AC line cycle, the voltage across sidac S 1  exceeds the breakdown rating of the device (approximately 120 volts). At this time, sidac S 1  switches from an off state to an on state and connects the AC line to diode D 4 , this diode becomes forward biased causing the rapid charging of capacitor C 2 . During the rapid charging of capacitor C 2  a pulse of current with a peak value of approximately 15 amperes is drawn from the AC line during the positive portion of the AC line cycle, this in turn causes the voltage across capacitor C 2  to charge in a positive direction. The charging of C 2  creates a voltage step change across this capacitor equal to the 120-volt breakdown voltage of sidac S 1 . This 120-volt pulse will also appear across capacitors C 3  and C 4  since they are series connected across C 2 . Since the ratio of C 3  to C 4  is 3.3 to 1, a positive going step chance across capacitor C 4  of approximately 40 volts will occur at this time. This voltage step across C 4  has the effect of lowering the voltage across it by 40 volts. This lowering of voltage across C 4  insures that during the next negative going portion of the AC line cycle, the voltage breakdown rating of sidac Si will be exceeded, causing diode D 5  to become conductive. Capacitor C 4  will then rapidly charge in a negative direction, at this time a 15-ampere pulse of current will be drawn from the AC line during the negative half of the line cycle. This current pulse will occur during the next negative half line cycle immediately following the turn on of sidac S 1  during the previous positive half of the line cycle. The discharging effect of resistors R 5 , and series connected resistors R 3  and R 4  causes a slow decay in voltage across C 2  and C 4 , and after approximately 143 ms has elapsed the cycle described above will repeat. As can be seen from the voltage waveform in  FIG. 4 , the voltage across capacitor C 2  will reach a peak value of approximately 170 volts when sidac S 1  fires. The resistor divider comprised of R 3 , R 4  form a voltage divider, and the voltage at the junction of these resistors will be sufficient to forward bias the base emitter junction of Q 1 . Q 1  will then turn on and remain on until the voltage across C 2  drops to approximately 95 volts at which time Q 1  will turn off. Thus every time C 2  is recharged by the firing sidac S 1 , transistor Q 1  will turn on for approximately 4 ms. The turning on of Q 1  in turn causes beeper B 1  and LED D 3  to provide visual and audible indications to the user that the outlet is receiving power from the AC outlet. 
   Receiver  20   
     FIG. 5  is a schematic of the receiver  20 . The combination of C 5 , L 1 , and R 9  will produce a 90 kHz ring wave when L 1  is placed at a right angle to a wire or circuit breaker carrying a fast rise-time impulse of current. In this case, the current impulse from the transmitter  10  produces a current that has a peak value of approximately 15 amperes with a rise time of approximately 2 to 3 microseconds. Resistors R 6 , R 7 , and R 8  form a voltage divider, this in turn supplies the necessary DC base bias that flows through L 1  into the base of transistor Q 2 . When detecting a current pulse, one side of pick-up coil L 1  sees a low impedance AC path to circuit common through capacitor C 6  while the other side of the coil is free to supply a signal to the base of amplifier Q 2 . Resistor R 6  in addition to being part of the base bias network for Q 2  also serves as a collector load resistor. When the base of Q 2  receives a signal from the pick-up coil, transistor Q 2  will turn on causing a negative going voltage drop at the junction of R 6  and the collector of Q 2 . If the signal produced by L 1  is sufficient, the negative going voltage drop at the collector of Q 2  will fall to a value below one third of the 8.5-volt DC supply voltage. U 1  is a 555 timer integrated circuit (IC) configured as a single shot pulse stretcher; pin  2  of this IC is the trigger control input and is connected to the junction of R 6  and the collector of Q 2 . When the voltage applied to pin  2  of U 1  falls below one third of the supply voltage the output of the IC, pin  3 , will be driven high by its internal switches. When not triggered, the output of IC U 1  will be low, this creates a path to circuit common for LED D 8  through current limiting resistor R 16  and zener diode D 9 . The value of zener diode D 9  is chosen to come out of conduction if the battery voltage drops below 8 volts, thus LED D 8  will cease to light if the battery voltage is low, thus serving as a low battery indicator. When the battery voltage is normal, LED D 8  will flash on and off in time with the switching at the pin  3  output of U 1 . The output pin  3  of U 1  is also connected to an audible beeper B 2 . The timing interval produced at the output of U 1  is controlled by the values of R 15  and C 14 . When pin  3  is forced high by the negative going trigger pulse applied to pin  2 , it remains high for 68 ms. During this timing interval, beeper B 2  is energized and LED D 8  de-energized. 
   The purpose of field effect transistor M 1  is to control the sensitivity of signal amplifier transistor Q 2 . When M 1  is not in conduction the voltage at the emitter of Q 2  is 1.72 volts. If the emitter voltage of Q 2  is forced to increase, it has the effect of reverse biasing the base emitter junction, thus the sensitivity of Q 2  to the signal produced by pick-up coil L 1  can be reduced by increasing the voltage applied to its emitter. While switch S 2  is not depressed, the voltage across memory capacitor C 9  remains near zero and the receiver&#39;s  20  amplifier Q 2  operates at maximum sensitivity. When switch S 2  is pressed, the output pulses produced by U 1  at pin  3  are connected to the anode of diode D 7 . During the positive portion of these pulses diode D 7  is forward biased and charging current flows through current limiting resistor R 13  into memory capacitor C 9 , resistor R 11  also has an effect on limiting the current flowing into C 9 . Additionally, resistor R 11  is part of a voltage divider that establishes a positive voltage reference for the gate of M 1  with respect to circuit common. The values for R 14  and R 11  are chosen to produce 3.3 volts at the junction of memory capacitor C 9 , resistor R 14 , and resistor R 11 . Resistor R 12  is normally shorted by a second section on switch S 2 , when S 2  is pushed the short is removed, and 100 mV appears across this resistor R 7 . This additional 100 mV adds to the voltage already present at the gate of M 1  and in turn causes the voltage present at the emitter of Q 2  to increase by an additional 100 mV. 
   The waveforms shown in  FIG. 6  show the relationship of the pin  3  output voltage of U 1  (upper waveform) to the stepped voltage applied to the emitter of signal amplifier Q 2 . The conditions shown in the graph waveforms of  FIG. 6  are as follows: The upper waveform is the pin  3  output voltage of U 1 ; the lower waveform is the stepped sensitivity control voltage, applied to the emitter of signal amplifier Q 2 . At time zero the receiver  20  is being triggered by a signal from pick-up coil L 1 , 0.5 seconds into the plot switch S 2  is pressed and the voltage applied to the emitter of Q 2  begins to increase by approximately 100 mV every time the output of U 1  at pin  3  goes high. When the voltage steps applied to the emitter of Q 2  are sufficiently high to reverse bias the emitter base junction of Q 2 , the negative going voltage pulse at Q 2 &#39;s collector no longer falls below that required to trigger U 1 . At this time, the output voltage of U 1  remains low and the voltage at Q 2 &#39;s emitter stops increasing. As long as the output voltage of U 1  remains low, beeper B 2  is off and LED D 8  ceases to flash. When none of the circuit breakers in the panel causes the receiver  20  to respond, the user would release switch S 2  (shown as 2.5 seconds on the graph), this will cause a 100 mV drop in the voltage applied to the emitter of Q 2 . This drop in voltage will now allow the signal amplifier to resume responding to the signal from pick-up coil L 1 , but at a now reduced sensitivity level such that only the circuit breaker with the strongest signal is capable of triggering the receiver  20 . When the receiver  20  power is shut-off with switch S 3 , the DC voltage in the receiver  20  will rapidly collapse to zero. This will in turn cause memory capacitor C 9  to discharge through diode D 6  thus resetting C 9  to an un-charged condition. 
   The features of the invention illustrated and described herein is the preferred embodiment. Therefore, it is understood that the appended claims are intended to cover the variations disclosed and unforeseeable embodiments with insubstantial differences that are within the spirit of the claims.