Patent Publication Number: US-2007109135-A1

Title: Transmitter loop monitor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. provisional patent application No. 60/732,980 filed on Nov. 3, 2005, which is incorporated herein in its entirety by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
      (Not applicable)  
     BACKGROUND OF THE INVENTION  
      This invention relates to a transmitter for a pet containment system and, more particularly, to a transmitter having an antenna wire-loop monitor for monitoring and visually displaying an indication of the status of a boundary signal provided by the antenna wire loop.  
      Pet containment systems are used to confine domesticated pets, such as dogs or other animals, within a pre-defined area or, alternatively, to keep pets outside of a pre-defined area. Typical containment systems include an antenna wire, an electrical power source, a transmitter, and a receiver.  
      The antenna wire is buried in a desired pattern or arrangement, usually a closed loop, to define the perimeter or boundary of an area across which one&#39;s pet is conditioned not to cross. The transmitter and electrical power source are electrically-coupled to the buried antenna wire. More particularly, the electrical power source provides current to the transmitter and the transmitter drives current through the antenna wire, causing the antenna wire to radiate or induce an electromagnetic field.  
      Referring to  FIG. 3 , a buried antenna wire  15  for a pet containment system is shown. The antenna wire  15  is buried at a relatively shallow depth, D, and further, connected to a power source (not shown). Current is driven through the antenna wire  15 , causing a three-dimensional electromagnetic field  40  to radiate  360  degrees about the antenna wire  15 . The “signal field”  42  corresponds to the two-dimensional extent of the electromagnetic field on either side of the antenna wire  15 .  
      Within the “signal field”  42  there is a first (audible signal) zone A and a second (electrical stimulation) zone B. The second zone B corresponds to the area to either side of the projection of the antenna wire  15  at the ground surface  45  in which a pet wearing a receiver will experience electrical stimulation if the pet enters the second zone B. In  FIG. 3 , the second zone B extends for a distance d B  in both directions orthogonal to the projection of the antenna wire  15  at the ground surface  45 . The lineal extent of the second zone B corresponds to a point  49  at which, for a pre-determined current of magnitude I B , the strength of the electromagnetic field is sufficient to cause the receiver to apply an electrical stimulation to the pet wearing the receiver.  
      The first zone A extends beyond the second zone B for an additional distance d A  in both directions orthogonal to the projection of the antenna wire  15  at the ground surface  45 . The lineal extend of the first zone A is defined by the area between point  49  and point  48  at which, for a pre-determined current of magnitude I A , the strength of the electromagnetic field is sufficient to cause the receiver to provide an audible warning signal but not sufficient to cause the receiver to apply an electrical stimulation.  
      Thus the receiver attached to an animal collar is structured and arranged to detect the electromagnetic field and, moreover, to differentiate between zone A and zone B field strengths. Thus, depending on the intensity of transmission of the electromagnetic field, the depth of burial, and the proximate distance between the receiver and the buried antenna wire  15 , the pet hears an audible warning signal or receives an appropriate stimulus when he or she enters either zone A or zone B, respectively.  
      For example, one well-known pet containment system is the Hidden Fence System manufactured by DogWatch®, Inc. of Natick, Mass. In the Hidden Fence System, the transmitter controls the transmission intensity of antenna wire so that the receiver detects the electromagnetic field at various, predetermined distances from the antenna wire. Typically, in the first zone A of detection, the receiver senses a relatively weak electromagnetic field and provides an audible warning, such as a chirping or ticking noise, to the animal wearing the receiver. In the second zone B, which is closer to the antenna wire  15 , the receiver senses a stronger electromagnetic field, causing an electrical stimulus to be applied to the animal through the receiver as an indication to the animal that it is too close to the perimeter. Through appropriate training and conditioned response, the animal learns to stay away from the perimeter to avoid both the audible warning and the electrical stimulus.  
      From time to time, the closed-loop antenna wire  15  is subject to interruption from natural causes, such as from rain, age or burrowing rodents, or from artificial causes, such as from a garden implement or lawn tool. Interruptions due to artificial causes, typically, result in an immediate open circuit of the antenna wire  15  loop at a discrete location. Conventionally, interruptions or open circuits cause the transmitter to emit an audible and/or visual signal to alert the user of the open circuit condition. Such interruptions and their location in the antenna wire  15  loop, thus, are immediately known and can be quickly corrected.  
      However, interruptions due to natural causes or a combination of natural and artificial causes, which can occur over a relatively long period of time or are unseen, are less easily known or corrected. Indeed, when a break in the buried antenna wire  15  loop occurs due to natural causes, the location of the break is uncertain. As a result, it may be necessary to excavate the entire antenna wire  15  loop, to locate the break.  
      Therefore, it would be desirable to provide a pet containment system that includes a loop monitoring system or device that is capable of detecting the current flow through the antenna wire  15  and displaying the results of the same so that the problem area can be located before the problem area becomes a break in the antenna wire  15  loop, at which point the problem area cannot be located without excavating the antenna wire  15 .  
     BRIEF SUMMARY OF THE INVENTION  
      A device for monitoring the integrity of an antenna wire loop, such as for a pet containment system, and a system using the monitoring device are disclosed. The device can be incorporated in the transmitter portion of the pet containment system or can be a stand-alone device electrically and operationally coupled thereto. The device includes a current monitoring portion to monitor the current in the antenna wire loop and a display portion to display the intensity of the electromagnetic field. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
       FIG. 1  is a block diagram of a monitoring portion and display portion according to the device of the present invention;  
       FIG. 2  is a circuit diagram of a containment system according to the present invention; and  
       FIG. 3  is a diagram of a buried antenna wire and the electromagnetic field generated thereby. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A device for monitoring and visually displaying the intensity of an electromagnetic field generated by an antenna wire, such as a buried antenna wire for a pet containment system, is disclosed. Referring to  FIG. 1 , the device  10  includes a current or loop monitor  12  and a display portion  14 . The loop monitor  12  provides an indirect measure of the intensity of the electromagnetic signal being radiated by the antenna wire  15  ( FIG. 3 ) by measuring the loop current. The display portion  14  visually displays the monitored intensity in suitable units, such as feet.  
      More specifically, the loop monitor  12  measures current flow through the antenna wire  15  and is operative to denote deterioration or a partial break of the antenna wire  15 , to predict or indicate, respectively, a potential or an actual failure condition, i.e., an open circuit. More particularly, for a given voltage potential, more current will flow through an undamaged antenna wire  15 , having minimal impedance, than will flow through a deteriorated or partially broken antenna wire  15  that has a greater impedance. Hence, the magnitude of current flowing through the antenna wire  15  provides indicia of the condition and integrity of the antenna wire  15 . Because the intensity of the electromagnetic field about the antenna wire  15  is proportional to the magnitude of current flowing through an antenna wire  15  and, moreover, because the intensity of the electromagnetic field varies linearly with distance from the source, the magnitude of the current can be related to distance from the source for display purposes.  
      For example, in operation, a decrease in the intensity of the electromagnetic signal can denote a loop problem, such as a corroding wire splice in the buried antenna wire  15 . The indication of a loop problem is provided long before an open circuit condition in the antenna wire  15 , such as by a wire break, develops. A troublesome or problematic antenna wire  15  loop can thus be identified and serviced before a wire break.  
      In the event of an open loop condition, the loop alarm will sound. Thus, the loop monitor provides a warning long before a failure condition.  
      Although the monitoring and displaying device  10  can be a stand-alone device that is electrically- and operatively coupled to a transmitter, the transmitter may, instead, be structured and arranged to include the monitoring and displaying device. A block diagram of a transmitter  20  having a monitoring and displaying device  10  is shown in  FIG. 1 . In addition to the monitoring and displaying device  10 , the transmitter  20  further includes a signal source  22 , a current driver and loop detector  24 , and a power amplifier  26 .  
      The signal source  22  is electrically-coupled to the current driver and loop detector  24 , which is electrically-coupled to the power amplifier  26 . The power amplifier  26  includes a plurality of output terminals  25  and  27  that are electrically-coupled to the antenna wire  15 . As previously described, the antenna wire  15  can be buried in a predetermined arrangement, such as around the perimeter of a yard or other area in which a dog is to be contained or from which a dog is to be restrained from entry.  
      The input of the loop monitoring portion  12  of the device  10  is electrically-coupled to the power amplifier  26  and the output of the loop monitoring portion  12  of the device  10  is electrically-coupled to the display portion  13 . The loop monitoring portion  12  includes a low pass filter  11  and a peak detector  13 .  
      In operation, the signal source  22  provides a continuous signal to the current driver and loop detector  24 , which, in turn, uses the signal to drive a power amplifier  26 . Monitor circuitry (not shown) disposed in the power amplifier  26  (or, alternatively, disposed in the loop monitoring portion  12  of the monitoring and display device  10 ) monitor the magnitude of the current flowing through the power amplifier  26  to the antenna wire  15  and provide these data to the loop monitoring portion  12 .  
      The loop monitoring portion  12  processes these data, e.g., by filtering the data, first, through a Low-pass filter  11  to remove high frequency noise and harmonics. The filtered data are, then, passed through a peak detection device  13 . The peak detection device  13  provides an output signal to the displaying portion  14 , which provides a visual indication of the electromagnetic field intensity associated with the loop current magnitude.  
      An illustrative circuit diagram of a transmitter  20  for a pet containment system, including a monitoring and displaying device  10 , is shown in  FIG. 2 . The transmitter  20  and all portions thereof are energized by a power source  30 . The power source  30  is structured and arranged to provide power to the transmitter  20  using a DC battery, such as a 12-volt battery, via a jack  32 , and/or using a power adapter, such as a 24-volt, 500 mA power adapter, via a jack  34 , that is capable of connection to a standard 110-volt power outlet.  
      The power source  30  includes a manual operating switch  35  for changing the state of the transmitter  20  from ON to OFF and vice versa. When the switch  35  is ON, the emitter (or gate) of a switching device  21 , e.g., an impedance-changing switching device Q3, is appropriately driven so that current at the collector (or source electrode) of the switching device  21  flows to the base(or drain electrode) of the switching device  21 .  
      The signal source  22  of the transmitter  20  produces output signals, I o , that are input into the current driver and loop detector  24 . More specifically, the output signals, I o , are input into the current driver and loop detector  24  via the switching device  21 , e.g., typically an npn bi-polar junction transistor or an n-type field effect transistor. When the emitter (or gate) of the switching device  21  is closed (with power switch  35  is ON), current from the signal source  22  flows into the current driver and loop detector  24 . This occurs on every positive half-cycle of the signal current waveform. When the output signal drops to near zero, the switching device  21  stops conducting, and no current from the signal source  22  flows into the current drive and loop detector  24 .  
      Those skilled in the art can appreciate that the same principle can occur be using a different configuration using other transistor types. Whether the emitter (or gate) of switching device  21  is open or closed depends on whether the voltage at the emitter (or gate) is driven HI or driven LO and on whether the switching device  21  is an n-type or p-type switching device.  
      The signal, I o , from the signal source  22  passes through the current driver and loop detector  24  and is output (I′ o ) to the power amplifier  26 , where the current (I′ o ) is amplified to a desired, pre-determined, changeable magnitude. Referring to  FIG. 3 , the amplified current is output to the antenna wire  15  as loop current, I loop . The loop current, I loop , induces the electromagnetic field  40 . Current also flows through a resistive element  23  (R 19  in  FIG. 2 ) having a pre-determined resistance. Thus, the voltage across the resistive element (R 19 )  23  is representative of the loop current, I loop .  
      The voltage representative of the loop current is processed for driving the loop monitor display  14 . More specifically, a Low-pass filter  11  filters out unwanted higher frequency signals and noise. The Low-pass filter  11  can also include one or more manually-operable switches (SW 4-3 and SW 4-4)  18 , to accommodate different operating frequencies of the transmitter  20 . The Low-pass filter  11  then provides the filtered signal to the peak detector  13 .  
      The peak detector  13  provides the filtered signal to a converter, e.g., a converter on an integrated circuit chip. The converter converts the filtered signal to an analog output voltage, V o . The magnitude of the analog output voltage, V o , drives the display portion  14 .  
      For example, as shown in  FIG. 2 , the output voltage, V o , is input into an integrated circuit device  19 , such as an LM3914, which drives a linear analog display  16 , digital/analog meter or any other form of visual indicator. The linear analog display  16  can be a bar type or dot-type display. The linear analog display  16  of the display portion  14  includes a plurality, e.g., ten (10), light emitting diodes (LEDs)  17  (or similar light-emitting devices such as liquid crystal display devices (LCDs), vacuum fluorescent devices, and the like). The peak detector  13  and the LED driver device  19  are structured and arranged so that more of the LEDs  17  are illuminated when the output voltage, V o , and loop current, I loop , are relatively high and so that fewer of the LEDs  17  are illuminated when the output voltage, V o , and loop current, I loop , are relatively low, or one LED  17  can be lit at a time, corresponding to the amount of the loop current, I loop .  
      Thus, the display portion  14  of the transmitter system  20  provides a continuous, visible indication of the strength of the electromagnetic field radiated by the antenna wire  15  and, furthermore, provides real-time signal strength or range indication, by continuous monitoring of the current in the antenna wire  15 .  
      In a typical implementation, the loop current indication is accurate to within about five percent (5%) of the actual electromagnetic field strength  40 . The loop monitor  12  is typically calibrated in the transmitter  20  for receivers that placed about two (2) feet off the ground surface  45 . For smaller and larger pets, the monitor can be recalibrated or a correction factor can be applied to account for the particular height of the receiver from the ground surface on a particularly sized dog.  
      The loop monitor  12  is accurate for traditional boundary wire configurations, which provide an antenna wire loop about a yard or around a garden or other area. For loop configurations that are non-traditional, such as where the loop is in a narrow banana or boomerang shape, the correction range is dependent on loop spacing as well as the magnitude of the current signal provided to the loop. In such instances the indicated loop range will usually have to be corrected according to a correction table provided for the particular non-traditional loop configuration.  
      To establish a correction zone, the range control on the transmitter  20  can be set to an intended correction range and the loop monitor display  14  is observed to indicate the actual range setting provided by the loop antenna  15 . The range control can be adjusted to produce the actual intended range as denoted by the loop display.  
      While the invention is described through the above-described exemplary embodiments, it will be understood by those of ordinary skill in the art that modifications to, and variations of, the illustrated embodiments may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited, except by the scope and spirit of the appended claims.