Buried cable break detector and method

A buried perimeter loop wire break detector with a base unit and probe unit. The base unit injects different frequencies into the two ends of the loop wire and the probe unit detects the frequencies at a test location along the wire. If a signal is not detected, that indicates the direction toward the break. By halving the distance along the wire toward the break and retesting, the location is quickly determined. Both frequencies and amplitude are measured, sometimes with amplification, both earth and wired grounds may be employed, and a micro-ohmmeter measures resistance of the loop wire to indicate satisfactory operation.

BACKGROUND OF THE INVENTION

Related Applications

Field of the Invention

The present disclosure generally relates to locating and repairing breaks in buried cables or wires. More particularly, the present disclosure relates to locating breaks in buried perimeter loop wires used for electronic perimeter control systems.

Description of Related Art

Robotic lawn mowers, invisible dog fences, and other similar perimeter control systems often employ a buried loop of wire that forms an electronic perimeter, which serves to constrain and limit movement of equipment or animals therein. Such loop wires are routed about a perimeter and are then buried in the ground, typically a few inches deep. The loop wire is then connected to a host system, which sends signals through the loop wire. The terminal units operating in such electronic perimeter control systems are responsive to the signals on the loop wire, to thereby constrain movement of the terminal units within the defined perimeter. Such loop wires are subject to damage over time, which may be due to harsh handling during installation, exposure to the elements, landscaping operations, pet activities, exposure to vermin, corrosion, robotic mower operations, and the like. Such damage may result in complete or partial breaks in the loop wire.

Those skilled in the art are aware that complete breaks and partial breaks are a near-constant source of ongoing maintenance requirements. Prior art loop wire break detectors use radio frequency signals injected into the loop wire in conjunction with a handheld receiver coil and detector that is held above the ground, which output tones that are used to locate the loop wire and any breaks therein. In practice, moisture in the ground, external interference or poor connections can cause the RF signals to couple or pass over the troubled location, resulting in failure to detect breaks in the loop wire. Many times the only option is to rewire the entire perimeter loop wire, with associated costs. The presence of both original and replacement loop wires also results in later wire identification confusion, resulting in further diagnostic problems. More sophisticated loop wire break detections techniques are known, however teaching the use of complicated test equipment to measure the loop resistance to field technicians has proven difficult. Thus is can be appreciated that there is a need in the art from an improved system and method for locating complete and partial breaks in buried perimeter loop wires.

SUMMARY OF THE INVENTION

The need in the art is addressed by the teachings of the present disclosure. The present disclosure teaches a system for locating breaks in a buried loop wire, which includes a base unit that has a signal generator coupled to first and second terminals for connection to ends of the loop wire, and where the signal generator is enabled to sequentially couple first and second frequency signal to the first and second terminals. A a probe unit has a signal detector responsive to the first and second frequency signals, which is coupled to a probe terminal, and also has first and second direction indicators, which correspond to directions along the loop wire to the first and second terminals. The base unit and probe unit each have a ground terminal. An electrical ground means is connected between the ground terminals. A test probe is connected to the probe terminal and to a test location along the loop wire. In operation, the probe unit, upon detecting one of the signals activates one of the indicators to indicate there is a break in the loop wire in the direction of the corresponding first or second terminal on the non-detected frequency.

In a specific embodiment of the foregoing system, the electrical ground means includes a first earth ground rod connected to the first ground terminal, and a second earth ground rod connected to the second ground terminal, which thereby establishes an earth ground path between the base unit and the probe unit. In a refinement to this embodiment, when the signal detector detects both frequencies, which correspondingly activates both of the first and second direction indictors, the system further includes replacement of the first and second earth ground rods with a wire ground conductor connected between the first and second ground terminals. In a further refinement to this embodiment, the probe unit further includes an amplifier and a mode selector switch selectable between a STAKED mode and a WIRED mode.

In a specific embodiment of the foregoing system, during operation, while the earth ground path is connected, actuation of the mode selector switch to the STAKED mode connects the probe terminal directly to the signal detector, and while the wire ground conductor is connected, actuation of the mode selector switch to the WIRED mode connects the probe terminal through the amplifier and to the signal detector. In a refinement to this embodiment, while the WIRED mode is selected, the signal detector compares amplitudes of the first and second frequencies, and is responsive to activate either of the first or second direction indicators that corresponds with the lower amplitude signal.

In a specific embodiment of the foregoing system, the base unit further includes an indicator and a micro-ohmmeter coupled to measure a resistance value between the first and second terminals, and the base unit compare the measured resistance value with a resistance threshold value, such that the base unit indicates that there is no break in the loop wire if the resistance value is less than the resistance threshold value, and indicates that there is a break in the loop wire if the resistance value is greater than the threshold resistance value. In a refinement to this embodiment, the indicator is a display that displays the measured resistance value.

In a specific embodiment of the foregoing system, the first and second frequency signal are square wave signals at different frequencies within the audible frequency range.

In a specific embodiment of the foregoing system, the signals detector distinguishes the first frequency signal from the second frequency signal by measuring the frequencies thereof.

In a specific embodiment of the foregoing system, the signal generator repetitively and sequentially couples the first test frequency for a first time period followed by the second test frequency for a second time period.

The present disclosure teaches a method of locating breaks in a loop wire that is buried in the soil, using a base unit with a signal generator, and a probe unit with a signal detector. The method includes connecting the base unit to the ends of the loop wire, and connecting an electrical ground between the base unit and the probe unit to establish a ground reference between them. The method also includes sequentially coupling a first frequency signal into the first end of the loop wire, and a second frequency signal into the second end for the loop wire. Also, connecting a test probe between the probe unit and a first location along the loop wire, and detecting either of the first test signal or the second test signal by the signal detector. Upon detecting the first frequency signal, indicating there is a break in the loop wire in the direction of the second end, and upon detecting the second frequency signal, indicating there is a break in the loop wire in the direction of the first end. The method continues by relocating the test probe to a second location along the loop wire in the indicated direction of the break in the loop wire and repeating the detecting step.

In a specific embodiment of the foregoing method, the connecting an electrical ground step further includes connecting a first earth ground rod to the base unit, and a second earth ground rod to the probe unit, thereby establishing an earth ground path as the ground reference. In a refinement to this embodiment, the method includes, upon detecting both of the first frequency and the second frequency at the detecting step; replacing the earth ground path with a wire ground conductor, and repeating the detecting step.

In a specific embodiment of the foregoing method, where the probe unit includes and amplifier and a mode selector for either a STAKED mode or a WIRED mode, the method further includes, while the earth ground path is connected, the detecting step is initiated using the mode selector to engage a STAKED mode, which connects the test probe to the signal detector, and while the wire ground conductor is connected, the detecting step is initiated using the mode selector to engage a WIRED mode, which amplifies the test probe connection to the signal detector. In a refinement to this embodiment, the detecting step in the WIRED mode is accomplished by comparing the amplitude of the first frequency signal with the amplitude of the second frequency signal, where the lower amplitude signal is indicative of the direction of the break in the loop wire.

In a specific embodiment of the foregoing method, where the base unit includes a micro-ohmmeter, the method further includes measuring a resistance value between the first and second end of the loop wire, and comparing that with a resistance threshold value. And, upon determining that the measured resistance value is less than the resistance threshold value, indicating that there is no break in the loop wire, and terminating the detection step, or, upon determining that the resistance value is greater than the threshold value, indicating that there is a break in the loop wire, and continuing the determining step. In a refinement to this embodiment, the method includes displaying the resistance value by the base unit.

In a specific embodiment, the foregoing method further includes, upon measuring a resistance value this is greater then the resistance threshold value, setting a BREAK variable, and upon measuring a subsequent resistance value that is less then the resistance threshold value while set BREAK variable is set, indicating that the loop wire break has been eliminated.

In a specific embodiment of the foregoing method, the first frequency signal and second frequency signal are square wave signals at different frequencies within the audible frequency range.

In a specific embodiment of the foregoing method, the detecting step is accomplished by identifying the frequency of either the first test frequency or the second test frequency.

In a specific embodiment of the foregoing method, the sequentially coupling step includes repetitively coupling the first test frequency for a first time period followed by coupling the second test frequency for a second time period, wherein the time periods are the same duration.

DESCRIPTION OF THE INVENTION

While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope hereof, and additional fields in which the present invention would be of significant utility.

In considering the detailed embodiments of the present invention, it will be observed that the present invention resides primarily in combinations of steps to accomplish various methods or components to form various apparatus and systems. Accordingly, the apparatus and system components, and method steps, have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the disclosures contained herein.

The present disclosure teaches a wire or cable break finder system that locates both partial breaks and complete breaks in buried perimeter loop wires, which are used to carry guidance signals in perimeter control systems. Examples include robotic lawn mowers, dog fences, and other perimeter systems, which employ a buried loop of wire that forms an electronic perimeter to serve as a constraining system for such equipment or pets, and etc. The present disclosure teaches a system that consists of a battery powered base unit and a battery powered detector probe unit. An illustrative embodiment of the present disclosure differs from other commercial buried cable break finders in that, when a “WIRED” mode is chosen, the perimeter loop wires are resistively loaded by the detecting probe unit to reveal the direction to poor connections, and which avoids signal confusion caused by conductance through the soil itself. A partial break meaning that there is some reduced conductivity across a physical break in an electric conductor, which may result from soil conditions and moisture levels.

The systems of the present disclosure employ the use of relatively low frequency break detecting signals, which are generated by the base unit. Since the low frequency signals generated by the base unit are less capable of coupling across breaks in the loop wire and poor connections, regardless of moisture, loop wire breaks can be found more reliably. By sending alternate, differing, frequencies down opposing ends of the loop wire, the probe unit can distinguish, and inform, which direction the break is from any point probed along the length of the loop wire. The base unit features a display that continuously measures, and displays, the loop wire resistance which, when used in conjunction with selectively dividing the length of sections, and probing the loop wire, results in the rapid locating of breaks and poor connections.

An illustrative embodiment of the present teachings features two distinct operational modes, referred to as the “STAKED” mode and the “WIRED’ mode. The STAKED mode is useful for locating completely open circuits in dry ground where the loop wire resistance displayed is infinite or very large. By grounding the base unit to the soil using a ground rod, and by grounding the probe unit to the soil using another ground rod, both of which are “staked” into the soil, convenient operation and rapid break location is achieved. On the other hand, WIRED mode is useful for partial breaks in the loop wire, such as those in wet conditions or where a connection is poor. WIRED mode involves connecting a long ground wire from the base unit to the probe unit at its test location. When the WIRED mode is selected on the probe unit, an additional resistive load is applied to assist in isolating the direction along the loop wire toward the partial break, thereby rejecting false positives caused by signal wire ground conductance and poor soil connections.

The type of wire used to build perimeter loop wires for robotic mowers and dog fences are rated at a given number of milli-ohms per foot. Knowing the total resistance of the perimeter loop wire around a property is helpful to technicians repairing a broken perimeter loop wire, because higher resistance values are indicative of a wire break condition. The base unit of an illustrative embodiment is equipped with a built-in micro-ohmmeter that repeatedly measures the end to end loop wire resistance. Common US yards range from approximately one ohm to fifteen ohms total. Thus, it an be appreciated that be defining a threshold resistance value, perhaps approximately thirty ohms, virtually all loop wire lengths can be measured, and determined to be break-free if the total resistance is below that threshold.

During operation in the STAKED mode, a portable probe unit is carried to approximately halfway around the perimeter loop wire and a ground rod is staked into the soil and connected to a GROUND terminal on the probe unit. A test probe is connected to a PROBE terminal in the probe unit, and the test probe tip is attached to the loop wire at that location. A STAKED mode switch is actuated, which causes the probe unit to test for the first and second test signals injected into the loop wire by the base unit. The probe unit illuminates either of a LEFT LED or a RIGHT LED, indicating the direction of the good connection to the base unit, and conversely indicating the direction to move towards the break in the loop wire. By halving the suspect perimeter loop wire again and again, the target break can be quickly located. Once the halving distance is small, typically less than twenty feet, the short length of the perimeter wire is pulled up and replaced.

During operation in the WIRED mode, such as for wet conditions where test signals could be coupled accrues a loop wire break or a poor connection, a physical ground wire is connected between the base unit and the probe unit such that their respective chassis grounds are coupled at near-zero resistance. Thusly, when the WIRED actuator is actuated, the probe unit resistively loads the detected signals so as to isolate any test signal reception caused by coupling across the break or other poor connection. Again, the probe unit detects the stronger test signal, and illuminates either the RIGHT LED or the LEFT LED to indicate direction of the good and broken conductor path.

Reference is directed toFIG.1, which is a front view drawing of a cable break detector base unit6according to an illustrative embodiment of the present invention. The base unit6provides a hand-holdable enclosure with internal electronic circuitry (not shown) and certain user interface components, as follows. A POWER/NEXT actuator18presents a momentary contact switch that is used both for turning the power to the unit6on and off, and to step through menu selections, as will be more fully discussed hereinafter. Opposing ends of a buried perimeter loop wire (not shown) are connected to the LEFT LOOP terminal10and the RIGHT LOOP terminal12during test operations. A GROUND terminal14is presented, which is used to connect either an earth ground rod (also referred to as a ground stake) or a ground coupling wire (neither shown), which may be connected to a similar ground terminal on a cable break detector probe unit (seeFIG.2). An alpha-numeric display16is also provided on the base unit6for presentation of instructions and operational parameters, which are further detailed elsewhere in this disclosure.

Reference is directed toFIG.2, which is a front view drawing of a cable break detector probe unit8according to an illustrative embodiment of the present invention. The probe unit8provides a hand-holdable enclosure with internal electronic circuitry (not shown) and certain user interface components, as follows. A GROUND terminal20is presented, which is used to connect either an earth ground rod (also referred to as a ground stake) or a ground coupling wire (neither shown), which may be connected to the GROUND terminal14of the base unit6(seeFIG.1). Both of a LEFT LOOP illuminator24and a RIGHT LOOP illuminator26are presented for providing visual directional guidance to the user. In the illustrative embodiments, light emitting diodes (LED) are employed as illuminators. A rocker switch28is presented, which rests at a center OFF position, and may be rocked to either of a WIRED position or a STAKED position, as illustrated, to power the probe unit8in one of two modes of operation. This nomenclature corresponds to the type of ground connection that is employed during operation. WIRED mode is appropriate where a ground conductor (not shown) is connected to the GROUND terminal20, and STAKED mode is appropriate where a ground rod that has been staked into soil (not shown) is connected to the GROUND terminal20.

Reference is directed toFIG.3, which is a diagram of a cable break detector system operating in the STAKED mode according to an illustrative embodiment of the present invention. The system consists of a base unit6and a probe unit8, and certain accessories as will be described herein. A buried perimeter loop wire4is normally coupled to a host system2, but is disconnect therefrom during the test procedures discussed herein. Note that the loop wire4has a complete break3in this illustrative embodiment. Such a break3may present infinite resistance, or a resistance so great that it is de facto infinite in value. The opposing ends of the loop wire4are connected to the base unit6LEFT LOOP terminal10and RIGHT LOOP terminal12, as illustrated. Note that the directional references will be used to assist the user in determining which direction the break3is located, and which direction to move about the loop wire4as the test procedure is carried out. The base unit6GROUND terminal14is connected to a ground rod30that is staked into the soil adjacent the base unit6. Note that during test operations, the base unit6injects two electric signals36,38into the two ends of the loop wire4, respectively, through the LEFT LOOP terminal10and RIGHT LOOP terminal12. In the illustrative embodiment, these are square wave signals operating between zero volts and five volts at 125 Hz and 250 Hz, respectively. The frequencies are selected to be low enough to have no FCC conducted or radiated emissions limitation requirements, and also do not traverse moisture well. The 125 Hz and 250 Hz frequencies may be adjusted slightly to avoid the possibility that harmonics or edge conditions that could cause false detections. Other waveforms and other frequencies may be employed effectively as well. It is noteworthy that higher frequencies may couple though damp or wet soil more easily, so frequencies under 1 kHz are generally recommend, but any audio frequency may be effective, and radio frequencies, perhaps greater then 10 kHz may present stay coupling challenges that degrade system testing performance.

FIG.3also illustrates a cable break detector probe unit8. The probe unit8is moved along the length of the loop wire4as the testing procedure commences. A ground rod32is staked into the soil adjacent the test position, and is connected to the GROUND terminal20of the probe unit8. A test probe34is connected to the PROBE terminal22of the probe unit8. At each test position the loop wire is exposed and the tip of the probe34is electrically coupled to a conductor in the loop wire4, to thereby sense and detect one of the two electrical signals36,38emitted by the base unit6. In this manner, the direction of the break3can be discerned by which frequencies are detected and not detected, because the break3prevents one of the frequencies from reaching the test probe34, while the other frequency flows easily through the low resistance loop wire4. The LOOP LEFT illuminator24and LOOP RIGHT illuminator26on the probe unit8indicate to the user from which direction the detected signal is coming, as well as in which direction to move along the loop wire so as to isolate the precise portion of the loop wire4having the break3therein. In practice, the distance along the loop wire4that the user moves is halved on each subsequent test, and this halving very quickly locates the break3, as exponential calculations will quickly reveal to one skilled in the art.

Note inFIG.3that the use of ground rods30,32facilitates quick set-up and movement about the perimeter loop4as the testing and distance-halving operations commence. Of course, the use of ground rods30,32presumes a suitably high ground conductivity such that the voltage swings of the test frequency can be detected, relying on the input impedance of the circuits (not shown) measuring the signal are much greater than the resistivity of the ground rod conductivity path, as will be appreciated by those skilled in the art.

Reference is directed toFIG.4, which is a diagram of a cable break detector system operating in the WIRED mode according to an illustrative embodiment of the present invention. The system consists of a base unit6and a probe unit8, and certain accessories as will be described herein. A buried perimeter loop wire4is normally coupled to a host system2, but is disconnect therefrom during the test procedures discussed herein. Note that the loop wire4has a partial break5in this illustrative embodiment. A partial break5may present a lower resistance than the previously discussed infinite resistance of a complete break, but still substantially higher than the intrinsic resistance of the perimeter loop resistance. The intrinsic loop wire resistance is low, and depends on the length, gauge, and wire material. This will typically be less than thirty ohms. A partial break5may result from a damaged loop wire4conductor, or may present itself with some level of conductance induced by damp soil conditions, soil high in salts, and other factors. Such partial break5resistance may be frequency dependent, decreasing with increasing frequency, which is a reason the present system employee low frequency test signals. The opposing ends of the loop wire4are connected to the base unit6LEFT LOOP terminal10and RIGHT LOOP terminal12, as illustrated. In the WIRED mode, the base unit6GROUND terminal14is connected using ground wire31to GROUND terminal20of the probe unit8, thereby obviating the issues related to ground conductivity and resistance.

During test operations inFIG.4, the base unit6injects two electric signals36,38into the two ends of the loop wire4, respectively, through the LEFT LOOP terminal10and RIGHT LOOP terminal12. The base unit also measure and displays the loop resistance using a micro-ohmmeter circuit, which is more fully discussed hereinafter.

FIG.4also illustrates a cable break detector probe unit8. The probe unit8is moved along the length of the loop wire4as the testing procedure commences. A test probe34is connected to the PROBE terminal22of the probe unit8. At each test position the loop wire is exposed and the tip of the test probe34is electrically coupled to a conductor in the loop wire4, to thereby sense and detect the two electrical signals36,38emitted by the base unit6. In this manner, the direction of the break5can be discerned by which frequency has a stronger signal, because that frequency amplitude will be larger signal in that it is less attenuated than the other frequency, which must pass through the resistance of the break5. The LOOP LEFT illuminator24and LOOP RIGHT illuminator26on the probe unit8indicate to the user from which direction the stronger detected signal is coming, as well as in which direction to move along the loop wire so as to isolate the precise portion of the break3therein. In practice, the distance along the loop wire4that the user moves is halved on each subsequent test, and this halving very quickly locates the break3. Note inFIG.4that the use of a ground wire31requires the task of running the wire and moving it as the test procedure is carried out.

Reference is directed toFIG.5, which is process flow diagram of system operation of a cable break detector system according to an illustrative embodiment of the present invention. This process flow diagram is that of a loop wire break and repair process. The process begins at step40and at step42, the user presses and holds the power/next (“PWR/NXT”) actuator on the base unit for at least two seconds. This action powers the base unit, whose internal processor commences operation. At step44, the processor in the base unit displays a message on the base unit display for the user to disconnect the buried perimeter loop wire from the host system, and then pauses to allow the user to attend to that task. After which, the user presses PWR/NXT. At step46, the display instructs the user to connect the loop wire left and right ends to the LEFT and RIGHT terminals on the base unit, and pauses. Once complete, the user presses PWR/NXT, and the process continues to step48.

At step48inFIG.5, the base unit processor measures the loop resistance using an internal micro-ohmmeter. Note that this resistance may be low, typically less than thirty ohms indicating that there is no break in the loop wire, or it may be higher, near infinite, or infinite indicating the there is a complete break in the loop wire. But more commonly, the resistance may be greater than the thirty ohm threshold, indicating that is a break of some lesser degree than an infinite resistance break. Accordingly, at step48a test of the loop wire resistance is conducted, and if the resistance is less than thirty ohms, indicating there is no break in the loop wire, the base unit processor displays that resistance value, indicating to the user the the loop wire is in good condition, so the test process is complete at step52. On the other hand, if the resistance is greater than thirty ohms at step48, then a break in the loop wire has been detected, and the processor display “BREAK” at step54.

Continuing inFIG.5, at step56, the user stakes a ground rod into the soil adjacent to the base unit and connects that to the base unit GROUND terminal. The user moves to the approximate middle of the perimeter loop wire at step58, and at step60, the user stakes a probe unit ground rod into the soil at that location, and connects that to the probe unit GROUND terminal, and thereby creates a ground conductive pathway between the two units, albeit of unknown earth ground resistance. At step62, the user exposes the loop wire at the chosen test location and connects the test probe tip of the probe unit to the loop wire at that location. At step64, the user presses and holds the STAKED switch of the probe unit and views the LEFT and RIGHT LED illuminators.

At step66inFIG.5, the user views the LED illuminator status, and proceeds as follows. If neither LED is illuminated, then neither of the two test frequency signals emitted by the base unit are being detected by the probe unit, which may indicate a double break in the loop wire, where the test probe may be connected to an unconnected section of the loop wire. In this case, the user moves the test probe location, in either direction they choose, and returns to step60to relocate the probe unit ground rod and repeats the foregoing test steps. On the other hand, at step66, if either one of the LEFT or RIGHT LEDs is illuminated, then the process continues to step70, where the user moves in the indicated direction approximately one-half the distance to the base unit to repeat the test. However, if the distance moved is short at step72, the user may simple decide to replace that section of wire, by preparing it at step74. If the length of loop wire is too long to replace at step72, then the process repeats by going to step60, driving the probe unit ground rode and repeating the foregoing test sequence.

Now, returning to step66inFIG.5, if both LEDs are illuminated, that indicates that both test frequencies are being detected by the probe unit, so the test is inconclusive. This is probably due to the poor earth ground path between the base unit and the probe unit, so the process continues to step78where the user connects a direct wire ground conductor between the base unit and the probe unit, which assures a low resistance ground path between the two units. Once complete, the process continues to step80where the users presses and holds the “WIRED” actuator switch to conduct a wired ground test procedure. At step82, either one of the LEFT or RIGHT LEDs will illuminate, indicating the direction of movement for the subsequent test probe connection, which the users follows at step84. However, if the distance moved is short at step86, the user may simple decide to replace that section of loop wire, by preparing it at step74. If the length of loop wire is too long to replace at step86, then the users connects the test probe tip to the loop wire at that location at step88, and returns to step80to repeat the forgoing WIRED test sequence. In either case, once the loop wire is repaired at step74, the repair process is complete at step76.

Reference is directed toFIG.6, which is a functional block diagram of a cable break detector base unit6according to an illustrative embodiment of the present invention. The base unit6operates under control of a micro controller96, as are known to those skilled in the art to incorporate digital logic level inputs and outputs, as well as analog to digital conversion circuits and interfaces to parallel and serial communications external devices, such as an alpha-numeric display16. The controller96has a crystal98as a clock reference. In this illustrative embodiments, a battery90is coupled through an on/off switch92to a power supply circuit94, which provides a Vcc power supply to the base unit6, typically at five volts DC. An annunciator100, which is a “buzzer” is also driven by the controller96. A loop wire4, which has a break3along its length, is connected to LEFT LOOP10and RIGHT LOOP12terminals. The LEFT LOOP terminal10is coupled to a signal port114in the controller96, which is operable to transmit a first test frequency36into the loop wire4from the LEFT LOOP terminal10. Similarly, the RIGHT LOOP terminal12is coupled to a signal port112in the controller96, which is operable to transmit a second test frequency38into the loop wire4from the RIGHT LOOP terminal12. The test frequency signals36,38are square waves that have an amplitude equal to Vcc, and frequencies of 125 Hz and 250 Hz, respectively, in the illustrative embodiment. During test procedures, these two signals36,38are driven alternatingly for short durations, for example 250 ms.

FIG.6illustrates another feature of the base unit6capabilities, and that is the measurement of the loop wire resistance using a micro-ohmmeter circuit. The micro-ohmmeter comprises a current source102, which outputs a known current “I-ohm” from Vcc. The output voltage “V-ohm” of the current source102is coupled to an analog to digital converter input port108of the controller96, such that the controller can measure that voltage. Having both I-ohm and V-ohm, the calculation of the resistance by the controller96is accomplished using Ohm's Law, yielding a micro-ohmmeter value reading. The current flow path of I-ohm is from Vcc, through MOSFET104, the RIGHT LOOP terminal12, the loop wire4, the LEFT LOOP terminal10, and MOSFET106, which is coupled to ground. As such, the ability to measure loop resistance is controlled by switching the two MOSFETs104,106between conductive and non-conductive states. It is noteworthy that the measurement of loop resistance is also multiplexed in time with the coupling of test signals36,38into the loop wire4. This is necessary because either of MOSFETs104,106in the conductive states will load the respective terminals10,12and prevent the test signals36,38from flowing into the loop wire4.

Reference is directed toFIG.7, which is schematic diagram of a cable break detector base unit6according to an illustrative embodiment of the present invention. This schematic diagram presents a specific circuit design in an illustrative embodiment, which comprises the following component specifications, and which are identified in the drawing figure with the references in the following Table 1:

InFIG.7, the controller U4is coupled to a sixteen character OLED alphanumeric display that is driven by serial interface, SCL, SDA in the controller U4, which serves to present operational parameters and instructions to a user. In the illustrate embodiment, the display16is an OLED 128×64 display, as are provided by multiple manufacturer, and are known to those skilled in the art. It is useful to incorporate a display the is sunlight readable. A momentary contact switch18“PWR/NXT” is input to the controller U4and serves to turn on DC power to the base unit6and to sequence through operational steps. A six volt battery pack90provides power to the base unit, which is switch by Q4and Q5to drive voltage regulator U5providing a five volt DC Vcc source to the entire circuit.

FIG.7illustrates a micro-ohmmeter circuit comprising an LM317voltage regulator102configured as a current source outputting “I-ohm” amperes. “V-ohm” is the current source output voltage sensed using analog port PDO, labeled as108, in the controller U4. In the illustrative embodiment, R1is set to twelve ohms and Vcc is five volts, thius the current source102delivers approximately one hundred milliamps through the circuit. Power HEXFET Q2is switched by port PD6, labeled as110, of the controller U4, and is used to deliver “I-ohm” to the RIGHT LOOP terminal12. Similarly, power HEXFET Q7is switched by port PD3, labeled as110, of the controller U4, and is used to couple “I-ohm” from the LEFT LOOP port10to ground, as illustrated. Power HEXFETS are employed because their higher voltage and current carrying capabilities accommodate real-world exposure to the environment more reliably than similar low paper devices. With this circuit, the loop wire4and break3resistance can be measure accurately. Note that GROUND terminal14provides coupling between the base unit6chassis ground and earth ground when a ground rod (not shown) is employed.

InFIG.7, the first test frequency36is output from controller U4port PD4, labeled as114, and is drive into the LEFT LOOP terminal by MOSFETs Q5and Q1. Similarly, the second test frequency38is output from controller U4port PD2, labeled as112, and is driven into the RIGHT LOOP terminal by MOSFETs Q3and Q6.

Reference is directed toFIGS.8A and8B, which are schematic diagrams of a cable break detector probe unit8, and an amplifier and filter circuit120, respectively, according to an illustrative embodiment of the present invention. These schematic diagrams present specific circuit designs in an illustrative embodiment, which comprises the following component specifications, and which are identified in the drawing figure with the references in the following Table 2:

FIG.8Aalso illustrates the loop wire4, with break3, that is connected to the LEFT LOOP terminal12and RIGHT LOOP terminal14of the base unit (not shown). The loop wire test probe34is attached to the loop wire4and also connected to the PROBE terminal20of the probe unit8. The GROUND terminal22of the probe unit8may either be connected to an earth ground rod128or to the base unit chassis130via a solid ground conductor, as described hereinbefore.

The probe unit8inFIG.8Aemployees the same micro controller U4as the base unit, primarily for development and parts inventory commonality. The controller U4provides digital inputs and outputs for logic level control, as well as analog to digital convertor inputs for voltage measurement purposes. A crystal124provides a clock reference. LEFT and RIGHT LEDs24,25for driven by the controller U4to provide output to the user. Power is supplied by a six volt battery pack122, which is switch into circuit by the rocker switch28, having a center-off position as well as both STAKED and WIRED positions selectable by the user. In either of these positions, power is coupled to voltage regulator U2to produce Vcc at five volts DC. Inputs D6and D7of controller U4inform as to which switch position the user has selected.

The STAKED/WIRED switch28also switches the PROBE terminal20through different circuits prior to input to the controller U4,121. R10, a ten ohm resistor and D3, a zener diode, clamp the probe signal to approximately five volts before being switched. In the WIRED mode, the probe is loaded with R8, a thirty-three ohm resistor, and is then coupled to both a digital input D4, labeled as123, and an ADC input A0, labeled as125, to the controller121. The signal is also coupled to an amplifier and filter circuit120through C6and R2. This is useful so that when the LEFT and RIGHT LEDs24,26, are illuminated, in accordance with the greater signal detection amplitude on A0,125, after the signal has been loaded with R8(thirty ohms) the signal may drop below a logical one signal level at input D4,123, and the detection may no longer function reliably. The signal coupled through R2and C6enables the system to reliably detect partial breaks with higher resistance values. In this manner, the controller is enabled to read the PROBE signal in plural level formats. If the wired ground connection to the base unit is low resistance (as it should be), and if the PROBE34is connected without the break3in line, then the PROBE signal can be sensed with logic level input D4. If not, then either analog input A0can read the actual voltage level to compare levels between the first and second test frequencies, or that level can be amplified to above logic levels and read by a digital input (D5). The amplifier and filter120will be more fully discussed hereinafter.

When the STAKED/WIRED switch28is set to the STAKED position, then it is anticipated that the ground path has some added resistance. This results in a signal level that is lower than digital logic levels, so amplifier and filter circuit120is employed to raise the levels above logic level, which can be sensed by digital input D5. In any of these scenarios, the signal input to the controller U4is a sampling of the first or second test frequencies present on the loop wire4, and the controller U4is programed to determine each signal's frequency and presence at the input, and also to compare signal levels at input A0when that is the determining factor as to which signal is greater in amplitude, thereby establishing the location of the break3in the loop wire4.

Note further that when the STAKED/WIRED switch28is set to STAKED, the signal from the probe34is heavily amplified and applied to the probe unit controller U4for sampling. Each of the two test frequencies is detected in real time and the associated LEFT LED and & RIGHT LED are illuminated to indicate this detection. Since the majority of loop wire4breaks3are complete in nature, such that the resistance across the break3is in mega-ohms range, the STAKED mode can be used quickly to find those breaks without the extra time needed to run an independent ground wire between the base unit and the probe unit. If the Base unit displays “BREAK” and the STAKED mode shows both directions are are being receved, a partial break is suspected and the WIRED mode should be employed. When STAKED/WIRED switch28is set to WIRED, the direct signal from the probe34is applied across a small resistance, R8, to ground prior to being sampled by the controller U4. By reading the analog level of the two differing frequency signals coming from the base unit, when subjected to this load, the controller can show which signal is likely poor using the LEFT24and RIGHT26LEDs.

The amplifier and filter circuit120inFIG.8Ais detailed inFIG.8B. U1is an operational amplifier in two stages with a total gain of approximately110dB. The gain level is selected to ensure that the amplified PROBE signal reaches digital logic levels. The filter, comprising R20and C5is a first order low-pass filter with half-power point at about 1 kHz, to reduce higher frequency noise. The topology of the filters will be recognized by those skilled in the art.

Reference is directed toFIG.9, which is a process flow diagram of a cable break detector base unit operation according to an illustrative embodiment of the present invention. The process begins at step130when the power is switched on. At step132, the LEFT LOOP terminal, RIGHT LOOP terminal, and micro-ohmmeter coupling FETs are set to the high impedance state to unload all circuits. At step134, the first test frequency (“F1”) is coupled to the RIGHT LOOP terminal for 250 ms and then switched off. The duration is not critical, and is selected of reliable operation without sluggish behavior of the user experience. At step136, the second test frequency (“F2”) is coupled to the LEFT LOOP terminal for 250 ms and then switched off. This is followed by step138where both of the micro-ohmmeter FETs are turned on, and the loop wire resistance is measured. As will be described below, this sequence of F1, F2, resistance measurement is repeated as long as the power remains on in the base unit.

At step140inFIG.9, the controller tests for the loop resistance, and if that resistance is less than a predetermined threshold, thirty ohms in this embodiment, then flow continues to step142where a test of a “BREAK” variable is conducted. For now, assuming the state is NO (variable set to false), then flow continues to step146where the controller writes the actual loop resistance to the base unit display, which is a value lower than the thirty ohm threshold, indicating that there is no break in the loop wire, and also informs the user as to what the “good” resistance value of the loop wire is. At step152, if the power remains on, flow recirculates to step132to repeat. Going back to step142, if the BREAK variable is set to YES (variable set to true), then the loop resistance has changed from above the resistance threshold to below the resistance threshold, indicating that the break in the loop wire has been successfully repaired, and an annunciator in the base unit is sounded to alert the user, and the state of the variable is reset to false.

Again referring to step140inFIG.9, if the loop resistance is greater than the threshold level, then this indicates there is a break on the loop wire, so process flow continues to step148. At step148, the word “BREAK” is displayed on the base unit to advise the user that the loop wire has a break, reducing its expected conductivity, and that corrective action is required. In alternative embodiment, the actual resistance value may be displayed. However, considering the user interface process ofFIG.5, it can be appreciated that simply informing the user that a break exists is sufficient, and provides a more informed user experience. At step150, the BREAK variable is set to true, and the process continues to step152, the test for power. If power remains on, flow recirculates to step132to repeat, and if power is off, the process ends at step154. Thus it can be appreciated that as long as the base unit power is on, the first and second test frequencies are repeatedly transmitted into the two ends of the loop wire, and the loop wire resistance is repeatedly tested, and if the loop wire is repaired during that time, an enunciator is sounded to advise the user that the repair has been accomplished.

Reference is directed toFIG.10, which is a process flow diagram of a cable break detector probe unit operation according to an illustrative embodiment of the present invention. With the base unit connected to the loop wire, and turned on to transmit the two test frequencies, F1and F2, into the two ends of the loop wire, the user operates the probe unit to locate the break in the loop wire, and the probe unit operates in accordance with the process ofFIG.10. The process begins at step160and proceeds to step162, where one of the two power-on switch positions, WIRED or STAKED, is selected. Of course, if neither is selected, the process ends at step184. If WIRED is selected at step162, then the power to the probe unit comes on at step164, and the PROBE terminal of the probe unit is coupled to both digital and analog input ports on the probe unit controller, for sampling of the test signals. At step168, the test frequencies are detected by the digital input and measured for relative amplitude by the analog input. At step170, the relative amplitudes are compared. If the F2test signal has the highest amplitude, then the LEFT LED is illuminated, indicating to the user to move in the opposite direction along the loop wire to isolate the break location, and the flow returns to step162, to repeated the break location narrowing process. In the other hand at step170, of the F1test signal has the higher amplitude, then flow continues to step182, where the RIGHT LED is illuminated, indicating to the user to move in the opposite direction along the loop wire to isolate the break location, and the flow returns to step162, to repeated the break location narrowing process.

InFIG.10, if the STAKED switch position is applied at step162, the flow continues to step174where the probe unit is powered on, and PROBE terminal is coupled to the amplifier input port of the controller. By amplifying the signal, it is assured that the peak level in the test single square waves will be greater than the logic level ‘ON’ threshold of the controller. At step178, the controller tests from the presence of the F1or F2signals. If F1is detected at step180, then the RIGHT LED is illuminated at step182, indicating to the user to move in the opposite direction along the loop wire to isolate the break location, and the flow returns to step162, to repeated the break location narrowing process. On the other hand, at step180, if F2is detected, then the LEFT LED is illuminated at step172, indicating to the user to move in the opposite direction along the loop wire to isolate the break location, and the flow returns to step162, to repeated the break location narrowing process. This testing and moving process continues until the break is repaired and the annunciator in the base unit sounds.

InFIG.10, note that the left LED and right LED are illuminated to indicate the direction to and or from the break in the loop wire based on detection and measurement of the two test tone frequencies. Whether and LED is turned on or off to indicted the presence of a test tone, or whether an LED is turned on or off to indicate the direction of movement, is an arbitrary design choice. At its essence, the LED status are indicators to the user as to what the test status is, and in which direction to move about the loop wire to pursue the distance-halving operations aimed at isolating the loop wire break. The indication is arbitrarily defined, and it is only significant that the user be informed as to what the indication means. For example, an LED in the on state could mean that the test frequency from that direction was detected, or, it could mean that that is the direction in which to move. In another embodiment, dual color LEDs could be employed, for example, green mean good signal and red means no signal, or to move in the red direction, etc. The indication could also be presented on an alphanumeric display, or perhaps even indicated with different audible tones, and so forth. The key design goal is to inform the user as to which direction they should move in the distance-halving operation, as well as an indication when the break has been successfully repaired.