Abstract:
Diagnosing electrical circuit faults can be accomplished with a variety of tools. Voltmeters are frequently used to measure voltage to determine whether a short is present, but are not well-suited for finding intermittent faults caused by corroded connectors or excessive voltage drop under operating loads. Measuring a static voltage without load using a voltmeter can yield misleading results. A diagnostic tool that is simple to use and that yields a definitive result is preferred in certain applications such as automotive electrical system diagnosis due to the varying skill level of technicians and the variation in field conditions in automotive shops. A simple, inexpensive diagnostic tool that can be used with minimal or no training allows rapid diagnosis of circuit faults that result from a the inability of a measured circuit to supply a minimum current at a minimum voltage.

Description:
COPYRIGHT STATEMENT 
       [0001]    All of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to a diagnostic tool that can measure voltage under controlled conditions and vary a point load in order to determine the capacity of a given circuit to operate under typical or extreme conditions rather than ideal conditions. 
         [0004]    2. Background 
         [0005]    A conventional voltmeter measures voltage at a given point in a circuit using a high-impedance input. The goal with such a voltmeter is to determine the voltage present at the measured contact point without imposing any significant load on the point. A high-impedance input (relative to the impedance of the point contact) ensures that the voltmeter measures the point contact without changing the current flow within the measured circuit. 
         [0006]    In certain applications however it is important to be able to measure a circuit&#39;s ability to deliver a minimum or threshold voltage under a specified constant or variable load that provides an indication of the health of the circuit. While such diagnostic tools may exist in certain fields, such tools are often expensive or difficult to use. One example of such a diagnostic tool is a curve tracer for semiconductor (active) and passive devices. A curve tracer can load an active or passive device with a varying voltage to induce a range of currents in such devices and display a graph of voltage versus current that provides the characteristics of the measured device. The use of a curve tracer requires some training and user expertise in the types of devices being measured. Curve tracers are relatively expensive diagnostic tools, and are generally designed for laboratory use only. Therefore, a need exists for improvement in the field of diagnostic tools that are inexpensive and require no user training, expertise or special training. 
         [0007]    In the case of automobile electrical systems, it is increasingly common to find control units and actuators that are switched on and off with pulse-type signals rather than direct connections to a switch that provides a driving current. It is difficult to diagnose a fault in such a system because although a suitable voltage is typically present when the system is energized, it is not possible to determine whether a suitable current can be delivered to the control unit or actuator under an actual load, or whether a required minimum operating voltage will be present under a worst case current load condition. A digital voltmeter cannot be used in such an instance because such a device cannot respond as quickly as the circuit is switched, and may therefore indicate suitable average voltage while the necessary minimum voltage is not present under a momentary pulse-type switching condition. The diagnostic tool of the present invention can initiate a pulse-type load and measure the voltage level during the pulse-type load, as well as the available current capability of the measured circuit when the measured voltage drops to a pre-determined threshold voltage. 
         [0008]    3. Description of Related Art 
         [0009]    There are numerous types of diagnostic tools used to measure voltages in circuits including voltmeters, oscilloscopes, curve tracers, logic analyzers, and the like. A simple voltmeter allows a user to select a voltage range and apply test leads to the circuit to be measured. Voltmeters are high-impedance devices intended to measure a point contact without loading the measured circuit, since circuit loading can cause the circuit characteristics to change and thereby yield an incorrect voltage reading. A voltmeter is relatively simple to use, but does require the user to apply the test leads to the point contact as well as a reference point (often a ground or zero voltage reference, but also a secondary point contact). All voltmeters can measure a constant voltage, and some can measure a time varying voltage such as 50/60 cycle alternating current. However, the measurement of a time varying voltage requires that the voltmeter be optimized for a known time varying voltage such as those present in ordinary household sinusoidal alternating current circuits. An oscilloscope allows a user to measure a constant or time varying voltage and display the result in a graphic format. Oscilloscopes also use high impedance inputs in order to measure circuit voltages without loading the measured circuit. A curve tracer can be used to measure the electrical characteristics of a device by varying an input voltage and then displaying the result graphically. 
         [0010]    While each of the above diagnostic tools are useful in varying instances, the cost of the device, limited diagnostic ability, and need for varying degrees of user skill limits the usefulness of such tools in certain applications. 
         [0011]    The most cost-effective diagnostic tool for measuring a voltage at a point contact is generally a voltmeter. Prior art voltmeters are effective in the instance where a voltage measurement without load is desired. However, if a user desires to measure a point contact under a varying load, or needs to determine the load under which the measured voltage drops below a predetermined minimum value, a more sophisticated diagnostic tool is required. However, there currently exists no diagnostic tool that combines the ease of use of a conventional voltmeter with the ability to automatically measure a voltage under a varying load and determine the load at which the point contact measurement crosses a minimum value. 
         [0012]    In one application of a diagnostic tool of the present invention, an automotive mechanic can use the diagnostic tool to measure a point contact voltage and receive an audible or visual indication from the diagnostic tool that the desired minimum voltage is present upon the automatic application of a predetermined minimum circuit load. 
         [0013]    The diagnostic tool of the present invention provides for a small, relatively inexpensive device that can be used by an unskilled user to determine whether a point contact voltage can be delivered through the measured circuit under a given load. An objective of the present invention therefore is to be able to automatically measure such a point contact voltage and determine the load at which the voltage drops below a specific or predetermined value. 
       SUMMARY OF THE INVENTION 
       [0014]    The diagnostic tool of the present invention accomplishes the above objectives in the manner described below. 
         [0015]    In one embodiment of the present invention, the diagnostic tool comprises a handheld device with a pigtail lead that can be attached to a ground or other voltage reference point contact, a probe for contacting the desired point contact to be measured, a button for initiating a test measurement, a microprocessor or microcontroller for running a test measurement sequence, voltage and current measuring elements, an element that can apply a time-varying load to the circuit under test, and a display that yields a diagnostic result. The display can show an indication that the diagnostic device is properly calibrated and ready for use, the measured voltage difference between the probe and the pigtail lead, an indication that the diagnostic test is being run, and an indication that the measured circuit passed a load test. Such a diagnostic tool can be powered from the circuit being measured, or by an internal battery. 
         [0016]    In another embodiment of the present invention, the diagnostic tool described above may also comprise a non-volatile memory for storing test results and an output port for exporting test results stored in such non-volatile memory. 
         [0017]    In another embodiment of the present invention, the diagnostic tool may be embedded in a comprehensive vehicle diagnostic system that simultaneously probes a plurality of point contacts in an electrical system, and that automatically measures a plurality of circuits simultaneously when such a comprehensive vehicle diagnostic system is connected to a vehicle test/diagnostic connector. 
         [0018]    It is an objective of the diagnostic tool of the present invention to be able to automatically determine voltage drop across measured elements of an electrical circuit. It is a further objective of the present invention to be able to automatically determine voltage drop across measured elements of a motor vehicle electrical system thereby determining whether a given circuit element or device is defective or whether such circuit element or device “tests bad” because the electrical system is incapable of delivering adequate current and/or a minimum required voltage. 
         [0019]    It is recognized that a variety of form factors may be employed for the diagnostic tool disclosed herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    One or more preferred embodiments of the present invention now will be described in detail with reference to the accompanying drawings, wherein the same elements are referred to with the same reference numerals. 
           [0021]      FIG. 1  illustrates an exploded view of the diagnostic tool in accordance with one or more preferred embodiments of the present invention; 
           [0022]      FIG. 2   a  illustrates a top view of the diagnostic tool in accordance with one or more preferred embodiments of the present invention; 
           [0023]      FIG. 2   b  illustrates a side view of the diagnostic tool in accordance with one or more preferred embodiments of the present invention; 
           [0024]      FIG. 3  illustrates a schematic diagram of the diagnostic tool of  FIG. 1 ; 
           [0025]      FIG. 4  is a flowchart illustrating a process for measuring a point voltage and determining whether a circuit can supply a given current, all in accordance with one or more preferred embodiments of the present invention; and 
           [0026]      FIG. 5  is a flowchart illustrating a process for determining whether a circuit is capable of supplying a given current while maintaining a given minimum voltage, all in accordance with one or more preferred embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    As a preliminary matter, it will readily be understood by one having ordinary skill in the relevant art (an “Ordinary Artisan”) that the present invention has broad utility and application. Furthermore, any embodiment discussed and identified as being “preferred” is considered to be part of a best mode contemplated for carrying out the present invention. Other embodiments also may be discussed for additional illustrative purposes in providing a full and enabling disclosure of the present invention. Moreover, many embodiments, such as adaptations, variations, modifications, and equivalent arrangements, will be implicitly disclosed by the embodiments described herein and fall within the scope of the present invention. 
         [0028]    Accordingly, while the present invention is described herein in detail in relation to one or more embodiments, it is to be understood that this disclosure is illustrative and exemplary of the present invention, and is made merely for the purposes of providing a full and enabling disclosure of the present invention. The detailed disclosure herein of one or more embodiments is not intended to, nor is to be construed to, limit the scope of patent protection afforded the present invention, which scope is to be defined by the claims and the equivalents thereof. It is not intended that the scope of patent protection afforded the present invention be defined by reading into any claim a limitation found herein that does not explicitly appear in the claim itself. 
         [0029]    Thus, for example, any sequence(s) and/or temporal order of steps of various processes or methods that are described herein are illustrative and not restrictive. Accordingly, it should be understood that, although steps of various processes or methods may be shown and described as being in a sequence or temporal order, the steps of any such processes or methods are not limited to being carried out in any particular sequence or order, absent an indication otherwise. Indeed, the steps in such processes or methods generally may be carried out in various different sequences and orders while still falling within the scope of the present invention. Accordingly, it is intended that the scope of patent protection afforded the present invention is to be defined by the appended claims rather than the description set forth herein. 
         [0030]    Additionally, it is important to note that each term used herein refers to that which the Ordinary Artisan would understand such term to mean based on the contextual use of such term herein. To the extent that the meaning of a term used herein—as understood by the Ordinary Artisan based on the contextual use of such term—differs in any way from any particular dictionary definition of such term, it is intended that the meaning of the term as understood by the Ordinary Artisan should prevail. 
         [0031]    Furthermore, it is important to note that, as used herein, “a” and “an” each generally denotes “at least one,” but does not exclude a plurality unless the contextual use dictates otherwise. Thus, reference to “a picnic basket having an apple” describes “a picnic basket having at least one apple” as well as “a picnic basket having apples.” In contrast, reference to “a picnic basket having a single apple” describes “a picnic basket having only one apple.” 
         [0032]    When used herein to join a list of items, “or” denotes “at least one of the items,” but does not exclude a plurality of items of the list. Thus, reference to “a picnic basket having cheese or crackers” describes “a picnic basket having cheese without crackers”, “a picnic basket having crackers without cheese”, and “a picnic basket having both cheese and crackers.” Finally, when used herein to join a list of items, “and” denotes “all of the items of the list.” Thus, reference to “a picnic basket having cheese and crackers” describes “a picnic basket having cheese, wherein the picnic basket further has crackers,” as well as describes “a picnic basket having crackers, wherein the picnic basket further has cheese.” 
         [0033]    Referring now to the drawings, one or more preferred embodiments of the present invention are next described. The following description of one or more preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its implementations, or uses. 
         [0034]      FIG. 1  illustrates an exploded view of the diagnostic tool in accordance with one or more preferred embodiments of the present invention. As shown therein, the electrical circuit diagnostic tool  100  of the present invention includes two case halves  10  and  20 , and a circuit board  30 . The bottom case half  10  shows a first opening  11  for a measurement probe  12  and a second opening  13  for a pigtail-type lead wire  14 , as well as bosses  15  for accepting screws  16  when assembled to the top case half  20 . The top case half  20  also shows a first opening  21  for a probe  14 , a second opening  23  for a pigtail-type lead wire  14 , a third opening  24  for the bezel of a display element  31 , a fourth opening  25  for a push button  32 , as well as holes  26  (with bosses) for passing screws  16  through the top case half  20  for use in engaging bosses  15  to secure the top case half  20  to the bottom case half  10 . The circuit board  30  shows a display element  31  and a button  32 . The probe  12  and the pigtail-type lead  14  are mechanically and electrically affixed to the circuit board  30 . The circuit board  30  is assembled with the bottom case half  10  by being positioned over bosses  15  and fastened securely between the bosses  15  of the bottom case half  10  and the bosses  26  of the top case half  20  with screws  16 . 
         [0035]      FIGS. 2   a  and  2   b  illustrate a top and side view, respectively, of the electrical circuit diagnostic tool  100  in accordance with one or more preferred embodiments of the present invention.  FIG. 2   a  shows a pigtail-type lead wire  14  with an attached alligator-type clip  40  passing through one side of the assembled bottom and top case halves of the diagnostic tool, and a measurement probe  14  passing through one end of the diagnostic tool. A display element  31  is visible from the top elevation and displays the operational status and measurements of the diagnostic tool of the present invention. A button  32  is accessible from the top elevation of the diagnostic tool.  FIG. 2   b  illustrates a side view of the diagnostic tool in accordance with one or more preferred embodiments of the present invention. 
         [0036]      FIG. 3  illustrates a schematic diagram  300  of the diagnostic tool in accordance with one or more preferred embodiments of the present invention. As shown therein, the apparatus illustrated in schematic diagram  300  comprises an active circuit element  312 , a passive load element  303 , a microcontroller or microprocessor  340 , a display  320 , a button  330 , a power storage element  315 , a minimum voltage detector  314 , a voltage measurement element  313 , a digital-to-analog converter  311 , and a voltage measurement element  310 . 
         [0037]    In order to measure a voltage and the capability of a circuit to deliver a given current at a given voltage using an apparatus embodied in the present invention, a contact  302  is connected to a reference point or to a ground, and a circuit probe  301  is connected to the circuit at the point to be measured. A fixed load element  303  such as a resister of known value and an active device element  312 , is suitably enabled to apply a varying load to the circuit being measure through circuit probe  301 . In one embodiment of the present invention, active device element  312  is a MOSFET transistor. A microprocessor  340  is suitably enabled to accept several inputs as described below, as well as to send a digital signal to a digital-to-analog converter  311 , and a message to a display device  320 . In a further embodiment of the present invention, a microprocessor  340  is suitably enabled to store the voltage values at inputs  341  and  345  for later retrieval and analysis. A digital-to-analog converter  311  sends an analog output voltage that is applied to an active circuit element  312 , thereby controlling the current that is allowed to flow through passive load element  303  and the current that is thereby drawn from the circuit being measured. A button  330  is used to initiate a measurement sequence pre-programmed and stored in the non-volatile memory of microprocessor  340 . A circuit element  315  is an energy storage element such as a capacitor capable of storing sufficient power derived from point contact  301  to power microprocessor  340  through an input  343  while a test measurement is being made. A circuit element  314  is a minimum voltage detector that provides a signal to input  342  of microprocessor  340  when a minimum threshold voltage is detected. A circuit element  313  is a voltage measurement device that provides a real-time voltage measurement to microprocessor input  341 . A voltage measurement element  310  determines the voltage present across a known load element  303 , and thereby can determine the instantaneous current flowing out of a point contact  301 . The voltage present across a known load element  303  is sent to input  345  of microprocessor  340 , which in turn can be used to determine the current load supplied by the measured circuit. 
         [0038]    Pressing a button  330  initiates a pre-programmed test sequence stored in microprocessor  340  that generates a digital signal on output pin  344  of microprocessor  340 . This digital output signal is presented to the input of a digital-to-analog converter  311 , which in turn presents an analog output voltage to a circuit element  312 . In one embodiment of the present invention, circuit element  312  is a MOSFET and the analog output voltage of digital-to-analog converter  311  is connected to the gate of the MOSFET, thereby controlling the current that is drawn from the point contact  301 . As the pre-programmed test sequence progresses, the microprocessor  340  provides a digital output signal on output  344  that ramps up over time, thereby causing the digital-to-analog converter  311  to apply a continuously ramping analog voltage to the gate of MOSFET  312 , which in turn results in a continuously ramping current draw on the point contact  301 . 
         [0039]    A voltage measurement circuit element  310  measures a voltage on the load side of circuit element  303 , and presents this voltage value to microprocessor input  345 . The microprocessor  340  is suitably enabled to determine the current drawn from a point contact  301  by comparing the voltage differential between the microprocessor inputs  345  and  346  and determining the current drawn through known circuit load element  303 . The current is measured at the moment that the microprocessor  340  senses that the pre-determined minimum voltage is present at the point contact  301  as determined by the voltage measurement element  313 . If the minimum required current is sensed before the voltage sensed at point contact  301  drops below the pre-determined reference voltage, the measured circuit is deemed to have passed the test and the microprocessor  340  sends an appropriate signal to a display element  320 . The microprocessor  340  is suitably enabled to stop the test once it is determined that the circuit passes the test, or it can continue to ramp the current draw until such time as the pre-determined minimum voltage measured at the contact point  301  is determined by the minimum voltage detector element  314 . An appropriate signal to be displayed on a display element  320  can be the word “pass” or the like, or it can merely display the measured current at the time the pre-determined minimum voltage is sensed at point contact  301 . 
         [0040]      FIG. 4  is a flowchart illustrating a process  400  for measuring a point voltage and determining whether a circuit can supply a given current, all in accordance with one or more preferred embodiments of the present invention. The process  400  can be used to test the condition of a circuit by determining the capability of a measured point contact to supply a given current under load while maintaining a pre-determined minimum voltage. The process  400  begins at process step  401  where a self-test routine is automatically run in the presence of adequate voltage at the measured point contact. The process then proceeds to step  402  where the process measures the voltage present at a point contact under no load and displays the measured voltage on a display device or other display indicator. At step  405 , the process determines whether a button is pushed to initiate a test sequence. If not, the process loops back to step  402  and the measured voltage continues to be displayed. If the button is pushed, the process proceeds to step  415  where the process determines whether a pre-determined minimum voltage is present at the point contact being measured. If such minimum voltage is not present at the point contact, the process loops back to step  402  where the measured voltage continues to be displayed and the process again proceeds to step  405  as above. 
         [0041]    If the process determines at step  415  that a pre-determined minimum voltage is present at the point contact, the process proceeds to step  420  where the process applies an incremental increase to the current load on the point contact. The process then proceeds to step  430  where the process measures the voltage at the point contact and determines if the voltage continues to exceed the pre-determined minimum voltage. If so, the process loops back to step  420  where the current load is increased incrementally. The loop of process steps  420  and  430  continue until such time as step  430  determines that the voltage at the point contact no longer exceeds the pre-determined minimum voltage, at which time the process proceeds to step  440 . 
         [0042]    At step  440 , the process measures the current being drawn from the measured circuit, and stores the value of the measured current load in a memory, and the process drops the current load on the point contact to zero. The process then proceeds to step  450  where the stored value of the measured current load is displayed. At step  460 , the process clears the stored value of the measured current load, and the process loops back to step  401  and the process  400  repeats until an adequate voltage is no longer present at the measured point contact. 
         [0043]    In another embodiment of the present invention, the process  400  may modified to store each voltage measured at step  402  and the corresponding load at step  420  for later retrieval and analysis. 
         [0044]      FIG. 5  is a flowchart illustrating a process  500  for a process for determining whether a circuit is capable of supplying a given current while maintaining a given minimum voltage, all in accordance with one or more preferred embodiments of the present invention. The process  500  can be used to test the condition of a circuit by determining the capability of a measured point contact to supply a given current under load while maintaining a pre-determined minimum voltage. The process  500  begins at process step  501  where an initial voltage measurement is made. The process then proceeds to step  502  when a button is pushed to initiate a test sequence. At step  505 , the process measures the voltage present at a point contact and measures a load current being drawn from such point contact. The process proceeds to step  510  where the measured voltage is displayed on a display device. The process then proceeds to step  515  where the process determines whether a pre-determined minimum voltage is present at the point contact. If such minimum voltage is not present, the process proceeds to step  540  where a message is generated to indicate that the minimum voltage is not present and the test has failed. The process then proceeds to step  560  where the status of the test is displayed on a display device, and then the process  500  ends. 
         [0045]    If the process  500  determines at step  515  that a pre-determined minimum voltage is present at the point contact, the process then proceeds to step  520  where the process determines if a pre-determined minimum current can be drawn from the point contact. If the pre-determined minimum current is not being drawn from the point contact, the process proceeds to step  530  where the process increases the current load drawn from the point contact. The process then returns to step  505  and continues. If the process determines at step  520  that a pre-determined minimum current is being drawn from the point contact, the process proceeds to step  550  where a message is generated to indicate that the minimum voltage is present at the time the pre-determined minimum current is being drawn from the point contact and the circuit has passed the test. The process then proceeds to step  560  where the status of the test is displayed on a display device, and then the process ends. 
         [0046]    In another embodiment of the present invention, the process  500  may modified to store each voltage and current measured at step  505  for later retrieval and analysis. 
         [0047]    Based on the foregoing description, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those specifically described herein, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing descriptions thereof, without departing from the substance or scope of the present invention. 
         [0048]    Accordingly, while the present invention has been described herein in detail in relation to one or more preferred embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purpose of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended to be construed to limit the present invention or otherwise exclude any such other embodiments, adaptations, variations, modifications or equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.