Abstract:
An apparatus for measuring electrical parameters for an electrical system measures a first and second parameters of the electrical system between connections to the electrical system. A processor determines a third electrical parameter of the electrical system as a function of the first parameter and the second parameter.

Description:
[0001]     The present application is a Divisional of and claims priority of U.S. patent application Ser. No. 10/656,526, filed Sep. 5, 2003, the content of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to the measurement of electrical parameters of a vehicle electrical system. More specifically, the present invention relates to measuring an electrical parameter of an electrical system of a vehicle through the use of multiple measurements.  
         [0003]     Electrical systems, such as those which are used in automotive vehicles, consist of a number of discreet components or systems which are interconnected. Techniques for measuring and utilizing parameters, such as dynamic parameters, of electrical systems are shown and disclosed in U.S. Pat. No. 3,873,911, issued Mar. 25, 1975, to Champlin; U.S. Pat. No. 3,909,708, issued Sep. 30, 1975, to Champlin; U.S. Pat. No. 4,816,768, issued Mar. 28, 1989, to Champlin; U.S. Pat. No. 4,825,170, issued Apr. 25, 1989, to Champlin; U.S. Pat. No. 4,881,038, issued Nov. 14, 1989, to Champlin; U.S. Pat. No. 4,912,416, issued Mar. 27, 1990, to Champlin; U.S. Pat. No. 5,140,269, issued Aug. 18, 1992, to Champlin; U.S. Pat. No. 5,343,380, issued Aug. 30, 1994,; U.S. Pat. No. 5,572,136, issued Nov. 5, 1996; U.S. Pat. No. 5,574,355, issued Nov. 12, 1996; U.S. Pat. No. 5,585,416, issued Dec. 10, 1996; U.S. Pat. No. 5,585,728, issued Dec. 17, 1996; U.S. Pat. No. 5,589,757, issued Dec. 31, 1996; U.S. Pat. No. 5,592,093, issued Jan. 7, 1997; U.S. Pat. No. 5,598,098, issued Jan. 28, 1997; U.S. Pat. No. 5,656,920, issued Aug. 12, 1997; U.S. Pat. No. 5,757,192, issued May 26, 1998; U.S. Pat. No. 5,821,756, issued Oct. 13, 1998; U.S. Pat. No. 5,831,435, issued Nov. 3, 1998; U.S. Pat. No. 5,871,858, issued Feb. 16, 1999; U.S. Pat. No. 5,914,605, issued Jun. 22, 1999; U.S. Pat. No. 5,945,829, issued Aug. 31, 1999; U.S. Pat. No. 6,002,238, issued Dec. 14, 1999; U.S. Pat. No. 6,037,751, issued Mar. 14, 2000; U.S. Pat. No. 6,037,777, issued Mar. 14, 2000; U.S. Pat. No. 6,051,976, issued Apr. 18, 2000; U.S. Pat. No. 6,081,098, issued Jun. 27, 2000; U.S. Pat. No. 6,091,245, issued Jul. 18, 2000; U.S. Pat. No. 6,104,167, issued Aug. 15, 2000; U.S. Pat. No. 6,137,269, issued Oct. 24, 2000; U.S. Pat. No. 6,163,156, issued Dec. 19, 2000; U.S. Pat. No. 6,172,483, issued Jan. 9, 2001; U.S. Pat. No. 6,172,505, issued Jan. 9, 2001; U.S. Pat. No. 6,222,369, issued Apr. 24, 2001; U.S. Pat. No. 6,225,808, issued May 1, 2001; U.S. Pat. No. 6,249,124, issued Jun. 19, 2001; U.S. Pat. No. 6,259,254, issued Jul. 10, 2001; U.S. Pat. No. 6,262,563, issued Jul. 17, 2001; U.S. Pat. No. 6,294,896, issued Sep. 25, 2001; U.S. Pat. No. 6,294,897, issued Sep. 25, 2001; U.S. Pat. No. 6,304,087, issued Oct. 16, 2001; U.S. Pat. No. 6,310,481, issued Oct. 30, 2001; U.S. Pat. No. 6,313,607, issued Nov. 6, 2001; U.S. Pat. No. 6,313,608, issued Nov. 6, 2001; U.S. Pat. No. 6,316,914, issued Nov. 13, 2001; U.S. Pat. No. 6,323,650, issued Nov. 27, 2001; U.S. Pat. No. 6,329,793, issued Dec. 11, 2001; U.S. Pat. No. 6,331,762, issued Dec. 18, 2001; U.S. Pat. No. 6,332,113, issued Dec. 18, 2001; U.S. Pat. No. 6,351,102, issued Feb. 26, 2002; U.S. Pat. No. 6,359,441, issued Mar. 19, 2002; U.S. Pat. No. 6,363,303, issued Mar. 26, 2002; U.S. Pat. No. 6,377,031, issued Apr. 23, 2002; U.S. Pat. No. 6,392,414, issued May 21, 2002; U.S. Pat. No. 6,417,669, issued Jul. 9, 2002; U.S. Pat. No. 6,424,158, issued Jul. 23, 2002; U.S. Pat. No. 6,441,585, issued Aug. 17, 2002; U.S. Pat. No. 6,437,957, issued Aug. 20, 2002; U.S. Pat. No. 6,445,158, issued Sep. 3, 2002; U.S. Pat. No. 6,456,045; U.S. Pat. No. 6,466,025, issued Oct. 15, 2002; U.S. Pat. No. 6,465,908, issued Oct. 15, 2002; U.S. Pat. No. 6,466,026, issued Oct. 15, 2002; U.S. Pat. No. 6,469,511, issued Nov. 22, 2002; U.S. Pat. No. 6,495,990, issued Dec. 17, 2002; U.S. Pat. No. 6,497,209, issued Dec. 24, 2002; U.S. Pat. No. 6,507,196, issued Jan. 14, 2003; U.S. Pat. No. 6,534,993; issued Mar. 18, 2003; U.S. Pat. No. 6,544,078, issued Apr. 8, 2003; U.S. Pat. No. 6,556,019, issued Apr. 29, 2003; U.S. Pat. No. 6,566,883, issued May 20, 2003; U.S. Pat. No. 6,586,941, issued Jul. 1, 2003; U.S. Pat. No. 6,597,150, issued Jul. 22, 2003; U.S. Pat. No. 6,621,272, issued Sep. 16, 2003; U.S. Pat. No. 6,623,314, issued Sep. 23, 2003; U.S. Pat. No. 6,633,165, issued Oct. 14, 2003; U.S. Pat. No. 6,635,974, issued Oct. 21, 2003; U.S. Pat. No. 6,707,303, issued Mar. 16, 2004; U.S. Pat. No. 6,737,831, issued May 18, 2004; U.S. Pat. No. 6,744,149, issued Jun. 1, 2004; U.S. Pat. No. 6,759,849, issued Jul. 6, 2004; U.S. Pat. No. 6,781,382, issued Aug. 24, 2004; U.S. Pat. No. 6,788,025, filed Sep. 7, 2004; U.S. Pat. No. 6,795,782, issued Sep. 21, 2004; U.S. Pat. No. 6,805,090, filed Oct. 19, 2004; U.S. Pat. No. 6,806,716, filed Oct. 19, 2004; U.S. Pat. No. 6,850,037, filed Feb. 1, 2005; U.S. Pat. No. 6,850,037, issued Feb. 1, 2005; U.S. Pat. No. 6,871,151, issued Mar. 22, 2005; U.S. Pat. No. 6,885,195, issued Apr. 26, 2005; U.S. Pat. No. 6,888,468, issued May 3, 2005; U.S. Pat. No. 6,891,378, issued May 10, 2005; U.S. Pat. No. 6,906,522, issued Jun. 14, 2005; U.S. Pat. No. 6,906,523, issued Jun. 14, 2005; U.S. Pat. No. 6,909,287, issued Jun. 21, 2005; U.S. Pat. No. 6,914,413, issued Jul. 5, 2005; U.S. Pat. No. 6,913,483, issued Jul. 5, 2005; U.S. Pat. No. 6,930,485, issued Aug. 16, 2005; U.S. Pat. No. 6,933,727, issued Aug. 23, 200; U.S. Pat. No. 6,941,234, filed Sep. 6, 2005; U.S. Pat. No. 6,967,484, issued Nov. 22, 2005; U.S. Pat. No. 6,998,847, issued Feb. 14, 2006; U.S. Pat. No. 7,003,410, issued Feb. 21, 2006; U.S. Pat. No. 7,003,411, issued Feb. 21, 2006; U.S. Pat. No. 7,012,433, issued Mar. 14, 2006; U.S. Pat. No. 7,015,674, issued Mar. 21, 2006; U.S. Pat. No. 7,034,541, issued Apr. 25, 2006; U.S. Pat. No. 7,039,533, issued May 2, 2006; U.S. Pat. No. 7,058,525, issued Jun. 6, 2006; U.S. Pat. No. 7,081,755, issued Jul. 25, 2006; U.S. Pat. No. 7,106,070, issued Sep. 12, 2006; U.S. Pat. No. 7,116,109, issued Oct. 3, 2006; U.S. Pat. No. 7,119,686, issued Oct. 10, 2006; and U.S. Pat. No. 7,126,341, issued Oct. 24, 2006; U.S. Ser. No. 09/780,146, filed Feb. 9, 2001, entitled STORAGE BATTERY WITH INTEGRAL BATTERY TESTER; U.S. Ser. No. 09/756,638, filed Jan. 8, 2001, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Ser. No. 09/862,783, filed May 21, 2001, entitled METHOD AND APPARATUS FOR TESTING CELLS AND BATTERIES EMBEDDED IN SERIES/PARALLEL SYSTEMS; U.S. Ser. No. 09/880,473, filed Jun. 13, 2001; entitled BATTERY TEST MODULE; U.S. Ser. No. 09/993,468, filed Nov. 14, 2001, entitled KELVIN CONNECTOR FOR A BATTERY POST; U.S. Ser. No. 10/042,451, filed Jan. 8, 2002, entitled BATTERY CHARGE CONTROL DEVICE; U.S. Ser. No. 10/109,734, filed Mar. 28, 2002, entitled APPARATUS AND METHOD FOR COUNTERACTING SELF DISCHARGE IN A STORAGE BATTERY; U.S. Ser. No. 10/112,998, filed Mar. 29, 2002, entitled BATTERY TESTER WITH BATTERY REPLACEMENT OUTPUT; U.S. Ser. No. 10/263,473, filed Oct. 2, 2002, entitled ELECTRONIC BATTERY TESTER WITH RELATIVE TEST OUTPUT; U.S. Ser. No. 10/310,385, filed Dec. 5, 2002, entitled BATTERY TEST MODULE; U.S. Ser. No. 10/462,323, filed Jun. 16, 2003, entitled ELECTRONIC BATTERY TESTER HAVING A USER INTERFACE TO CONFIGURE A PRINTER; U.S. Ser. No. 10/653,342, filed Sep. 2, 2003, entitled ELECTRONIC BATTERY TESTER CONFIGURED TO PREDICT A LOAD TEST RESULT; U.S. Ser. No. 10/656,526, filed Sep. 5, 2003, entitled METHOD AND APPARATUS FOR MEASURING A PARAMETER OF A VEHICLE ELECTRICAL SYSTEM; U.S. Ser. No. 10/441,271, filed May 19, 2003, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/653,963, filed Sep. 1, 2000, entitled SYSTEM AND METHOD FOR CONTROLLING POWER GENERATION AND STORAGE; U.S. Ser. No. 10/174,110, filed Jun. 18, 2002, entitled DAYTIME RUNNING LIGHT CONTROL USING AN INTELLIGENT POWER MANAGEMENT SYSTEM; U.S. Ser. No. 10/258,441, filed Apr. 9, 2003, entitled CURRENT MEASURING CIRCUIT SUITED FOR BATTERIES; U.S. Ser. No. 10/681,666, filed Oct. 8, 2003, entitled ELECTRONIC BATTERY TESTER WITH PROBE LIGHT; U.S. Ser. No. 10/748,792, filed Dec. 30, 2003, entitled APPARATUS AND METHOD FOR PREDICTING THE REMAINING DISCHARGE TIME OF A BATTERY; U.S. Ser. No. 10/783,682, filed Feb. 20, 2004, entitled REPLACEABLE CLAMP FOR ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/791,141, filed Mar. 2, 2004, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Ser. No. 10/864,904, filed Jun. 9, 2004, entitled ALTERNATOR TESTER; U.S. Ser. No. 10/867,385, filed Jun. 14, 2004, entitled ENERGY MANAGEMENT SYSTEM FOR AUTOMOTIVE VEHICLE; U.S. Ser. No. 10/896,834, filed Jul. 22, 2004, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/897,801, filed Jul. 23, 2004, entitled SHUNT CONNECTION TO A PCB FOR AN ENERGY MANAGEMENT SYSTEM EMPLOYED IN AN AUTOMOTIVE VEHICLE; U.S. Ser. No. 10/958,821, filed Oct. 5, 2004, entitled IN-VEHICLE BATTERY MONITOR; U.S. Ser. No. 10/958,812, filed Oct. 5, 2004, entitled SCAN TOOL FOR ELECTRONIC BATTERY TESTER; U.S. Ser. No. 11/008,456, filed Dec. 9, 2004, entitled APPARATUS AND METHOD FOR PREDICTING BATTERY CAPACITY AND FITNESS FOR SERVICE FROM A BATTERY DYNAMIC PARAMETER AND A RECOVERY VOLTAGE DIFFERENTIAL, U.S. Ser. No. 60/587,232, filed Dec. 14, 2004, entitled CELLTRON ULTRA, U.S. Ser. No. 11/018,785, filed Dec. 21, 2004, entitled WIRELESS BATTERY MONITOR; U.S. Ser. No. 60/653,537, filed Feb. 16, 2005, entitled CUSTOMER MANAGED WARRANTY CODE; U.S. Ser. No. 11/063,247, filed Feb. 22, 2005, entitled ELECTRONIC BATTERY TESTER OR CHARGER WITH DATABUS CONNECTION; U.S. Ser. No. 60/665,070, filed Mar. 24, 2005, entitled OHMMETER PROTECTION CIRCUIT; U.S. Ser. No. 11/141,234, filed May 31, 2005, entitled BATTERY TESTER CAPABLE OF IDENTIFYING FAULTY BATTERY POST ADAPTERS; U.S. Ser. No. 11/143,828, filed Jun. 2, 2005, entitled BATTERY TEST MODULE; U.S. Ser. No. 11/146,608, filed Jun. 7, 2005, entitled SCAN TOOL FOR ELECTRONIC BATTERY TESTER; U.S. Ser. No. 60,694,199, filed Jun. 27, 2005, entitled GEL BATTERY CONDUCTANCE COMPENSATION; U.S. Ser. No. 11/178,550, filed Jul. 11, 2005, entitled WIRELESS BATTERY TESTER/CHARGER; U.S. Ser. No. 60/705,389, filed Aug. 4, 2005, entitled PORTABLE TOOL THEFT PREVENTION SYSTEM, U.S. Ser. No. 11/207,419, filed Aug. 19, 2005, entitled SYSTEM FOR AUTOMATICALLY GATHERING BATTERY INFORMATION FOR USE DURING BATTERY TESTER/CHARGING, U.S. Ser. No. 60/712,322, filed Aug. 29, 2005, entitled AUTOMOTIVE VEHICLE ELECTRICAL SYSTEM DIAGNOSTIC DEVICE, U.S. Ser. No. 60/713,169, filed Aug. 31, 2005, entitled LOAD TESTER SIMULATION WITH DISCHARGE COMPENSATION, U.S. Ser. No. 60/731,881, filed Oct. 31, 2005, entitled PLUG-IN FEATURES FOR BATTERY TESTERS; U.S. Ser. No. 60/731,887, filed Oct. 31, 2005, entitled AUTOMOTIVE VEHICLE ELECTRICAL SYSTEM DIAGNOSTIC DEVICE; U.S. Ser. No. 11/304,004, filed Dec. 14, 2005, entitled BATTERY TESTER THAT CALCULATES ITS OWN REFERENCE VALUES; U.S. Ser. No. 60/751,853, filed Dec. 20, 2005, entitled BATTERY MONITORING SYSTEM; U.S. Ser. No. 11/304,004, filed Dec. 14, 2005, entitled BATTERY TESTER WITH CALCULATES ITS OWN REFERENCE VALUES; U.S. Ser. No. 60/751,853, filed Dec. 20, 2005, entitled BATTERY MONITORING SYSTEM; U.S. Ser. No. 11/352,945, filed Feb. 13, 2006, entitled BATTERY TESTERS WITH SECONDARY FUNCTIONALITY; U.S. Ser. No. 11/356,299, filed Feb. 16, 2006, entitled CENTRALLY MONITORED SALES OF STORAGE BATTERIES; U.S. Ser. No. 11/356,436, field Feb. 16, 2006, entitled ELECTRONIC BATTERY TESTER WITH RELATIVE TEST OUTPUT; U.S. Ser. No. 11/356,443, filed Feb. 16, 2006, entitled ELECTRONIC BATTERY TESTER WITH NETWORK COMMUNICATION; U.S. Ser. No. 11/410,263, filed Apr. 24, 2006, entitled QUERY BASED ELECTRONIC BATTERY TESTER; U.S. Ser. No. 11/498,703, filed Aug. 3, 2006, entitled THEFT PREVENTION DEVICE FOR AUTOMOTIVE VEHICLE SERVICE CENTERS; U.S. Ser. No. 11/507,157, filed Aug. 21, 2006, entitled APPARATUS AND METHOD FOR SIMULATING A BATTERY TESTER WITH A FIXED RESISTANCE LOAD; U.S. Ser. No. 11/511,872, filed Aug. 29, 2006, entitled AUTOMOTIVE VEHICLE ELECTRICAL SYSTEM DIAGNOSTIC DEVICE; U.S. Ser. No. 11/519,481, filed Sep. 12, 2006, entitled BROAD-BAND LOW-CONDUCTANCE CABLES FOR MAKING KELVIN CONNECTIONS TO ELECTROCHEMICAL CELLS AND BATTERIES; U.S. Ser. No. 60/847,064, filed Sep. 25, 2006, entitled STATIONARY BATTERY MONITORING ALGORITHMS; which are incorporated herein in their entirety.  
         [0004]     There is an ongoing need to measure parameters of electrical systems of vehicles and heavy equipment. Such measurements can be used to diagnose operation, failure or impending failure of components or subsystems of electrical systems. For example, in electrical systems used in vehicles, measurement of electrical parameters of such systems can be used to diagnose operation of system or indicate that maintenance is required before ultimate failure.  
         [0005]     One particular measurement is the resistance of cabling used in large equipment such as heavy trucks. For example, one such cable or set of cables connects the battery of vehicle to the starter motor. The starter motor has a relatively large current draw and even a relatively small cable resistance can have a significant impact on operation of the starter motor.  
         [0006]     Because the cable resistance is relatively small it typically cannot be measured using a standard ohm meter or other techniques which are normally used to measure resistance. One technique which has been used to measure the cable resistance is to run a very large current through the cable and measure the voltage drop. However, this is cumbersome and requires components capable of handling the large current.  
       SUMMARY OF THE INVENTION  
       [0007]     An apparatus for measuring electrical parameters for an electrical system includes measurement circuitry which is configured to measure a first parameter of the electrical system between a first connection to the electrical system and a second connection to the electrical system. The measurement circuitry is further configured to measure a second parameter of the electrical system between a third connection to the electrical system and the second connection to the electrical system. A processor determines a third electrical parameter of the electrical system as a function of the first parameter and the second parameter. A method can also be employed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a simplified diagram of an electrical system of a vehicle.  
         [0009]      FIG. 2  is a diagram showing test equipment for determining the resistance of cables of the electrical system shown in  FIG. 1 .  
         [0010]      FIG. 3  shows another example embodiment of test equipment for determining cable resistance. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]      FIG. 1  is a diagram of an electrical system  10  of large equipment  12  such as a heavy truck. Electrical system  10  includes a battery  20 , a high current load  22  and cables  24  and  26 . Cables  24  and  26  have resistances R 1  and R 2 , respectively and connect load  22  to battery  20 .  FIG. 1  also shows connection points C, D and C′, D′. Connections C and D are cross load  22  and connections C′ and D′ are cross battery  20 .  
         [0012]     As discussed in the Background section, the resistances R 1  and R 2  of cables  24  and  26  can have a significant impact on the amount of power which can be delivered to load  22 . Even if the resistance values are relatively small, because a relatively large current passes through cables  24  and  26 , the resultant voltage drop can significantly reduce the voltage at points C and D and therefore the amount of power (or voltage) which can be delivered to load  22 . In industrial equipment, it is often desirable to measure the resistance R 1  and R 2  of cables  24  and  26 , respectively, in order to identify a cable with a resistance which is too high. One technique which has been used to measure the resistance of the cables is to pass a large current through the cable and measure the resulting voltage drop across the cable. However, this is a cumbersome test and requires electrical test equipment which is capable of handling the large current draw. The present invention provides an apparatus and technique for measuring the resistance of a cable in a configurations similar to that shown in  FIG. 1 .  
         [0013]      FIG. 2  is a simplified block diagram of one example embodiment of electrical test equipment  50  for measuring electrical parameters of the electrical system  10  shown in  FIG. 1 . Test equipment  50  includes measurement circuitry  52 , microprocessor  54 , memory  56  and output  58 . Measurement circuitry  52  is configured to couple to electrical system  10  of  FIG. 1  through electrical connections  60  and  62 . Measurements obtained by measurement circuitry  52  are used by microprocessor  54  in accordance with program instructions contained in memory  56 . Based upon the measurements, an output is provided through output  58 , for example, to a user or to other equipment. Connectors  60  and  62  are configured to couple to points C, D and C′, D′ in order to measure parameters of system  10 . Any number of connectors may be used and the invention is not limited to the two illustrated in  FIG. 2 .  
         [0014]     In one aspect of the present invention, test equipment  50  measures a parameter P(C,D′) between points C and D′ and a parameter P(C′,D′) between points C′ and D′. These measurements are used to determine the resistance of R 1  in accordance with the formula: 
 
 R   1   =F[P ( C,D ′),  P ( C′,D ′)]  EQ. 1 
 
 Further, a third measurement can be taken to obtain a parameter P(C′,D) between points C′ and D in  FIG. 1 . With this additional parameter, the resistance of R 2  can be determined as: 
 
 R   2   =F[P ( C′,D ),  P ( C′,D ′)}  EQ. 2 
 
         [0015]     Microprocessor  54  can determine the actual values of R 1  and R 2 , or can make some other determination related to R 1  and R 2 , for example a pass/fail determination, a relative determination, a gradient based determination, etc. Microprocessor  54  provides an output through output  58  based upon the determination related to R 1  and R 2 . The output can be a visual output, audible output, or the like, to an operator. In another example, the output is suitable for receipt by other circuitry.  
         [0016]      FIG. 3  is a simplified diagram showing another example embodiment of circuitry in accordance with the present invention. In  FIG. 3 , test equipment  100  includes a microprocessor  54 , memory  56  and output  58 , similar to the configuration discussed with respect to  FIG. 2 . Additionally, measurement circuitry  102  is provided for coupling to the C,D and C′,D′ connections shown in  FIG. 1 . More specifically, Kelvin connections  104  and  106  are provided and are identified as A, B, C and D with connections  104 B,  106 A,  104 A and  106 B, respectively. Kelvin connection  104  is configured to couple to location C shown in  FIG. 1 . Kelvin connection  106  is configured to couple to location D shown in  FIG. 1 . An additional pair of connections  108  and  110  are configured to couple to locations C′ and D′ shown in  FIG. 1 . A forcing function  120  couples to connections  104 B and  106 A (A and B) and is configured to apply a time varying signal therebetween. The signal can be any type of time varying signal including a periodic signal and may have any type of waveform at a desired frequency or multiple frequencies. Further, in some embodiments, measurements are taken using different forcing functions at differing frequencies or waveforms. The forcing function can be an active signal which is injected through the A/B connection, or can be a passive signal in which a signal is drawn from points A/B through selective application of a resistance, etc.  
         [0017]     An amplifier  122  couples to connections  104 A and  106 B (C and D) and provides an output to an analog to digital converter  124 . Connections  108  and  110  (C′ and D′) couple to an amplifier  126  which provides an output to analog to digital converter  124 . Note that this configuration is for explanation only and other configurations can be implemented in accordance with the present invention including different amplifier configurations, different analog to digital converter configurations, etc. Further, the forcing function  120  can be an active forcing function in which a signal is actively applied or can be a passive forcing function in which a signal is applied passively through a resistance or the like which is selectively applied to draw current from battery  20  shown in  FIG. 1 . The circuitry can be implemented in analog or digital circuitry, or their combination. Circuitry in accordance with techniques set forth in the Background section can be implemented, or other measurement techniques can be used.  
         [0018]     Using the configuration set forth in  FIG. 3 , Kelvin connections  104  and  106  can be applied to points C and D identified in  FIG. 1 . Additional connections  108  and  110  can be applied to points C′ and D′ shown in  FIG. 1 . Using this configuration, the parameters measured in accordance with  FIGS. 1 and 2  can be dynamic parameters which are functions of the applied forcing function  120 . In another example embodiment, a single pair of Kelvin connections is used in which the connections are moved between various positions C, D, C′ and D′ shown in  FIG. 1  and the resistance R 1  and R 2  of the cables  24  and  26  are determined.  
         [0019]     Using the circuitry set forth in  FIG. 3 , conductance values between the various connections shown in  FIG. 1  can be obtained. Using these conductance values, the resistances R 1  and R 2  can be determined using the following equations: 
 
 R   1 =( K   1   /G   CD′ )−( K   2   /G   C′D′ )   EQ. 3 
 
 R   2 =( K   3   /G   C′D )−( K   4   /G   C′D′ )   EQ. 4 
 
 Where G CD′  is the conductance measured between points C and D′, G C′D′  is the conductance measured between points C′ and D′ and G C′D  is the conductance measured between points C′ and D. The values K 1 , K 2 , K 3  and K 4  are constants and can be, in some examples, the same value, for example unity. The conductance values can be either direct conductance values or can be conductance values converted to a cold cranking amps (CCA) scale. When CCA values are measured, he values of R 1  and R 2  can be determined using the formula: 
 
 R   1 =(3.125 /CCA   —   CD ′)−(3.125 /CCA   —   C′D ′)   EQ. 5 
 
 R   2 =(3.125 /CCA   —   C′D )−(3.125 /CCA   —   C′D ′)   EQ. 6 
 
 The value of 3.125 can be adjusted based upon the particular CCA scale employed. 
 
         [0020]     The load  22  can be any type of load including loads which draw high current levels, for example, a starter motor, a magnetic switch, a ground connection, wiring harness, a terminal which may be susceptible to corrosion, a connection through a bolt which may have inappropriate torque or otherwise provide a poor connection, trailer wiring, etc. In one example output, a particular voltage drop is provided for a particular current draw through the cabling. For example, the output can comprise an indication that there is a 0.5 volt drop through the cable under a 500 amp current. Such a parameter can also be used, for example, in a pass/fail test, i.e., if the voltage drop is more than a particular threshold at a given current level, a failure indication can be provided as an output. In one embodiment, the measured parameters comprise dynamic conductance. However, any dynamic parameter can be used in accordance with the present invention including dynamic resistance, reactance, impedance, conductance, susceptance, and/or admittance, including any combination of these parameters.  
         [0021]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. The measurements can be taken using multiple connections to the electrical system or by moving a single pair of connections to various positions on the electrical system. An output can be provided to instruct the operator where to place the connections.