Abstract:
An electronic battery tester for testing a storage battery is provided. The tester includes a pair of Kelvin connectors that can electrically couple to terminals of the battery. Also included, is a source that can apply a time varying forcing function to the battery through the Kelvin connectors. A sensor that electrically couples to the Kelvin connectors can sense a response of the storage battery to the applied forcing function and provide a response signal. An analog to digital converter digitizes the response signal. Processing circuitry converts the digitized response signal into multiple Fourier components and determines noise in the response signal from a subset of the multiple Fourier components.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to testing of storage batteries. More specifically, the present invention relates to detecting noise in an electronic battery tester while it conducts a battery test.  
           [0002]    Storage batteries, such as lead acid storage batteries of the type used in the automotive industry, have existed for many years. However, understanding the nature of such storage batteries, how such storage batteries operate and how to accurately test such batteries has been an ongoing endeavor and has proved quite difficult. Storage batteries consist of a plurality of individual storage cells electrically connected in series. Typically each cell has a voltage potential of about 2.1 volts. By connecting the cells in series, the voltages of the individual cells are added in a cumulative manner. For example, in a typical automotive storage battery, six storage cells are used to provide a total voltage when the battery is fully charged of 12.6 volts.  
           [0003]    There has been a long history of attempts to accurately test the condition of storage batteries. A simple test is to measure the voltage of the battery. If the voltage is below a certain threshold, the battery is determined to be bad. However, this test is inconvenient because it requires the battery to be charged prior to performing the test. If the battery is discharged, the voltage will be low and a good battery may be incorrectly tested as bad. Furthermore, such a test does not give any indication of how much energy is stored in the battery. Another technique for testing a battery is referred as a load test. In a load test, the battery is discharged using a known load. As the battery is discharged, the voltage across. the battery is monitored and used to determine the condition of the battery. This technique requires that the battery be sufficiently charged in order that it can supply current to the load.  
           [0004]    More recently, a technique has been pioneered by Dr. Keith S. Champlin and Midtronics, Inc. for testing storage batteries by measuring the conductance of the batteries. This technique is described in a number of United States patents, for example, U.S. Pat. No. 3,873,911, issued Mar. 25, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 3,909,708, issued Sep. 30, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,816,768, issued Mar. 28, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,825,170, issued Apr. 25, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING; U.S. Pat. No. 4,881,038, issued Nov. 14, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING TO DETERMINE DYNAMIC CONDUCTANCE; U.S. Pat. No. 4,912,416, issued Mar. 27, 1990, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH STATE-OF-CHARGE COMPENSATION; U.S. Pat. No. 5,140,269, issued Aug. 18, 1992, to Champlin, entitled ELECTRONIC TESTER FOR ASSESSING BATTERY/CELL CAPACITY; U.S. Pat. No. 5,343,380, issued Aug. 30, 1994, entitled METHOD AND APPARATUS FOR SUPPRESSING TIME VARYING SIGNALS IN BATTERIES UNDERGOING CHARGING OR DISCHARGING; U.S. Pat. No. 5,572,136, issued Nov. 5, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,574,355, issued Nov. 12, 1996, entitled METHOD AND APPARATUS FOR DETECTION AND CONTROL OF THERMAL RUNAWAY IN A BATTERY UNDER CHARGE; U.S. Pat. No. 5,585,416, issued Dec. 10, 1996, entitled APPARATUS AND METHOD FOR STEP-CHARGING BATTERIES TO OPTIMIZE CHARGE ACCEPTANCE; U.S. Pat. No. 5,585,728, issued Dec. 17, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,589,757, issued Dec. 31, 1996, entitled APPARATUS AND METHOD FOR STEP-CHARGING BATTERIES TO OPTIMIZE CHARGE ACCEPTANCE; U.S. Pat. No. 5,592,093, issued Jan. 7, 1997, entitled ELECTRONIC BATTERY TESTING DEVICE LOOSE TERMINAL CONNECTION DETECTION VIA A COMPARISON CIRCUIT; U.S. Pat. No. 5,598,098, issued Jan. 28, 1997, entitled ELECTRONIC BATTERY TESTER WITH VERY HIGH NOISE IMMUNITY; U.S. Pat. No. 5,656,920, issued Aug. 12, 1997, entitled METHOD FOR OPTIMIZING THE CHARGING LEAD-ACID BATTERIES AND AN INTERACTIVE CHARGER; U.S. Pat. No. 5,757,192, issued May 26, 1998, entitled METHOD AND APPARATUS FOR DETECTING A BAD CELL IN A STORAGE BATTERY; U.S. Pat. No. 5,821,756, issued Oct. 13, 1998, entitled ELECTRONIC BATTERY TESTER WITH TAILORED COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,831,435, issued Nov. 3, 1998, entitled BATTERY TESTER FOR JIS STANDARD; U.S. Pat. No. 5,914,605, issued Jun. 22, 1999, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 5,945,829, issued Aug. 31, 1999, entitled MIDPOINT BATTERY MONITORING; U.S. Pat. No. 6,002,238, issued Dec. 14, 1999, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX IMPEDANCE OF CELLS AND BATTERIES; U.S. Pat. No. 6,037,751, issued Mar. 14, 2000, entitled APPARATUS FOR CHARGING BATTERIES; U.S. Pat. No. 6,037,777, issued Mar. 14, 2000, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Pat. No. 6,051,976, issued Apr. 18, 2000, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Pat. No. 6,081,098, issued Jun. 27, 2000, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,091,245, issued Jul. 18, 2000, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Pat. No. 6,104,167, issued Aug. 15, 2000, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,137,269, issued Oct. 24, 2000, entitled METHOD AND APPARATUS FOR ELECTRONICALLY EVALUATING THE INTERNAL TEMPERATURE OF AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,163,156, issued Dec. 19, 2000, entitled ELECTRICAL CONNECTION FOR ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,172,483, issued Jan. 9, 2001, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX IMPEDANCE OF CELL AND BATTERIES; U.S. Pat. No. 6,172,505, issued Jan. 9, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,222,369, issued Apr. 24, 2001, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Pat. No. 6,225,808, issued May 1, 2001, entitled TEST COUNTER FOR ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,249,124, issued Jun. 19, 2001, entitled ELECTRONIC BATTERY TESTER WITH INTERNAL BATTERY; U.S. Pat. No. 6,259,254, issued Jul. 10, 2001, entitled APPARATUS AND METHOD FOR CARRYING OUT DIAGNOSTIC TESTS ON BATTERIES AND FOR RAPIDLY CHARGING BATTERIES; U.S. Pat. No. 6,262,563, issued Jul. 17, 2001, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX ADMITTANCE OF CELLS AND BATTERIES; U.S. Pat. No. 6,294,896, issued Sep. 25, 2001; entitled METHOD AND APPARATUS FOR MEASURING COMPLEX SELF-IMMITANCE OF A GENERAL ELECTRICAL ELEMENT; U.S. Patent No. 6,294,897, issued Sep. 25, 2001, entitled METHOD AND APPARATUS FOR ELECTRONICALLY EVALUATING THE INTERNAL TEMPERATURE OF AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,304,087, issued Oct. 16, 2001, entitled APPARATUS FOR CALIBRATING ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,310,481, issued Oct. 30, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,313,607, issued Nov. 6, 2001, entitled METHOD AND APPARATUS FOR EVALUATING STORED CHARGE IN AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,313,608, issued Nov. 6, 2001, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,316,914, issued Nov. 13, 2001, entitled TESTING PARALLEL STRINGS OF STORAGE BATTERIES; U.S. Pat. No. 6,323,650, issued Nov. 27, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,329,793, issued Dec. 11, 2001, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,331,762, issued Dec. 18, 2001, entitled ENERGY MANAGEMENT SYSTEM FOR AUTOMOTIVE VEHICLE; U.S. Pat. No. 6,332,113, issued Dec. 18, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,351,102, issued Feb. 26, 2002, entitled AUTOMOTIVE BATTERY CHARGING SYSTEM TESTER; U.S. Pat. No. 6,359,441, issued Mar. 19, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,363,303, issued Mar. 26, 2002, entitled ALTERNATOR DIAGNOSTIC SYSTEM, U.S. Ser. No. 09/595,102, filed Jun. 15, 2000, entitled APPARATUS AND METHOD FOR TESTING RECHARGEABLE ENERGY STORAGE BATTERIES; U.S. Ser. No. 09/703,270, filed Oct. 31, 2000, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/575,629, filed May 22, 2000, entitled VEHICLE ELECTRICAL SYSTEM TESTER WITH ENCODED OUTPUT; U.S. Ser. No. 09/780,146,filed Feb. 9, 2001, entitled STORAGE BATTERY WITH INTEGRAL BATTERY TESTER; U.S. Ser. No. 09/816,768, filed Mar. 23, 2001, entitled MODULAR 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. 09/483,623, filed Jan. 13, 2000, entitled ALTERNATOR TESTER; U.S. Ser. No. 09/870,410, filed May 30, 2001, entitled INTEGRATED CONDUCTANCE AND LOAD TEST BASED ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/960,117, filed Sep. 20, 2001, entitled IN-VEHICLE BATTERY MONITOR; U.S. Ser. No. 09/908,389, filed Jul. 18, 2001, entitled BATTERY CLAMP WITH INTEGRATED CIRCUIT SENSOR; U.S. Ser. No. 09/908,278, filed Jul. 18, 2001, entitled BATTERY CLAMP WITH EMBEDDED ENVIRONMENT SENSOR; U.S. Ser. No. 09/880,473, filed Jun. 13, 2001; entitled BATTERY TEST MODULE; U.S. Ser. No. 09/876,564, filed Jun. 7, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/878,625, filed Jun. 11, 2001, entitled SUPPRESSING INTERFERENCE IN AC MEASUREMENTS OF CELLS, BATTERIES AND OTHER ELECTRICAL ELEMENTS; U.S. Ser. No. 09/902,492, filed Jul. 10, 2001, entitled APPARATUS AND METHOD FOR CARRYING OUT DIAGNOSTIC TESTS ON BATTERIES AND FOR RAPIDLY CHARGING BATTERIES; and U.S. Ser. No. 09/940,684, filed Aug. 27, 2001, entitled METHOD AND APPARATUS FOR EVALUATING STORED CHARGE IN AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Ser. No. 09/977,049, filed Oct. 12, 2001, entitled PROGRAMMABLE CURRENT EXCITER FOR MEASURING AC IMMITTANCE OF CELLS AND BATTERIES; U.S. Ser. No. 10/047,923, filed Oct. 23, 2001, entitled AUTOMOTIVE BATTERY CHARGING SYSTEM TESTER, U.S. Ser. No. 10/046,659, filed Oct. 29, 2001, entitled ENERGY MANAGEMENT SYSTEM FOR AUTOMOTIVE VEHICLE; U.S. Ser. No. 09/993,468, filed Nov. 14, 2001, entitled KELVIN CONNECTOR FOR A BATTERY POST; U.S. Ser. No. 09/992,350, filed Nov. 26, 2001, entitled ELECTRONIC BATTERY TESTER, U.S. Ser. No. 10/042,451, filed Jan. 8, 2002, entitled BATTERY CHARGE CONTROL DEVICE; U.S. Ser. No. 10/042,451, filed Jan. 8, 2002, entitled BATTERY CHARGE CONTROL DEVICE, U.S. Ser. No. 10/073,378, filed Feb. 8, 2002, entitled METHOD AND APPARATUS USING A CIRCUIT MODEL TO EVALUATE CELL/BATTERY PARAMETERS; U.S. Ser. No. 10/093,853, filed Mar. 7, 2002, entitled ELECTRONIC BATTERY TESTER WITH NETWORK COMMUNICATION; U.S. Ser. No. 60/364,656, filed Mar. 14, 2002, entitled ELECTRONIC BATTERY TESTER WITH LOW TEMPERATURE RATING DETERMINATION; U.S. Ser. No. 10/101,543, filed Mar. 19, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/112,114, filed Mar. 28, 2002; U.S. Ser. No. 10/109,734, filed Mar. 28, 2002; U.S. Ser. No. 10/112,105, filed Mar. 28, 2002, entitled CHARGE CONTROL SYSTEM FOR A VEHICLE BATTERY; U.S. Ser. No. 10/112,998, filed Mar. 29, 2002, entitled BATTERY TESTER WITH BATTERY REPLACEMENT OUTPUT; U.S. Ser. No. 10/119,297, filed Apr. 9, 2002, entitled METHOD AND APPARATUS FOR TESTING CELLS AND BATTERIES EMBEDDED IN SERIES/PARALLEL SYSTEMS; U.S. Ser. No. 10/128,790, filed Apr. 22, 2002, entitled METHOD OF DISTRIBUTING JUMP-START BOOSTER PACKS; U.S. Ser. No. 10/143,307, filed May 10, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/___,___, (C382.12-0112), filed Jul. 29, 2002, entitled KELVIN CLAMP FOR ELECTRICALLY COUPLING TO A BATTERY CONTACT, which are incorporated herein in their entirety.  
           [0005]    However, there is an ongoing need to improve battery testing techniques to increase the accuracy of battery test results. One prior art battery testing technique involves the use of a differential amplifier to measure battery voltage during the application of a time varying current signal to the battery. The presence of noise at the output of the amplifier while the amplifier measures battery voltage during the application of the current signal can introduce errors into test results.  
         SUMMARY OF THE INVENTION  
         [0006]    An electronic battery tester for testing a storage battery is provided. The tester includes a first Kelvin connector that can electrically couple to a first terminal of the battery and a second Kelvin connector that can electrically couple to a second terminal of the battery. Also included, is a source that can apply a time varying forcing function to the battery through a first conductor of the first Kelvin connector and a first conductor of the second Kelvin connector. A sensor that electrically couples to a second conductor of the first Kelvin connector and a second conductor of the second Kelvin connector can sense a response of the storage battery to the applied forcing function and provide a response signal. An analog to digital converter digitizes the response signal. Processing circuitry converts the digitized response signal into multiple Fourier components and determines noise in the response signal from a subset of the multiple Fourier components. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a simplified block diagram of a battery tester in accordance with the present invention.  
         [0008]    [0008]FIG. 2 is a graph of voltage and current waveforms generated using a modeling technique.  
         [0009]    [0009]FIG. 3 is a graph of a computed Fourier Transform of the current and voltage values of FIG. 2.  
         [0010]    [0010]FIG. 4 is a simplified flow chart showing steps in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]    [0011]FIG. 1 is a simplified block diagram of battery monitoring circuitry  16  in accordance with the present invention. Apparatus  16  is shown coupled to battery  12  which includes a positive battery terminal  22  and a negative battery terminal  24 .  
         [0012]    In a preferred embodiment, circuitry  16  operates, with the exceptions and additions as discussed below, in accordance with battery testing methods described in one or more of the United States patents obtained by Dr. Champlin and Midtronics, Inc. and listed above. Circuitry  16  operates in accordance with one embodiment of the present invention and determines the conductance (G BAT ) of battery  12  and the voltage potential (V BAT ) between terminals  22  and  24  of battery  12 . Circuitry  16  includes current source  50 , differential amplifier  52 , analog-to-digital converter  54  and processing circuitry  56 . Current source  50  provides one example of a forcing function for use with the invention. Amplifier  52  is capacitively coupled to battery  12  through capacitors C 1  and C 2 . Amplifier  52  has an output connected to an input of analog-to-digital converter  54 . Processing circuitry  56  can be a microprocessor, digital signal processor, etc. Processing circuitry  56  is connected to system clock  58 , memory  60 , and analog-to-digital converter  54 . Processing circuitry  56  is also capable of receiving an input from input devices  66  and  68 . Processing circuitry  56  also connects to output device  72 .  
         [0013]    In operation, current source  50  is controlled by processing circuitry  56  and provides a current I in the direction shown by the arrow in FIG. 1. In one embodiment, this is a sine wave, square wave or a pulse. Differential amplifier  52  is connected to terminals  22  and  24  of battery  12  through capacitors C 1  and C 2 , respectively, and provides an output related to the voltage potential difference between terminals  22  and  24 . In a preferred embodiment, amplifier  52  has a high input impedance. Circuitry  16  includes differential amplifier  70  having inverting and noninverting inputs connected to terminals  24  and  22 , respectively. Amplifier  70  is connected to measure the open circuit potential voltage (V BAT ) of battery  12  between terminals  22  and  24  and is one example of a dynamic response sensor used to sense the time varying response of the battery  18  to the applied time varying forcing function. The output of amplifier  70  is provided to analog-to-digital converter  54  such that the voltage across terminals  22  and  24  can be measured by processing circuitry  56 .  
         [0014]    Circuitry  16  is connected to battery  12  through a four-point connection technique known as a Kelvin connection. This Kelvin connection allows current I to be injected into battery  12  through a first pair of connections while the voltage V across the terminals  22  and  24  is measured by a second pair of connections. Because very little current flows through amplifier  52 , the voltage drop across the inputs to amplifier  52  is substantially identical to the voltage drop across terminals  22  and  24  of battery  12 . The output of differential amplifier  52  is converted to a digital format and is provided to processing circuitry  56 . Processing circuitry  56  operates at a frequency determined by system clock  58  and in accordance with programming instructions stored in memory  60 .  
         [0015]    Processing circuitry  56  determines the conductance of battery  12  by applying a current pulse I using current source  50 . This measurement provides a dynamic parameter related to the battery. Of course, any such dynamic parameter can be measured including resistance, admittance, impedance or their combination along with conductance. Further, any type of time varying signal can be used to obtain the dynamic parameter. The signal can be generated using an active forcing function or using a forcing function which provides a switchable load, for example, coupled to the battery  12 . The processing circuitry determines the change in battery voltage due to the current pulse I using amplifier  52  and analog-to-digital converter  54 . The value of current I generated by current source  50  is known and is stored in memory  60 . In one embodiment, current I is obtained by applying a load to battery  12 . Processing circuitry  56  calculates the conductance of battery  12  using the following equation:  
               G   BAT     =       Δ                 I       Δ                 V               Equation                 1                               
 
         [0016]    where ΔI is the change in current flowing through battery  12  due to current source  50  and ΔV is the change in battery voltage due to applied current ΔI. Based upon the battery conductance G BAT  and the battery voltage, the battery tester  16  determines the condition of battery  12 . Battery tester  16  is programmed with information which can be used with the determined battery conductance and voltage as taught in the above listed patents to Dr. Champlin and Midtronics, Inc.  
         [0017]    The tester can compare the measured CCA (Cold Cranking Amp) with the rated CCA for that particular battery. Processing circuitry  56  can also use information input from input device  66  provided by, for example, an operator. This information may consist of the particular type of battery, location, time, the name of the operator. Additional information relating to the conditions of the battery test can be received by processing circuitry  56  from input device  68 . Input device  68  may comprise one or more sensors, for example, or other elements which provide information such as ambient or battery temperature, time, date, humidity, barometric pressure, noise amplitude or characteristics of noise in the battery or in the test result, or any other information or data which may be sensed or otherwise recovered which relates to the conditions of the test how the battery test was performed, or intermediate results obtained in conducting the test. Additional test condition information is provided by processing circuitry  56 . Such additional test condition information may include the values of G BAT  and battery voltage, the various inputs provided to battery tester  16  by the operator which may include, for example, type of battery, estimated ambient or battery temperature, type of vehicle (i.e., such as provided through the Vehicle Identification Number (VIN) code for the vehicle) or the particular sequence of steps taken by the operator in conducting the test.  
         [0018]    Typically, prior art battery testers do not take into consideration the presence of noise at the output of amplifier  52  while amplifier  52  measures battery voltage during the application of the current pulse I. However, one aspect of the present invention includes the recognition that the conductance, impedance, resistance or admittance computed as a function of the battery voltage measured using the prior art measurement technique may include a degree of error due to the presence of noise while obtaining the voltage measurement. Noise components that may be present at the output of amplifier  52 , while battery voltage measurements are being carried out by amplifier  52 , can also be taken into consideration to more accurately determine the condition of battery  12 . Thus, processing circuitry  56  utilizes different components corresponding to different frequencies of voltage measured by amplifier  52  to determine condition information of battery  12 .  
         [0019]    In accordance with the present invention, the digitized response signal, corresponding to the battery voltage measured by amplifier  52 , obtained at the output of analog-to-digital converter  54 , is converted into a plurality of Fourier components by processing circuitry  56 . Processing circuitry  56  also determines noise in the response signal from a subset (less than all) of the plurality of Fourier components. The condition of battery  12  is then output by processing circuitry  56  if the noise in the response signal is below a predetermined threshold. As used herein, Fourier components are values obtained as a result of applying a Fourier Transform to a current or voltage signal. The Fourier components provide a frequency domain representation of the current or voltage signal.  
         [0020]    In a narrower aspect of the present invention, a first battery capacity measurement (peak-to-peak battery capacity measurement) is obtained as a function of the peak-to-peak battery voltage measured by amplifier  52  during the application of current pulse I to battery  12 , and a second battery capacity measurement (DFT battery capacity measurement) is obtained as a function of the Fourier components of the battery voltage measured by amplifier  52  during the application of current pulse I to battery  12 . The current or actual battery capacity is then determined as a function of the first battery capacity measurement and the second battery capacity measurement. In some embodiments of the present invention, if the difference between the first battery capacity measurement and the second battery capacity measurement is within a predetermined threshold, the first battery capacity measurement is output as the actual battery capacity. If the difference between the first battery capacity measurement and the second battery capacity measurement is greater than or equal to the predetermined threshold, the first battery capacity measurement is discarded, and a message is output notifying the tester user of the presence of noise in the battery testing system. Tester  16  can then automatically retest battery  12  after a brief waiting period (for example, 3-4 seconds). Tester  16  carries out the retest by reapplying the current pulse, carrying out a new voltage measurement, recalculating the first and second capacity measurements and comparing these measurements. The tests are repeated until the difference between the first battery capacity measurement and the second battery capacity measurement is below the preset threshold. In some embodiments of the present invention, the output can include a measured noise energy value. An algorithm for determining the peak-to-peak battery voltage measurement, the Fourier components of the measured voltage, and the noise energy can be derived experimentally or through modeling techniques. One such algorithm is described below in connection with FIGS. 2 and 3.  
         [0021]    [0021]FIG. 2 shows current and voltage waveforms from which first and second battery capacity measurements can be obtained. These waveforms are generated as  
           IDiff   i   =IMag·if ( modulus ( i,p )&gt; q,IMax,IMin )  Equation 1  
         [0022]    and  
           VDiff   i   =VMag·if ( modulus ( i,p )&gt; q,VMax,VMin )  Equation 2  
         [0023]    where IDiff i  and VDiff i  are the respective values of current and voltage computed for a particular sample index i (i=0 . . . n−1, where n is the number of samples), IMag and VMag are the respective current and voltage magnitudes, IMax and VMax are the respective maximum current and voltage values, IMin and VMin are the respective minimum current and voltage values and p and q are integers that determine the frequency at which maximum and minimum voltage and current values occur.  
         [0024]    In FIG. 2, IDiff i  and VDiff i  are plotted along the vertical axis as functions of index i plotted along the horizontal axis to produce voltage waveform  80  and current waveform  82 . To generate these example current and voltage waveforms shown in FIG. 2 the following values were used in Equations 1 and 2:  
         [0025]    n=384  
         [0026]    IMag=100  
         [0027]    IMin=0  
         [0028]    IMax=1  
         [0029]    VMag=1500  
         [0030]    VMax=0  
         [0031]    VMin=1  
         [0032]    The peak-to-peak magnitude of current (IDiffPP) and the peak-to-peak magnitude of voltage (VDiffPP) for current and voltage signals generated utilizing equations 1 and 2 are computed as  
           IDiffPP=|IMax−IMin|   Equation 3  
         [0033]    and  
           VDiffPP=|VMax−VMin|   Equation 4  
         [0034]    IDiffPP and VDiffPP values determined using Equations 3 and 4 are employed to determine peak-to-peak battery capacity as described further below in connection with Equation 11.  
         [0035]    [0035]FIG. 3 shows a Discrete Fourier Transform (DFT) current magnitude response and a DFT voltage magnitude response for the respective current and voltage waveforms shown in FIG. 2. In general, the DFT current and voltage magnitude responses are generated as  
         DFT(x(m))=x(k)=Σ m=0   N−1 (x(n)*e −j(2*π/N) )  Equation 5  
         [0036]    where x(m) is input series IDiff m  (current) or VDiff m  (voltage) in time and x(k) is the output current or voltage series in frequency calculated for an input sample index m (m=0 . . . N−1, where N is the number of samples) and an output sample index k  
         (     k   =       0                 …                   N   2       -   1       )     .                         
 
         [0037]    In one embodiment of the present invention, to compute the DFT current magnitude response and the DFT voltage magnitude response, the direct current (DC) or zero Hz frequency component of the current magnitude response (IDiffMag 0 ) and the DC component of the voltage magnitude response (VDiffMag 0 ) are first set to zero.  
         IDiffMag 0 =0  Equation 6  
         [0038]    and  
         VDiffMag 0 =0   Equation 7  
         [0039]    The remaining components of the DFT current magnitude response (IDiffMag k1 ) and the DFT voltage magnitude response (VDiffMag k1 ) are then computed as  
         IDiffMag k1 =DFT(IDiff m )  Equation 8  
         [0040]    and  
         VDiffMag k1 =DFT(VDiff m )  Equation 9  
         [0041]    In FIG. 3, IDiffMag k1  and VDiffMag k1  are plotted along the vertical axis as functions of index k along the horizontal axis to produce current magnitude response plot  90  and voltage magnitude response plot  92 . To generate the example current and voltage magnitude response plots shown in FIG. 3 the following values were used in Equations 5:  
         [0042]    N=256  
         [0043]    m=0 . . . 255  
         [0044]    k=0 . . . 127  
         [0045]    The battery capacity is separately determined from peak-to-peak current and voltage values and DFT magnitude values as  
               CapacityPP   =       K   ·   IDiffPP     VDiffPP            
        and           Equation                 11               CapacityDFT   =       K   ·     IDiffMag   F         VDiffMag   F               Equation                 12                               
 
         [0046]    where CapacityPP is the peak-to-peak battery capacity expressed in cold cranking amps (CCA), CapacityDFT is the capacity calculated from the DFT magnitude response also expressed in CCA, K is a constant having units of (CCA*Volts)/Amperes, IDiffMag F  is the DFT current magnitude response value at the fundamental frequency (frequency at which the current pulse is applied to the battery) and VDiffMag F  is the DFT voltage magnitude response value at the fundamental frequency.  
         [0047]    In the example DFT magnitude response shown in FIG. 3, IDiffMag F  and VDiffMag F  values are at k=43 for a fundamental frequency F=100 Hz.  
         [0048]    A determination is made that system noise is present if the absolute value of the error between peak-to-peak capacity and the DFT capacity is greater than a predetermined threshold percentage. This capacity error is computed as  
             CapacityError   =            CapacityPP   -   CapacityDFT       100   ·   CapacityPP                    Equation                 13                               
 
         [0049]    Also, if the sum of the noise energy of VDiffMag k  is above a “Floor” level and is more than a predetermined percentage of the fundamental frequency component a determination is made that system noise is present. The noise energy is computed as  
             NoiseEnergy   =               ∑     k   =   0         N   2     -   1            if                   (              VDiffMag   k          &gt;   Floor     ,          VDiffMag   k          ,   0     )                          VDiffMag   F          -          VDiffMag     F   -   1            -          VDiffMag     F   +   1                      100   ·          VDiffMag   F                      Equation                 14                               
 
         [0050]    where VDiffMag F−1  is the DFT voltage magnitude response value immediately previous to VDiffMag F , and VDiffMag F+1  is the DFT voltage magnitude response value immediately after VDiffMag F .  
         [0051]    In the example DFT magnitude response shown in FIG. 3, IDiffMag F  and VDiffMag F  values are at k=43, VDiffMag f−1  is at k=42, VDiffMag F+1  is at k=44 and the Floor magnitude is equal to 400. The Floor magnitude is represented by reference numeral  94  in FIG. 3.  
         [0052]    [0052]FIG. 4 is a simplified flow chart  100  showing steps in accordance with one aspect of the present invention. Step  102 , a time varying forcing function is applied to the battery through a first pair of connectors of a Kelvin connection. At step  104 , the response of the battery to the applied time varying forcing function is sensed through a second pair of connectors of the Kelvin connection to provide a response signal. At step  106 , the response signal is digitized. At step  108 , the digitized response signal is converted into multiple Fourier components. At step  110 , an output related to a condition of the battery is provided as a function at least one of the multiple Fourier components.  
         [0053]    The present invention may be implemented using any appropriate technique. For simplicity, a single technique has been illustrated herein. However, other techniques may be used including implementation in all analog circuitry.  
         [0054]    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. A Fast Fourier Transform (FFT) algorithm may be utilized instead of the DFT algorithm to determine the Fourier components described above. The forcing function can be formed by a resistance, by a current sink, through an existing load of the vehicle or any other suitable means. The dynamic parameter determined for the battery may be real or imaginary.