Suppressing interference in AC measurements of cells, batteries and other electrical elements
First Claim
1. A method for evaluating a component of a signal at a measurement frequency while suppressing potential components at one or more interference frequencies comprising:
- sampling said signal M times per period of said measurement frequency for N said periods, said number N being an integral multiple of said measurement frequency divided by the greatest common factor of said measurement frequency and said interference frequencies;
summing each of said M signal samples per period over said N periods to obtain M sample sums;
evaluating said component of said signal at said measurement frequency from said M sample sums.
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Abstract
The disclosed invention relates to measuring an ac dynamic parameter (e.g., impedance, admittance, resistance, reactance, conductance, susceptance) of an electrochemical cell/battery or other electrical element under conditions of possible interference from potential sources such as ac magnetic fields and/or ac currents at the powerline frequency and its harmonics. More generally, it relates to evaluating a signal component at a known frequency f1 under conditions of possible hum, noise, or other spurious interference at one or more other known frequencies. A microprocessor or microcontroller commands A/D circuitry to sample a band-limited signal at M evenly spaced times per period 1/f1 distributed over an integer number N of such periods and calculates time-averaged Fourier coefficients from these samples. The frequency response of the calculated Fourier coefficients displays perfect nulls at evenly spaced frequencies either side of frequency f1. By choosing N according to algorithms disclosed herein, null responses are made to coincide with the one or more frequencies of potential hum, noise, or other spurious interference.
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Citations
98 Claims
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1. A method for evaluating a component of a signal at a measurement frequency while suppressing potential components at one or more interference frequencies comprising:
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sampling said signal M times per period of said measurement frequency for N said periods, said number N being an integral multiple of said measurement frequency divided by the greatest common factor of said measurement frequency and said interference frequencies;
summing each of said M signal samples per period over said N periods to obtain M sample sums;
evaluating said component of said signal at said measurement frequency from said M sample sums. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for evaluating a component of a signal at a measurement frequency while suppressing potential components at one or more interference frequencies comprising:
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obtaining (M×
N) samples of said signal by sampling at (M×
N) discrete times distributed uniformly over N consecutive periods of said measurement frequency, where N is an integral multiple of said measurement frequency divided by the greatest common factor of said measurement frequency and said discrete interference frequencies;
evaluating said component of said signal at said measurement frequency from said (M×
N) samples.- View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method for introducing a response peak at a desired response frequency and response nulls at one or more undesired response frequencies in the detected response of a measurement signal comprising:
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obtaining (M×
N) samples of said measurement signal by uniformly sampling at (M×
N) discrete times distributed over N consecutive periods of said desired response frequency, where N is an integral multiple of said desired response frequency divided by the greatest common factor of said desired response frequency and said undesired response frequencies;
determining said detected response from said (M×
N) samples.- View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A method for introducing a response peak at a desired response frequency and response nulls at one or more undesired response frequencies in the detected response of a measurement signal comprising:
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sampling said measurement signal M times per period of said desired response frequency for N said periods, said number N being an integral multiple of said desired response frequency divided by the greatest common factor of said desired response frequency and said undesired response frequencies;
summing each of said M signal samples per period over said N periods to obtain M sample sums;
determining said detected response from said M sample sums. - View Dependent Claims (36, 37, 38, 39, 40, 41, 42, 43, 44)
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45. Apparatus for detecting a signal component at a measurement frequency while suppressing potential interference components at one or more interference frequencies comprising:
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sample and convert circuitry adapted to provide digital representations of sampled values of said signal, said sampled values acquired at (M×
N) sampling times distributed uniformly over N periods of said measurement frequency, where N is an integral multiple of said measurement frequency divided by the greatest common factor of said measurement frequency and said interference frequencies; and
,computation and control circuitry coupled to said sample and convert circuitry and adapted to initiate said sampling times, to accept said digital representations as inputs, and to compute said signal component at said measurement frequency from said digital representations. - View Dependent Claims (46, 47, 48, 49, 50, 51, 52, 53, 54, 55)
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56. Apparatus for determining a Fourier coefficient of a band-limited signal at a desired response frequency and nulling out response at one or more undesired response frequencies comprising:
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sample and convert circuitry adapted to provide digital representations of sampled values of said band-limited signal, said sampled values acquired at (M×
N) sampling times distributed uniformly over N periods of said desired response frequency, where N is an integral multiple of said desired response frequency divided by the greatest common factor of said desired response frequency and said undesired response frequencies; and
,computation and control circuitry coupled to said sample and convert circuitry and adapted to initiate said sampling times, to accept said digital representations as inputs, and to compute said Fourier coefficient from said digital representations. - View Dependent Claims (57, 58, 59, 60, 61, 62, 63, 64, 65, 66)
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67. Apparatus for evaluating a dynamic parameter of an electrochemical cell or battery at a measurement frequency while suppressing possible signals at one or more interference frequencies comprising:
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excitation circuitry coupled to said cell or battery and adapted to apply periodic excitation to said cell or battery, said periodic excitation characterized by a period equal to the reciprocal of said measurement frequency;
excitation signal sensing and processing circuitry coupled to said excitation circuitry and adapted to provide an excitation signal in response to said periodic excitation;
response signal sensing and processing circuitry coupled to said cell or battery and adapted to provide a periodic response signal in accordance with the response of said cell or battery to said periodic excitation;
excitation signal sampling circuitry coupled to said excitation signal sensing and processing circuitry and adapted to provide sampled values of said excitation signal, said sampled values acquired at discrete excitation signal sampling times synchronized with said periodic excitation and uniformly distributed in time over consecutive periods of said periodic excitation;
response signal sampling circuitry coupled to said response signal sensing and processing circuitry and adapted to provide sampled values of said response signal, said sampled values acquired at (M×
N) discrete response signal sampling times synchronized with said periodic excitation and uniformly distributed in time over N periods of said periodic excitation where N is an integral multiple of said discrete measurement frequency divided by the greatest common factor of said discrete measurement frequency and said one or more discrete interference frequencies; and
,computation and control circuitry coupled to said excitation signal sampling circuitry and to said response signal sampling circuitry and adapted to combine said sampled values of said excitation signal and said sampled values of said response signal to evaluate said dynamic parameter of said electrochemical cell or battery at said discrete measurement frequency. - View Dependent Claims (68, 69, 70, 71, 72, 73, 74, 75, 76)
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77. A method for measuring a dynamic parameter of an electrochemical cell or battery at a measurement frequency while reducing errors due to possible interfering signals at one or more interference frequencies comprising:
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exciting said cell or battery with a periodic time-varying current characterized by a smallest period equal to the reciprocal of said measurement frequency;
forming a current signal in accordance with said periodic time-varying current and a voltage signal in accordance with a time-varying response voltage across said cell or battery;
sampling said current signal at equally spaced times over an integer number of consecutive periods of said periodic time-varying current;
sampling said voltage signal at (M×
N) equally spaced times over N consecutive periods of said periodic time-varying current, where N is an integral multiple of said measurement frequency divided by the greatest common factor of said measurement frequency and said one or more interference frequencies;
converting said sampled values of said current signal and said (M×
N) sampled values of said voltage signal to digital format;
evaluating current signal Fourier coefficients from said sampled values of said current signal converted to digital format and evaluating voltage signal Fourier coefficients from said (M×
N) sampled values of said voltage signal converted to digital format; and
,numerically combining said current signal Fourier coefficients and said voltage signal Fourier coefficients to evaluate said dynamic parameter of said electrochemical cell or battery at said measurement frequency. - View Dependent Claims (78, 79, 80, 81, 82, 83, 84, 85, 86, 87)
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88. A method for measuring a dynamic parameter of an electrical element at a measurement frequency while reducing errors due to possible interfering signals at one or more interference frequencies comprising:
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exciting said electrical element with periodic time-varying excitation characterized by a smallest period equal to the reciprocal of said measurement frequency;
forming an excitation signal in accordance with said periodic time-varying excitation and a response signal in accordance with a time-varying response of said electrical element;
sampling said excitation signal at equally spaced times over an integer number of consecutive periods of said periodic time-varying excitation;
sampling said response signal at (M×
N) equally spaced times over N consecutive periods of said periodic time-varying excitation, where N is an integral multiple of said measurement frequency divided by the greatest common factor of said measurement frequency and said interference frequencies;
converting said sampled values of said excitation signal and said (M×
N) sampled values of said response signal to digital format;
evaluating excitation signal Fourier coefficients from said sampled values of said excitation signal converted to digital format and evaluating response signal Fourier coefficients from said (M×
N) sampled values of said response signal converted to digital format; and
,numerically combining said excitation signal Fourier coefficients and said response signal Fourier coefficients to evaluate said dynamic parameter of said electrical element at said measurement frequency. - View Dependent Claims (89, 90, 91, 92, 93, 94, 95, 96, 97, 98)
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Specification