Importance

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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 f.sub.1 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/f.sub.1 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 f.sub.1. 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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First Claim