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Sensor and method for discriminating coins using fast fourier transform

  • US 7,552,810 B2
  • Filed: 10/12/2004
  • Issued: 06/30/2009
  • Est. Priority Date: 03/11/2002
  • Status: Active Grant
First Claim
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1. A sensor assembly for determining an authenticity of coins, comprising:

  • an excitation device configured to receive an excitation signal having multiple fixed excitation frequency components and to produce a magnetic field over a coin path, said magnetic field coupling to said coins to induce eddy currents within said coin;

    a reception device configured to receive first and second reception signals corresponding to said eddy currents, the voltage difference of said first and second reception signals being termed a detection signal, said detection signal having the same multiple fixed frequency components as said excitation signal; and

    first logic circuitry coupled to analog-to-digital (ADC) circuitry, said ADC circuitry coupled to said reception device, said first logic circuitry configured to produce a coin signature representing at least one of amplitudes and phase angles of said multiple fixed frequency components of said detection signal by application of a Fast Fourier Transform (FFT) to digital samples representing said detection signal,wherein said ADC circuitry is configured to sample said detection signal at a sampling frequency greater than a highest frequency of said multiple fixed excitation frequency components to produce digital samples representative of said detection signal.

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