Patent ID: 7584833
Filing Date: 2009-09-08
Classification: G07D

Abstract:
1. A method of distinguishing between minted coins of a predetermined type and bogus coins of a similar metal content, the method comprising subjecting at least one coil adjacent to a coin under test to both low and high frequency currents, monitoring an apparent change of impedance of the at least one coil resulting from eddy currents induced in the coin to produce first and second signals representative of changes of said impedance, the first signal corresponding to eddy currents produced in the coin by the high frequency current, and the second signal corresponding to eddy currents produced in the coin by the low frequency current, the frequency of said low frequency current being chosen such that said second signal is substantially not dependent on the thickness of the minted coins of said pre-determined type, performing a calibration procedure with minted coins to measure reference sets of data for the first and second signals for the minted coins, the reference sets of data being representative of a known range of data for minted coins, computing a ratio for the measured reference sets of data for the first and second signals for minted coins to define an acceptable parameter for minted coins, and comparing a ratio of said first and second signals for the coin under test with the computed ratio for the measured reference sets of data for the first and second signals for minted coins and determining whether the ratio for the coin under test fits within the determined acceptable parameter for minted coins.