Sensor and method for discriminating coins of varied composition, thickness, and diameter

摘要

A coin discrimination sensor having an excitation coil and two detector coils arranged to detect eddy currents in a passing coin. The excitation coil is provided a composite waveform formed by adding a low frequency signal (30 KHz) with a high frequency signal (480 KHz). The two detector coils are arranged at different distances from the passing coin, and are calibrated to eliminate the common-mode voltage when no coin is present. As a coin passes by the sensor, eddy currents are induced in the coin which result in phase and amplitude shifts in the low and high frequency components of the detector signal. The low and high frequency components are separated from the detector signal, and their respective phases and amplitudes are ascertained and compared against values stored in a lookup table. These values represent the composition, thickness, and diameter characteristics of known coins, and if the signature of the processed coin does not appear in the lookup table, it can be flagged as an invalid coin.