ABSTRACT
ABSTRACT: The measurement of electrical conductivity using eddy current (electro magnetic induction) sensors is the most promising solution for validation of metal coins in coin handling devices, as the electrical conductivity is a very distinctive property of specific alloys. Low cost, simple and robust nature, and also possibility for high-speed precise measurements are the advantages of electromagnetic sensors. Multi-frequency scanning the coins under test at various field penetration depths is preferred due to the sophisticated “construction” of various alloys in nowadays coins. Air-core measurement coils have an additional advantage-a possibility to measure absolute values of conductivity without repetitive calibration of sensors and the measurement systems. Development of solutions for eddycurrent validation of metal coins has been investigated together with comparing the experimental results with the values derived from theoretical models. Frequency range of 10 kHz to 10 MHz have been considered (particularly up to 500 kHz for precision measurements) and conductivity values to be measured from 4 to 40% of IACS (International Annealed Copper Standard) conductivity (about 60 MS/m). The results demonstrate that the precise, highspeed, low-cost and robust coin validation system can be developed on the basis of air-core coil arrays.
