what is the technique used in coin changer/selector/validator
Hi
i have read about coin identification , and found the best technique is :
tow coils placed in oscillator circuit , if the coin passed through the frequency will be changed , i have applied this technique for denominations of coins but there are 2 denominations have the same frequency .
is there parameters another with frequency such as amplitude of frequency - instead of length , thickness or weight ?
When we used to measure flaws in continuous steel tubing, We excited dual coils and measured the difference in amplitude and phase (Current Vector) to find signature defects. Our sensitivity was 50ppm. Here you have the opposite trying to find the a metal signature going past air gap. Consider the quadrature vector impedance change with a fixed excitation frequency rather than the minor pull frequency of an induction tuned oscillator. Imagine the impedance change as a polar plot normalized to the center and the resulting signature beings a pattern that changes with metal type and size.
For it to be effected by non magnetic materials you need to measure Eddy currents. Thats why I drew on my experience.