| 摘要 |
A metal detector has three magnet/coil units positioned end-to-end. Each magnet/coil unit has a generally rectangular bobbin supporting a coil and a pair of bar magnets at opposite ends thereof. The three coils are connected electrically in a three-phase "Y" configuration. The voltages generated by all three coils are received by a microprocessor-based signal processing unit (SPU). The SPU generates a three difference signals V(x-y), V(y-z) and V(z-x) which represent the differences between the individual coil voltages. The SPU generates a sum signal representing a sum of the absolute values of all the difference signals and generates a trip signal if the sum signal is greater than a threshold. The SPU determines over which side of the coil assembly the piece of metal passes by comparing to a threshold the difference signal corresponding to a difference between the voltages from the coils at opposite ends of the coil assembly. The SPU more precisely determines the position of the piece of metal by comparing the difference signals to each other.
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