| 摘要 |
An electromagnetic detection system comprising: a transmitter loop for generating a primary magnetic field, and a first pair of spaced apart receiver coils and second pair of spaced apart receiver coils for measuring a secondary magnetic field generated in response to the primary magnetic field. The transmitter loop drives the transmitter to generate the primary magnetic field. The system automatically switches between a first signal measuring mode and a second signal measuring mode, wherein in the first signal measuring mode a difference between signals induced in the receiver coils of the first pair is measured to provide a first receiver coil pair difference signal and a difference between the signals induced in the receiver coils of the second pair is measured to provide a second receiver coil pair difference signal, and in the second signal measuring mode a sum of the signals induced in the receiver coils of the first pair is measured to provide a first receiver coil pair sum signal and a sum of the signals induced in the receiver coils of the second pair is measured to provide a second receiver coil pair sum signal, and the difference between the first receiver coil pair signal and the second receiver coil pair signal is determined.
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