Patent ID: 8129987

Claim:
An electromagnetic detection system comprising: a transmitter loop for generating a primary magnetic field; 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; a processing and control module connected to the transmitter loop for driving the transmitter to generate the primary magnetic field and connected to the first and second pairs of receiver coils, the processing and control module being configured to automatically switch 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.