| 摘要 |
PROBLEM TO BE SOLVED: To suppress the number of signal lines to the number receptible within a cable and improve the spatial resolution and defect detectability by providing a switching circuit for time sharing and driving a plurality of magnetic field exciting element and magnetic field detecting element and a detection signal amplifier circuit on measuring instrument side. SOLUTION: A multiplexer is used as a switching circuit, and an excitation coil (magnetic field exciting element) group 13 and a detection coil (magnetic field detecting element) group 14 are connected to an excitation multiplexer 16 and to a detection multiplexer 18, respectively. The output of the detection multiplexer is amplified, through a detection signal line 22, by a detection signal amplifier circuit including an amplifier 20 in the course, and outputted to a measuring instrument side. The number of the signal line necessary for this line is reduced to 15, compared with at least 18 in the case using no multiplexer. Accordingly, the narrowing of signal lines is dispensed with, and the improvement in spatial resolution for a subject to be detected can be attained without changing the total diameter of signal cables.
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