| 摘要 |
<p>PROBLEM TO BE SOLVED: To effectively eliminate noise from the outside so as to detect weak in-phase noise in a cable to be measured with high sensitiveness by arranging a plurality of near magnetic field probe parts symmetrically with respect to the central line of the cable to be measured. SOLUTION: Near magnetic field probes P1, P2 are arranged symmetrically with respect to a cable C to be measured, while a magnetic field M1 based on the current in the cable C is concentric on the plane vertical to the cable C. Therefore, loop coils of the probes P1, P2 are vertical to the magnetic field M1, and the magnetic field M1 passes through the loop coils of the probes P1, P2 in the opposite directions mutually. External noise M2 generated from a noise source S passes parallelly in the same direction in the vicinities of the loop coils of the probes P1, P2. Although sensitiveness of the probe has polarity, a pair of the opposed probes P1, P2 are provided with opposite polarities mutually, so that only the signals of the probes P1, P2 due to the noise M2 are cancelled while a signal based on the magnetic field M1 by the current in the cable C is not canceled. When a plurality of pairs of probes are used, detection sensitiveness can be improved.</p> |
