| 摘要 |
PURPOSE:To eliminate the influence of the magnetic field of a main pipe even nearby a branch point of a duct by arranging two magnetic sensors which have equal characteristics coaxially, putting their outputs together differentially, and performing measurement so that sensitivity is high and an error is small. CONSTITUTION:A high-frequency current (10-100kHz) is supplied to a buried metallic pipe 1, etc., directly or inductively and a generated electromagnetic wave is detected by using two magnetic sensor coils L1 and L2. The sensor coils L1 and L2 which have equal characteristics are arranged coaxially at an interval (d) and connected differentially. Those sensor coils L1 and L2 are moved over the buried metallic pipe 1 to be measured and then the sensor coils L1 and L2 at respective positions on a center point O generate electromotive forces +M and -M. Therefore, it is found that the buried metallic pipe 1 is right below the point O where the composite reception output waveform is minimum. Further, when the buried metallic pipe 1 is a branch pipe, lines (p) of magnetic force by the current of the main pipe 2 are not cross-linked with the sensor coils L1 and L2, so only the lines (q) of magnetic force of the branch pipe generate electromotive force, so that a differential voltage is outputted. |
