Abstract: A layered insulated conductor pair is provided which can be easily manufactured in inexpensive facilities and with which a highly precise and stable degree of electromagnetic coupling can be obtained. A guide cable also is provided using such a layered insulated conductor pair. The layered insulated conductor pair 10A of one embodiment includes a plurality of film-shaped insulators 13, 13' placed one over another, and each insulator has line conductors 11, 11' of specified shape fixed to its front surface or its inside. The layered insulated conductor pair 10B of a second embodiment includes a single film-shaped insulator having line conductors 11, 11' of specified shape fixed to its front surface or its inside. The layered insulated conductor pair 10C of a third embodiment includes electromagnetic screening layers 20 arranged at intervals in close contact with the conductors 11, 11'.

Abstract: A plurality of radiation receiving elements disposed outside a pipe at equal distances from the axis thereof so that radiation from a radiation source is received through the pipe wall. As the thickness of the pipe wall varies, the received radiation varies accordingly. If the received radiation fluctuates in excess of the allowable range, the thickness of the pipe wall is judged to be outside the allowable range. When the fluctuation of the received radiation is within the allowable range, the thickness of the pipe wall is within the preset tolerances.