| 摘要 |
PURPOSE:To detect the position of the opening part for connecting a branch pipe in a steel pipe by running a truck having electrodes in the steel pipe wherein resin coating is applied on the inside of gas pipe and the like and is burried under the ground, and utilizing the change in capacity of a capacitor comprising the steel pipe and the electrode. CONSTITUTION:The thermosetting resin coating 4 is applied on the entire inner surface of the steel pipe 1 comprising a conductor, and the opening part 2 for connecting the branch pipe is covered by the coating 4. The truck 6 is inserted into the steel pipe 1 by drawing it with cable 5, and the truck is advanced along the axial line of the steel pipe 1. A pair of electrodes 7 and 8 are provided in the truck 6. The capacity C1 between the steel pipe 1 and the electrode 7 and the capacity C2 between the steel pipe 1 and the electrode 8 are connected to the arms of bridge circuits, respectively. When the truck 6 comes directly under the opening part 2, the capacity C1 is changed, the bridge circuit is unbalanced, and an output is generated at the output terminals (a) and (b). The position of the opening part 2 is detected by said output, the truck 6 is stopped, the coating 4 which covers the opening part 2 is removed by a built-in drill and the like, and the steel pipe and the branch pipe 3 are communicated. |
