| 摘要 |
PURPOSE:To reliably detect the presence of a drain material lifted togetherwith a mandrel, by a method wherein a detecting signal pertaining to the length of the mandrel pulled from a drain material and a reference signal relative to the length of the mandrel pulled from a ground are compared with each other. CONSTITUTION:After a drain material 2 is driven through a mandrel 1, the mandrel 1 is started to be pulled out. Thereafter, when a detector 5 is raised togetherwith raising of the mandrel 1, when the detector passes through the fronts of objects 4 to be detected of the drain material 2, pulse signals are generated in order. When a pulling speed is constant, a detecting signal (a) is inputted to observing and recording devices 8 and 9, and when the speed is varied, a signal a' is inputted thereto. Meanwhile, when the pulling speed of the mandrel 1 is constant, a reference signal (b) is generated by a depth detecting and reference signal detecting device 10, and when said speed is varied, a signal b' is generated by said depth detecting and reference signal generating device. Thus, if the two signals are forced to coincide in the starting point of their generation with each other, the presence of the drain material lifted togetherwith the mandrel can be ascertained according to coincidence of the generating point of times of the signals (a) and (b) with each other or discordance therebetween. |
