| 摘要 |
<p>PROBLEM TO BE SOLVED: To previously prevent an accident in which a cable is damaged by a drill by connecting a lead wire to a protection tube, connecting a lead wire conducted to the drill to a drilling device, and connecting the respective lead wires to a monitoring circuit. SOLUTION: A lead wire 13 for a drilling device 1 is connected to an input terminal E1 , while a lead wire 14 for a protection tube 9 is connected to an input terminal E2 . If a drill 3 breaks a wall of a cable insertion hole 7 and touches the protection tube 9 by an error in its direction in the midway of drilling, conduction between the input terminals E1 , E2 is attained, so that a divided potential ratio in a monitoring circuit is changed and a base potential of a monitoring transistor conducted when a power source is turned on is reduced, and consequently, the transistor is cut off. As a result, a switching relay is excited, and a power source for the drilling device 1 connected to the output terminals E1 , E2 is cut off, and the drill 3 is stopped.</p> |
