| 摘要 |
<p>PURPOSE:To facilitate the detection of metal by a method wherein a pulse-like current is applied to a sensor coil to detect the existence of the metal depending on a change in transient response characteristic of a reflected wave when the current is cut. CONSTITUTION:The tip part 1 of a drilling rod of an excavator has a cylindrical ERP resin-made tip part 4 provided at a pipe joint 3 at a tip opening of a pipe 2 and a sensor coil 10 for detecting metal is provided centered on the axial direction of the tip part 4. When the operation of a comparator 22 is OFF, a pulse applied to the sensor coil 10 for detecting metal falls, a waveform across both ends of the coil 10 increases from a negative level and then, rises at a point exceeding a reference voltage. Therefore, an output waveform is expressed by a change in the waveform converted to time as caused with the approaching of metal, where a pulse width at the OFF part appears at both ends of the coil 10. An output signal of the comparator 22 is outputted to a gate circuit 23 and a clock pulse outputted from a clock pulse circuit 15 is outputted with the gate circuit 23 corresponding to the OFF part of the output signal of the comparator 22. The number of clock pulses is counted with a counter and when the number is larger than the number of reference counts, a signal indicating the existence of metal is outputted.</p> |
