| 摘要 |
PURPOSE:To discriminate deterioration with high accuracy, by detecting the displacement velocity of a drill and discriminating disappearance of annual ring patterns at the velocity signal. CONSTITUTION:An output signal of an amplifier circuit 6 of a displacement signal of a drill is compared with a reference level L at a comparator 7 to obtain a pulse and the periods Ti, Ti+1, Ti+2- are detected at a period detection circuit 8. That is, the maximum value of the period is predetermined and the period Ti which becomes greater than the value is detected or the ratio Ti+1/Ti is set to detect that the measured value is greater than the set value of the Ti+1/Ti. Thus, when a signal pattern in response to annual rings is disappeared, a deterioration detection signal (d) is outputted for display or recording. Thus, the dicrimination with high accuracy can be performed. |
