CRACK DIAGNOSTIC APPARATUS

PURPOSE:To make it possible to easily grasp the deterioration of insulating coating through nondestructive measurement by sliding a contact needle in the longitudinal direction along with a substrate, while bringing the contact needle into pressure contact with the insulation coating of an insulated wire. CONSTITUTION:A retractable contact needle 14 projects perpendicularly to the longitudinal direction of an insulated wire 1. When a substrate 11 is brought into contact with a sound insulation coating 3, the contact needle 14 compresses a piezoelectric element 16 through a spring 15. At that time, the electric output from an external conduction terminal 17 makes a transition from 0 to 1. When the substrate 11 is loaded to the cracked insulation coating of the insulated wire 1 and slid in the longitudinal direction, the contact needle 14 falls into the cracked part 4 to released the piezoelectric element 16 and thereby the electric output from the external conduction terminal makes a transition from 1 to 0. The transition of electric output from 1 to 0 upon reaching the cracked insulation coating 3 is expressed in terms of the thickness of coating thus obtaining a signal corresponding to the depth of crack.