Patent ID: 7808250

Claim:
A test method for a cylindrical spark plug insulator, comprising: providing a first test electrode having either a rod shape or a column shape, a second test electrode and a reference insulator formed of the same material and having the same shape and size as the spark plug insulator; determining a reference voltage to be higher than or equal to a short-circuit voltage between the first and second test electrodes when the first and second test electrodes are located apart from each other with a predetermined space left there between for placement of the spark plug insulator; determining a test area in which the second test electrode can be moved along an outer peripheral side of the reference insulator without the occurrence of a flashover under the application of the reference voltage between the first and second test electrodes when the first test electrode is in a position in an axial hole of the reference insulator corresponding to a given part of the spark plug insulator to be tested; determining a test voltage to be a maximum value lower than a flashover voltage of the reference insulator between the first and second test electrodes when the first test electrode is in said position in the axial hole of the reference insulator and the second test electrode is within the test area on the outer peripheral side of the reference insulator; placing the spark plug insulator between the first and second test electrodes by inserting the first test electrode in an axial hole of the spark plug insulator and arrange the second test electrode on an outer peripheral side of the spark plug insulator; after said placing, detecting an electric current between the first and second test electrodes under the application of the test voltage between the first and second test electrodes while fixing the first test electrode in position relative to the spark plug insulator and moving the second test electrode to an arbitrary position within the test area along the outer peripheral side of the spark plug insulator; and judging the presence or absence of a defect in the spark plug insulator based on the detected electric current between the first and second test electrodes.