| 摘要 |
PURPOSE:To enable pulling up the withstand voltage characteristic of a test sample tube to a predetermined level and prevent its destruction or the like, by determining applicability of high voltages, the voltage value, and a voltage application period according to the detection level of leakage current between an anode and a lower part electrode. CONSTITUTION:A micro-current ammeter 8is connected between focusing electrode 3 and the earth, and the focusing electrode leakage current is measured in a test process m1. If the measured current is below the predetermined value, it is supposed that the necessary withstant voltage characteristic is achieved and the high voltage application process after position POS m2 is not performed. On the other hand, if the measured value is above the predetermined value, the process after position POS m2 is continued and further, similar process is repeated until spot knocking process finishes with the leakage current below the predetermined value. Since each test sample tube is thus checked for its reached level of the withstand voltage characteristic, and according to the result, spot knocking process is performed, the withstand voltage characteristic satisfying the predetermined distribution is obtained and generation of various side effect is prevented.
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