| 摘要 |
PROBLEM TO BE SOLVED: To monitor the emission current at need while displaying an accurate value by starting the display of the emission current on the basis of the signal for showing the conclusion of automatic start-up by an automatic start-up control means. SOLUTION: After concluding the flashing, a control part 21 controls the extraction voltage between an emitter 11 and an extraction electrode 12 with an extraction voltage generating circuit 3. The extraction voltage is controlled step by step at about 50 V, and raised to the predetermined extraction voltage, and rise of a field emission type electron gun FEG 10 is concluded. The control unit 21 holds a switch 24 in the short-circuit condition during a period from a start to the finish of the start-up in consideration that it is unnecessary to display the emission current during this period. After completion of the start-up, the control unit 21 inputs the emission current display signal to a switch driving circuit 22, and the switch 24 is switched for open so as to display the emission current.
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