| 摘要 |
PURPOSE:To obtain an electron beam device of a high safety to human body, by controlling the irradiation current minutely with a D/A converter, and preventing the maximum irradiation current from exceeding a preset value. CONSTITUTION:When the acceleration voltage of an acceleration power source 8 is converted, the data of a lens current responding to the maximum irradiation beam current is read and fed at every acceleration voltage to a latch circuit 10a from a memory 9a which is connected to an arithmetic control circuit 9. Therefore, when the acceleration voltage is converted by the power source 8, a signal to show the acceleration voltage is fed to the circuit 9 from the power source 8, and a data to be the maximum radiant current is fed to the circuit 10a from the circuit 9, and D/A converted 10b. On the other hand, to a latch circuit 11a of an irradiation current setting circuit 11, a radiant beam current set signal is fed from an external control unit 12 and D/A converted. The analog signals from the circuits 10b and 11b are added 13, and a lens power source 7 is controlled by the resultant output, to control the lens current of a focus lens 3.
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