| 摘要 |
PURPOSE:To make it possible to display an accurate image while maintaining constant deflecting-coil current, by adjusting the variation width of a deflecting signal voltage applied to the deflecting coil of a cathode-ray tube in combination with an adjustment of the frequency of a scanning deflecting signal. CONSTITUTION:Circuit 1, generating a scanning signal of a desired frequency with a control signal from frequency control circuit 4, inputs a scanning signal to the electron-beam deflecting electric power source of the electron microscope via terminal P and also inputs the scanning signal to deflecting coil 3 of the cathode-ray tube for displaying a sample scanning image of the electron microscope via other terminal Q. Deflecting coil 3 is provided with resistance groups R51-R5n and R31- R3n which can selectively be connected and when the frequency of the scanning signal is changed over, those resistances can selectively be connected. Even when the voltage applied to coil 3 varies, the current is kept constant through those resistances. |
