| 摘要 |
PURPOSE:To make complicated replacement of the detector unnecessary by using a switch to turn on and off the multiplication voltage applied across the ends of the second diode plate upon which secondary electrons multiplied by the first diode plate become incident. CONSTITUTION:A control circuit 17 compares the signal from an ampere meter 16 for measuring the current flowing through a sample 1 with a preset value. When the measured current of the sample 1 is greater than the preset value and a relatively small amount of electron rays are incident upon a diode plate 7, an on-signal is delivered to a detection mode change-over switch 13. As the result, the switch 13 is turned on, and while a multiplication voltage is applied from a first multiplication power supply 9 across the ends of the plate 7 a detection voltage is applied from a second multiplication power supply 12 across the ends of a plate 8. As the result, a gain produced by multiplying the gains of the plates 7 and 8 together is obtained, which is advantageous for pulse operation. When the measured current level of the sample 1 is not higher than the preset value and a relatively large amount of electron rays becomes incident upon the plate 7, an off-signal is delivered from the switch 13. As the result, a multiplication voltage is not applied across the ends of the plate 8. Therefore, this device can be used for both AC technique and DC technique. |
