Structure of Cathode Ray Oscilloscope

The cathode-ray oscilloscope (C.R.O.) consists of the following components:
  1. The electron gun.
  2. The deflecting plates.
  3. A fluorescent screen.

The electron gun

Parts of Electron Gun Function
 Filament  To heat the cathode.
 Cathode  Release electrons when heated by filament.
 Grid
  •  The grid is connected to a negative potential. The more negative this potential, the more electrons will be repelled from the grid and fewer electrons will reach the anode and the screen.
  • The number of electrons reaching the screen determines the brightness of the light. Hence, the negative potential of the grid can be used as a brightness control.
 Focusing Anode and 
  •  The other feature in the electron gun is the use of the anode.
  • The anode at positive potential accelerates the electrons and the electrons are focused into a fine beam as they pass through the anode.
 Accelerating anode


The deflecting plates

Part of the deflecting system Function 
 Y-plate The Y-plates will cause deflection in the vertical direction when a voltage is applied across them.
  X-plate  On the other hand, the X-plates will cause the electron beam to be deflected in the horizontal direction if a voltage is applied across them.


The fluorescent screen

  1. The screen is coated with a fluorescent salt, for example, zinc sulphide.
  2. When the electrons hit the screen, it will cause the salt to produce a flash of light and hence a bright spot on the screen.