Oscilloscope Tutorial: Basics and Construction

Cathode Ray Oscilloscope Tutorial:

Oscilloscope Introduction and Construction:

The CRO is used to measure both AC and DC voltages. In this post we will discuss about internal components of the oscilloscope.


Oscilloscope_constructionThe basic arrangements of the scope is given above. The main components are the electron gun, a focusing system, a beam deflection system and screen.

Electron gun assembly:
It produces a beam of electrons. This beam can be accelerated, down the axis of the tube, by a series of high potential anodes.

Focusing system:

  • The beam generated by an electron gun consists of electrons completely.
  • As they are negatively charged, they will tend to repel each other. So the beam will tend to spread out, it leads to a very fuzzy display.
  • The focusing system consists of high potential anodes as shown in the figure.
  • oscilloscope_ScreenThey will provide the acceleration for the electron beam.
  • Each successive anode along the tube, towards the screen, is at a higher potential than the previous one.
  • As a double convex optical lens used, the electric fields in between the anodes will be of the same shape.
  • The double convex optical lens are called as electron lens which causes the beam to converge to a small spot by the time it reaches the screen.

Deflection system:

  • Two sets of parallel plates are placed after the last anode.
  • One set is mounted in the horizontal manner,and the other set in mounted in the vertical manner.
  • They are called as X-plates and Y-plates.
  • When a potential difference is developed between a pair of plates, an electric field will exist between them.
  • This field will cause the electrons in the beam to be deflected, towards the more positive of the two plates.
  • Thus the beam can be made to deflect in both planes.

The screen:

  • The inner surface of the screen is coated with a phosphor.
  • When an electron beam strikes the phosphor, that particular place will glow very briefly.
  • It happens because the kinetic energy of the bombarding electrons is converted into light energy.
  • On the inside of the bell shape of the tube, a graphite coating is applied. It gives a conducting path to return the electrons to the internal power supply and thus complete the circuit back to the electron gun.
  • In order for a waveform to be displayed on the screen, the beam must be swept at a constant speed across the screen. At the same time, it has to be deflected up and down.
  • The X-plates makes the beam to be swept across the screen at a constant rate. The Y-plates makes the beam to deflect up and down, according to the voltage to be displayed.

We recommend you to read about What are the things to be considered while buying an Oscilloscope?

Read More:

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2 Responses

  1. Laison says:

    I appreciate your service

  2. Prit says:

    Thank you for giving lesson in very simple language

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