# 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.

Construction:

The 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.
• They 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.

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