CATHODE-RAY OSCILLOSCOPE (C.R.O)

What is Cathode-Ray Oscilloscope?

The cathode ray oscilloscope is an instrument which is used to display the magnitudes of changing electric current or potentials. The information is displayed on the screen of a "Cathode Ray Tube". This screen appears as a circular or rectangular window usually with a centimeter graph superimposed on it.For example, the pitcher tube in our TV set and display terminal of most computers are cathode-ray tubes.

The cathode-ray tube oscilloscope (C.R.O) consist of following component :

• The electronic gun with control grid
• The deflecting plates 
• A fluorescent screen

The Electronic Gun

The electronic gun consist of an electrons source which is an electrically heated cathode that ejects electrons. Electron gun also has an electrode called grid "G" for controlling the flow of electrons in the beam. The grid is connected to a negative potential. The more negative this potential, the more electrons will be repulsed from the matrix and consequently less will achieve the anode and the screen. The number of electrons reaching the screen determines the brightness of the screen. Hence, the negative capability of the network can be utilized as a lights up control. The anode is connected to positive potential and hence is used to accelerate the electrons. The electrons are engaged into a fine bar as they go through the anode.

The Deflecting plates

After leaving the electron gun, the electron beam passes between a pair of horizontal plates. A potential difference applied between these plates deflects the beam in vertical plane. This pairs of plates provides the Y-axis or vertical movement of the spot on the screen. A pair of vertical plates provide the X-axis or horizontal movement of the spot on the screen.

The Fluorescent Screen

 The screen of the cathode-ray tube consist of the thin layer of phosphor, which is a material that gives light as a result of bombardment by fast moving electrons.

The C.R.O is used in many field of science, displaying waveform, measuring voltages, range finding (as in radar), echo-sounding (to find the depth of sea-beats.