Explanation to the Block Diagram Of CRO

Block diagram of CRO

The below fig gives the block diagram of a CRO. A CRO consists of the following main blocks.

1.       Cathode Ray Tube (CRT)

2.       Vertical amplifier

3.       Delay line

4.       Trigger circuit

5.       Time-base generator

6.       Horizontal amplifier

7.       High / low voltage supply.

Pic 1 Block Diagram of CRO

CRT is the heart of the CRO. It produces visual pattern on its screen. An electron gun assembly produces a sharp beam of electrons which is accelerated and made to strike fluorescent screen. On the other side of this screen, a small visual spot is produced. In this journey from the electron gum, the electron beam passes through a pair of vertical deflecting plates and another pair of horizontal deflecting plates.

The vertical deflecting plates move the beam vertically up and down. The horizontal deflecting plates move the beam the sideways. They are independently operated by the application of voltages to the corresponding plates with required polarities. By properly applying the potentials on the deflecting plates, the electron beam can be made to move to any part of the fluorescent screen.

The signal whose waveform is to be analyses is given to the vertical input terminals of the CRO. An amplifier called the vertical amplifier amplifies the input signal. The output in the push-pull form to applied to the vertical deflection plates through a delay line. The time base generator or sweep generator produces a saw tooth wave form. The rate of this waveform is controlled by a control on the front panel of CRO. The time base generators output is amplified in an amplifier is called the horizontal amplifier. After amplification it is given to the horizontal deflection plates in push-pull form. Application of the voltage to the horizontal deflection plates makes the spot on the screen to deflect from left to right.

The trigger circuit controls the instants at which the sweet voltage is to be applied to the horizontal deflection plates. There are two power supplies called HT supply and LV supply. The HT supply, supplies the voltage to the electrodes of CRT whereas LV supply supplies to other devices used in CRO.