CRO Block Diagram and Working Principle

Hi friends, in this article we will learn Cathode Ray Oscilloscope (CRO). We will see the introduction, a block diagram of CRO and CRO Working.

CRO Working

Every electronic circuit has multiple electronic components connected to each other. At some point in time, we need to test the working of a circuit with the help of some parameters like current, voltage, power, etc. For such kind of testing, a very commonly used electronic device is Cathode Ray Oscilloscope i.e. CRO. Lets first study the block diagram of CRO first and then we will move to Cathode Ray Oscilloscope CRO working.

Block Diagram of CRO:

CRO is made up of different blocks such as

  1. Cathode Ray Tube (CRT)
  2. Vertical amplifier
  3. Delay Line
  4. Trigger circuit
  5. Timebase generator
  6. Horizontal amplifier
CRO Block Diagram
CRO Block Diagram

CRO Working:

1. Cathode Ray Tube (CRT):

CRT Produces a sharply focused beam of electrons, accelerated to a very high velocity. This electron beam travels from the electron gun to the screen. The electron gun consists of filament, cathode, control grid, accelerating anodes and focusing anode. While travelling to the screen, electron beams passes between a set of vertical deflecting plates and a set of horizontal deflection plates. Voltages applied to these plates can move the beam in vertical and horizontal plane respectively. The electron beam then strikes the fluorescent material (phosphor) deposited on the screen with sufficient energy to cause the screen to light up in a small spot.

2. Vertical Amplifier:

The input signal is applied to the vertical amplifier. The gain of this amplifier can be controlled by VOLT/DIV knob. Output of this amplifier is applied to the delay line.

3. Delay Line:

The delay Line retards the arrival of the input waveform at the vertical deflection plates until the trigger and time base circuits start the sweep of the beam. The delay line produces a delay of 0.25 microsecond so that the leading edge of the input waveform can be viewed even though it was used to trigger the sweep.

4.Trigger (Sync.) Circuit:

A sample of the input waveform is fed to a trigger circuit which produces a trigger pulse at some selected point on the input waveform. This trigger pulse is used to start the time base generator which then starts the horizontal sweep of CRT spot from left hand side of the screen.

5. Time base (Sweep) Generator:

This produces a saw-tooth waveform that is used as horizontal deflection voltage of CRT. The rate of rise of a positive going part of the sawtooth waveform is controlled by TIME/DIV knob. The sawtooth voltage is fed to the horizontal amplifier if the switch is in the INTERNAL position. If the switch is in EXT. position, an external horizontal input can be applied to the horizontal amplifier.

6. Horizontal Amplifier:

This amplifies the saw-tooth voltage. As it includes a phase inverter two outputs are produced. Positive going sawtooth and negative going sawtooth are applied to right – hand and left – hand horizontal deflection plates of CRT.

7. Blanking Circuit:

The blanking circuit is necessary to eliminate the retrace that would occur when the spot on CRT screen moves from right side to left side” This retrace can cause confusion if it is not eliminate. The blanking voltage is produced by sweep generator. Hence a high negative voltage is applied to the control grid during retrace period or a high positive voltage is applied to the cathode in CRT.

When a sawtooth voltage is applied to horizontal plates and an input signal is applied to vertical plates, display of vertical input signal is obtained on the screen as a function of time.

8. Power Supply:

A high voltage section is used to operate CRT and a low voltage section is used to supply electronic circuit of the oscilloscope.

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Tags: Working of CRO, How CRO generates waveforms, Working principle of CRO, CRO working.

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