Block Diagram of CRO (Cathode Ray Oscilloscope), Components of CRO and CRT with Structure and Working

In this post we will learn what is a Cathode Ray Oscilloscope. In short we call it as CRO. Here we will discuss the block diagram and working of CRO. Functioning of each block of CRO will be explained here in detail. 
Before understanding the structure and working of the cathode ray oscilloscope, let's see applications of CRO.

Watch the Complete Video Here-

Applications of Cathode Ray Oscilloscope (CRO)

#CRO can be used for measuring voltage
#For measuring current
#For measuring phase and frequency of the signal
and 
#For analyzing the waveform of the signal in various ways

Components of Cathode Ray Oscilloscope (CRO)

Observe the image shown below-

Block Diagram of Cathode Ray Oscilloscope (CRO)

#Cathode Ray Tube (CRT)
#Vertical amplifier
#Delay line
#Trigger circuit
#Time base generator
#Horizontal Amplifier

Components of the Cathode Ray Tube (CRT)

#Filament
#Cathode plate
#Grid
#Accelerating anode plates
#Deflection plates (vertical deflection plates and horizontal deflection plates)
#Phosphor screen

The filament, cathode plate, grid and accelerating anode plates together make the electron gun.
The job of this electron gun is to produce high velocity electron beam.
Cathode ray tube (CRT) is the main part of the cathode ray oscilloscope. Therefore CRT is called as the 'Heart of the CRO'.


Now you are familiar with the terms and parts used in the cathode ray oscilloscope. So let's discuss the working of CRO.
First of all we will see the functioning of cathode ray tube

Cathode Ray Tube (CRT)

The main parts of cathode ray tube are-
#1-Electron gun (filament, cathode plate, grid, accelerating anodes)
#2-Deflection plates (vertical deflection plates and horizontal deflection plates) and
#3-Phosphor screen
As I describe its structure and functioning, please carefully see the image-

#1-Electron Gun in CRT (filament, cathode plate, grid, accelerating anodes)

The filament present in the cathode ray tube emits electrons when it is heated. If this filament acts as a cathode, then we call it the direct cathode but if we use a cathode plate and this cathode plate works as the cathode then we call it as indirect cathode (see the image shown).
We also have a grid here and we apply negative potential to this grid. The job of this grid is to control the number of electrons emitted. So as the negative potential of this grid is increased, the number of electrons emitted decreases and vice versa.
In this way by changing the negative potential applied on the grid we can control the number of electrons emitted. There is a small hole in this grid that allows the electrons to pass through it.
We also have 3 accelerating anodes in the cathode ray tube. They have positive potential. As these have positive potential, so they attract the negatively charged electrons, therefore electrons get accelerated.
Here it is important to note that, the positive potential applied on these accelerating anodes is in increasing order.
In the image these three accelerating anodes are shown by A1, A2 and A3. So the A1 has least positive voltage, while A3 has highest positive voltage. So all these parts that include filament, cathode plate, grid and accelerating anodes make the electron gun of CRT.

#2-Deflection Plates in CRT (Vertical deflection plates and Horizontal deflection plates)

Now this high velocity electron beam after acceleration passes through two types of deflection plates system.
First of all it passes through the vertical deflection plates and then the horizontal deflection plates.
It is very clear by the name itself that the job of the vertical deflection plates is to deflect the electron beam vertically, while horizontal deflection plates cause the electron beam to deflect in horizontal direction.
As you can see in the image that the input signal that we want to analyse on the screen of the CRO, is applied on the vertical plates through vertical amplifier and delay line. And on the screen of the CRO gets the waveform of the applied input signal.
Actually screen of the CRO is the phosphor screen which produces luminous spot, when the electron beam strikes the screen. 
The deflecting plates deflect the electron beam according to the input signal, therefore when this electron beam strikes on the phosphor screen then the waveform of the input signal to be analyzed is produced on it

#3-Phosphor Screen in CRT

The screen of Cathode Ray Tube (CRT) is a Phosphor Screen which produces luminous spot when the electrons strike on it. So the complete waveform of the input signal is traced on the CRT screen. This happens because the electron beam is deflected by the deflection plates according to the signal to be analysed. Waveform of the signal is produced with time as the x axis on the screen. We will see here, that this time axis is produced by the time base generator used in the CRO.

Now we will understand functioning of other blocks used in the block diagram of Cathode Ray Oscilloscope (CRO)-

Block Diagram of Cathode Ray Oscilloscope (CRO)

Construction and Components of Cathode Ray Oscilloscope (CRO)

Look once again at the image carefully-
The input signal that we want to analyse is applied on the vertical amplifier, so that it can be raised to enough voltage which is necessary for the vertical deflection plates to deflect the accelerating electron beam. After this vertical amplifier, a delay line is used. The purpose of this delay line is to produce delay, equal to the delay caused in the trigger circuit and time base generator combined. Because it is very necessary that the signal should reach to both of the deflection plates (vertical and horizontal) simultaneously (at the same time). Because if the signal doesn't reach to these deflecting plates at the same time, then difference in phase will be created and we will not get the correct shape of the wave on the CRT screen. So in this way this delay line compensates for the delay caused in the trigger circuit and time base generator.
As you can observe that the output of the vertical amplifier is divided into two parts. The first part goes into the delay line and then to the vertical deflection plates while another part goes into the trigger circuit and it finally reaches to the horizontal deflection plates after passing through the time base generator and horizontal amplifier.
Now you will see what is the purpose of this Trigger circuit and the time base generator.

Trigger circuit in CRO

The main job of the triggering circuit is to provide synchronization between the horizontal and vertical deflections, so that the horizontal deflection start at the same point of the input vertical signal, each time it sweeps. Because it is required that the signal should reach simultaneously at the both deflecting plates.
The output of this trigger circuit is applied to the time base generator. Now let's understand the working and function of the time base generator.

Time base generator in CRO

The purpose of time base generator in CRO is to develop the horizontal sweep voltage, that deflects the beam left to right which represents the time axis. 
As on the screen of CRO we get a plot of signal against time. This time is shown on the x-axis on the screen. It is also clear by the name ' time base generator', that it is used to produce or generate the time base used for plotting the waveform.
It repeats a sawtooth waveform at a rate that determines the time per division on the screen.
Now the output of this time base generator is supplied to the horizontal amplifier. This horizontal amplifier amplifies the signal to a level enough to deflect the electron beam horizontally.
One more thing that is important here is, high voltage is supplied to the cathode ray tube but to all other circuits of the CRO, we apply low voltage. The reason behind this is; to accelerate electrons to high velocity, high voltage supply is necessary.
So this was all about the basic structure and functioning of the cathode ray oscilloscope (CRO) with the help of block diagram along with its applications.

Read More-

Go To HOME Page
   
FREQUENCY SPECTRUM OF AMPLITUDE MODULATION (WAVEFORMS AND EQUATIONS DERIVATION)

AMPLITUDE MODULATION (TIME DOMAIN EQUATIONS AND WAVEFORMS)

ADVANTAGES AND DISADVANTAGES OF DIGITAL COMMUNICATION SYSTEM

ADVANTAGES OF OPTICAL FIBER COMMUNICATION

STEP INDEX OPTICAL FIBER (MULTIMODE AND SINGLE MODE STEP INDEX FIBERS)

PULSE MODULATION TECHNIQUES (PAM, PWM, PPM, PCM)

OPTICAL FIBER: STRUCTURE AND WORKING PRINCIPLE

PULSE AMPLITUDE MODULATION (PAM)

COMPARISON OF PAM, PWM, PPM MODULATION TECHNIQUES

PULSE WIDTH MODULATION (PWM)

CONTINUOUS TIME AND DISCRETE TIME SIGNALS (C.T. AND D.T. SIGNALS)

NEED AND BENEFITS OF MODULATION

PULSE POSITION MODULATION (PPM)

OPTICAL FIBERS IN COMMUNICATION: COVERS ALL IMPORTANT POINTS

OPTICAL FIBER SOURCES (DESIRABLE PROPERTIES)

AMPLITUDE MODULATION Vs FREQUENCY MODULATION (ADVANTAGES AND DISADVANTAGES)

PULSE CODE MODULATION (PCM) [ADVANTAGES AND DISADVANTAGES]

SAMPLING THEOREM AND RECONSTRUCTION (SAMPLING AND QUANTIZATION)

SUPERPOSITION THEOREM (BASICS, SOLVED PROBLEMS, APPLICATIONS AND LIMITATIONS)

Digital Modulation Techniques (ASK, FSK, PSK, BPSK)/ Amplitude, Frequency and Phase Shift Keying

Conventional AM Vs DSB-SC Vs SSB-SC Vs VSB (Comparison of AM Systems)

Quadrature Amplitude Modulation (QAM)/ QAM Transmitter and QAM Receiver Block Diagram

Single-Mode Optical Fiber Advantages

What are Microwaves and their Applications (Uses) in various fields

Microwaves Properties and Advantages (Benefits)

Basic Structure of Bipolar Junction Transistor (BJT) - BJT Transistor - Working and Properties

Polar Plots of Transfer Functions in Control Systems (How to Draw Nyquist Plot Examples)

Generation of Binary Phase Shift Keying (BPSK Generation) - Block Diagram of Binary Phase Shift Keying (BPSK)

Low Level and High Level Modulation Block Diagram (AM Transmitter Block Diagram)

Block Diagram of CRO (Cathode Ray Oscilloscope), Components of CRO and CRT with Structure and Working

Slope Overload Distortion and Granular (Idle Noise), Quantization Noise in Delta Modulation

Frequency Translation/Frequency Mixing/Frequency Conversion/Heterodyning (Basic Concepts and Need)

Quadrature Phase Shift Keying Modulation (QPSK) Basics, Waveform and Benefits

Pulse Code Modulation (PCM) Vs Differential Pulse Code Modulation (DPCM)

Digital Modulation Techniques (Coherent and NonCoherent Digital Modulation Techniques)