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14EE603 Hall Ticket Number:

III/IV B.Tech (Regular/Supplementary) DEGREE EXAMINATION

April, 2018 Electrical &Electronics Engineering

Sixth Semester Electrical Measurements &Instrumentation Time: Three Hours Maximum: 60 Marks

Answer Question No.1 compulsorily. (1X12 = 12 Marks)

Answer ONE question from each unit. (4X12=48 Marks)

1. Answer all questions (1X12=12 Marks) a) How Creeping adjustment is provided in induction type energy meter? b) What are the advantages of Two Wattmeter Method? c) What are the different types of damping torques in an electrical instrument? d) What is synchroscope? e) What is meant by instrument transformer? f) What do you understand by the term burden of a CT? g) Give the difficulty associated with the measurement of low resistances. h) Name the commonly used detectors for ac bridges. i) How can the range of ballistic galvanometer be increased. j) Enlist the applications of CRO k) What are the applications of Transducers? l) List the various focusing techniques

UNIT I 2. a) Distinguish between indicating, recording and integrating types of instruments. 6M b) Explain with neat sketch the working of attraction type moving iron instruments. 6M

(OR) 3. a) Explain the construction and working of a single phase induction type energy meter. Show that the total

number of revolutions made by its disc during a particular time is proportional to the energy consumed. 8M

b) The disc of an energymeter makes 600 revolutions per unit of energy. When a 1,000 watt load is connected, the disc rotates at 10.2 rpm. If the load is on for 12 hours, how many units are recorded as error?

4M

UNIT II 4. a) With the help of circuit diagram explain how capacitance can be measured by the use of a Schering

bridge. 6M

b) In an Anderson bridge for measurement of inductance Lx and Resistance Rx in the arm AB, the arm CD and DA have resistances of 600 Ω each and the arm CE has a capacitor of 1µ F capacitor with A.C. supply at 100 Hz supplied across A and C, balance is obtained with a resistance of 400 Ω in arm DE and 800 Ω in the arm BC. Calculate the value of Lx and Rx.

6M

(OR) 5. a) Distinguish between current transformer and potential transformer. 6M b) Explain the major sources of errors in current transformers? Draw the equivalent circuit of current

transformer. 6M

UNIT III 6. a) What is strain gauge? Explain the working of semiconductor strain gauge with neat diagram. 6M b) Explain the operation of LVDT with neat diagram and Give its applications. 6M

(OR)

7. a) Derive an expression for equation of motion of a ballistic galvanometer? 6M

b) A flux meter is connected to a search coil having 500 turns and a mean area of 500 mm2 . The search coil is placed at the center of a solenoid 1 metre long, wound with 800 turns. When a current of 5A is reversed, there is a deflection of 25 scale divisions. Calculate the flux linkages per scale division

6M

UNIT IV

8. a) Draw Lissajoes pattern for various phase angles. 8M b) Explain how to measure frequency. 4M

(OR) 9. a) Explain the theory and working of a LCD display devices and Give its merits. 6M b) with neat diagram explain the construction and working of a CRO 6M

Bapatla Engineering College: Bapatla (AUTONOMOUS) EEE Department

Class: 3/4 EEE SCHEME OF VALUATION Date: 09/04/2018 Sub. Code: 14EE603 SIXTH SEMESTER Max.Marks:60M

Electrical Measurements &Instrumentation

1. Answer all questions 1X12=12M

a) Two diametrically opposite holes are drilled in the disc of energy meters. Due to this hole, the disc

will come to rest when the hole comes under the edge of pole of shunt magnet. Thus creeping is

limited to a maximum of half of the rotation. Now we will discuss how the disc comes to rest

when hole comes under the edge of pole of shunt magnet.

b) Advantages of Two Wattmeter Method. The various advantages of two wattmeter method are ,

The method is applicable for balanced as well as unbalanced loads. Neutral point for star

connected load is not necessary to connect the watt meters. ... Only two watt meters are sufficient

to measure total 3 phase power.

c) There are three types of damping instruments: 1.Critical damp- Pointer rises quickly to its final

position without oscillation. ... Air friction or pneumatic damping 2. Eddy current or

electromagnetic damping 3. Fluid friction damping.

d) In AC electrical power systems, a synchro scope is a device that indicates the degree to which two

systems (generators or power networks) are synchronized with each other. Synchro

scopes measure and display the frequency difference and phase angle between two power systems.

e) Instrument transformers are high accuracy class electrical devices used to isolate or transform

voltage or current levels. The primary winding of the transformer is connected to the high voltage

or high current circuit, and the meter or relay is connected to the secondary circuit.

f) The load, or burden, in a CT metering circuit is the (largely resistive) impedance presented to its

secondary winding.

g) The major problem in measurement of low resistance values is the contact resistance or lead

resistance of the measuring instruments, though being small in value is comparable to the

resistance being measured and hence causes serious error.

h) Head phones, tuned amplifiers, vibration galvanometers

i) By using shunts

j) The CRO stands for a cathode ray oscilloscope. It is typically divided into four sections which are

display, vertical controllers, horizontal controllers, and Triggers. Most of the oscilloscopes are

used the probes and they are used for the input of any instrument.

k) A transducer is an electrical device which is used to convert one form of energy into another form.

The best examples of the transducer are mic, fluorescent bulb and speaker can be considered as

a transducer. Likewise, there are different kinds of transducers used in electrical and electronic

projects.

l) Electrostatic focusing & Magneto static focusing.

UNIT – I

2 a) Measuring instruments (i.e. secondary instruments) may be classified according to their function as:

1. Indicating instruments

2. Integrating instruments

3. Recording instruments

1. Indicating instruments: “Indicating instruments are those which indicate the magnitude of an

electrical quantity at the time when it is being measured.”

Their indications are given by a pointer moving over calibrated dial.

Example: Ordinary voltmeters, ammeters and wattmeter’s, etc.

2. Integrating instruments: “Integrating instruments are those which measure and register by a set of

dials and pointer either the total quantity of electricity (In amp-hours) or the total amount of electrical

energy (in watt-hours or kWh) supplied to a circuit in a given time.”

Example: The ampere-hour meters and energy (watt-hour) meters

3. Recording instruments: “Recording instruments are those which give a continuous record of the

variation of the electrical quantity over a selected period of time.”

The moving system of the instruments carries an inked pen which rests lightly on a chart or graph,

wrapped over a drum moving with a slow uniform speed. The motion of the drum is in a direction

perpendicular to that of the pointer. The path traced out by the pen indicates of the electrical quantity.

Example: Recording voltmeter and ammeter.

Uses: These instruments are generally used in supply stations (i.e. power houses) where continuous

information is required.

2.b) Attraction Type – The instrument in which the iron plate attracts from the weaker field towards the

stronger field such type of instrument is known as the attraction type instrument.

Construction of Attraction Type Instrument – The stationary coil of the attraction type instrument is flat

and has a narrow opening. The moving element is the flat disc of the iron core. The current flow through

the stationary coil produced the magnetic field which attracts the iron coil.

The iron vane deflects from the low magnetic field to the high magnetic field, and the strength of the

deflection is directly proportional to the magnitude of the current flow through it. In short, we can say that

the iron coil attracts towards in. The attraction type instruments use spring, which provided the

controlling torque. The deflection of the coil is reduced by the aluminium piston which is attached to the

moving coil.

(OR)

3.a) Induction type energy meter essentially consists of following components:

1. Driving system 2. Moving system 3. Braking system and 4. Registering system

It consists of two electromagnets, called “shunt” magnet and “series” magnet, of laminated construction.

A coil having large number of turns of fine wire is wound on the middle limb of the shunt magnet. This

coil is known as “pressure or voltage” coil and is connected across the supply mains. This voltage coil

has many turns and is arranged to be as highly inductive as possible. In other words, the voltage coil

produces a high ratio of inductance to resistance.

An adjustable copper shading rings are provided on the central limb of the shunt magnet to make the

phase angle displacement between magnetic field set up by shunt magnet and supply voltage is

approximately 90 degree. The copper shading bands are also called the power factor compensator or

compensating loop. The series electromagnet is energized by a coil, known as “current” coil which is

connected in series with the load so that it carry the load current. The flux produced by this magnet is

proportional to, and in phase with the load current.

Moving system

The moving system essentially consists of a light rotating aluminium disk mounted on a vertical spindle

or shaft. The shaft that supports the aluminium disk is connected by a gear arrangement to the clock

mechanism on the front of the meter to provide information that consumed energy by the load. The time

varying fluxes produced by shunt and series magnet induce eddy currents in the aluminium disc. The

interaction between these two magnetic fields and eddy currents set up a driving torque in the disc. The

number of rotations of the disk is therefore proportional to the energy consumed by the load in a certain

time interval and is commonly measured in kilowatt-hours (Kwh).

Braking system

Damping of the disk is provided by a small permanent magnet, located diametrically opposite to the a.c

magnets. The disk passes between the magnet gaps. The movement of rotating disc through the magnetic

field crossing the air gap sets up eddy currents in the disc that reacts with the magnetic field and exerts a

braking torque. By changing the position of the brake magnet or diverting some of the flux there form, the

speed of the rotating disc can be controlled.

Working of Single phase induction type Energy Meter

1. Mechanism of rotation of an aluminum disc which is made to rotate at a speed proportional to the

power.

2. Mechanism of counting and displaying the amount of energy transferred.

Mechanism of rotation of an aluminum disc, Which is made to rotate at a speed proportional to the

power.

The metallic disc is acted upon by two coils. One coil is arranged in such a way that it produces a

magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the

current. The field of the voltage coil is delayed by 90 degrees using a lag coil. This produces eddy

currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of

the instantaneous current and voltage. A permanent magnet exerts an opposing force proportional to the

speed of rotation of the disc this acts as a brake which causes the disc to stop spinning when power stops

being drawn rather than allowing it to spin faster and faster. This causes the disc to rotate at a speed

proportional to the power being used. The register is a series of dials which record the amount of energy

used.

3. b) Since load power is one KWH, energy actually consumed is = 1KW X 12Hr= 12KWHr

Total number of revolutions made by the disk during the period of 12Hrs = 10.2 X 12=122.4

Since 600 revolutions record 1KWHr, energy record by the meter is 122.4/600 = 0.204KWHr

UNIT – II

4 a) Let, C1=capacitor whose capacitance is to be measured. r1= a series resistance representing the loss in the capacitor C1. C2= a standard capacitor. R3= a non inductive resistance. C4= a variable capacitor. R4= a variable non inductive resistance. At balance,

or

Equating the real and imaginary terms in equa. (2), we obtain

and Two independent balance equations (3) and (4) are obatined if C4 and R4 are chosen as the variable elements. Dissipation factor

.

4. b)

RX=(R2*R4)/R3=800*600/600=800

LX=C*R2/R3[R4(R3+R4)+R4*R3=

=10^-6*800/600[400(600+600)+600*600]=1.12 hendry

(OR)

5. a)

Basis for Comparison Current Transformer Potential Transformer

Definition Transform the current from high value to the low value.

Transform the voltage from high value to the low value.

Circuit Symbol

Core Usually built up with lamination of silicon steel.

It is made up of with high quality steel operating at low flux densities

Primary Winding It carries the current which is to be measured

It carries the voltage which is to be measured.

Secondary Winding It is connected to the current winding of the instrument.

It is connected to the meter or instrument.

Connection Connected in series with the instrument Connected in parallel with the instrument.

Primary Circuit Has a small number of turns Has a large number of turns

Secondary Circuit Has a large number of turns and cannot be open circuit.

Has a small number of turns and can be open circuit.

Range 5A or 1A 110v

Transformation Ratio High Low

Burden Does not depends on secondary burden Depends on the secondary burden

Input

Full line current

Types

Impedance

Applications

5. b)

The total primary current is not actually transformed in CT. One part of the primary current is consumed

for core excitation and remaining is actually

current transformer means there are both

in current transformer.

6. a) A device for indicating the strain of a material or structure at the point of attachment.semiconductor strain gauge is formed by the wafers or filaments of length varying from 2 mm to 10 mm and thickness of 0.05 mm are bonded on suitable insulating substratescontacts. The electrodes are formed by vapour deposition. The assembly is placed in a protective box as shown in the figure below.

Constant current Constant Voltage

The primary winding consists the full line current.

The primary winding consists the full line voltage.

Two types ( Wound and Closed Core ) Two types (Electromagnetic and Capacitor voltage)

Low High

Measuring current and power, monitoring the power grid operation, for operating protective relay,

Measurement, power source, operating protective relay,


for core excitation and remaining is actually transformers with turns ratio of CT so there is

means there are both ratio error in current transformer as well as a

UNIT – III

A device for indicating the strain of a material or structure at the point of attachment.semiconductor strain gauge is formed by the semiconductor technology i.e., the semiconducting wafers or filaments of length varying from 2 mm to 10 mm and thickness of 0.05 mm are bonded

substrates. The gold leads are usually employed for making electrical odes are formed by vapour deposition. The assembly is placed in a protective

box as shown in the figure below.

The primary winding consists the full line

Two types (Electromagnetic and Capacitor

Measurement, power source, operating


of CT so there is error in

as well as a phase angle error

A device for indicating the strain of a material or structure at the point of attachment. A typical semiconductor technology i.e., the semiconducting

wafers or filaments of length varying from 2 mm to 10 mm and thickness of 0.05 mm are bonded . The gold leads are usually employed for making electrical

odes are formed by vapour deposition. The assembly is placed in a protective

The strain sensitive,elements used by the semiconductor strainsuch as, silicon and germanium. When the change in resistance occur which can be measured with the help of a wheatstone bridge. The strain can be measured with high degree of accuracy due to relatively high change in resistance.

A temperature compensated semiconductor strain gauge can be used to measure small strains of the order of 10-6 i.e., micro-strain. This type of gauge will have a gauge factor of 130 ± 10% for a semiconductor material of dimension 1 x 0.5 x 0.005 inch havi

6.b) Principle of LVDT: LVDT works under the principle of mutual induction, and the displacement which is a non

energy is converted into an electrical energy. And the way how the energy is getting converted is

described in working of LVDT in a detailed manner.

LVDT consists of a cylindrical former where it is surrounded by one primary winding in the centre of the

former and the two secondary windings at the sides. The number of turns in both the secondary windings

are equal, but they are opposite to each other,

direction, the right secondary windings will be in the anti

voltages will be the difference in voltages between the two secondary coil. The two secondary coi

represented as S1 and S2. Esteem iron core is placed in the centre of the cylindrical former which can

move in to and fro motion as shown in the figure. The AC excitation voltage is 5 to 12V and the operating

frequency is given by 50 to 400 HZ.

Working of LVDT:

Let’s study the working of LVDT by splitting the cases into 3 based on the iron core position inside the

insulated former.

Case 1:On applying an external force which is the displacement, if the core reminds in the null position

itself without providing any movement then the voltage induced in both the secondary windings are equal

which results in net output is equal to zero

i.e., Esec1-Esec2=0

Case 2:When an external force is appilied and if the steel iron core tends to move in the left hand side

direction then the emf voltage induced in the secondary coil is greater when compared to the emf induced

in the secondary coil 2.

Therefore the net output will be Esec1

Case 3:When an external force is applied and if the steel iron core moves in the right hand side direction

then the emf induced in the secondary coil 2 is greater when compared to the emf voltage induced in the

secondary coil 1. therefore the net output voltage will be Esec2

The strain sensitive,elements used by the semiconductor strain gauge are the semiconductorgermanium. When the strain is applied to the semiconductor element a large of

resistance occur which can be measured with the help of a wheatstone bridge. The strain can measured with high degree of accuracy due to relatively high change in resistance.

temperature compensated semiconductor strain gauge can be used to measure small strains of strain. This type of gauge will have a gauge factor of 130 ± 10% for

semiconductor material of dimension 1 x 0.5 x 0.005 inch having the resistance of 350 Ω.

LVDT works under the principle of mutual induction, and the displacement which is a non


ibed in working of LVDT in a detailed manner.



are equal, but they are opposite to each other, i.e., if the left secondary windings is in the clockwise

direction, the right secondary windings will be in the anti-clockwise direction, hence the net output

voltages will be the difference in voltages between the two secondary coil. The two secondary coi




applying an external force which is the displacement, if the core reminds in the null position


which results in net output is equal to zero

When an external force is appilied and if the steel iron core tends to move in the left hand side


e net output will be Esec1-Esec2

:When an external force is applied and if the steel iron core moves in the right hand side direction


il 1. therefore the net output voltage will be Esec2-Esec1

gauge are the semiconductor materials strain is applied to the semiconductor element a large of

resistance occur which can be measured with the help of a wheatstone bridge. The strain can

temperature compensated semiconductor strain gauge can be used to measure small strains of strain. This type of gauge will have a gauge factor of 130 ± 10% for

ng the resistance of 350 Ω.

LVDT works under the principle of mutual induction, and the displacement which is a non-electrical




i.e., if the left secondary windings is in the clockwise

clockwise direction, hence the net output

voltages will be the difference in voltages between the two secondary coil. The two secondary coil is




applying an external force which is the displacement, if the core reminds in the null position


When an external force is appilied and if the steel iron core tends to move in the left hand side


:When an external force is applied and if the steel iron core moves in the right hand side direction


LVDT is used to measure displacement ranging from fraction millimeter to centimeter. Acting as a

secondary transducer, LVDT can be used as a device to measure force, weight and pressure, etc..

(OR)

7. a) Definition: The galvanometer which is used for estimating the quantity of charge flow through

it is called the ballistic galvanometer. The working principle of the ballistic galvanometer is very

simple. It depends on the deflection of the coil which is directly proportional to the charge passes

through it. The galvanometer measures the majority of the charge passes through it in spite of

current.

Theory of Ballistic Galvanometer

Consider the rectangular coil having N number of turns placed in a uniform magnetic field. Let l be the

length and b be the breadth of the coil. The area of the coil is given as

When the current passes through the coil, the torque acts on it. The given expression determines the

magnitude of the torque.

Let the current flow through the coil for very short duration says dt and it is expressed as

If the current passing through the coil for t seconds, the expression becomes

The q be the total charge passes through the coil. The moment of inertia of the coil is given by l, and the

angular velocity through ω. The expression gives the angular momentum of the

coil

The angular momentum of the coil is equal to the force acting on the coil. Thus from equation (4) and (5),

we get.

The Kinetic Energy (K) deflects the coil through an angle θ, and this deflection is restored through the

spring.

The resorting torque of the coil is equal to their deflection. Thus s,

The periodic oscillation of the coil is given as

By multiplying the equation (7) from the above equation we get

On substituting the value of equation (6) in the equation (8) we get

The K is the constant of the ballistic galvanometer.

7.b) Field strength of solenoid H=N1I/l=800*5/1=4000A/M

Flux density B=µ0H=4Π*10^-7*4000=16Π*10^-3Wb/m2

Flux linkages of flux meter search coil=N2BA=500*16Π*10^-3*500*10-6=0.4Π*10^-3 Weber turn.

Change in flux linkages= 2*0.4Π*10^-3= 0.8Π*10^-3 Weber turn

Flux linkages per scale division= 0.8Π*10^-3/25=0.1005*10^-3 Weber turn.

UNIT – IV

8. a) It is a very important oscilloscope used to analyse the waveform and measure them. Now here

we will discuss how the measurement of waveform i.e measurement of phase difference and

frequency using CRO which are Lissajous patterns.

It is interesting to consider the characteristics of patterns that appear on the screen of a

CRT when sinusoidal voltages are simultaneously applied to horizontal and vertical plates. These

patterns are called 'Lissajous Patterns'.

Phase measurement of CRO:

When two sinusoidal voltages of equal frequency which are in phase with each other are

applied to the horizontal and vertical deflection plates, the pattern appearing on the screen is a

straight line as is clear from the below figure.

8. b)

Lissajous patterns may be used for accurate measurement of frequency. The signal, whose frequency is

to be measured, is applied to the Y plates. An accurately calibrated standard variable frequency source

is used to supply voltage to the X plates, with the internal sweep generator switched off.

The standard frequency is the adjusted unit the pattern appears as a circle or an ellipse,

indicating that both signals are of the same frequency. Where it is not possible to adjust the standard

signal frequency to the exact frequency of the unknown signal, the standard if adjusted to multiple or a

submultiple of the frequency of the unknown source so that the pattern appears stationary.

Let us consider an example. Suppose sine waves are applied to X and Y plates as shown in the

figure below. Let the frequency of wave applied to Y plates is twice that of the voltage applied to X

plates. This means that the CRT spot travels two complete cycles in the vertical direction against one in

the horizontal direction.

There are some restrictions on the frequencies which can be applied to the deflection plates.One

obviously, is that the CRO must have the bandwidth required for these frequencies. The other

restriction is that the ratio of the two frequencies should not be such as to make the pattern too

complicated otherwise measurement of frequency would become difficult. As a rule ratios as high as 10

: 1 and as low as 10 : 9 can be determined comfortably.

(OR)

9. a)

A liquid crystal display or LCD draws its definition from its name itself. It is combination of two states of

matter, the solid and the liquid. LCD uses a liquid crystal to produce a visible image. Liquid crystal

displays are super-thin technology display screen that are generally used in laptop computer screen, TVs,

cell phones and portable video games. LCD’s technologies allow displays to be much thinner when

compared to cathode ray tube (CRT) technology.

LCD is composed of several layers which include two polarized panel filters and electrodes. LCD

technology is used for displaying the image in notebook or some other electronic devices like mini

computers. Light is projected from a lens on a layer of liquid crystal. This combination of colored light

with the grayscale image of the crystal forms the colored image. This image is then displayed on the

screen.

Working of LCD:

The principle behind the LCD’s is that when an electrical current is applied to the liquid crystal molecule, the molecule tends to untwist. This causes the angle of light which is passing through the molecule of the polarized glass and also cause a change in the angle of the top polarizing filter. As a result a little light is allowed to pass the polarized glass through a particular area of the LCD. Thus that particular area will become dark compared to other. The LCD works on the principle of blocking light. While constructing the LCD’s, a reflected mirror is arranged at the back. An electrode plane is made of indium-tin oxide which is kept on top and a polarized glass with a polarizing film is also added on the bottom of the device. The complete region of the LCD has to be enclosed by a common electrode and above it should be the liquid crystal matter. Next comes to the second piece of glass with an electrode in the form of the rectangle on the bottom and, on top, another polarizing film. It must be considered that both the pieces are kept at right angles. When there is no current, the light passes through the front of the LCD it will be reflected by the mirror and bounced back. As the electrode is connected to a battery the current from it will cause the liquid crystals between the common-plane electrode and the electrode shaped like a rectangle to untwist. Thus the light is blocked from passing through. That particular rectangular area appears blank.

Advantages of an LCD’s:

LCD’s consumes less amount of power compared to CRT and LED LCD’s are consist of some microwatts for display in comparison to some mill watts for LED’s LCDs are of low cost Provides excellent contrast LCD’s are thinner and lighter when compared to cathode ray tube and LED

9.b) Construction of Cathode Ray Oscilloscope The main parts of the cathode ray oscilloscope are as follows.

1. Cathode Ray Tube 2. Electronic Gun Assembly 3. Deflecting Plate 4. Fluorescent Screen For CRT 5. Glass Envelop

1. Cathode Ray Tube: The cathode ray tube is the vacuum tube which converts the electrical signal into the visual signal. The cathode ray tube mainly consists the electron gun and the electrostatic deflection plates (vertical and horizontal).The electron gun produces a focused beam of the electron which is accelerated to high frequency. The vertical deflection plate moves the beams up and down and the horizontal beam moved the electrons beams left to right.

2. Electronic Gun Assembly: The electron gun emits the electrons and forms them into a beam. The

electron gun mainly consists a heater, cathode, a grid, a pre-accelerating anode, a focusing anode and an

accelerating anode.

3. Deflecting Plate: The electron beam after leaving the electron gun passes through the two pairs of the

deflecting plate. The pair of plate producing the vertical deflection is called a vertical deflecting plate

or Y plates, and the pair of the plate which is used for horizontal deflection is called horizontal

deflection plate or X plates.

4. Fluorescent Screen for CRT: The front of the CRT is called the face plate. It is flat for screen sized

up to about 100mm×100mm. The screen of the CRT is slightly curved for larger displays. The face plate

is formed by pressing the molten glass into a mould and then annealing it.

5. Glass Envelope:It is a highly evacuated conical shape structure. The inner surface of the CRT between

the neck and the screen is coated with the aquadag. The aquadag is a conducting material and act as a

high-voltage electrode. The coating surface is electrically connected to the accelerating anode and hence

help the electron to be the focus.

Working of Cathode Ray Oscilloscope

When the electron is injected through the electron gun, it passes through the control grid. The control grid controls the intensity of electron in the vacuum tube. If the control grid has high negative potential, then it allows only a few electrons to pass through it. Thus, the dim spot is produced on the lightning screen. If the negative potential on the control grid is low, then the bright spot is produced. Hence the intensity of light depends on the negative potential of the control grid. After moving the control grid the electron beam passing through the focusing and accelerating anodes. The accelerating anodes are at a high positive potential and hence they converge the beam at a point on the screen. After moving from the accelerating anode, the beam comes under the effect of the deflecting plates. When the deflecting plate is at zero potential, the beam produces a spot at the centre. If the voltage is applied to the vertical deflecting plate, the electron beam focuses at the upward and when the voltage is applied horizontally the spot of light will be deflected horizontally.

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