beee lab manual

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Experiment 1 Verification OF Ohms Law

Aim

To verify the relationship between current, voltage and resistance (Ohms law) in an electric circuit

experimentally.

Components Required

Sl. No. Apparatus/Instrument Type Range Quantity

1. Regulated power supply (RPS) Variable (030) V 1

2. Potentiometer (01) K 1

3. Resistor Carbon film 470 1

4. Voltmeter Moving coil (030) V 1

5. Ammeter Moving coil (0100) mA 1

6. Breadboard 1

Ohms Law

Under constant temperature, the potential difference (V) across the ends of a conductor is proportional to

the current (I) flowing through it.

Mathematically,

V I

or V = I R



where, the constant of proportionality R is the resistance of conductor in ohms.

Theory

Ohm's Law gives the relationship between electric voltage, current and resistance. A simple comparison with an over-head tank helps to understand these terms in a better way. Consider that a pipe connects a tap to the water tank. There exists a difference in water pressure between the water in the tank and that coming out of the tap. The diameter of the connecting pipe and the size of the tap outlet govern this difference in pressure which is equivalent to potential difference or voltage in an electrical circuit.

The rate of flow of water through the connecting pipe depends on the diameter of the pipe and the difference in water pressure between the water in the tank and that coming out of the tap. This flow rate of

water is equivalent to electric current (rate of flow of electric charges) circulating in a circuit.

Water flow through the connecting pipe is restricted by the diameter of the pipe and the outlet tap. If the diameter of the pipe and tap is increased, the water flow increases. Reducing the size of the pipe and tap on the other hand reduces the water flow. A connecting element like wire in an electric circuit is analogous to

the pipe. Increasing the thickness of the wire reduces the electrical resistance and hence increases the current flowing in the circuit and vice versa.

When the diameter of the pipe and outlet tap is fixed (and if the water pressure difference between the tank and outlet reduces), the rate of flow of water gets reduced. Applying this to Ohms law, when the resistance of a circuit is fixed, decreasing the voltage results in reduced current flow. When the rate of flow of water is unaltered and a larger connecting pipe is used, water flows more freely and the water pressure difference decreases. Likewise, if the current in a circuit is unaltered, decreasing the resistance of the wire (by increasing the thickness of the wire) will cause the potential difference or voltage to decrease. If on the other hand, water pressure difference is maintained constant and a narrow connecting pipe is used, the water flow is reduced. Similarly, with constant voltage, increasing the resistance (by reducing the thickness of the wire) will reduce the current flowing in the circuit.

Considering the above equivalencies, Ohm's law can be stated by mathematical equations. Let V be the voltage measured in volts, I be current measured in amperes and R be the resistance measured in ohms.

Knowing any two of the quantities of a circuit, the third quantity can be determined using Ohm's law wheel as shown below.



Figure 1 Ohms law wheel.

The wheel above is divided into three sections V, I and R. X represents the (multiply by sign). When the unknown quantity is covered, what is left is the formula to find the unknown. To help us understand the relationship between the various quantities a little further, all of Ohm's law equations for finding voltage, current, resistance and power can be condensed into a simple Ohms law pie chart as shown.

Figure 2 Ohms law pie chart. Electrical devices or components that obey Ohms law (viz., resistors or cables) are said to be Ohmic devices, and devices that do not (viz., transistors or diodes) are said to be non-ohmic devices.

Circuit Diagram



Figure 3 Circuit to verify Ohms law.

Formulae Used

Rtotal = V/I

But for the circuit as shown in Fig. 3,

Rtotal = R1 + R2 = R1 + 470 (1)

Hence

R = V/I 470

Procedure

1. Construct the circuit as shown in Fig. 3. 2. Do not switch on the power supply. Disconnect the variable resistor R (POT or Decade resistance

box) from the circuit and set it to a desired value R1 by using ohmmeter and reconnect it. 3. Using the regulated power supply, vary the applied voltage in steps of say 5 V and note down the

ammeter and voltmeter reading in each step. 4. Repeat the above procedure for another value of resistance R2. 5. Calculate the value of resistance R using Eq. (1) and compute the mean value of resistance. 6. These mean value will match the value of resistance connected in the circuit. 7. Plot a graph of I versus V. The inverse of slope of this characteristic also gives the value of total

resistance connected in the circuit.

Observations

Fixed resistance R2 = 470 .

Mean = Mean =

Model Graph



Figure 4

Inference

The theoretical value of resistance so computed from the graph and using the formula in Eq. (1)

approximately matches the actual value of the resistor used in the circuit. The slight mismatch is due to the

fact that the internal resistance of the power supply and ammeter are neglected.

Result

Thus, the relationship between current, voltage and resistance (Ohms law) in an electric circuit has been

verified experimentally.

Best Practices and Safety Measures 1. Wear rubber soled shoes

2. Make sure the experiment is grounded and dont touch a closed circuit with anything that can conduct current.

3. Use wire wound resistors, and a digital multimeter.

4. As long as you use a low voltage (such as the voltage from a battery), your experiments will be relatively safe.

5. The main thing is to be sure to avoid any kind of short circuits. When measuring the resistance of wire, you will need quite long lengths of wire indeed to get accurate readings, since wire has a very low resistance.

Viva Voce Questions

1. State Ohms law.



Ans: Ohms law states that the electric current I flowing through the conductor is directly proportional to the potential difference V across the two ends of the conductor, provided that the conditions of the conductor remains the same.

2. Define resistance of a conductor.

Ans: The ratio of potential difference across the ends of a conductor to the current flowing through it is called the resistance of a conductor.

3. Define one ohm.

Ans: The resistance of a conductor is said to be 1 if a current of 1 A flowing through it is able to develop a potential difference of 1 V across its ends.

2. Define one volt. Ans: The potential difference between the two points is said to be 1 V if 1 J of work is done in bringing 1 C of charge from one point to another.

3. What are ohmic resistances? Ans: Resistances that obey Ohms law are called ohmic resistances.

4. What are the SI units of current, potential difference, and resistance? Ans: The SI unit of current is Ampere, potential difference is Volt, and resistance is Ohm.



Experiment 2 Verification of Kirchhoffs Laws

Aim

To experimentally verify Kirchhoffs voltage law and current law for a given electric circuit.

Components Required

Sl. No. Apparatus/Instrument Type Range Quantity

1. Regulated power supply (RPS) Variable (030) V 1

2. Resistors Carbon film

1.1 k, 2.2

k, 3.3 k 1

3. Voltmeter Moving coil (030) V 3



6. Breadboard 1

Theory

Ohms law can be used to analyze the voltage and currents in circuits that can ultimately be reduced to

series or parallel combination of resistors. Thus using Ohms law for solving a complex circuit consisting of

bridge networks or stardelta connections will be laborious. Two circuit laws, such as, voltage law and

current law introduced by Gustav Kirchhoff comes handy for analyzing these types of circuits. The first law

called Kirchhoffs current law deals with conservation of charges and it describes how current is distributed

when it enters a node or a junction. The second law called Kirchhoffs voltage law deals with conservation of

energy and describes how voltage is distributed within a closed loop.

To get a better understanding of various circuit analysis techniques, acquaintance of the basic terminologies

used in the context of circuit analysis is essential. The following section describes the most frequently used

terms.

Circuit: A path between two or more points along which an electrical current can be carried.



Component: An individual part or element of an electrical circuit which performs a specified function within

that circuit.

Node: A point or connection where two or more circuit elements meet, represented pictorially by a dot.

Branch: A branch is any path in the circuit that has a node at each end and does not contain any other node

in-between.

Path: Path is a branch or a continuous sequence of branches that can be traversed from one node to

another node.

Loop: Loop is a closed path that originates and terminates on the same node, and along the path no node is

met twice.

Mesh: A mesh is a loop that does not contain other loops.

Figure 1 Terminologies used in circuit analysis.

Kirchhoffs Current Law

Kirchhoffs current law or KCL, states that the "total current entering a junction or node is exactly equal to

the charge leaving the node ". Stated differently, the currents entering a node and those leaving a node add

up to zero. Since current is nothing but the rate of flow of charges in an electric circuit, it can also be said

that the sum of charges entering a junction is the same as the sum of charges leaving a junction. In effect,

the electrical charge in the entire circuit is conserved. Hence KCL is also called law of conservation of charge.

Compare this to a main pipe that diverges into two sub-pipes at a particular point. The total amount of

water that flows in the sub-pipes is exactly equal to the water flowing in the main pipe.



Figure 2 Kirchhoffs current law.

In the circuit shown, currents i1 and i2 are leaving the node, whereas currents i3 and i4 are entering the node.

Because of the difference in the direction of flow of current, the following sign convention may be adopted:

Currents entering a junction may be considered positive and that leaving a junction may be considered

negative. The sign convention can be assigned the other way also. However once a certain convention is

adopted, it must be followed uniformly throughout the analysis. Applying KCL to the part of circuit as shown

in Fig. 2, sum of currents entering and leaving a node = 0.

That is,

i1 i2 + i3+ i4 = 0

i1 + i2 = i3+ i4

The above equation shows that the sum of currents entering the node (i3, i4) equals the sum of currents

leaving the node (i1, i2). Since KCL deals with the distribution of current at a common node or junction, it is

very much suitable for analysis of parallel circuits wherein the parallel branches bifurcate from one common

node.

Kirchhoffs Voltage Law

Kirchhoffs Voltage Law or KVL, states that the algebraic sum of the product of currents and the resistances

of the various branches of a closed path is equal to the total EMF of that path. In simple terms, the sum of

potential rise and potential drop in a closed loop equals zero. On traversing a closed path, moving from a

point of higher potential to a point of lower potential is termed potential rise and moving from a point of

lower potential to a point of higher potential is termed potential drop.



Figure 3 Kirchhoffs voltage law. Consider a closed circuit as shown in Fig. 3. There exists a single source of EMF with voltage V4. V1, V2, V3 are

the voltage across the resistors R1, R2 and R3, respectively. Assume that current flows in clockwise direction

in the circuit. It can also be assumed the other way. Proceeding from the negative terminal of the voltage

source to the positive terminal, a potential rise is observed. Also, moving from left end of R1 to its right end

encounters a potential drop. This is indicated by + and signs in Fig. 3. Going from + to is considered

potential rise and moving from to + is considered potential drop. Thus, V1, V2, V3 are potential drops and V4

is potential rise.

Applying KVL to the circuit,

IR1 + IR2 + IR3 = V4

That is,

V1 + V2 + V3 = V4

The above expression shows that the sum of potential drops equals the sum of potential rise.

Suppose an electric charge at a particular potential moves round a closed path in a circuit. It doesn't gain or

lose energy since it has gone back to initial potential. Voltage is nothing but energy per unit charge, and

hence Kirchhoffs voltage law is also known as the law of conservation of energy.

Circuit Diagram For KVL



Figure 4 Circuit for verification of KVL.

Theoretical Calculation

As per Kirchhoffs voltage law,

Req = R2 R3/(R2 + R3)

= 2.2k 3.3 k/ (2.2 k +3.3 k) =1.32 k

RT = Req + R1

= 1.32 k + 1 k

= 2.32 k

I = V/RT

= V/2.32 k

By current divider rule,



Current flowing in one resistor of a parallel circuit=

I1= I R3 /(R2 + R3)

= I 3.3/(2.2 + 3.3)

= I 0.6

By current division rule,

I2 = I R2 /(R2 + R3)

= I 2.2/(2.2 + 3.3)

= I 0.4

I = V/ RT = V /2.32 k

V1 = I R1 Volts

V2 = I R2 Volts

V3 = I R3 Volts

Considering closed loop ABFGA,

Potential rise = E

Potential drop = V = V1 + V2

From KVL,

E = V = V1 + V2

Similarly for closed loop ABCDFGA,

Potential rise = E

Potential drop = V = V1 + V3

From KVL,



E = V = V1 + V3

Observation: Kirchhoffs Voltage Law Verification

Theoretical

Value

Sl.

No.

E

(Volts)

V1

(Volts)

V2

(Volts)

V3

(Volts)

VA =

V1 + V2

(Volts)

E ~ VA

(Volts)

VB =

V1+V3

(Volts)

E ~ VB

(Volts)

Practical

Value

Procedure

1. Construct the circuit as shown in Fig. 4. 2. Switch ON the power supply. 3. Vary the applied voltage in steps of say 2 V and note down the voltmeter readings and the applied

voltage in each step. 4. Calculate VA, VB and their difference from E, that is, E ~ VA and E ~ VB. 5. The validity of the KVL is verified with the difference values close to zero.

Circuit Diagram For KCL



Figure 5 Circuit for verification of KCL.

Theoretical Calculation

Kirchhoffs Current Law

Req = R2 R3 /(R2 + R3)

RT = Req + R1

I = V/ RT

By current divider rule,

Current flowing in one resistor of a parallel circuit=

I1= I R3 /(R2 + R3)

By current division rule,

I2 = I R2 /(R2 + R3)

Applying KCL at node X,



I= I1 + I2

Observation: Kirchhoffs Current Law Verification

Theoretical

Value

E

(volts)

I1 (mA) I2 (mA) I (mA) IA = I1 +

I2(mA)

I ~ IA

(mA)

Practical

Value

Procedure

1. Construct the circuit as shown in Fig. 5. 2. Switch ON the power supply. 3. Vary the applied voltage in steps of say 2 V and note down the ammeter readings and the applied

voltage in each step. 4. Calculate IA and the difference from I, that is, I ~ IA. 5. The validity of the KCL is verified with the difference value close to zero.

Inference

It is observed that in the given circuit:

1. The sum of voltage drops in any closed loop existing in the circuit is equal to the value of voltage source present in that loop.

2. The sum of currents flowing away from the junction is the same as the current flowing towards the junction.

Result

Thus, Kirchhoffs voltage and current laws are verified for the given electric circuit.

Best Practices and Safety Measures

1. Connect voltmeter and ammeter with appropriate polarities as shown in the circuit diagram. 2. Do not switch on the power supply if you have not checked the circuit connections as per the circuit

diagram.



3. When doing the experiment, do not exceed the voltage beyond the breakdown voltage of the diode. The high current may cause the diode to burn.

Viva Voce Questions

1. What is Kirchhoffs current law?

Ans: Kirchhoffs current law deals with conservation of charges and it describes how current is distributed

when it enters a node or a junction. It states that in a closed circuit, the algebraic sum of all the currents

meeting at a junction or node is zero.

2. What is Kirchhoffs voltage law?

Ans: Kirchhoffs voltage law deals with conservation of energy and describes how voltage is distributed

within a closed loop. It states that in a closed circuit or mesh, the algebraic sum of all the EMFs and the

voltage drops is zero.

3. What is a circuit?

Ans: Circuit is a path between two or more points along which an electrical current can be carried.

4. What is a component?

Ans: A component is an individual part or element of an electrical circuit which performs a specified function

within that circuit.

5. What is a node?

Ans: A node is a point or connection where two or more circuit elements meet, represented pictorially by a

dot.

6. What is a branch? Ans: A branch is any path in the circuit that has a node at each end and does not contain any other node in-

between.

7. What is a path? Ans: A path is a branch or a continuous sequence of branches that can be traversed from one node to

another node.

8. What is a loop? Ans: A loop is a closed path that originates and terminates on the same node, and along the path no node is

met twice.



9. What is a mesh? Ans: A mesh is a loop that does not contain other loops.

10. What are the instruments required for the verification of Kirchhoffs law? Ans: Resistors, Voltmeter, Ammeter, Bread board, etc. and regulated power supply.



Experiment 3 Measuring Resistance and Inductance of a Coil by Ammeter-

Voltmeter Method

Aim

To measure the values of unknown resistance, inductance of a coil by ammeter-voltmeter method.

Components Required

Sl.

No. Apparatus Range Type Quantity

1 Inductor coil (0300V), 5 A 1

2 Rheostat 300 ,1.7 A 1

3 Voltmeter (0300) V MC 3

4 Ammeter (01) A MI 1

5 Autotransformer (0270 V), 10A,

1Ph Variable 1

Theory

For a series connected R, L, C circuit, if V and I be the rms values of applied voltage and the circuit

current then,

Voltage drop across R, VR = I R (in phase with I)

Voltage drop across L, VL = I XL (leading I by 90)

Voltage drop across C, VC = I XC (lagging I by 90)

The values of XL and XC plays important role in determining the behavior of R-L-C series circuit. In

general according to the values of XL and XC there are three possible cases.

Case 1

XL > XC

When XL is greater than XC, voltage drop across XL is obviously greater than that across XC, that is,



VL > VC

Hence total applied voltage V is

V = VR2 + (VL VC)

2

V = I R2 + (XL XC)

2

Z = R2 + (XL XC)

2

Case 2

XL < XC

In this case, Vc is greater than VL. Therefore, their resultant (VC VL) is along the direction of VC.

Hence V is

V = VR2 (VC VL)

2

V = I R2 + (XC XL)2

Z = R2 + (XC XL)

2

Case 3

XL = XC

In this case, VL and Vc being equal and in direct phase opposition with each other, their resultant is

zero. Therefore applied voltage equals the voltage drop across resistance.

Hence,

V = VR = I R

Circuit Diagram



Figure 1

Procedure

1. Make connections as shown in circuit diagram.

2. Slowly increase the voltage applied through autotransformer to the circuit (current value should

not exceed 1 A).

3. Note down the values of voltage across resistance, inductance and capacitor and current through

circuit.

Observation Table

Calculations

1. VR = I R

2. VL = I XL

3. cos = R/Z

Result

Thus the resistance and inductance of a coil by ammeter voltmeter method is measured.

Best Practices and Safety Measures 1. Make the connections according to the circuit diagram. Power supply should be switched off.



2. Connections should be tight. 3. Handle the CRO carefully. 4. Note the readings carefully.

Viva Voce Questions

1. Define resonance. 2. Define bandwidth. 3. Define selectivity. 4. What is the effect of resistance on the frequency response curve? 5. Does resonance occurs in DC or AC circuits? 6. What is the effect of resistance on the frequency response curve?



Experiment 4 VoltageCurrent Relationship in a RL Series Circuit and Power Factor Determination

Aim

To find voltagecurrent relationship in a RL series circuit and determine power factor of the circuit.

Components Required

Sl. No. Items Range

1. Single-phase autotransformer 230 V

2. Single-phase energy meter 75 V, 5 A

3. Voltmeter 0100 V

4. Ammeter 05 A

5. Connecting wires

6. Power factor meter

7. Double pole, single throw switch

(DPST)

Theory

In an electric circuit, power can be measured by using a wattmeter. A wattmeter consists of two types of coils: (1) potential coil or pressure coil and (2) current coil. The current coil measures the quantity proportional to the current in the circuit and the pressure coil measures the quantity that is proportional to the voltage in the circuit.



The current (I) flowing through an AC circuit is given by

V

IZ

where,

V = AC supply voltage (in volts) and

Z = impedance of the circuit (in ohms).

Hence the power factor (cos ) of the AC circuit is given by

cosP

VI

where,

P = power of the circuit (in watts),

V = voltage (in volts) and

I = current flowing in the circuit (in amperes)

Circuit Diagram

Figure 1



Procedure

Connect variac, load, ammeter, wattmeter, power factor meter, voltmeter through double pole, single

throw switch to single-phase supply mains as in the circuit diagram. Bring the variac at the lowest point and

switch ON the DPST switch. Increase the voltage in steps and take the readings of the ammeter,

wattmeter, pf meter and voltmeter.

Tabulation

Sl. No. Voltmeter

Reading (volts)

Wattmeter

Reading (watts)

Ammeter

Reading (I)

Power Factor

Meter Reading

cos W

VI

1.

2.

3.

4.

Inference

The current (I) increases to a proportionate degree to the applied voltage. Calculated power factor value

matches measured one and for a given load, the power factor of the circuit is the same.

Result

Thus, the electrical quantities, such as, voltage, current, power, and power factor are measured by using RL series circuit.

Best Practices and Safety Measures 1. Wear rubber soled shoes





4. The main thing is to be sure to avoid any kind of short circuits.

Viva Voce Questions

1. How to measure power?

Ans: Power can be measured by using a wattmeter.

2. What are the types of coils a wattmeter possesses?

Ans: A wattmeter consists of two types of coils: (1) potential coil or pressure coil and (2) current coil.

3. What is the procedure of finding voltagecurrent relationship and to determine the power factor?

Ans: Connect variac, load, ammeter, wattmeter, power factor meter, voltmeter through double

pole, single throw switch to single-phase supply mains as in the circuit diagram. Bring the variac at

the lowest point and switch ON the DPST switch. Increase the voltage in steps and take the

readings of the ammeter, wattmeter, pf meter and voltmeter.

4. What inference could you gather from the experiment?

Ans: The current (I) increases to a proportionate degree to the applied voltage. Calculated power

factor value matches measured one and for a given load, the power factor of the circuit is the same.



Experiment 5 Voltage and Current Relations in Three-Phase StarDelta

Connections Systems

Aim

To verify the voltage and current relations in three-phase stardelta connections systems.

Components Required

Sl.


1 Three-phase

autotransformer (0 415) V,

10 A, 8.14 KVA 1

2 Voltmeter (0300) V MI 1

3 Ammeter (05) A MI 4

4 Lamp bank 230 V, 10 A 1

Theory

In case of three-phase supply, instead of connecting all the phases separately, it is interconnected

normally in two ways as follows:

1. Star connections (Y): Here all the phases are connected across one point, that is, all similar ends

are connected together and remaining three terminals are taken out as shown in Fig. 1.

Line voltages: VRY, VYB, VBR

Line currents: IR, IY, IB

Phase Voltages: VR, VY, VB

Phase currents- IR, IY, IB

For star connection IL = Iph, that is, I line (IR, IY, IB) = I phase (IR, IY, IB) and line voltage = Three-

phase voltage as seen from phasor diagram.

2. Delta connections (): Here finishing end of one phase is connected to starting of second and finishing end of second phase is connected to starting of third and so on. Finally, three common

terminals are taken out as shown in Fig. 2.



Line voltages: VRY, VYB, VBR

Line currents: IRY, IYB, IBR

Phase Voltages: VR, VY, VB

Phase currents: IR, IY, IB

For delta connection VL = Vph

That is V line (VRY, VYB, VBR) = V phase (VR, VY, VB) and line current = Three-phase current as seen

from phasor diagram.

Procedure

1. Make connections as shown in the circuit diagram.

2. Slowly increase the phase voltage to 120 V applied through autotransformer to the circuit.

3. Note down the values of voltage and current form in meters.

4. Increase the voltage in steps of 20 V from autotransformer and note down the readings.

Figure 1 Balanced star connection.



Figure 2 Balanced delta connection.

Observation Table

1. For Star Connection

2. For Delta Connection



Result

Thus the voltage and current relations in star and delta connection system were verified.


1. Wear rubber soled shoes




Viva Voce Questions

1. What is the phase sequence of a three phase supply in general?

2. Define transformer.

3. List out the types of transformer.

4. Write the emf equation of the transformer.

5. What is meant by ideal transformer?

6. Define transformer ratio.

7. What is meant by hysteresis loss in a transformer?



Experiment 6 Power and Power Factor in a 1-Phase AC Circuit Aim

To measure the power and power factor in a single-phase AC circuit by three voltmeter and three

ammeter method.

Components Required

Sl.


1 Auto transformer (0300 V) 1Phase 1

2 Transformer 230/115 V, 1 KVA 1

3 Rheostat 45 , 5 A 1

4 Voltmeter (0300 V) MI 1

5 Voltmeter (0150 V) MI 2

6 Ammeter (010 A) MI 1

7 Ammeter (05 A) MI 2

Theory

In electrical engineering, single-phase electric power refers to the distribution of alternating current

electric power using a system in which all the voltages of the supply vary in unison. Single-phase

distribution is used when loads are mostly lighting and heating, with few large electric motors. A

single-phase supply connected to an alternating current electric motor does not produce a revolving

magnetic field; single-phase motors need additional circuits for starting, and such motors are

uncommon above 10 or 20 kW in rating.

In contrast, in a three-phase system, the currents in each conductor reach their peak instantaneous

values sequentially, not simultaneously. In each cycle of the power frequency, first one, then the

second, then the third current reaches its maximum value. The waveforms of the three supply

conductors are offset from one another in time (delayed in phase) by one-third of their period. When



the three phases are connected to windings around the interior of a motor stator, they produce a

revolving magnetic field; such motors are self-starting.

Standard frequencies of single-phase power systems are either 50 or 60 Hz. Special single-phase

traction power networks may operate at 16.67 Hz or other frequencies to power electric railways.

Three Voltmeter method:

Power Factor 2 2 2

1 2 1 2(cos ) ( ( )) / (2 )V V V VV

Power consumed by the Inductor 2 2 2

1 2( ) ( ( )) / (2 )LP V V V R

Three Ammeter method:

Power Factor 2 2 2

1 2 1 2(cos ) ( ( )) / (2 )I I I I I


1 2( ) ( ( )) / (2 )LP I I I R

Procedure

1. Three-Voltmeter Method Circuit is constructed as per Circuit Diagram.



The moving contact of the rheostat is kept at maximum resistance position and auto-transformer is at zero position.

Now the single phase ac supply is given to the circuit. Rated voltage is applied across the transformer by using the auto-transformer. The readings of Voltmeters and Ammeter are tabulated.

2. Three-Ammeter Method Circuit is constructed as per Circuit Diagram. The moving contact of the rheostat is kept at maximum resistance position and auto-transformer is at zero position.

Now the single phase ac supply is given to the circuit. The rated current is made pass through the transformer by using the auto-transformer. The readings of Voltmeter and Ammeters are tabulated.

Three-Voltmeter Method

Ammeter

Reading

(AMPS)

Voltmeters Readings Power factor

(cos )

Power

Consumed by

Inductive Load V1

(Volts)

V2

(Volts)

V

(Volts)



Three-Ammeter Method

Voltmeter

Reading

(Volts)

Ammeters Readings Power factor

(cos )

Power

Consumed by

Inductive Load I1

(Amps)

I2

(Amps)

I

(Amps)

Precautions Loose connections should be avoided. Initially moving contact of the rheostat should be kept at maximum position.

Formula Required

Power Factor 2 2 2

1 2 1 2(cos ) ( ( )) / (2 )V V V VV

Power Factor 2 2 2

1 2 1 2(cos ) ( ( )) / (2 )I I I I I


1 2( ) ( ( )) / (2 )LP V V V R


2 2( ) ( ( )) / (2 )LP I I I R



Result

Thus the power is measured in a 1-Phase AC circuit by three voltmeter and three ammeter method.






Viva Voce Questions:

1. What do you meant by phase sequence? 2. What are the two types of AC supply? 3. List out the types of MI instruments. 4. Define power factor. 5. What is meant by apparent power, real power and active power?



Experiment 7 Series and Parallel Resonance in AC Circuits

Aim

To verify series and parallel resonance in AC circuits.

Components Required Sl. No. Component Specification Quantity

1 Function Generator (03) MHz 1

2 Decade Inductance Box --- 1

3 Voltmeter (05)V, MC 1

4 Bread board - 1

5 Resistors 1 K 1

6 Decade Capacitance box ---- 1

7 wires ---- -

Theory A circuit is said to be in resonance if the voltage and current are in phase. In RLC series circuit the impedance is minimum, at resonance; therefore the current and voltage across resistor are maximum. The frequency at which the

voltage across resistor reaches maximum is called resonant frequency.

1

2rf

LC

The frequency below resonant frequency at which the voltage is 1/ 2 times maximum value is called lower cutoff

frequency. The frequency above resonant frequency at which the voltage is 1/ 2 times maximum value is called

upper cutoff frequency. The difference between lower and upper cutoff frequency is called band width. The circuit

with low band width has better selectivity. The ratio between resonant frequency and band width is called quality

factor (Q factor). Thus selectivity is the reciprocal of Q factor.



In RLC parallel circuit the current is minimum, and voltage is maximum at resonance. The frequency at which the voltage across resistor reaches maximum is called resonant frequency.

21

22

/1

2 /r

R L Cf

LC R L C

The frequency below resonant frequency at which the current is 2 times minimum value is called lower cutoff

frequency. The frequency above resonant frequency at which the voltage is 2 times minimum value is called

upper cutoff frequency.

Procedure 1. Make the circuit in bread board as per the circuits given below (Figure 2 & 3).

2. Gradually increase the frequency using function generator and note down the voltage and frequency.

3. Construct frequency response curve.

4. The frequency corresponding to maximum voltage is resonant frequency.

5. Find frequency below resonant frequency at which the voltage is 1/ 2 times maximum value is the lower

cutoff frequency (f1).

6. Find the frequency above resonant frequency at which the voltage is 1/ 2 times maximum value is the upper

cutoff frequency (f2). 7. Find the difference between upper and lower cutoff frequency which is the band width.

8. Find the Q-factor.

2 1

rfQf f

9. Find the selectivity.

Selectivity 1/ Q

10. Calculate resonant frequency and cutoff frequencies theoretically for series circuit.

1 2

1; ;

4 42r r r

R Rf f f f f

L LLC

11. Calculate resonant frequency theoretically for parallel circuit: 2

1r 2

2

1

2

R L Cf

R L CLC

Table 1 Frequency Response of Series Circuit

Sl. No. Frequency (Hz) Voltage (V)

1

2

3



4

5

6

7

8

9

Table 2 Frequency Response of Parallel Circuit

Sl. No. Frequency (Hz) Voltage (V)

1

2

3

4

5

6

7

8

9

Result Thus resonance characteristics of series and parallel RLC circuits are practically studied along with

theoretical calculations.








Viva Voce Questions

1. Define time constant of RL circuit.

2. Define time constant of RC circuit.

3. Define quality factor.

4. What is bandwidth and selectivity?

5. What are the properties of a series RLC circuit?

6. What are the properties of a parallel RLC circuit?



Experiment 8 B-H Loop of Ferromagnetic Core Material on CRO

Introduction

Those substances in which each individual atom/molecule has a non-zero magnetic moment are known as

ferromagnetic materials. When such materials are placed in an external magnetic field, they get strongly

magnetized in the direction of the field. Examples of ferromagnetic materials are cobalt, nickel, iron, etc.

Ferromagnetism is a property of iron, nickel, and certain other elements and their compounds and

alloys. Some of the electrons in these materials have their resultant magnetic dipole moments aligned, and

this produces regions of strong magnetic dipole moments. An external magnetic field can then align the

magnetic moments of such regions, producing a strong magnetic field for a sample of the material. This field

partially persists when external magnetic field is removed. We usually use the terms ferromagnetic material

and magnetic material to refer to materials that exhibit primarily ferromagnetism.

The phenomenon of lagging of I or B behind H when a specimen of a magnetic material is subjected

to a cycle of magnetization is known as hysteresis. Magnetization curves for ferromagnetic materials are not

retraced as we increase and then decrease the external magnetic field B0. Figure 1 is a plot of BM versus B0

during the following operations with a Rowland ring: (1) Starting with the iron un-magnetized (point a),

increase the current in the toroid until B0 (= 0In) has the value corresponding to point b; (2) reduce the

current in the toroid winding (and thus B0) back to zero (point c); (3) reverse the toroid current and increase

it in magnitude until B0 has the value corresponding to point d; (4) reduce the current to zero again (point e);

(5) reverse the current once more until point b is reached again.

Figure 1 A magnetization curve (ab) for a ferromagnetic specimen and an associated hysteresis loop (bcdeb).



The lack of retraceability shown in Fig. 1 is called hysteresis, and the curve bcdeb is called a hysteresis loop. Note that at points c and e the iron core is magnetized, even though there is no current in the toroid windings. This is the familiar phenomenon of permanent magnetism. At B0 = 0, Bm = 0 (curve ac). The value

of Bm at B0 = 0 is known retentivity. The value of magnetic induction B left in the specimen when the magnetizing force is reduced to zero is called retentivity or remanence or residual magnetism of the material. The negative value of B0 at which Bm becomes zero is known as coercivity. The value of magnetizing force which is applied to reduce the residual magnetism or retentivity to zero is known as coercivity. Hysteresis can be understood through the concept of magnetic domains. Evidently the motions of the domain boundaries and the reorientations of the domain directions are not totally reversible. When the applied magnetic field B0 is increased and then decreased back to its initial value, the domains do not return completely to their original configuration but retain some memory of their alignment after the initial increase. This memory of magnetic materials is essential for the magnetic storage of information.

This memory of the alignment of domains can also occur naturally. When lightning sends currents along multiple tortuous paths through the ground, the currents produce intense magnetic fields that can suddenly magnetize any ferromagnetic material in nearby rock. Because of hysteresis, such rock material retains some of that magnetization after the lightning strike (after the currents disappear). Pieces of the rock later exposed, broken, and loosened by weathering are nothing but lodestones.

Aim

To determine the hysteresis loss in a ferromagnetic material by tracing the BH curve using CRO.

Apparatus

1. Cathode Ray Oscilloscope (CRO)

2. Given specimen

3. BH curve unit

Theory

Hysteresis loss is given by the following equation,

Hysteresis loss = 1 2 V H2 1

N R CS S

N R V Area of the hysteresis loop

Where N1 Number of turns in the primary coil



N2 Number of turns in the secondary coil

V Volume of the specimen

SV Vertical sensitivity of the CRO

SH Horizontal sensitivity of the CRO

C capacitance in the circuit

R1 and R2 Resistances in the circuit

d Thickness of the given bad conductor

Procedure

< NL >

1. CRO is calibrated as per the instructions in the CRO manual. The horizontal and vertical position

controls are adjusted such that the spot falls on the center of the CRO.

2. The connections are made as shown in the Fig. 2.

Figure 2

3. The specimen used here is made using transformer stampings.

4. Primary and secondary windings are made on the specimen with N1 and N2 as the number of turns

in the primary and secondary coils respectively.

5. When the low A. C. voltage is switched on, it produces a magnetic field H in the specimen.

6. This causes a voltage to be introduced in the secondary coil proportional to dB/dt.



7. The voltage developed across the resistance R1 is proportional to H which is fed to the horizontal

input of CRO.

8. The voltage developed across the secondary is fed to an integrating circuit gives an output voltage

proportional to B which is fed to the vertical input of CRO.

9. With a voltage proportional to H applied to the horizontal axis and a voltage proportional to B to the

vertical axis, a loop is formed on the screen as shown in the Fig. 3.

Figure 3 Hysteresis curve for ferromagnetic specimen.

10. The horizontal and vertical gains are adjusted such that the loop occupies maximum area on the

screen. Using a translucent paper, the loop is traced and the area of the loop is found out.

11. Now remove the connections from the CRO without disturbing the horizontal and vertical gain

controls.

12. The vertical sensitivity of the CRO is found by applying a voltage say, 1 V and note the deflection of

the peak. Vertical sensitivity of the CRO SV = 1/y where y is the deflection made by the spot (in m).

13. Similarly horizontal sensitivity is found, by applying a voltage say 1 V, using the relation SH = 1/x.

The hysteresis loop is then calculated using the formula,


N R CS S


14. Top view of the B-H unit is shown in Fig. 4. There are 12 terminals on the panel; sin patch cords are

applied with the kit. The value of resistance R1 can be selected by connecting terminals D to A, B or

C. If we connect A and D then the resistance R1 will be 50 , for B and D it would be 150 , and for

C and D it would be 50 .



Figure 4 Top view of BH curve unit.

15. Terminals A and D are connected. Primary terminal of the specimen is connected to P and secondary

terminal to S .The GND terminal of the panel is connected to ground of CRO and power supply of the

BH unit is switched on. The hysteresis curve is formed.

< NL >

Observations

Number of turns in the primary coil N1 = ..

Number of turns in the secondary coil N2 =

Vertical sensitivity of the CRO SV = Vm-1

Horizontal sensitivity of the CRO SH = Vm-1

Capacitance in the circuit C = F

Resistance R1= ohm

Resistance R2 = ohm

Calculation



Area of the loop (see Fig. 3)

Area of 1 mm2 = 0.01 cm2

Area of the loop = number of mm squares covered by the loop 0.01 cm2

Volume of the specimen (transformer core)

Figure 5 Dimensions of the specimen.

From the figure, volume of the core is given by

tblblV iioo

lo = . cm

li = . cm

bo = . cm

bi = . cm

t = . cm

V = .

=. cm3.


N R CS S




= .

=.. J cycle1 m3

Result

Hysteresis loss = J cycle1 m3

Best practices and Safety measures

1. All the connections should be proper.

2. The power supply of the unit should be switched off after taking the reading.

3. The AC voltage should be applied to the primary coil on the specimen.

4. The CRO should be calibrated as per instructions given in the instruction manual.

Viva Voice Questions

< NL >

1. Define ferromagnetism.

Ans: Ferromagnetism is a mechanism by which certain materials form permanent magnets, or are

attracted to magnets.

2. Give examples of ferromagnetic materials?

Ans: Iron, nickel, cobalt, etc.

3. Define hysteresis loss?

Ans: The energy lost or dissipated in the form of heat when a magnetized ferromagnetic material is

demagnetized.

4. Hysteresis loop of material A has a much smaller area than material B. If the materials have to go

through repeated cycles of magnetization, which material will dissipate greater heat energy.



Ans: The dissipated heat energy is directly proportional to the area of the hysteresis loop. Material

B will dissipate greater heat energy, since it has more loop area than material B, dissipates more

heat energy.

5. Define retentivity.

Ans: The value of the intensity of magnetization of the magnetic material, when the magnetizing

field is reduced to zero is called retentivity.

6. Define coercivity.

Ans: The value of reverse magnetizing field applied to the magnetic material to reduce its

magnetism to zero is called coercivity.

7. Coercivity of soft iron is less than that of steel. Which of these materials can be easily

demagnetized?

Thus coercivity measures the resistance of a ferromagnetic material to becoming demagnetized.

Hence since soft iron is with lesser coercivity it is easily demagnetized.

< NL >



Experiment 9 Full-Wave Rectification of AC Supply and Relationship Between RMS and Average Values of the Rectified Voltage

Aim

To use a bridge rectifier for full-wave rectification of AC supply and to determine the relationship

between RMS and average values of the rectified voltage.

Components Required

Sl.


1 Step-down

transformer 230/(6-0-6) V 1

2 Silicon diodes IN4001 4

3 Resistance 1 k 1

4 Capacitor 470 F 1

5 CRO

1

Theory The bridge rectifier is a circuit, which converts an AC voltage to DC voltage using both half cycles

of the input AC voltage. The bridge rectifier circuit is shown in the figure. The circuit has four

diodes connected to form a bridge. The AC input voltage is applied to the diagonally opposite ends

of the bridge. The load resistance is connected between the other two ends of the bridge.

For the positive half cycle of the input AC voltage, diodes D1 and D3 conduct, whereas diodes D2

and D4 remain in the OFF state. The conducting diodes will be in series with the load resistance RL

and hence the load current flows through RL.

For the negative half cycle of the input AC voltage, diodes D2 and D4 conduct, whereas D1 and D3

remain OFF. The conducting diodes D2 and D4 will be in series with the load resistance RL and

hence the current flows through RL in the same direction as in the previous half cycle. Thus a bi-

directional wave is converted into a unidirectional wave.



Peak Inverse Voltage

Peak inverse voltage represents the maximum voltage that the non-conducting diode must withstand. At the

instance the secondary voltage reaches its positive peak value, Vm the diodes D1 and D3 are conducting,

whereas D2 and D4 are reverse biased and are non-conducting. The conducting diodes D1 and D3 have

almost zero resistance. Thus the entire voltage Vm appears across the load resistor RL. The reverse voltage

across the non-conducting diodes D2 (D4) is also Vm. Thus, for a bridge rectifier the peak inverse voltage is

given by .

Ripple Factor The ripple factor for a full-wave rectifier is given by

The average voltage or the DC voltage available across the load resistance is

RMS value of the voltage at the load resistance is



Efficiency

Efficiency, is the ratio of the DC output power to AC input power, that is,

The maximum efficiency of a full-wave rectifier is 81.2%.

Figure 1



Procedure 1. Connect the circuit as per the circuit diagram.

2. Connect CRO across the load.

3. Note down the peak value VM of the signal observed on the CRO.

4. Switch the CRO into DC mode and observe the waveform. Note down the DC shift.

5. Calculate Vmis and Vdc values by using the formulae

Vrms = Vm/2, Irms = Im/2 VDC = 2VM/, Idc=2IM/

6. Calculate the ripple factor by using the formula

R= (Vrms/Vdc)2 1 7. Remove the load and measure the voltage across the circuit take down the value as VNL.

Calculate the percentage of voltage regulation using the formula

Regulation = (VNL VFL)/VFL 100

Input Wave and Output Wave Form

Figure 2



Result Thus, the full-wave rectifier circuit design output waveforms are studied and the required parameters

are calculated.

Best Practices and Safety Measures 1. Wires should be checked for good continuity.

2. Carefully note down the readings without any errors.

Viva Voce Questions 1. What are the applications of CRT?

2. What is cathode ray oscilloscope (CRO)?

3. Define ripple factor.

4. What is the purpose of using capacitor in rectifier?

5. What is meant by rectifier?



Experiment 10 Minimum Operating Voltage, Current, Power Consumed and the

Power Factor of a Fluorescent Tube Light

Aim To measure the minimum operating voltage, current, power consumed and the power factor of a fluorescent tube light.

Theory Compact fluorescent light bulbs, also known as CFLs, are energy-efficient alternatives to conventional

incandescent bulbs. In an incandescent bulb, electric current heats a thin filament to the point that it

glows. This design produces a warm, soft light, but the bulb loses most of its energy in the form of heat.

In CFLs, electric current energizes argon and mercury vapor, which excites a glowing phosphor coating

inside the bulb. This design loses very little energy to heat, which means it consumes much less power

than an equivalent incandescent bulb.

CFL bulbs generally cost slightly more than incandescent bulbs, but they can pay for themselves in

power bill savings. There is no industry standard for measuring energy efficiency, so energy savings

ratings will vary from manufacturer to manufacturer. In general, a CFL will use around 75% less

electricity than an incandescent bulb with the same light output, while lasting about 10 times longer.

Additionally, since CFLs produce less heat, they can help you save on cooling costs.

CFLs come in a range of shapes, sizes, color temperatures, and brightness levels, making it simple to replace most incandescent bulbs with an energy-efficient CFL alternative. While the first generation of CFLs had a characteristic blue tint, newer designs do a good job recreating the warm glow of incandescent bulbs. This buying guide will explain the available CFL options, so you can feel confident youre selecting the light bulbs that will work best for you.

Limitations CFLs do have a few limitations as follows:

1. They do not perform well at cold temperatures.

2. If they're used in a fixture that vibrates, such as a ceiling fan, that may shorten their life.

3. You'll need to buy specially marked bulbs if you plan to use them outdoors, in closed fixtures, or with

dimmer switches.



Components Required

Theory When the supply is switched ON, as electric arc is established between the electrodes of the starter due to the flow of current through small air gap between the electrodes. Due to this arc, heat is produced which is sufficient to bend the bimetallic strip which makes contact with fixed electrode. This closes the circuit and therefore choke carries large current. Once the electrodes close, arc vanishes and bimetallic strips cool down again. Now the electrodes A and B become hot and due to cooling the choke circuit opens. The current through the choke coil is suddenly reduced to a small value. This change in current



induces an emf which is very high of the order of 1000 V, in the choke coil. This emf induced is sufficient for ionizing the gas molecules between electrodes A and B, which establishes the discharge between the electrodes A and B through the gas. The potential difference across the tube falls to about 100110 V which is sufficient to maintain the discharge, but not sufficient to restart the glow in the circuit. So even if starter is removed from the circuit, discharge continues as the current flows from electrode A and B due to ionization of gas. If the supply voltage is low, there is difficulty in starting the tube, as the low voltage is insufficient to establish a glow in the starter. As choke lowers the power factor, the capacitor C1 used in the circuit improves the power factor of the circuit. The capacitor C2 suppresses the radio interference developed due to arcing. The function of the inductive choke coil is to supply a large voltage surge for establishing discharge between the electrodes A and B.

Procedure 1. Connect the circuit as shown in the circuit diagram (Fig. 1).

2. Switch on the power supply.

3. Observe the reading of ammeter, voltmeter and power for the load.

4. Calculate the power by given formulae.

.

Tabulation



Circuit Diagram

Figure 1

Result Thus the minimum operating voltage, current, power consumed and the power factor of a fluorescent

tube light were measured.






Viva Voce Questions 1. What do mean by fluorescence?



2. What are the commonly used fluorescent materials?

3. What are the types of MI instruments?

4. Differentiate between DC and AC supply.

5. Define apparent power.



Experiment 11 Working of Thermocouple, Strain Gauge and LVDT

(a) Thermocouples

Aim

To determine the characteristic features of thermocouple.

Theory

A thermocouple consists of two dissimilar metals, joined together at one end, which produce a small unique

voltage at a given temperature. This voltage is measured and interpreted for temperature measurement.

Thermocouples provide an economic means of measuring temperature with the following practical

advantages for the user:

1. They can be extremely robust by using thick wire.

2. Fine wire thermocouples respond very rapidly to temperature changes (less than 0.1 s). For ultra-fast

response (10 s typical), foil thermocouples are used.

3. They are capable of measuring over very wide temperature ranges, from cryogenics to engine exhausts.

4. Thermocouples are easy to install and are available in many packages, from probes to bare wires or foil.

The number of free electrons in a piece of metal depends on both temperature and composition of the metal.

Therefore, pieces of dissimilar metal in isothermal contact will exhibit a potential difference that is a

repeatable function of temperature.

Since the thermocouple is basically a differential rather than an absolute temperature-measuring device, one

junction must be at a known temperature if the temperature of the other junction is to be found from the value

of the output voltage.



This is used in most practical applications. The reference junction temperature is allowed to change, but some

type of absolute thermometer carefully measures it. A measurement of the thermocouple voltage combined

with a knowledge of the reference temperature can be used to calculate the measurement junction

temperature. Usual practice, however, is to use a convenient thermoelectric method to measure the reference

temperature and to arrange its output voltage so that it corresponds to a thermocouple referred to 0C.

Thermocouples are available in different combinations of metals. The four most common types are J, K, T

and E. Each type has a different temperature range and environment, although the maximum temperature

varies with the diameter of the wire used in the thermocouple.

Procedure

Characteristics of Thermocouple

1. Keep the thermocouple probe and thermometer in the hot water.

2. Connect the RTD output to multimeter to measure resistance in ohms.

3. Note the reading of thermometer and corresponding output of thermocouple in ohms in the

following observation table.

4. Note the readings of thermometer and multimeter.

5. Repeat above step to note reading at 20C.

6. Tabulate the readings and Plot the graphs.

Observation Table (Thermocouple)

Sl. No. Temperature

(C)

Output of

Thermocouple

(mV)

1

2



Model Graph

Figure 3

Result

Thus, the characteristics of temperature sensor is determined.

(b) Strain Gauge

Aim

To determine the input-output characteristics of the given strain gauge.



Theory

The change in value of resistance by straining the gauge may be partly explained by the normal

dimensional behavior of elastic material. If a strip of elastic material is subjected to tension or in

other words positively strained, its longitudinal dimensional will increase while there will be a

reduction in the lateral dimension. So when a gauge is subjected to a positive strain, its length

increases while its area of cross-reaction decreases and the resistance of the gauge increases with

positive strain. The change in the value of resistance of strained conductor is more than what can

be accounted for an increase in resistance due to dimensional changes. The extra change in the

value of resistance is attributed to a change in the value of conductor when strained. This

property, as described earlier, is known as piezoelectric effect.

In the cantilever of four strain gauge for the measurement of strain, all the four strain gauges are

similar and have equal resistance when it is strained, that is,

Rg1=Rg2=Rg3=Rg4=R

These gauges are connected in the arms of a Wheatstone bridge. Since the bridge has four

arms with one gauge in each of the four arms, it is called a FULL BRIDGE. When no strain is

applied, the potential of points b and d is equal to ei/2 and hence the output voltage eo = 0

When strained, the resistance of various gauges are for Rg1 and Rg4: R(1+R/R) and for

Rg2 and Rg3:R(1 R/R)

Potential of b when strain is applied:

(1 / ) 1 /

(1 / ) (1 / ) 2

ii

R R R e R Re

R R R R R R

Potential of d when strain is applied:

(1 / ) 1 /

(1 / ) (1 / ) 2i i

R R R R Re e

R R R R R R

Therefore, the change in output voltage is given by

1 / 1 /( / )

2 2o i i i

R R R RE e e R R e



f iandG e

Four active-active arm bridges are extensively used when strain gauges are used as secondary

transducer to give maximum sensitivity combined with full temperature compensation. The

effect of increasing the number of active gauge is the same if a low impedance detector is used.

Apparatus Required

Procedure

1. Connect the

strain simulator module to the control unit.

2. Make the interconnections as shown in the figure.

3. Switch ON the unit.

4. Adjust the zero adjustment potentiometer to read zero in the digital meter.

5. Keep first pro weight of 100 g on both weigh pans.

6. Monitor the strain in micro strain in the digital meter.

7. Repeat steps 5 and 6 and note down the corresponding digital output readings in microstrain.

8. Monitor the voltage through multimeter in the buffer terminal.

9. Tabulate the readings in the tabular column.

10. Unload the weight and tabulate the corresponding readings in the tabular column.

Sl. No. Name of the Apparatus Quantity

1 Strain gauge trainer kit 1

2 Multimeter 1

3 Dead weights 010 kg

4 Patch Cords 1



11. Draw the characteristics curve.

Tabulation

Applied

Weights (g)

Displayed

Strain (s)

Output

Voltage (V) % Error

Result

Thus, the gauge factor of the given strain gauge is found out and its input and output characteristics

are drawn.

(c) LVDT

Aim

To determine the characteristics of LVDT.

Theory

This LVDT is the most useful mutual inductance transducer, which provides an AC voltage output

proportional to the displacement of core passing through the winding. For measuring other physical

quantities, they must be converted into displacement by an auxiliary mechanism.



It consists of three coils mounted on a hollow concentric non-former. The winding kept at the

centre is primary and the other two are secondary windings. The concentric coil is energized by the

external AC power by 5 V to 25 V and 50 to 20 kHz, and the two secondary coils are connected in

phase opposition and acts as opposite side. The position of the core placed within the former or the

relative mutual coupling between the primary and secondary winding will determine the output

amplitude and phase.

At null position a position of the core for which the voltage induced in each of the output

secondary coils will be of the same magnitude and since the windings are in opposition the output

will be zero.

The output voltages are connected in series opposition, and so the net voltage is the difference

of the two voltages in these windings and is a direct measure of the displacement of the core.

Characteristics

The output voltage versus the core movement gives the characteristics of LVDT up to a certain limit

on either of the null position (0). The output is proportional to the core displacement. The linear

range depends upon the length of the secondary coils. Beyond the linear range the output increases

until it reaches to a maximum and then the output drops again to the balanced condition where the

core is removed.

Components Required

Sl. No. Name of the Apparatus Quantity

1 LVDT trainer kit 1

2 LVDT module 1

3 Digital multimeter 1

4 Patch cords As required



Procedure

1. Connect the LVDT module to the main unit; all the interconnections are made using patch

cords.

2. The power supply of the unit is switched on.

3. Initially adjust the screw gauge to the marked numerical number 10.

4. Adjust the zero ADJ potentiometer provided on the trainer, to read 00.0 on the digital

display.

5. Adjust the screw gauge to the marked of numerical value 20.

6. Adjust the CAL potentiometer provided on the trainer to the read 10.0 on the digital display

7. Adjust the screw gauge to the marked numerical value 0.

8. Adjust the CAL potentiometer to the read 10.0 on the digital display.

9. Repeat this CAL adjustment twice or thrice and then now the trainer is the calibrated to read

10 mm displacement.

10. Now adjust the screw gauge to the marked of numerical number 10 and display will read

00.0 mm.

11. Adjust the screw gauge to the marked of numerical number 12 and note down the

corresponding positive displacement of 2.0 mm.

12. Similarly note down for the other positive displacement of 4.0 mm, 6.0 mm, 8.0 mm and

10 mm and also negative displacements up to 10 mm.

13. The corresponding voltage reading for each displacement is taken using multimeter (or)

voltmeter when it is connected in the rectifier circuit.

Formula

Error = Indicated value True value

% error = Indicated value True value



__________________________________ 100

True value

Diagram

Figure 1

Tabulation

Sl.

No.

Position of Core

(in mm)

Indicated value (in

mm)

True Value (in

volts)

% Error



Model Graph

Figure 2

Result

Thus, the inputoutput characteristics of LVDT are plotted.








Viva Voce Questions 1. Mention some important points about a thermnocouple.

Ans: A thermocouple is basically a differential rather than an absolute temperature-measuring device. A

thermocouple consists of two dissimilar metals, joined together at one end, which produce a small unique

voltage at a given temperature. This voltage is measured and interpreted for temperature measurement.

Thermocouples provide an economic means of measuring temperature

2. What type of thermocouples are used for ultra-fast response?

Ans: For ultra-fast response (10 s typical), foil thermocouples are used.

3. What are the most common types of thermocouples available?

Ans: Thermocouples are available in different combinations of metals. The four most common types are J, K,

T and E. Each type has a different temperature range and environment, although the maximum temperature

varies with the diameter of the wire used in the thermocouple.

4. What is the usual practice to measure a reference temperature?

Ans: The usual practice is to use a convenient thermoelectric method to measure the reference temperature

and to arrange its output voltage so that it corresponds to a thermocouple referred to 0C.



Experiment 12 Rating of Compact Fluorescent Lamp (CFL)

Aim

To verify the rating of a compact fluorescent lamp.

Components Required

Theory

Procedure

Inferences


Viva Voce Questions



Experiment 13 Characteristics of a p-n Junction Diode

Aim

To analyze the characteristics of a p-n junction diode in both forward and reverse bias.

Components Required

Ammeter, resistor, voltmeter, diode, power supply, breadboard and wires

Theory

The process in which the electronic device is connected to an external source of current is known as biasing. It can be of two types:

1. Forward bias: It is the condition when the positive terminal of the battery (or power supply) is connected to the anode or the p-region of the p-n diode and the negative terminal is connected to the n-region or the cathode. In this condition, the current flow is relatively large because the charge carriers are the electrons in the n-region and holes in the p-region. Under the applied voltage, these charge carriers cross the p-n junction in the opposite direction and travel in the closed circuit carrying current. The amount of current through the diode is determined by the applied voltage and resistance.

2. Reverse bias: It is the condition when the negative terminal of the battery (or power supply) is connected to the anode or the p-region of the p-n diode and the positive terminal is connected to the n-region or the cathode. In this condition, the flow of current is not supported because the holes in the p-region and the electrons in the n-region move away from the p-n junction. A very small reverse current is observed due to minority charge carriers. However, the reverse current is increased if the applied voltage is increased a value called breakdown voltage.

A p-n junction is formed at the boundary between a p-type and n-type semiconductor. If two separate pieces of material are used, this would bring in a grain boundary between the semiconductors that severely inhibits its utility by dissipating the electrons and holes.

Figure 1

p-n junctions are primary building blocks of most semiconductor electronic devices, such as solar cells, diodes, transistors, LEDs, and integrated circuits. They are the dynamic sites where the electronic action of the device



takes place. A common type of transistor (the bipolar junction transistor) consists of two p-n junctions in series in the form of either n-p-n or p-n-p.

Figure 2

Procedure

Forward-Biased Condition

1. Identify the positive and negative ends of the diode and connect in the circuit in forward bias as per the circuit

diagram.

Figure 3

2. Use a regulated power supply of range 030 V and a series resistance of 1 k. Increase the power supply voltage insteps and for various values of applied voltage observe the forward voltage (Vf) through the diode and the corresponding values of forward current (If).

Reverse-Biased Condition

1. Connect the p-n junction diode in reverse bias as per the circuit diagram.



Figure 4

2. For various values of power supply voltage, note down the reverse voltage (Vr) through the diode and the corresponding values of reverse current (Ir).

Observations and Calculations

1. Tabulate the observed values for forward and reverse voltage and current.

Forward Bias

Power Supply Voltage (volts) Diode Voltage Vf (volts) Diode Current If (mA)

Reverse Bias

Power Supply Voltage (volts) Diode Voltage Vr (volts) Diode Current Ir (A)

2. Plot the graph for voltage versus current for forward and reverse bias as follows:

Take a graph sheet and divide it into four equal parts. Mark origin at the center of the graph sheet.

Now label the positive x-axis as Vf and the negative x-axis as Vr.

Then label the positive y-axis as If and he negative y-axis as Ir.

Plot the readings for diode forward biased condition in the first quadrant and diode reverse biased condition in the third quadrant.

The voltagecurrent (VI) graph obtained for a p-n junction diode in forward and reverse bias is:



Figure 5

From the graph, the characteristic features of forward and reverse bias noted are as follows:

For the forward bias, there is a threshold voltage (V) below which the current is negligible or almost zero.

Beyond the threshold voltage the current rises rapidly. For reverse bias, the reverse current is very small and

increase in voltage does not have significant effect on it. This current is known as the reverse saturation current.

The reverse current increases significantly when the value of reverse voltage is increased beyond the break down

voltage.

Result

Thus the forward and reverse bias characteristics of a junction diode were studied and the voltagecurrent characteristics verified.


1. Connect voltmeter and ammeter with appropriate polarities as shown in the circuit diagram. 2. Do not switch on the power supply if you have not checked the circuit connections as per the circuit diagram. 3. When doing the experiment, do not exceed the voltage beyond the breakdown voltage of the diode. The high

current may cause the diode to burn.

Viva Voce Questions

1. State some applications of p-n junction diode.

Ans: Ranging from rectifiers to LED TV to voltage regulators, these diodes are used almost everywhere in

electronics.

2. What are the components needed to study the characteristics of a p-n junction

diode?

Ans: Ammeter, resistor, voltmeter, diode, power supply, breadboard and

wires.

3. What is the precaution related to value of voltage in reverse bias?

Ans: In reverse bias, the value of applied voltage should not be increased beyond breakdown voltage. The

increase in current may cause the diode to burn.



Experiment 14 Study of Logic Gates

Aim

To study and verify the truth tables of OR, AND, NOT, NAND, NOR, EX-OR gates and realization of all the above gates using NAND and NOR gates.

Components Required

IC trainer kit, regulated power supply, connecting wires and patch cords.

(IC trainer kit: The kit has built-in power supplies which provide all the necessary voltage for experimentation. The trainer kit is suitable for performing experiments on logic gates and many other experiments.)

Theory

Logic gate is a kind of circuit (or assemblage of transistors and resistors) that determines the flow of electricity (or optical signals in fiber-optic computing systems), and the Boolean logic computers use it to make complex logical decisions. The on or off state of a logic gate matches with the binary values. There are seven logic gates. When all the input combinations of a logic gate are written in a series and their corresponding outputs written along with them, then this input/output combination is called a Truth table. Using logic 1 for true and logic 0 for false, it shows how a logic circuits output reacts to several combinations of the inputs. Logic gates process signals which interpret true or false. Normally the positive supply voltage (+Vs) represents true and 0 V represents false. Gates are recognized by their functions: NOT, AND, NAND, OR, NOR, EX-OR and EX-NOR. Capital letters are usually applied to clarify that the term denotes a logic gate.

Various Types of Logic Gates

AND Gate

When all its inputs are 1, AND gate gives an output as 1; otherwise the output is 0. Although there is always a single output, this gate can have minimum two inputs.



Figure 1

OR Gate

When any or all its inputs are 1, OR gate produces an output as 1; otherwise the output is 0. This gate can have minimum two inputs, but has single output only.

Figure 2

NOT Gate

NOT gate gives the complement of its input. This gate is also known as INVERTER. Constantly, it has one input and one output. Its output is 0 when input is 1, and output is 1 when input is 0.

Figure 3

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