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Department ofApplied Sciences

LAB MANUALBasic Electrical & Electronics Lab (BTEE 102)

B.Tech 1st Year – All branches [2012-13]tof

V KCT COLLEGE OF ENGG & TECH, FATEHGARHPunjab Technical University

LAB MANUAL

KCT College of Engg. & Tech. Department- AS

BEEE Lab 1

INDEX

Sr no Name of Experiment

1 To experimentally verify the ohm’s law

2 To verify Kirchhoff's Voltage law in a series circuit and parallel circuit

3 To find voltage, current relationship and power factor of a given R-L circuit

4 To find out the line voltage, phase voltage relationship, line current and phaseCurrent relationship in case of star-connected and delta connected, 3-phase

balanced load.5

To measure resonance in AC circuits6 To study Hysteresis property of the given magnetic material

7 Full-Wave Rectification

8 To verify the working of LVDT

9 Semiconductor (or crystal) diode characteristics.

10 gatesTo study the truth table of all the

11 To study the input and output characteristics of a PNP/ NPN transistors incommon base configuration

12 To perform open-circuit and short-circuit test on a transformer

13 To study the speed control of a dc shunt motor

14 To connect, start and reverse the direction of rotation of a 3-phase induction

motor.


BEEE Lab 2

EXPERIMENT-1

Objective: To find voltage, current relationship and power factor of a given R-L circuit.

Apparatus Required: Variac or 1-phase auto-transformer-1, Single-phase ac load [or lamps

and choke coils], Moving-iron voltmeter [0-250 V]-1, Moving iron ammeter [0-5 A]-1,

Dynamometer .~-pe wattmeter (250 V, 5 A)-1, Double pole, single throw switch (DPST

Switch)-1, Connecting ieads.

Theory: Current flowing through an ac circuit is given as

I= V/Z

where V is the ac supply voltage (voltage applied to the circuit) and Z is the impedance of

the circuit in ohms.

Power factor of an ac circuit is given as P

Power factor, cos ~ = VI

Where P is power of the given load circuit in watts, V is the voltage applied to the

circuit in volts and I is the current in amperes flowing through the circuit. Connection

Diagram:

Procedure: Variac, ammeter, wattmeter, voltmeter, load, (lamps in series with choke coils)

are connected, through double pole single throw switch, to single phase


BEEE Lab 3

supply mains as shown in fig. 1. The readings of ammeter, voltmeter and

wattmeter are noted for var~ous settings of variac.

Observations:

S.No. Voltmeter Reading,

V in Volts

Ammeter Reading,

I

in Amperes

Wattmeter

Reading,

P in Watts

Power Factor of

the Circuit,

Cos ~ = P

VI

1.2.3.4.

Conclusion: 1. Current I increases directly in proportion to applied voltage V.

2. Power factor of the circuit is same through out for a given load.

Note: If required, the readings of the instruments can be recorded with the different loads

(by varying the number of lamps and chokes connected in series).


BEEE Lab 4

EXPERIMENT-2

Objective: To find out the line voltage, phase voltage relationship, line current and phase

Current relationship in case of star-connected and delta connected, 3-phase balanced

load.

Apparatus Required: TPIC switch (500 V, 15 A)-1, Moving iron type voltmeter (0-

500 V)-2, Moving iron ammeter (0-10 A)-2, 3-phase balanced load (say a 3-phase, 440 V,

50 Hz, 7.5 kW induction motor), Board containing six open terminals-1 and Connecting

leads.

Theory: In star-connections

Line voltage, VL =~ phase voltage =~ V p

Line current, IL = Phase current, Ip In delta-

connections

Line voltage, VL = Phase voltage, Vp

Line current, IL =~ phase current Ip

Connection Diagram:


BEEE Lab 5

Procedure: The connections of the terminal box of the induction motor to the stator phase

windings of the motor are shown in fig. 3.3 (a). First of all the connections in terminal box

are made, as shown in fig. 3.3 (b). The motor is started and put on load and readings of both

voltmeters and ammeters are noted for different loads on the motor.

Now the TPIC switch is made off and the connections in terminal board are changed,

as illustrated in fig. 3.3 (c) for delta connections. The motor is started and put on

load and the readings of both ammeters and voltmeters are noted for different loads

on the motor.

Connection

s

S. No. ~ Voltmeter

Reading Vl,

Line Voltage

in Volt5, VI

Voltmeter

Reading V2,

Phase Voltage

in Volts, Vp

Ammeter

Reading Al,

Line Current

in Amperes, IL

Ammeter

~

Reading A2,

Phase Current

in Amperes, Ip

V~

Vp

IP

1Star 2

3

Deltal

23Results : In star connections, line voltage V comes out to be ~ times phase voltage

Vp and line current IL comes out to be equal ~o phase current Ip. In delta connections,

lines voltage VL comes out ,;o be equal to phase voltage Vp and line current IL comes

out to be times ~ phase current Ip


BEEE Lab 6


BEEE Lab 7

Experiment-3

Objective: To perform open-circuit and short-circuit test on a transformer and

determine the following:

(a.) the transformation ratio.

(b) the transformer efficiency at 25%, 50%. 75%, 100%, l50% load at pf of 0.8 lagging

and to pplot the characteristic

Apparatus Required: Single phase transformer (preferably 1 kVA with one winding

rated at 230 V)-1, V ariac-1, Low range voltmeter-1, Low range ammeter-1, Low range

low power factor wattrneter-1, W~attmeter, ammeter and voltmeter of normal ranges

(depending upon the rating of transformer under test) one each, DPIC switch-1 and

connecting leads.

Theory: Open-circuit test is performed to determine the iron loss and the

transformation ratio. Since during this test no current flows in the open-circuited

secondary, the current in the primary is merely that necessary to magnetise the core at

normal voltage. Moreover, the magnetising current is very sma11 fractioii of the full-

load current (usually 3 to 10 per cent of full-load current) and may be neglected as far

as copper loss is concerned consequently, this test gives this core loss alone practically.

The transformation ratio, K-_ Secondary turns _ Secondary voltage on open-

circuit Primary turns Voltage applied to primary

=V2 / V1

The short-circuit test is performed to determine the full-load copper loss. In this test

~ince the terminals of the low voltage winding are short-circuited, therefore, the

trans:ormer becomes equivaTent to a coil having animpe~arice-equal--t-o the

impedance of both the windings. The applied voltage is very small as it is adjusted

to cause flow of rated current in the windings, so the flux linking with the core is

very small and, therefore, iron losses are negligible. The power drawn from the

supply, therefore, represents full-load copper loss.

Transformer efficiency at any given load is given as

_ Output ______________ x

100 Output + iron loss + copper loss at given load

where Output = Voltmeter reading in open-circuit test, Vl


BEEE Lab 8

x ammeter reading during short-circuit test, I5 x pf

Iron loss, Pi = Power input in open-circuit test with rated voltage = Po and

Copper loss, P~ = Power input in short-circuit test

Connection Diagrams: See figures 8.20 and 8.21

Procedure: 1. (ipen-circuit Test. The transformer is connected, as shown in fig. 8.20

on the low voltage side. The ammeter A is a low range ammeter and W is a low

range and low power factor wattmeter. The high voltage side is kept open-

circuited. AC supply at rated voltage is switched on to the transformer through DPIC

switch. High range voltmeter V2 is connected across the secondary of the transformer.

Readings of voltmeters Vl and V2, ammeter A and wattmeter W are noted and

tabulated as below.

2. Short-circuit test. The transformer is connected as shown in fig. 8.21, the low

voltage winding is short-circuited by connection having negligible resistance and

good contacts. The voltage applied to the primary is increased in steps so that

ammeter A carries 0.25, 0.5, 0.75 time rated current, rated current, and 1.5 times

rated current.

The efficiency of the transformer is calculated at different loads as mentioned

above and a curve is plotted between efficiency and load current.

Observations:

(i) Open-circuit test:

Primary voltmeter reading, Vl = ........

Secondary voltmeter reading, V2 = .......

Input power on no load, Po = Wattmeter reading, W= .........

V _

Transformation ratio, K = Vl ...................

(ii) Short-circuit test: Rated primary current,

I Rated kVA X 1,000

- _ ...........

f Rated primary voltage

Power factor, cos ~ = 0.8 (lag)


BEEE Lab 9

S. No. Ammeter Reading Wattmeter Reading Transformer Efficiency,

in Amperes, IS in Watts, PSV~ Is cos~

~~ = x

100Vlls cos~+Po+Ps

_ V~Is x 0.8 x

100

Vlls x0.8+Pa +Ps

1.2.3.4.5.

Result: 1.During short-circuit test, power input, PS varies as the square of the input

current, I5 i.e. copper loss varies as the square of the load current.

2. The curve plotted between the transformer efficiency and load current [fig. 4)

shows that the efficiency becomes maximum when copper loss equals iron loss.


BEEE Lab 10

EXPERIMENT-4

Objective: To study the speed control of a dc shunt motor and to draw the speed variation

with respect to change of (a) field current (field control) and (b) armature current (armature

control).

Apparatus Required: 250 V dc shunt motor of capacity, say, 2 kW-1, PMMC

ammeter (0-2.5 A)-1 and (0-10 A)-1, Rheostats-high resistance, low current-1 andlow

resistance, high current-1, Tachometer-1, DPIC switch-1 and Connecting leads.

Theory: The speed of a dc shunt motor is given as

Hence the speed of a dc shunt motor can be changed by either changing the shunt fie7d

azn~xit h~~ (by inserting an external resistance in the field circuit) or changing the back

emf, Eh, (i.e. V- IQ Ro) by inserting an external resistance in the armature circuit.

Connection Diagram:

Procedure: The connections are made, as shown in fig. 10, and the rheostats are put in

zero positions. The dc supply is switched on by closing the DPIC switch.

Field control: The reading of ammeter A1 is noted and the speed of the motor is

measured by tacliometer. Now the field rheostat setting is changed in steps

(increasing the resistance)


BEEE Lab 11

and ammeter Al readings are noted and the motor speed is measured and

recorded. Now the field rheostat setting is brought back to zero.

Armature Control: Resistance is increased in steps in the armature circuit for

armature resistance control. The ammeter Az readings are noted and the motor speeds

are measured

and recorded.

Armature control rheostat is brought back to zero and the supply is switched off through

DPIC switch.

Observations:

S.No. Field Control Armature ControlAmmeter A1 Read-

ings in Amperes, Ish

Speed of Motor

in RPM

Ammeter A~ Read-

ings in Amperes, Io

Speed of Motor

in RPM

12345

Result: l. With the increase in resistance in the field circuit, the field current

decreases i.e. field becomes weaker and, therefore, speed increases.

2. With the increase in resistance of the armature circuit, voltage drop in

armature increases i.e. back emf Eh decreases and, therefore, speed

decreases.


BEEE Lab 12

EXPERIMENT-5

Objective: To connect, start and reverse the direction of rotation of a 3-phase induction

motor.

Apparatus Required: Three phase induction motor-1, Star-delta starter-1, TPIC

switch1, Tools such as screw driver, plier, test pen etc. and connecting leads.

Theory: Motor is connected to the 3-phase ac supply mains through star-delta

starter and TPIC switch, as shown in fig. 11 (a). The direction of rotation of a 3-phase

induction motor can be reversed by interchanging any two terminals at the TPIC

switch, as shown in fig.l l(b)

Procedure: The connections of a 3-phase induction motor are made to the star-

delta starter and to the TPIC switch, as shown in fig. 11 (a). The TPIC switch is

closed and the motor is started !-y taking the lever of the starter to the start (star)

position and then with a jerk to the run position (or delta connections). The

direction of the rotation of the motor is observed. Say, it is in clock-wise direction.

Now the motor is stopped by pushing the stop button and supply to the motor is

r'emoved by opening the TPIC switch. The two leads of the motor are interchanged to

the T1~I~C\switch, as shown in fig. 11 (b). TPIC switch is closed and the motor is started

again. Tl,~e direction of rotation of the motor is observed.

The push button is pushed and the TPIC switch is made off.

Observations and Results: The direction of rotation of the motor in second case


BEEE Lab 13

is found opposite to that in first case.

EXPERIMENT NO 6


BEEE Lab 14


BEEE Lab 15

Procedure : lnsert IC 7432 on the IC base of the logic experimental trainer board.

Give + 5 V input to pin 14 and graund pin 7. Give inputs A and B to pins 1 and 2 using

binary switches. Connect output pin 3 to LED. ~witch on the trainer. Observe LED

output. Try with different combinations of t A, B. Prepare truth tabie. Repeat for other

gates.


BEEE Lab 16


BEEE Lab 17

EXPERIMENT NO 7

Title: Semiconductor (or crystal) diode characteristics.

Objective:

1. Trace the circuit meant to draw the diode-characteristics;

2. Measure the current through the diode for a particular value of forward voltage;

3. Plot the forward characteristics of a germanium and a silicon diode;

4. Compare the forward characteristic of a Ge diode with that of a Si diode;

5. Calculate the forward static and dynamic resisrance of the diode at a particular

operating point.

APPARATUS REQUIRED: Experimentai board, regulated power supply,

milliammeter, electronic multimeter.

CIRCUIT DIAGRAM: The circuit diagram is given in Fig.

Brief Theory: A diode cr5~duets in forward bias (i.e. when its anode is at higher poi~ntiai

than its cathode). It does not conduct in reverse bias. When the diode is forward-biased, the

barrier potential at junction reduce~.

The majority carriers then diffuse across the junction. This causes current to flow

through the diode. In-reverse bias, the barrier -potential increases, and almost no current

can flow through the diode.

The external battery is connected so that its positive terminal goes to the anode and

its negative terminal goes to cathode. The diode is then forward biased, The amount of

forward bias can be varied by changing the externally applied voltage. As shown in


BEEE Lab 18

Fig. E.4.1.1, the external vo7tage applied across the diode can be varied by the

potentiometer Ri. A series resistor (say, 1 ks2) is connected in the circuit so `that

excessive current does not flow through the diode. VVe can note down different

values of the current through the diode for various values of the v~lta,ge across it. A

nlat between this voltage and current gives the clzode forward characteristics

At a given operating point we can determine the static rcsastance (Ra) and dynamic

resistance (ra) of the diode T'rom its characteristic. The static resistance is defined as the

ratio of the dc voltage to dc current, i.e.

Rd =V/I

The dynamic resistance is the ratio of a small change in voltage to a- small ~hange in current, i.e.

PROCEDURE:

1 Find the type number of the diodes connected in the experirnental board.

2. Trace the circuit and identify different components used in the cii•cuit.

Read the value of the resistor using the colour code.

3. Connect the milliammeter and voltmeter of suitable ranges, say, (i, to

25 mA for ammeter and 0 to 1.5 V for voltmeter.

4. Switch on the pawer supply. With the help of the potentiometer R t,

increase the voltage slowly.

5. Note the milliammeter and voltmeter readings for each setting of t~e potentiometer.

Tabulate the observations.

6. Draw the graph between voltage and current.

7 At a suitable operating point, caiculate the static and dynamic resis tance of tlte

diode, as

illustrated in Fig. E.4.L2.


BEEE Lab 19


BEEE Lab 20


BEEE Lab 21

Experiment no 8Objectives:To experimentally verify the ohm’s law.

Apparatus:DC Power SupplyDC current sourceFew ResistorsWheatstone bridgeMultimeter

THEORY:

Ohm’s Law:

The voltage across an element is directly proportional to the current through it. Theohm’s law can be written mathematically as:

IRV

where R = ResistanceV = voltage across the resistance RI = Current through the resistance R

PROCEDURE:

A. Ohm’s Law:

1. Connect the circuit as shown in figure 2.2. Set the DC voltage supply to 10 Volts.3. Set the resistance R to 100 ohms.4. Measure the voltage across the resistor and the current through the resistor and write

the results in Table 1.5. Determine the value of the resistance using Ohm’s law R=V/I and record in the Table

1.6. Repeat step 2 to 5 for the other resistors (1000 ohms, 10 K ohms).


BEEE Lab 22

Vs=10V R

1 K ohms

Figure 1: Ohm's Law

TABLE 1

Resistor (Nominal Value) 100 1 K 10 K

Ohm-meter Reading

R = V / I

Percent Deviation from Nominal Value

Percent Deviation = (Nominal Value – Ohm-meter Reading) / (Nominal Value)


BEEE Lab 23

EXPERIMENT NO 9Kirchhoff’s Laws

Objective: To verify Kirchhoff's Voltage law in a series circuit. To verify Kirchhoff's Current law in a parallel circuit.

Series Circuit Parallel Circuit

Kirchhoff's Voltage law: VS = VR1 + VR2 Kirchhoff's Current law: IT= IR1 + IR2

in a loop at ajunction

Part A - Series Circuit:

1. Calculate the total resistance, circuit current and voltage drop across each resistor ifwired in a series circuit as shown in the figure.

Total Resistance: Circuit Current:

Voltage Drop across the 470 Ohm Resistor, R1:

Voltage Drop across the 1K Ohm Resistor, R2 :

Power-supply Voltage using Kirchhoff's Voltage law :(should be equal to the sum of the voltage drops)

2. Obtain a 470 Ohms and a 1K Ohms resistors and make sure you got the correct ones.Measure and record their actual resistances.

R1 = ___________________ R2 = ___________________

3. Using the Breadboard, connect the resistors in SERIES as shown in the figure below:R1 is the 470 Ohm resistor and R2 is the 1K Ohm resistor.

R1R2 R1 R2VS = 10V VS = 10V

R1R2


BEEE Lab 24

4. Measure the total circuit resistance.

Total Resistance:

5. Connect the Power-supply to the SERIES resistors as shown in the figure below.

6. Set the Power-supply to 10 Volts.

7. Measure the voltage drop across each resistor and the Power-supply voltage.

Voltage Drop across the 470 Ohm Resistor:

Voltage Drop across the 1K Ohm Resistor:

Power-supply Voltage (should be equal to the sum of the voltage drops):

8. Verify that all the measured values tally (matches) with the calculated values.

Part B - Parallel Circuit:

1. Using the Breadboard, connect the PARALLEL circuit. R1 is the 470 Ohm resistorand R2 is the 1K Ohm resistor.

2. Calculate the current flow through each of the resistors, and the total circuit current.

To calculate current through each of these resistors use ohm’s law: I = V/R

Current through: IR1 = IR2 =

Total Circuit Current using Kirchhoff's Current law : IT =

Total Circuit Current using Ohm’s law : IT = VS / RP = ?

1/RP = 1 / R1 + 1 / R2

RP = ( R1 + R2 ) / ( R1 x R2 )

R1 is the 470 Ohm resistor and R2 is the 1K Ohm resistor.

R1 R2 RP


BEEE Lab 25

RP = ?

3. Measure the current flow through each of the resistors, and the total circuit current.

Current through: IR1 = IR2 =

Total Circuit Current: IT =

9. Verify that all the measured values tally (matches) with the calculated values.


BEEE Lab 26

EXPERIMENT 10

Title: to measure resonance in AC circuits

INTRODUCTION

In this experiment the impedance Z, inductance L and capacitance C in alternatingcurrent circuits will be studied.

The parameters of the circuit will be varied to produce the condition called resonance.

The inductive and capacitive reactance are defined as follows:

Inductive Reactance = XL = 2fL

Capacitive Reactance = XC = fC21

.

The impedance in a seriesAC circuit is found byadding the individualreactances and resistanceas vectors as shown inFigure 1.

Z

R

XL

XC

XL XC

Fig. 1

Voltages are all equal tothe current I, times theindividual or combinedreactances. They can becalculated from a diagramwhich has the same formas that shown in Figure 2.

Vtotal = IZ

VR = IR

VL = IXL

VC = IXC

VL VC

Fig. 2

As the frequency is varied from low to high, a minimum value of total impedance Z isfound when XL = XC, or f =

LC21

. The value of Z at this resonance frequency is Z =


BEEE Lab 27

R. If the applied voltage is kept constant, then when Z is a minimum, I will be at amaximum, so both Z and I have the general form as shown in Figure 3.

Z

f

I

f

Fig. 3

The width of the curves in theabove is of great importancein such devices as radio andTV receivers (we only wantone channel at a time), and ismeasured by the ratio of thewidth to the center frequency,as shown in Figure 4.

Small R0.707 Imax

Larger R

I

f1 fo f2 f

Imax

Fig. 4

When the peak is narrow, thecircuit is said to have a high Q,where the quality Q is defined

as: Q =12

off

f

. A high Q

corresponds to a small value ofthe total series resistance (coilresistance plus any otherresistance). Q can also be

shown to be given by Q = RXL ,

where XL = 2foL, with fobeing the resonant frequency.Figure 5 indicates therelationship between Z, R, XLand XC as f varies from f1 to foto f2.

45o

45o

Z for f = f2

Z for f = f1

Z for f = fo (Z = R)

XC XL = R

Locus of points as f varies

XL XC = R

Fig. 5


BEEE Lab 28

EQUIPMENT & MATERIALS

Simpson 420 function generator Banana wires 2 multimetersDecade capacitor box Frequency counter Oscilloscope100- composition resistor Inductor, 0.01 Henry 2 alligator

clips2 BNC-to-banana adapters French curve Plastic

triangleCoaxial cable, BNC ends 1 sheet of graph paper

EXPERIMENTAL PROCEDURE

A. Capacitive and Inductive Reactance

1. Set up the circuit as shown in Figure 6. Bothmultimeters must be dialed to V to act asAC voltmeters. Set the decade capacitancebox to 0.5 F. Use alligator clips to connectthe 100- resistor in the circuit. Use thecoaxial cable to connect the functiongenerator’s TTL output to the frequencycounter’s A input, and use the counter to setthe frequencies accurately by using the“A Input”, setting the counter for a 1 secondgate time, and a frequency setting of<10MHz. Set the function generator tomaximum amplitude.

V100

V

5.0 X 107 F

Fig. 6

2. Take voltage readings across the function generator and resistor for each frequencysetting. Frequency settings may be made from 2,000 Hz to 10,000 Hz in 2,000-Hzsteps.

3. From Fig. 2, the voltage across the function generator Vfg (= Vtotal) is the vector sumof the voltage across the resistor VR and the voltage across the capacitor VC. Fromthe right-angle triangle, Vfg2 = VR2 + VC2. Use this equation and the observedvalues of voltage to calculate VC.

4. Ohm’s law for the resistor is VR = IR. Calculate the current through the resistor.

5. Ohm’s law for the capacitor is VC = IXC. Because the resistor and capacitor are inseries, they experience the same current. Calculate the measured reactance XC.

6. Theoretically, the reactance of a capacitor is XC = 1/2fC. Calculate this value anddetermine the percent difference between this and the measured value. A reasonableagreement between these two values of XC validates the vector calculation of VC andthe theoretical calculation of XC. Notice that the equation Vfg = VR + VC,


BEEE Lab 29

appropriate for a DC circuit, does not match your data for this circuit.

7. Repeat the above procedure with the 10-mH inductor in the circuit instead of thecapacitor. For an inductor, Vfg2 = VR2 + VL2 and VL = IXL. Theoretically, thereactance of an inductor is XL = 2fL.

B. RLC Series Resonance

1. Set up the apparatus as in Figure 1, byconnecting the output of the function generatorin series to the Hewlett-Packard multimeter (setto mA to make it an ammeter), the 10 mHinductor, the decade capacitance box set to0.10 F and the 100- resistor held byalligator clips. Turn on the ammeter and pressthe AC/DC button (beside the Range button) toproduce a ~ sign in the display. This indicatesthat the ammeter will measure AC instead ofDC current. Attach a BNC-to-banana adapterto the Ch 1 input of the oscilloscope, andconnect its positive input to the positive outputof the function generator. The TTL output ofthe function generator should remain connectedto the A input of the frequency counter.

~R

L C

OscilloscopeCh. 1

A

Fig. 7

2. Calculate the theoretical values of the resonance frequency fo, the bandwidth andthe quality from the values of resistance, inductance and capacitance.

3. Measure the root-mean-square current I on the multimeter over a range offrequencies, starting with f = 2000 Hz and increasing by 500-Hz intervals.Maintain Vtotal at 0.40 V peak-to-peak by monitoring the amplitude of the sinewave on the oscilloscope and adjusting the amplitude of the function generator. Asetting of 0.2 Volts/div gives a convenient size to the sine wave, and should peak2 squares above and 2 squares below the center-line. The wave can be centeredby rotating the POSITION dial on the oscilloscope. Place the measurements inData Table 3.

4. Plot current I vs. frequency f on a piece of graph paper. Obtain extra readings asnecessary near the resonance frequency to clearly define the resonance peak. Usea French curve to connect the data points as smoothly as possible.

5. Find f1 and f2 from this graph as the frequencies for which I = 0.707 Imax , asshown in Figure 4. Calculate fo as the average of f1 and f2, and calculate thebandwidth and quality from the values of f1 and f2. Find the percent difference ofthese three quantities from their theoretical values.


BEEE Lab 30

LABORATORY REPORT: AC CIRCUITS AND RESONANCE

Part A:

Data Table 1: Capacitive Reactance

Frequency (Hz) 2000 4000 6000 8000 10,000

Voltage acrossfunction generator (V)

Voltage acrossresistor (V)

Voltage acrosscapacitor (V)

Current (A)

Measuredreactance ()

Calculatedreactance ()

Percent difference

Data Table 2: Inductive Reactance

Frequency (Hz) 2000 4000 6000 8000 10,000

Voltage acrossfunction generator (V)

Voltage acrossresistor (V)

Voltage acrossinductor (V)

Current (A)

Measuredreactance ()

Calculatedreactance ()


BEEE Lab 31

Percent difference

Data for Part B:R = ___________ L =

__________

C = ___________ fo =LC2

1

=

__________

Bandwidth =L2

R

= ___________ Q =R

Lf2 o=

__________

Data Table 3

SourceFrequency f

(Hz)

I

(A)

SourceFrequency f

(Hz)

I

(A)

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

7500

8000

Experimental values from graph:

f1 = ________________ Hz f2 = ________________ Hz

Resonance frequency = fo = ________________ Hz % difference =


BEEE Lab 32

______________

Bandwidth = f2 f1 = ________________ Hz % difference =______________

Quality =12

off

f

= ________________ % difference =

______________


BEEE Lab 33

Experiment 11

B-H CurveAim: To study Hysteresis property of the given magnetic material and hence to

determine

a) Energy loss /cycle/ unit volume b) Remnant Flux Density and c) Coercive Field

Strength.

Apparatus: Specimen, B-H Curve tracer unit, Cathode Ray Oscilloscope (CRO).

Formula:

Energy loss is determined using the formula S S A

P L

E N v H

0.5 J/ per cycle/unit volume,

Where N is the Number of turns in the coil (300), P is the resistance in series with the coil

(65), L = Length of the coil (0.033m) and SH and SV are the horizontal, vertical

sensitivities

of the CRO and A= Area of the loop.

The Coercive field is determined from the formula

A turns m-1

P L

H N OC SH

C

The Remnant flux density = 2

0 0.5 B OB S WbmV

Procedure: Initially the following settings are made for CRO. The CRO is switched on

and is set to X-Y mode. The bright spot is adjusted to the centre of the display with the

help of Horizontal and Vertical shift knobs. Both the channels (X-Channel

(Horizontal,CH1) and Y-Channel (Vertical, CH2 ) are set to AC mode.

One terminal of the magnetizing coil is connected to point C of the main unit and the

other Terminal to any of the point between V1 to V3 (V3 is recommended). Outputs X &

Y of the main unit are connected respectively to CH1 & CH2 of the CRO. IC probe and

the Supply (P.S) are connected to the main kit. The main kit is switched on. The


BEEE Lab 34

resistance (P) is set for maximum

value with the help of the given knob. With no specimen, the horizontal gain of the CRO

is adjusted until a convenient X deflection is obtained on the CRO display. Specimen is

inserted

through the coil such that it touches only the probe at the centre not the conducting

tracks.

The Y gain of the CRO is adjusted to get appropriate Loop. Trace the loop on the graph

paper

by reading coordinates of the points A, B, C, D, E, F on the loop in CRO and area of the

loop is

Measured.

a) Energy loss is determined using the formula S S A

P L

E N v H

0.5 J/ per cycle/unit

Volume,

b) OC is measured from the graph. The Coercive field is determined from the

formulaA turns m1

P L

H N OC SH

C

c) OB is measured from the graph. The Remnant flux density is determined using the

Formula 20 B 0.5 OB S WbmV

Result: The Energy loss in the specimen= ……………..J/cycle/cubic meter

The Remnant Induction=……………..Wb m-2

The Coercive field = ……………...A turns m-2


BEEE Lab 35


BEEE Lab 36

Experiment no.12

Transistor characteristics BJT

Aim: To study the input and output characteristics of a PNP/ NPN transistors in commonbase configuration

Equipment: Power Supply ( 0-15V), DMMs and potentiometer and other components.

TheoryCircuit Diagrams:

Transistor used CK100

Fig: Common Base Configuration of PNP transistor

Procedure:A. Common Base configuration

1. For the input characteristics of common base configuration, set-up the ckt of fig4.1. Set VEE around 5-6 V and do not change it during the experiment (why?).Now vary VEB with the potentiometer and record IE keeping VCB at zero volt.Observations may be recorded up to a maximum of 30mA emitter current. Repeatthe observations (for four sets) for various values of VCB from 0 to 10 V.

2. For output characteristics follow the ckt of fig 4.1. Set VEE around 5-6 V and donot change it during the experiment. Set IE =0 with the pot and record the IC as afunction of VCB (from 0-10V). Record at least four sets of O/p curve by varying IEfrom 0-20mA.

3. Plot all the curves. Plot the load line. Find input and output resistances and currentgain dc.

VCC


BEEE Lab 37

Experiment

Title: to verify the working of LVDT

Objectives:

Measuring voltage with displacement variation using Linear Variable Differential

Transformer (LVDT).

Apparatus:

LVDT

Micrometer for LVDT

Voltmeter

Theory:

The Linear Variable Differential Transformer is a position sensing device that provides

an AC output voltage proportional to the displacement of its core passing through its

windings. LVDTs provide linear output for small displacements where the core remains

within the primary coils. The exact distance is a function of the geometry of the LVDT.

An LVDT is much like any other transformer in that it consists of a primary coil,

secondary coils, and a magnetic core. An alternating current, known as the carrier signal,

is produced in the primary coil. The changing current in the primary coil produces a

varying magnetic field around the core. This magnetic field induces an alternating (AC)

voltage in the secondary coils that are in proximity to the core. As with any transformer,

the voltage of the induced signal in the secondary coil is linearly related to the number of


BEEE Lab 38

coils. The basic transformer relation is:

where:

Vout is the voltage at the output,

Vin is the voltage at the input,

Nout is the number of windings of the output coil, and

Nin is the number of windings of the input coil.

As the core is displaced, the number of coils in the secondary coil exposed to the coil

changes linearly. Therefore the amplitude of the induced signal varies linearly with

displacement.

The LVDT indicates direction of displacement by having the two secondary coils whose

outputs are balanced against one another. The secondary coils in an LVDT are connected

in the opposite sense (one clockwise, the other counter clockwise). Thus when the same

varying magnetic field is applied to both secondary coils, their output voltages have the

same amplitude but differ in sign. The outputs from the two secondary coils are summed

together, usually by simply connecting the secondary coils together at a common center

point. At an equilibrium position (generally zero displacement) a zero output signal is

produced.

The induced AC signal is then demodulated so that a DC voltage that is sensitive to the

amplitude and phase of the AC signal is produced.

Procedure:


BEEE Lab 39

1. Connect the LVDT with the micrometer.

2. Connect the Voltmeter with the LVDT signal conditioner.

3. Connect the LVDT signal conditioner with the power supply of 110 Volts.

4. Set the position of LVDT such that a range of voltage from +10 to -10 volts can

be achieved.

5. Change the LVDT displacement and record the voltmeter reading in the table.

6. Plot the graph voltage versus displacement.

Table 1

S. No. Displacement(inch)

Resultant Displacement(x-a)

(inch)

Voltage(Volts)

1 a =

2

3

4

5

6

7

8

9

10

11

12

13


BEEE Lab 40

EXPERIMENT NO 14

Title: To study the working of thermocouple

Objectives:

To examine the thermocouple voltage and find corresponding temperature under the

following conditions:

1. To measure voltage of thermocouple without considering the intermediate

thermocouple effect of measurement setup.

2. To measure voltage of thermocouple with ice-point reference junction and

fine corresponding voltage using the thermocouple table.

3. To measure voltage of thermocouple using ambient reference block and

calculate the corrected voltage and then find the corresponding temperature.

Apparatus:

J type thermocouples

4-1/2 digit DVM.

Temperature Indicator.

Ice point water

Boiling water

Theory

Thermocouple:

Thermocouples plays very important role in industry. They are used as transducers to

produce electromotive force to actuate equipment. They are used directly in such devices

as furnace valves, recorders, and temperature-recording instruments.

The simplest electrical temperature-sensitive device is the thermocouple. It consists of a

pair of wires of dissimilar metals joined together at one end. The other ends are

connected to an appropriate meter or circuit. The joined ends are known as the hot

junction and the other ends are the cold ones. When the hot junction is heated, a

measurable voltage is generated across the cold ends.

With proper selection of the wires, the voltage varies in relationship to the temperature


BEEE Lab 41

being measured. Because of this, the thermocouple can be considered a thermoelectric

transducer because of its characteristic of converting thermal energy into electrical

energy. Figure 1 shows a typical circuit using a thermocouple to record temperature

changes in a heat chamber.

When the thermocouple is heated at the hot junction, while the cold junction is at a

relatively constant temperature, the difference in temperature of the two junctions causes

the meter to indicate a current. The indication of the meter is calibrated to be proportional

to temperature.

Procedure:

1. Setup the experiment as Figure 4 in theory sheets and measure voltage V.

V = _____________________

T = _____________________

2. Setup the experiment as Figure 6 of theory sheets and measure voltage V and

calculate V1. Find temperature (T1) corresponding to V1 from table.

)( 21

21

TTVVVV

where,

22

11

tVtV

15.273)()( 00 KTCt

V V1 T T1

3. Setup the experiment according to figure 12.


BEEE Lab 42

a. Note reference temperature, which will be ambient temperature from

temperature indicator.

b. Measure V and find V1.

REFTVV 1

c. Find the temperature from table corresponding to V.

TREF V V1 T T1

4. Compare voltages from setup 1, 2 and 3 and write your conclusions below.

Conclusions:

Explain:

Which set up gives the correct temperature?

Which set up gives maximum error?


BEEE Lab 43

EXPERIMENT NO 15

Title: To study the working of thermocouple

Objectives:

1. To find the effect of loading on strain gauge resistance using Wheatstone bridge.

2. To find the effect of loading on strain gauge and find voltage difference using

bridge circuit.

3. To find unknown load by using results and graphs obtained in part 1 and 2.

Apparatus:

Strain gauge

Different Weights 1 kg, 2k, 5 kg.

4-1/2 digit DVM.

Wheatstone bridge

Three resistances of 120 ohms.

Power supply

Theory:

The strain gauge is a transducer employing electrical resistance variation to sense the

strain produced by a force or weight. It is a very versatile detector for measuring weight,

pressure, mechanical force, or displacement.

Strain, being a fundamental engineering phenomenon, exists in all matters at all times,

due either to external loads or the weight of the matter itself. These strains vary in

magnitude, depending upon the materials and loads involved. Engineers have worked for

centuries in an attempt to measure strain accurately, but only in the last decade we have

achieved much advancement in the art of strain measurement. The terms linear de-

formation and strain are synonymous and refer to the change in any linear dimension of a

body, usually due to the application of external forces. The strain of a piece of rubber,

when loaded, is ordinarily apparent to the eye. However, the strain of a bridge strut as a

locomotive passes may not be apparent to the eye. Strain as defined above is often spoken

of as "total strain." Average unit strain is the amount of strain per unit length and has


BEEE Lab 44

somewhat greater significance than does total strain. Strain gauges are used to determine

unit strain, and consequently when one refers to strain, he is usually referring to unit

strain. As defined, strain has units of inches per inch.

Strain gauges work on the principle that as a piece of wire is stretched, its resistance

changes. A strain gauge of either the bonded or the unbonded type is made of fine wire

wound back and forth in such a way that with a load applied to the material it is

fastened to, the strain gauge wire will stretch, increasing its length and decreasing its

cross-sectional area. The result will be an increase in its resistance, because the

resistance, R, of a metallic conductor varies directly with length, L, and inversely with

cross-sectional area, A. Mathematically the relationship is

ALR

where is a constant depending upon the type of wire, L is the length of the wire in the

same units as , and A is the cross-sectional area measured in units compatible with .

Four properties of a strain gauge are important to consider when it is used to measure the

strain in a material. They are:

1. Gauge configuration.

2. Gauge sensitivity.

3. Gauge backing material.

4. Method of gauge attachment.

The sensitivity of a strain gauge is a function of the conductive material, size,

configuration, nominal resistance, and the way the gauge is energized.

Strain-gauge conductor materials may be either metal alloys or semiconductor material.

Nickel-chrome-iron-alloys tend to yield high gauge sensitivities as well as have long

gauge life. These alloys are quite good when used for dynamic strain measurements, but

because of a high temperature coefficient, they are not as satisfactory for static strain

measurements.

Copper-nickel alloys are generally use when temperatures are below 500 to 600°F. They


BEEE Lab 45

are less sensitive to temperature changes and provide a less sensitive gauge factor than

the nickel-chrome-iron alloys. Nickel-chrome alloys are useful in the construction of

strain gauges for high temperature measurements.

In using electric strain gauges, two physical qualities are of particular interest, the change

in gauge resistance and the change in length (strain). The relationship between these two

variables is dimensionless and is called the "gauge factor" of the strain gauge and can be

expressed mathematically as:

LL

RR

GF

StrainR

RGF

In this relationship R and L represent, respectively, the initial resistance and the initial

length of the strain gauge wire, while R and L represent the small changes in

resistance and length which occur as the gauge is strained along with the surface to which

it is bonded. The gauge factor of a strain gauge is a measure of the amount of resistance

change for a given strain and is thus an index of the strain sensitivity of the gauge. With

all other variables remaining the same, the higher the gauge factor, the more sensitive the

gauge and the greater the electrical output.

The most common type of strain gauge used today for stress analysis is the bonded

resistance strain gauge shown below.


BEEE Lab 46

These gauges use a grid of fine wire or a constantan metal foil grid encapsulated in a thin

resin backing. The gauge is glued to the carefully prepared test specimen by a thin layer

of epoxy. The epoxy acts as the carrier matrix to transfer the strain in the specimen to the

strain gauge. As the gauge changes in length, the tiny wires either contract or elongate

depending upon a tensile or compressive state of stress in the specimen. The cross-

sectional area will increase for compression and decrease in tension. Because the wire has

an electrical resistance that is proportional to the inverse of the cross-sectional area,

AR 1 , a measure of the change in resistance will produce the strain in the material.

Procedure:(A) Using Wheatstone bridge:

1. Connect strain gauge with Wheatstone bridge and find the resistance of strain

gauge with no load and record the value in the table.

2. Find the resistance of strain gauge with loads, 1 kg, 2 kg, 3 kg, 4 kg and 5 kg,

through Wheatstone bridge and record the values in the table.

Load (kg) Resistance (ohms)

0

1

2

3

4

5

Unknown

3. Plot Resistance versus Load in the graph paper and write your conclusions.


BEEE Lab 47

(B) Using Bridge Circuit:

1. Connect strain gauge with the bridge circuit as shown the following figure. Set the

power supply to 10 Volts and all three resistances are 120 ohms.

Vs=10V DVMa b

R 1 R 2

StrainGauge

R 3

V

2. Find the voltage difference ( V ) across nodes “a” and “b” using digital volt-

meter (DVM) with no load and record the value in the table.

3. Find the voltage difference ( V ) using digital volt-meter (DVM) with loads, 1

kg, 2 kg, 3 kg, 4 kg and 5 kg, and record the values in the following table.

Load (kg) V Voltage Difference (mV)

0

1

2

3

4

5

Unknown

4. Plot the voltage difference V versus Load in the graph paper and write your

conclusions.

(C) Find Unknown Load using Graphs:

1. Find the unknown load using resistance versus load graph (obtained in part A).


BEEE Lab 48

Unknown Load : _____________________ kg.

2. Find the voltage difference using voltage difference versus load graph (obtained in part

B).

Unknown Load : _____________________ kg.


BEEE Lab 49

EXPERIMENT

Title: Full-Wave RectificationObjectives:To calculate and draw the DC output voltages of half-wave and full-wave rectifiers.Without smoothing capacitor and with smoothing capacitorEquipment:

AC power supply or Function Generator 2 Voltmeters Function Generator Oscilloscope

Components Diode: Silicon 4×(D1N4002) or Silicon Bridge rectifier Resistors: 10 kΩ, Capacitor :( 0.47 F) Capacitor :( 4.7 F) Electrolytic Capacitor :( 2×100 F)

Fig. 5

1. Construct the circuit of Fig.5. Set the supply to 10 V p-p with the frequency of 50Hz. Put the Channel 1 of the oscilloscope probes at function generator (trainer board)and sketch the input waveform obtained.

Put Channel 1 of the oscilloscope probes across the resistor and sketch the outputwaveform obtained. Measure and record the DC level of the output voltage usingthe (Dc bottom in the C.R.O.) oscilloscope.

Keeping the x-y button of the C.R.O. at outside position i.e. do not press it.

Adjust the power supply unit at 10 V, then a sinusoidal or another type from function generatorinput voltage Vi will be displayed on the screen of the C.R.O.

Measure the input signal voltage Vinput and the Voutput signal voltage Vo using both thevoltmeter and C.R.O.

V input = 10 volts V (input) (Volt) VA (output) (Volt)


BEEE Lab 50

Table 1

Draw the input waveform, Vi : and the output waveform, Vo :

Calculate the effective value of the input signal Vrms which is give by:

Vrms = Vpp / (2√2) = Vm / √2

Transfer the graphs into a diagram , and determine the amplitude (peak value) Vin

and the frequency f of the Vin(t).

Determine the amplitude and the frequency of the output voltage.

The second of Kirchhoff's Laws is used to calculate the output voltage:

VA (T) = V MAX INPUT – 2× 0.7 V

V(th): threshold voltage across the diode for Si diode=0.7 V

Smoothing and filtering

ObjectivesRepresenting the ripple voltage on the load voltage

Determining the ripple voltage as a function of the charging capacitor and the loadresistor

Measuring and calculating the r.m.s. value of the ripple voltage

Fig. 6

With voltmeter 10 Va.c Vd.cWith oscilloscope Vp-p VP-P


BEEE Lab 51

1. Assemble the circuit as shown in Fig. 6 and apply an a.c. voltage 10 V, f = 50 Hz.

2. Use channel 1 of the oscilloscope to measure the voltage Vo across the load resistor.

3. Record the settings of the oscilloscope: Y1 = --- volts/div (dc) t, X = --- ms/div.trigger switch to line.

4. Insert smoothing (filter) capacitor C = 0.47F, 4.7F,100 F; in the circuit to

terminal parallel to the load one after other record the output voltage as shown in Fig.5,

5. determine the ripple voltage as a function of the charging capacitor and the load

resistor

6. Connect an ammeter between terminals 1 and 3 in Fig.6 to measure the d.c. current.

7. Measure the d.c. component of the load current IL and the peak-to-peak value of the

ripple voltage Vr pp for the combination of charging capacitor and load resistor as

a function of the capacitance value of the smoothing capacitor C=0.47F, 4.7F,

100 F and at the same time measure the ripple voltage Vr pp using CRO and Record

the values.

8. The r.m.s. value of the ripple voltage can be calculated using expression

.4.24.2f34

dc)( CR

VCI

CIV

L

dcdcrmsr Where Idc in mA, C is in F, and

RL is in k

9. Calculate the ripple frequencies for the values given in table 5 and enter your resultsinto table 2.

10. Calculate the ripple factor r using the following equation:

)CRF

1(32

1)(

L

VdcrmsVr r

11. Draw the output signal voltage in each case of using Cvalues.

12. Comment on the results you obtained.

C(F)

V2(voltmeter)

(Volts)

Vp-p(C.R.O. volts)

I dc( mA)

T(msec)

F = l/T(Hz)

0.474.7100


BEEE Lab 52

Table 2Questions:

1. Discuss the mechanism of operation of the Full-wave rectification usingSi-bridge rectifier.

2. What do you notice from the values of the average output voltage in both;the half- and full wave rectification circuits? Comment.

3. Describe the ripple voltage dependence on the charging capacitor and theload resistor RL.

4. Is it possible to display both input and output voltages simultaneously withchannel 1 resp. channel 2 give reasons for your answer in Full waverectifier circuit (fig. 6) that you used?

5. Determine the peak reverse voltage across diode V1in full wave rectifiercircuit (fig. 6) that you used.

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