n t lab (repaired)

7/31/2019 N T Lab (Repaired)

1/19

EXPERIMENT NO. 1

AIM: To study transient response of series R-C circuit to step input.

Appratus: Function Generator (for step input) , Cathode Ray Oscilloscope , Capacitor , Bread-board ,

Resistance , Connecting wires , Probes etc .

Fig 1.1: circuit diagram for transient response of R-C circuit to step input

THEORY:

Transient: Transient refers to the sudden change in steady state. This may be due to voltage, load etc. The

transient response of circuit is studied with the help of oscilloscope.

The behaviour of the current during charging & discharging is different .

Charging:

During charging at (t =0) the capacitor behaves like a short- circuit initially and i= V/R is the

maximum current in the circuit. The equation of current is given by

Let VR, VC be the voltage across resistance and capacitor respectively. VR is given by

VR The voltage VC is given by

VC

Discharging:

In this case, the capacitor is fully charged at voltage V and steady state has been achieved and the supply is

withdrawn . Now if the capacitor is allowed to discharge through the resistance after the circuit is closed, the

current at starting,


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At any time t ,

The voltage across capacitor VC during discharge is given by

VC PROCEDURE:

1. Connect the circuit as shown in fig1.1

2. Connect the two terminals of the capacitor across CRO.

3. Select square waveform from function generator.

4. Place graph on screen to CRO & trace the actual curve in fig 1.2 from CRO at different frequency.

5. Vary the frequency of input and observe the change in the waveform of output.

RESULT:

The variation of voltage across capacitor during charging and discharging is shown in fig 1.3. The current

through the circuit has also been shown to vary w.r.t. time.

CONCLUSION:

We infer from the above observation that the voltage across the capacitor during charging and discharging is

having transients and the transients can be controlled choosing proper values of R and C.

QUIZ ANSWERS:

Q1. What is the function of function generator? A1. To provide pulses of different shapes, variable

frequency and voltage

Q2.Capacitor does not allow sudden change: a) in

current b) in voltage c) in both (a & b) d) in none of

the above

A2. (b)

Q3. Transient behavior occurs in any circuit when:

a)there are sudden change of applied voltage

b) the voltage source is shorted

c) the ckt. Is connected or disconnected from the

supply

d) all the above happen

A3. (d)

Q4. Write time constant of series R-C circuit? A4. Time constant

Q5. Write


3/19

EXPERIMENT NO. 2

AIM: To study transient response of R-L circuit.

REQUIREMENTS: Resistance, inductor, bread-board, function generator, CRO, connecting wires, probes,

etc.

THEORY: Transient refers to the sudden change in steady state. This may be due to voltage, load etc. The

transient response of circuit is studied with the help of oscilloscope. The behaviour of the current during

charging & discharging is differed and is shown in figure.

Let a voltage V be applied at (t = 0+) by closing Switch S in the RL circuit. It is known as open circuit

test at charging apply KVL,

Solve of this different equation )

Since inductor behaves as open circuit at switching At t=0+

i=0

Therefore,

Voltage across resistance VR

VR ( )

Similarly voltage across inductor

VL [

]

VL PROCEDURE:

1. Connect the circuit elements as shown in fig.


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2. Apply square wave signal to the circuit. Observe the output on C.R.O.

3. Change the frequency and observe the variation in the output waveform.

RESULT: The variation of voltage across inductor during charging and discharging is shown in figure. The

current through the circuit has also been shown to vary w.r.t. time.

CONCLUSION: We infer from the above observation that the voltage across the inductor during charging

and discharging is having transients and the transients can be controlled choosing proper values of R and L.

PRECAUTIONS:

1. Make all the connection tight

2. The range of CRO selected must be proper.

3. The function Generator selected should have proper range.


5/19

EXPERIMENT NO. 3

AIM: To find the resonant frequency, bandwidth & Q factor of R-L-C series circuit.

REQUIREMENTS: Variable resistance, capacitor, variable inductor, function generator, CRO, bread-board

connecting wires, multi-meter etc.

THEORY: In RLC series circuit, the Impedance of ckt. is given by Z2

= [ R2+ (L - 1/C)

2]

The circuit is said to be in series resonance, when the applied voltage and the resulting current are in

phase. Hence, at resonance,

Z=R

So that L - 1/C =0 or or =

If L and C are kept constant and the frequency is varied, the condition for resonance will be given by

= , where is the resonant frequency in radians per second.The variation of current with frequency for series RLC circuit can be drawn by varying the frequency

with function generator and measuring the current for different frequencies.

The difference (f-f) is called bandwidth of the circuit where f and f are half power frequencies.

PROCEDURE:

1. Connect the circuit elements as shown in figure.

2. Connect CRO across the capacitance.

3. Connect the ammeter in series with the circuit.

4. Vary the frequency by the function generator and record the values of current in the ammeter at different

frequencies.

5. The frequency at which the current is maximum, is known as resonant frequency.


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6. If we decrease or increase the frequency with respect to resonant frequency, then the value of current will

decrease on both the sides.

7. Take above readings of current for different frequency keeping all factors constant.

8. Plot frequency f on X-axis and current I on Y-axis and draw the curve on the graph paper for current w.r.t.

different values of frequency.

9. We can also calculate the difference between the experimental value and the calculated value of resonant

frequency.

CALCULATION:

Q factor of series RLC circuit is ratio of the reactive power in the inductor or capacitor to the true power in the

resistance in series with the coil or capacitor.

Q = 2

Resonant frequency = f (Hz)Half power frequencies are f & f in HzBand width = f- fBandwidth can be calculated from graph and the difference between experimental and calculated value of

bandwidth can be ascertained.

Quality factor can also be calculated as Q =

RESULT: The variation of current with respect to frequency for the series RLC circuit is as shown in the

graph paper.

PRECAUTIONS:

1. All connections should be tight.

2. The range of ammeter selected must be proper.

3. The function Generator selected should have proper range.


7/19

EXPERIMENT NO. 4

AIM: To calculate and verify "Z" parameters of a two port network.

APPARATUS REQUIRED: 1. DC Power Supply 2. Multi-meter

3. Resistances 4. Bread board

5. Connecting wires, etc.

|THEORY & FORMULA USED: A two-port network is a special of multi-port network. Each port consists

of two terminals, one for entry and other for exit. From the definition of a port, the current at entry is equal to

that at the exit terminal of a port.

In the two port network there are four variables. These are the Voltages and currents at the input and

the outputs ports. Here only two of the four variables V1, I1, V2, I2 are independent.

Z- parameter of a two port network may be defined by expressing the port Voltages V 1 and V2 in

terms of the current I1 and I2. Here V1 and V2 are dependent variables and I1, I2 are independent variables.

The voltage at port 1- 1 is the response produced by two currents I1 and I2.

I1 I2

1

Input Port V1 Output Port V2

Thus, V1 = Z11 I1+ Z12 I2 --- (i)

V2 = Z21 I1+ Z22 I2 --- (ii)

Where Z11, Z12, Z21, Z22 are called impedance (Z) parameters.V1 = Z11 Z12 I1


8/19

V2 Z21 Z 22 I2

Z11 =

Z21=

Output Open

Z12=

Z22=

Input Open

Where,

Z11 - Input driving point impedance

Z12 - Reverse transfer impedance

Z21 - Forward transfer impedance

Z22 - Output driving point impedance

PROCEDURE:

In order to determine the open circuit (impedance Z) parameters, open the output port and excite

input port with a known voltage source Vs so that V1 = Vs and I2 = 0. We determine I1 and V2 to obtain Z11 &

Z21. Then the input port is open circuited and the output is the excited with the same voltage source Vs so that

V2 =Vs and I1 = 0. We determine V1 and I2 to obtain Z12 & Z22.

OBSERVATION TABLE:

CASEI. When Output Port is Open Circuited, I2 = 0

V1(V) I1 (A/mA) V2(V) Z 11 =V1/I1 Z21 =V2/I1

Applied Exp. The. Exp. The. Exp. The. Exp. The.

CASEII. When Output Port is Open Circuited, I1 = 0

V2(V) I2 (A/mA) V1(V) Z 12 =V1/I2 Z22 =V2/I2


RESULT: Z- Parameters of a given network are as follows:

Experimental Theoretical

Z11

Z12

Z21


9/19

EXPERIMENT NO. 5

AIM: To calculate and verify "Y" parameters of a two-port network

APPARATUS REQUIRED: 1. DC supply 2. Multi-meter







the output ports. Here only two of the four variables V1, I1, V2,I2 are independent.

The Y parameter of two port network for positive directions of voltage and currents may be defined

by expressing the port current I1 and I2 in terms of the voltages V1 and V2. Here I1 and I2 are dependent

variables and V1, V2 are independent variables. I1 may be superposition of two component, one caused by V1

and other by V2.

I1 I2


I1 = Y11V1 + Y12 V2 ---(1)

I2 = Y21 V1 +Y22 V2 ---(2)

Y11, Y12, Y21 and Y22 are network functions and also called admittance parameter

I1 = Y11 Y12 V2


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I2 Y21 Y 22

V2

Y11 =

Output Short

Y21 =

Y12 =

Input Short

Y22 =

Where,

V11 - Input driving point admittance

Y12 - Reverse transfer admittance

Y21 - Forward transfer admittance

Y22 - Output driving point admittance

PROCEDURE:

In order to determine the open circuit (admittance Y) parameters, short the output port and excite

input port with a known voltage source Vs so that V1 = Vs and V2 = 0. We determine I1 and I2 to obtain Y11 &

Y21. Then the input port is short circuited and the output is the excited with the same voltage source Vs so that

V2 =Vs and V1 = 0. We determine V1 and I2 to obtain Y12 & Y22.

OBSERVATION TABLE:

CASEI. When Output Port is Short Circuited, I2 = 0

V1(V) I1 (A/mA) I2(A/mA) Y 11 =I1/V1 Y21 =I2/V1


CASEII. When Output Port is Short Circuited, I1 = 0



RESULT: Y- Parameters of a given network are as follows:


Y11

Y12

Y21


11/19

EXPERIMENT NO. 6

AIM: To calculate and verify "ABCD" parameters of a two- port network.








the output ports. Here only two of the four variables V1, I1, V2,I2 are independent.

ABCD Parameters are widely use in transmission line theory and Cascade networks. Transmission

parameter provide the direct relationship between input and output and also known as general circuit

parameters.

I1 I2

Input or sending Port V1 Output or receiving Port V2

There are defined as

V1=AV2BI2 ---(i)

I1 = CV2DI2 ---(ii)

(-ice sign is used with I2, not for parameter B&D)

The above equation may be written in matrix form

V1 = A B V2

I1 C D -I2


12/19

A =

Output Open

B =

C = Output Short

D =

Where,A - Reverse voltage ratio with the receiving port open-circuited

B - Reverse transfer impedance with the receiving port short-circuited

C - Reverse transfer admittance with the receiving port open-circuited

DReverse current ratio with the receiving port short-circuitedPROCEDURE:

In order to determine the transmission (ABCD) parameters, open the output port and excite input port

with a known voltage source Vs so that V1 = Vs and I2 = 0. We determine I1 and I2 to obtain A & C. Then the

input port is short circuited and the input port is the excited with the same voltage source Vs so that V1 =Vs

and V2 = 0. We determine I1 and I2 to obtain B & D.

OBSERVATION TABLE:

CASEI. When Receiving (Output) Port is Open Circuited, I2 = 0

V1(V) I1 (A/mA) V2(V) A = V1/V1 C =I1/V2


CASEII. When Receiving (Output) Port is Short Circuited, V1 = 0

V1(V) I1 (A/mA) I2(A/mA) B = V1/-I2 D =I1/-I2


RESULT: ABCD- Parameters of a given network are as follows:


A


13/19

EXPERIMENT NO. 7 AIM: To calculate and verify "h" parameters of a two- port network.

APPARATUS REQUIRED: 1. DC supply 30V, 2A 2. Multi-meter

3. Resistances 4. Bread board Connecting .



that at the exit terminal of a port.In the two port network there are four variables. These are the Voltages and

currents at the input and the output ports. Here only two of the four variables V1, I1, V2, I2 are independent.

Hybrid parameters are generally used in transistor circuit. The hybrid matrices describe a two port network,

when the voltage of one port and current of other port are take as the independent variables.

1 I1 I2

Input or sending Port V1 Output or receiving Port V2 1

i.e.

voltage at the port 1-1 and current at port 2-2 as taken as dependent variables and we can express in cosine

of I1 and V2.

V1 = h11 I1 + h12 V2 --- (i)

I2 = h21 I1 + h22 V2 --- (ii)

V1 = h11 h12 I1

I2 h21 h22 V2

h11 =

Output Short

h12 =

h21 = Input Open

h22 =


14/19

Where,

h11 - Input driving point impedance with the output port short-circuited [1/Y11]

h12 - Reverse voltage ratio with the output port open-circuited [Z12/Z22]

h21 - Forward current ratio with output short-circuited.[Y21/Y11]

h22 - Output driving point admittance with the input port open-circuited. [1/Z22]

PROCEDURE:

In order to determine the transmission (h) parameters, short the output port and excite input port with

a known voltage source Vs so that V1 = Vs and V2 = 0. We determine I1 and I2 to obtain h11 & h21. Then the

input port is open circuited and the output port is the excited with the same voltage source Vs so that V 2 =Vs

and I1 = 0. We determine I2 and V1 to obtain h12 & h22.

OBSERVATION TABLE:

CASEI. When Output Port is Short-Circuited, V2 = 0

V1(V) I1 (A/mA) I2(A/mA) h11 = V1/I1 h21 =I2/I1


CASEII. When Intput Port is Open Circuited, I1 = 0V2(V) V1 (V) I2(A/mA) h12 = V1/V2 h22=I2/-V2


RESULT: h- Parameters of a given network are as follows:


h11

h12

h21

h22

PRECAUTIONS:

1. All connections should be tight.2. The range of ammeter selected must be proper.


15/19

3. EXPERIMENT NO. 8

AIM: To determine and verify the "y" parameters of the parallel connected two port network.








the output ports. Here only two of the four variables V1, I1, V2, I2 are independent.

I1 I1a I2a I2


I1b I2b

We know I1 = Y11V1 + Y12 V2 ---(i)

I2 = Y21 V1 +Y22 V2 ---(ii)

This implies I1a = Y11aV1a + Y12a V2a

I2a = Y21a V1a +Y22a V2a

Similarly I1b = Y11bV1b + Y12b V2b

I2b = Y21b V1b +Y22b V2b

From interconnection of network it is clear that:

V1 =V1a =V1b & I1 = I1a +I1b

V2 =V2a = V2b & I2 = I2a +I2b

I1 = Y11aV1 + Y12a V2 + Y11bV1 + Y12b V2

I1 = (Y11a + Y11b)V1 + (Y12b+ Y12b )V2Similarly I2 = Y21a V1 +Y22b V2 + Y21b V1 +Y22b V2

I2 = (Y21a +Y21b)V1 + (Y22b +Y22b )V2

The equivalent of parallel connected two-port network

I1 = Y11V1 + Y12 V2

I2 = Y21 V1 +Y22 V2

Where

Y11 = Y11a+Y11b Y12 = Y12a + Y12b

Y21 = Y21a + Y12b Y22 = Y22a + Y22b


16/19

I1 = Y11 Y12 V2

I2 Y21 Y22 V2

Y11 =

Output Short

Y21 =

Y12 =

Input Short

Y22 =

Where,Y11 - Input driving point admittance

Y12 - Reverse transfer admittance

Y21 - Forward transfer admittance

Y22 - Output driving point admittance

PROCEDURE: In order to determine the open circuit (admittanceY) parameters, short the output port and

excite input port with a known voltage source Vs so that V1 = Vs and V2 = 0. We determine I1 and I2 to obtain

Y11 & Y21. Then the input port is short circuited and the output is the excited with the same voltage source Vs

so that V2 =Vs and V1 = 0. We determine V1 and I2 to obtain Y12 & Y22.

OBSERVATION TABLE: CASEI. When Output Port is Short Circuited, V2 = 0

V1(V) I1 (A/mA) I2(A/mA) Y11 =I1/V1 Y21 =I2/V1


CASEII. When input Port is Short Circuited, V1 = 0



VERIFICATION: [N] = [Na] + [Nb];

Where

[N] = Mat [Y11 Y12 ; Y21 Y22 ]

[Na] = Mat [Y11a Y12a ; Y21a Y22a ]

[Nb] = Mat [Y11b Y12b ; Y21b Y22b ]


17/19

EXPERIMENT NO. 9

AIM: To plot the frequency responses of low-pass filter and determine half power frequency.

REQUIREMENTS: Cathode Ray Oscilloscope, Function Generator, Inductor, Capacitor, Bread- board,

connecting wires, etc.

THEORY: Low pass filter is one which passes without attenuation all frequencies up to the cut-off frequency (fc ) and

attenuates all other frequencies greater then cut of frequency. The attenuation characteristics of an ideal low pass filter in

show in Fig. 2. This transmits currents of all frequencies from 0 up to cut-off frequency. The band is called pass band or

transmission band. Thus, the pass band for the LP filter is the frequency range 0 to f cut-off frequency (fc ). The

frequency range over which transmission does not take place is called the stop band or attenuation band. The stop band

for a LP filter is the frequency range above cut-off frequency (fc ).

or -1

Or Or fc

PROCEDURE:

1. Make all the connections as shown in the figure.

2. In order to study low pass filter first of all connect capacitor and inductor as in figure..3. Calculate the theoretical value of cut off frequency and see reading.

4. Observe CRO carefully note where the graph stop vibrating.

5. Note down frequency and that is desired cut-off frequency (fc ).

RESULT:

PRECAUTIONS:


2. Take output voltage across the capacitor.

3. Connect the CRO cross the capacitor.


18/19

EXPERIMENT NO. 10

AIM: To plot the frequency response of high pass filter.

REQUIREMENTS: Experimental board, connecting leads, capacitance, resistance, CRO, function generator.

THEORY: These filters reject all the frequencies bellow cut-off frequency (fc ). Thus the pass band stop

band of the High Pass filter is the frequency range above fc and below fc respectively. The attenuation

characteristic of a HP filter is shown in figure.

Which gives fc

PROCEDURE:

1. Make all the connections as shown in the figure.

2. In order to study high pass filter first of all connect capacitor and inductor as in figure..

3. Calculate the theoretical value of cut off frequency and see reading.

4. Observe CRO carefully note where the graph stop vibrating.

5. Note down frequency and that is desired cut-off frequency (fc ).

RESULT:

PRECAUTIONS:


2. Take output voltage across the capacitor.

3. Connect the CRO cross the capacitor


19/19

GENERAL PRECAUTIONS FOR WORKING IN ELECTRICAL LABORATORY.

1. Make all the connections tight.

2. Don't leave loose wires on the table.

3. Don't touch live terminals control should be operated with one hand metallic pencils pens foot rules

wristwatches, finger rings etc. should be used with care.

4. Use suitable wire types and sizes so that they can carry the current of branch concerned and also

their insulation is good enough to with stand the voltage.

5. Get the connections checked by the concerned teacher and switch on supply after his approval.

6. Never exceed permissible value of current voltage speed of any machine apparatus wires load etc.

7. Introduce fuses in the circuit whenever there is possibility of accidental flow of over current chose

approximate rating of the fuse wires .

8. Ensure that the polarity of the all the instruments is correct .

9. In case instruments indicating in the reverse direction interchange the connections.

10. Mechanical damage to the instruments must be avoided. This can result from jarring of an instrument

placing it on unstable stands or at unstable places keeping an elbow on case or the instrument being

pulled off by its leads.

11. A precaution that can help in trouble shooting is to introduce ammeters in all the branches of

connections diagram though all readings are not essential for the data processing.

12. In general laboratory circuits are opened after reducing loads as far as possible. The circuit of a series

motor is however an exception.

13. Never apply full voltage to a device suddenly. Always increase the voltage from zero and graduallybring it to the rated value using autotransformers for AC and potential dividers for the DC.

14. Don't expose the eyes to electric arcs as they are powerful generators if UV rays.

15. Don't lift brushes from the commutator or slip rings while machine is in operation.

16. Don't open the section of a circuit while it's primary is energized. This is dangerous to operating

person.

17. Don't stand or sit near or pass through belts when in motion or even at rest.

18. All metallic electrical apparatus that is to be handled should be earthed properly before use.

19. Keep the power on only for the duration of the experiment.

20. Don't touch the output terminals of an auto transformer even if the knob setting has been brought to

zero resulting in zero voltage difference between the output terminals . The reason is that even when

the voltage difference between the output terminals is zero both the terminals may be at 230V above

ground.

n t lab (repaired)

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