eci lab manul

M.S.P.VELAYUTHA NADAR M.S.P.VELAYUTHA NADAR M.S.P.VELAYUTHA NADAR M.S.P.VELAYUTHA NADAR

LAKSHMITHAIAMMAL LAKSHMITHAIAMMAL LAKSHMITHAIAMMAL LAKSHMITHAIAMMAL

POLYTECHNIC COLLEGEPOLYTECHNIC COLLEGEPOLYTECHNIC COLLEGEPOLYTECHNIC COLLEGE

SIVAGAMIPURAM, PAVOORCHATRAM-627808

THIRUNELVELI DISTRICT, TAMILNADU

[email protected]

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

ELECTRICAL CIRCUITS & ELECTRICAL CIRCUITS & ELECTRICAL CIRCUITS & ELECTRICAL CIRCUITS & INSTRUMENTATIONINSTRUMENTATIONINSTRUMENTATIONINSTRUMENTATION

Lab ManualLab ManualLab ManualLab Manual YEAR: II SEMESTER: III

AUTHOR:

Mr. C. Saravana Sathya Seelan,, B.E Sr.Lecturer/ECE

Mr. P. Rama Ganesan, B.E Lecturer/ECE

PUBLISHER: M.S.P.V.L. POLYTECHNIC COLLEGE

PAVOORCHATRAM – 627 808

ECE Department ECE Department ECE Department ECE Department ECI Lab ManualECI Lab ManualECI Lab ManualECI Lab Manual

1

CONTENTS

S. NO NAME OF THE EXPERIMENT Page No.

1. VERIFICATION OF OHM’S LAW 3

2. VERIFICATION OF KIRCHOFF’S CURRENT &KIRCHOFF’S VOLTAGE LAW 7

3. VERIFICATION OF SUPER POSITION THEOREM 13

4. VERIFICATION OF THEVENIN’S THEOREM 17

5. VERIFICATION OF NORTONS THEOREM 23

6. VERIFICATION OF MAXIMUM POWER TRANSFER THEOREM

29

7. OC AND SC TEST ON A SINGLE PHASE TRANSFORMER

35

8. CALIBRATION OF AMMETER AND VOLTMETER 41

9. WHEATSTONE’S BRIDGE 47

10. WIEN BRIDGE 51

11. PHOTO ELECTRIC TRANSDUCER 57

12. MEASUREMENT OF FREQUENCY AND PHASE ANGLE 61

13. MEASUREMENT OF FREQUENCY AND AMPLITUDE USING CRO

67

14. RLC BRIDGE 71

15. STRAIN GAUGE MEASUREMENT 75

16. MEASUREMENT OF LOADCELL 79

17. LVDT MEASUREMENT 83

18. MEASUREMENT OF TEMPERATURE USING THERMISTOR 87

19. Extra syllabus: EXTENDING THE RANGE OF AMMETER

91


2

VERIFICATION OF OHM’S LAW:

CIRCUIT DIAGRAM:

RPS (0-30) V

+

-

DRB

A (0–10) mA

+

-


3

1. VERIFICATION OF OHM’S LAW Aim:

To verify the ohm’s law using standard resistances, Ammeter and voltmeter. Objective :

To know the relation between potential differences (v), current flow (I) and Resistance(R). Ohm’s law:

The ratio to potential difference (V) between any two points on a conductor to the current (i) flowing between them is constant, provided the temperature of the conductor does not change. V/I=constant. Apparatus Required:

S. No Apparatus Name Range Quantity 1. RPS (0-30)V 1

2 Ammeter (0-10)mA 1

3. Resistance 1 kΩ 1 4. Bread board - 1

5. Connecting wires - 10 Formula : V = IR Where V = Voltage (potential difference) in volts I = Current in milli Amperes R=Resistance in ohms. Theory :

Ohm’s law says that the current is directly proportional to the potential difference across the ends of the conductor, provided temperature is kept constant. This linear relation between V and I does not to all non metallic conductors and non linear devices such as Zener diodes and voltage regulators (VR) tubes. Procedure :

• Connections are made as shown in the circuit diagram. • The voltage is varied and the corresponding current is noted. • The ratio of voltage (v)and current (I)is noted


4

Tabulation:

S.NO Applied voltage (V) Current I (mA) Resistance R=V/I in ohm


5

Applications:

It is used in the electrical &electronics circuits.

Result:

Thus the ohm’s law was verified using standard resistances, ammeter and voltmeter.


6

Kirchoff’s Current Law Circuit Diagram:

TABULATION:

Voltage (V) Current (mA)

I3 = I1 + I2 (mA) I1 I2 I3


7

2. VERIFICATION OF KIRCHOFF’S CURRENT &KIRCHOFF’S VOLTAGE LAW

Aim:

To verify the Kirchoff’s current and kirchoff’s voltage law by using standard resistances, Ammeter and voltmeter. Kcl’s law:

This law states that the algebric sum of current at a junction of a network is zero. Kvl’s law:

This law states that the algebric sum of a voltage in a closed circuit is equal to zero Apparatus required:

S. No Apparatus Name Range Quantity

1. RPS (0-30)V 2

2 Ammeter (0-10)mA 3

3. Resistance 1 KΩ 1



6. Bread board - 1

7. Connecting wires - 10

Theory :

Kirchoff’s Current Law (First Law):

The KCL states that the sum of current flowing towards a junction is equal to the sum of current flowing away from the junction.


8

Kirchoff’s Voltage Law: Circuit Diagram:

Tabulation:

Voltage (V) Current I (mA) Resistance (K Ω) I(R1 + R2)

mA R1 R2


9

According to KCL,

i1 + i3 + i5 = i2 + i4 Sum of incoming current = Sum of Outgoing current (b) Second Law (or) Voltage Law:

The algebraic sum of voltage in a closed circuit is equal to zero. (i.e) Alvebraic sum of emfs + Algebraic sum of voltage droft = 0

E = IR1 + IR2

E – IR1 – IR2 = 0

Procedure :

KCL’s Law:

• Connections are made as shown in the circuit diagram.

• Switch on the power supply.

• The voltage is varied and the corresponding current is noted.

• Now verify the kirchoff’s current law

E – I (R1 + R2) = 0


10


11

KCL’s Law: • Connections are made as shown in the circuit diagram. • Switch on the power supply. • The voltage is varied and the corresponding current is noted.

Now verify the kirchoff’s voltage law Safety Devices:

• Tester • Fuse • Shoes

Precaution for Personal Safety:

• The safety material should be wearied. • Connection should be verified correctly • Maintain some distance from equipments and stand. • Keep the power supply “OFF” when making connection.

Precautions for Device Safety:

• Turn the voltage knob in minimum position in the RPS before switch ‘ON’ the RPS.

• The current knob in the RPS must be in maximum position before switch ‘ON’ the RPS.

• If the power supply indicates over load bring the voltage level to zero and switch off the supply voltage.

• Before making connections, check the components correctly.

Viva Questions:

1. State KCL 2. State KVL 3. What is meant by Current? 4. What is power? What is the unit of it?

Applications:

It is used in all the electrical &electronics circuits.

Result:

Thus the KCL and KVL was verified by using standard resistances, ammeter and voltmeter.


12

Verification of Super Position Theorem:

Circuit Diagram:

V1 Source Shorted:

10KΩ

RPS (0–30)V

+

- A (0–10) mA

+

-

10KΩ

+

-

RPS (0–30)V

V1

V2

5.6KΩ

10KΩ

RPS (0–30) V

+

-

A (0–10) mA

+

-

10KΩ

(5.6) KΩ


13

3. VERIFICATION OF SUPER POSITION THEOREM

Aim:

To device an experiment to verify super position theorem. Objective :

To acquire the knowledge about the replacement of voltage source by their internal resistance. Super Position Theorem :

In a network of linear resistances containing more than one generator, the current which flows at any point is the sum of all the currents which would flow at that points if the each generator were considered separately and all the other generators replaced for the time being by resistance equal to their internal resistances. Apparatus Required:

S.NO Apparatus Name Range Quantity 1. RPS (0-30)V 1 2 Ammeter (0-10) mA 1 3. Resistance 10 kΩ 2 4. Resistance 5.6 kΩ 1 5. Bread board - 1 6. Connecting wires - 10

Formula :

I = I1+I2 mA I1 = Current due to one source, mA I2 = Current due to one source, mA I = Total current at that point, mA Theory:

In a linear circuit the response at any element due to several sources is given by the super position of the responses due to individual sources acting one at a time while the next of the sources reduced to zero values. To apply the super position theorem for the analysis of a linear circuit, the constant voltage sources are reduced to zero voltages(short circuit) and the constant current sources are reduced to zero current(open circuit).


14

V2 Source Shorted:

Circuit Diagram:

Tabulation:

S.NO Source voltage(V 1) in volt

Source voltage(V 2) in volt Total current I(mA)

10KΩ

A (0–10) mA

+

-

10KΩ

+

-

RPS (0–30)V

V1

5.6KΩ


15

Procedure:

• Connections are made as shown in the circuit diagram. • Both Supplies are switched “ON” and the reading of ammeter is noted

as I. • The source v2 is replaced by short circuit and the source v1 is switched

“ON”, now the reading of Ammeter is noted asI1. • The source v1 is replaced by short circuit and the source v2 is switched

“ON”. Now the reading of Ammeter is noted as I2. Applications:

1. It is used for replacement of voltage sources. 2. It is used when source of power are provided.

Viva Questions:

1. State the super position theorem? 2. What is meant by network? 3. What is meant by bilinear network? 4. Application of super position Theorem.

Result:

Thus the super position theorem was verified.


16

Verification of Thevenin’s Theorem:

Circuit Diagram:

To Find I L:

To Find R TH:

10KΩ 10KΩ

+

-

RPS (0–30)V 5.6KΩ

A (0–10) mA

+

-

1.5KΩ

10KΩ 10KΩ

5.6KΩ M

+

-


17

4. VERIFICATION OF THEVENIN’S THEOREM Aim:

To device an experiment to verify Thevenin’s Theorem. Objective:

To make our complex circuit into equivalent simple circuit. Apparatus Required:

S.NO Apparatus Name Range Quantity 1. RPS (0-30) V 1 2. Ammeter (0-10) mA 1 3. Voltmeter (0-10)V 1 4. Resistor 10 kΩ 2 5. Resistor 5.6 kΩ 1 6. Resistor 1.5 kΩ 1 7. Bread board - 1 8. Multimeter - 1 9. Connecting wires - 10

Formula:

mA)RR(

VI

LTH

THL +

=

Where VTH = Thevenin’s voltage, (V)

RTH = Thevenin’s Resistance (KΩ)

RL = Load Resistance (KΩ)

Resistance (RTH) if viewed from any one point in a network.


18

10KΩ 10KΩ

+

-

RPS (0–30)V 5.6KΩ V

+

-

(0-10)V

To Find V TH:

To Find I L:

-

RTH

+

-

(0–10) mA A

+

RL

VTH


19

Theory:

In any linear network contains voltage sources and resistances can be replaced by equivalent voltage source (VTH) in series with equivalent Resistance(RTH) if viewed from any one point in a network.

Step1: Remove the load Resistor RL where current is required.

Step2: Label the terminal from which RL is removed.

Step3: Calculate the open circuit voltage across the labeled terminal.

This is the Thevenin’s voltage (VTH).

Step4: Draw the equivalent circuit.

Step5: Find the current in RL using the formula, LTH

THL RR

VI

+=

Procedure:

1. Connections are made as shown in the circuit diagram. 2. Switch “ON” the power supply. 3. The load current is noted from Ammeter. 4. The load resistance RL and ammeter are removed from the circuit and VTH

is formed. 5. The RPS is also removed and RTH is found. 6. Now we can draw Thevenin’s equivalent circuit which consists of RTH and

RL connected in series with VTH. 7. Now we can find IL.

Safety Devices:

Tester Fuse Shoes

Precautions for Machine Safety:

Turn the voltage knob in minimum position in the RPS before switch ‘ON’ the RPS.

The current knob in the RPS must be in maximum position before switch ‘ON’ the RPS.

If the power supply indicates over load bring the voltage level to zero and switch off the supply voltage.

Before making connections, check the components correctly.


20

Tabulation for Thevenin’s Theorem:

Load current(I L) in mA

Thevenin’s Resistance (RTH) in KΩ Thevenin’s Voltage(V TH) in V

Model Calculation for Thevenin’s Theorem:

LTH

THL RR

VI

+=

When VTH = 5.37V, RTH=13.33KΩ and RL=1.5 KΩ

3L 10

5.133.1337.5

I ×+

=

31083.1437.5 ×=

= 0.362mA


21


The safety material should be weared. Connection should be verified correctly Maintain some distance from equipments and stand. Keep the power supply “OFF” when making connection.

Application of the Skill in Professional Life:

Used to analyze the circuit and make it quit easy. Used to simplify the complex circuit into simple circuit.

Help in employment:

To become a circuit designer.

For example, in any power plant has many numbers of current (or) voltage sources it can be replaced by its equivalent circuit. Viva Questions :

1. State the Thevenin’s theorem?

2. What’s the use of it?

3. What is Network?

4. What is meant by branch?

5. What is a junction?

6. What are the elements contained in the Thevenin’s equivalent circuit? Result:

Thus the Thevenin’s Theorem was verified.


22

10KΩ 10KΩ

+

-

RPS (0–30)V 5.6KΩ

A

+

-

1.5KΩ

(0–10) mA

Verification of Norton’s Theorem:

Circuit Diagram: To Find R N:

10KΩ 10KΩ

5.6KΩ M

+

-


23

5. VERIFICATION OF NORTON’S THEOREM Aim:

To device an experiment to verify Norton’s theorem. Objective:

To make our complex circuit into equivalent simple circuit. Apparatus Required:

S.NO Apparatus Name Range Quantity 1. RPS (0-30)V 1 2. Ammeter (0-10) mA 1 3. Resistor 10 kΩ 2 4. Resistor 5.6 kΩ 1 5. Resistor 1.5 kΩ 1 6. Bread board - 1 7. Multimeter - 1 8. Connecting wires - 10

Formula:

mARR

RII

LN

NNL +

×=

Where IL = Load current in (mA)

IN = Norton current in (mA)

RN = Norton’s equivalent Resistance in (kΩ)

RL = Load Resistance in (kΩ)

Resistance (RTH) if viewed from any one point in a network

Norton’s Theorem:

Any two terminal active linear network containing voltage sources and resistance when viewed from its output terminals, is equivalent to a constant current source and a parallel resistance. The constant current is equal to the current which would flow ion a short circuit placed across the terminals and parallel resistance is the resistance of the network when viewed from these open circuited terminals after all voltage and current sources have been removed and replaced by their internal resistances.


24

To Find I N:

To Find I L:

10KΩ 10KΩ

+

-

RPS (0–30)V 5.6KΩ

A

+

-

(0–10)mA

1.5KΩ RN

IL

IN


25

Step1: Remove the load Resistor RL (if any) and put a short circuit across

Step2: Find the short circuit current.

Step3: Calculate the Norton’s looking back resistance RN from the Load Terminal.

Step4: Draw the equivalent circuit.

Step5: Find the current in RL using the formula, LN

NNL RR

RII

+= ×

Procedure:

1. Connections are made as shown in the circuit diagram.

2. Switch “ON” the power supply.

3. The load resistance RL and ammeter are removed from the circuit and

IN values is noted.

4. The RPS is also removed and RN is found.

5. Now we can draw Norton’s equivalent circuit.

6. Now we can find the value of load current IL. Safety Devices:

Tester

Fuse

Shoes Precautions for Machine Safety:

Turn the voltage knob in minimum position in the RPS before switch

‘ON’ the RPS.

The current knob in the RPS must be in maximum position before

switch ‘ON’ the RPS.

If the power supply indicates over load bring the voltage level to zero

and switch off the supply voltage.



26

Tabulation for Norton’s Theorem:

Load current(I L) in mA Norton’s Resistance (R N)in KΩ Norton’s Current(I N)in mA

Model Calculation for Norton’s Theorem:

mA)RR(

RII

LN

NNL +

×=

When IN = 0.28mA, RN=13.6KΩ&RL=1.5KΩ

)105.1106.13(

106.131028.0I 33

33

L ×+××××=

−

= 0.25mA


27


The safety material should be weared.

Connection should be verified correctly

Maintain some distance from equipments and stand.

Keep the power supply “OFF” when making connection. Viva Questions :

1. State the Norton’s theorem?

2. What’s the use of it?

3. What do you meant by linear network?

4. What are the elements contained in the Norton’s equivalent circuit?

Result:

Thus the Norton’s theorem was verified.


28

A 1.5 KΩ

1.5KΩ

+

-

RPS (0-30) V (0-10) V

(0–10) mA

V

1.5 KΩ + -

+

-

DRB

Verification of Maximum Power Transfer Theorem:

Circuit Diagram:


29

6. VERIFICATION OF MAXIMUM POWER TRANSFER THEOREM

Aim:

To verify the maximum power transfer theorem. Objective:

To observe when the maximum power is transferred from source to load. Apparatus Required:

S.NO Apparatus Name Range Quantity 1. RPS (0-30) V 1 2. Ammeter (0-10) mA 1 3. Resistor 1.5 kΩ 3 4. Multimeter - 1 5. voltmeter (0-10) V 1 6. DRB - 1 7. Bread board - 1

8. Connecting wires - 10

Theory:

A Resistive load will abstract maximum power from a network when the load resistance is equal to the resistance of the network as viewed from the output terminals, with all energy sources removed leaving behind their internal resistances. Procedure:

1. The connections are made as shown in the circuit diagram.

2. Keep the supply voltage constant by varying DRB and the

corresponding ammeter and voltmeter readings are noted.

3. Plot the curve between load resistance and power.


30

Model Graph:

Pow

er in

Wat

ts

Load Resistance in K Ω


31

Safety Devices :

Tester

Fuse

Shoes

Precautions for Machine Safety:

Turn the voltage knob in minimum position in the RPS before switch

‘ON’ the RPS.

The current knob in the RPS must be in maximum position before

switch ‘ON’ the RPS.

If the power supply indicates over load bring the voltage level to zero

and switch off the supply voltage.



The safety material should be weared.

Connection should be verified correctly

Maintain some distance from equipments and stand.

Keep the power supply “OFF” when making connection.


32

Tabulation:

S.NO Load resistor R L in KΩ Voltage in volt

Current in mA

Power P=VI in W

Model Calculation: If V = 3.75V&I=0.3mA

The power transferred to the load

P = V×I

= 3.75×0.3×10-3 W

= 1.125×10-3 W

= 1.125mW


33

Applications of the Skill:

1. In a public address system, the circuit is adjusted for maximum power transfer by making load (i.e. speaker) resistance equal to source (i.e. amplifier) resistance.

2. In starting a car engine, the power delivered to starter motor depend on the effective resistance of the motor and internal resistance of the motor and internal resistance of the battery. If the two resistances are equal, m maximum power will be transferred to the motor to turn the engine.

3. Telephone and TV aerial leads to be matched with telephone instrument and TV receiver respectively.

4. Used in transmission lines and Antennas. List of Viva Voice Questions:

1. State maximum power transfer theorem?

2. When the maximum power transfer theorem?

3. What is meant by power? Mention its unit?

4. What is meant by Energy?

5. What are the applications?

Result:

Thus the maximum power transfer theorem was verified and the graph was drawn.


34

Circuit diagram:

Tabulation for Open Circuit Test: Multiplying Factor =

Vo(volts) Io(A) Woc (watts) Actual Reading=Observed Reading *Multiplying Factor


35

7. OC AND SC TEST ON A SINGLE PHASE TRANSFORMER

Aim:

To conduct the open circuit and the short circuit test on a single phase transformer and determine the percentage of efficiency. Objective:

To calculate the losses occur in the transformer, the open &short circuit test is conducted. Apparatus Required:

S.NO Apparatus Name Range Type Quantity 1. Ammeter (0-5)A MI 1

2. Ammeter (0-10)A MI 1

3. Voltmeter (0-150)V MI 1

4. Voltmeter (0-300)V MC 1 5. Wattmeter 300V,5A Dynamometer 1 6. Auto transformer - - 1 7. Transformer - - 1 8. Connecting wires - - 10

Formula Used:

Iron loss = Woc

Copper loss = Wsc

Total loss = Woc+Wsc

Output power = capacity*cos Φ

100Power) Input(Power)Output(

efficiencyof% ×=

Theory:

Open Circuit Test:

Open circuit test is called as no load test. The purpose of this test is to determine no-load loss or core loss and no load current Io which is helpful in winding Ro&Xo.Supply is given to the primary winding through a wattmeter with secondary winding open circuited. The readings of the wattmeter gives the no load losses when rated voltage is applied to the primary. No load current is very small and the primary resistance is negligible.Therfore copper loss (I2R) is very small. The input to the transformer.


36

Tabulation for Short Circuit Test: Multiplying Factor=

Vsc(volts) Isc(A) Wsc(watts) Actual Reading=Observed Reading *Multiplying Factor


37

Short Circuit Test :

Short circuit test can be determined by the copper loss. The copper loss occurs when the current flows through the winding .It is equal to I2R. This loss varies as the square of the load current knowing the load current and the equivalent resistance of secondary side the copper loss can be calculated by using an auto transformer the input voltage is varied from zero to small value. This is applied to the primary winding .Secondary winding is short circuited using the ammeter. Voltage is varied slowly till the secondary side ammeter reads rated secondary rated current. As the primary voltage is very small, the iron loses are assumed to be small and neglected. The wattmeter reading gives the total copper losses at full load current.

100loss)corelosscopperoutput

watts)inoutputefficiency% ×++

=(

(

Procedure:

Open Circuit Test or No Load Test :


2. The primary terminal of the high voltage side of transformer is kept up

to n.

3. The power supply is switched ‘ON’ by adjusting the auto transformer.

The rate voltage is applied to their position the voltmeter readings are

noted.

4. Switch ‘OFF’ the power supply. Short Circuit Test or Impedance Test:

1. The connections are made as shown in the circuit diagram

2. The secondary terminal of the low voltage side of transformer is kept

as short circuit.

3. The power supply is switched ‘ON’ at this position of the voltage.

4. Ammeter and voltmeter readings are noted.

5. Switch ‘OFF’, the power supply. Safety Devices:

Tester

Fuse

Shoes


38

Model Calculation:

Iron loss Woc = 30w

Copper loss Wsc = 100w

Total loss = Woc+Wsc

= (30+100) w

= 130w

Capacity = 2KVA

= 2000VA

Cos Φ = 0.8

Output power = Capacity*CosΦ

= 2000 VA *0.8

= 1600w

Input power = output power+losses

= 1600+130

= 1730w

%Efficiency = output power/ input power

% = (1730/1600)*100

% = 92.49%


39

General Precautions:

• Understand the equipment to be tested and apparatus to be used.

• Select proper type (i.e. Ac or dc) and range of meters.

• Do not touch live terminals.

• Use suitable wires (type&size).

• All the connections should be tight.

• Do not leave wires not connected.

• Get the connections checked by staff-in –charge, before switching ‘ON’

the supply.

• Never exceed permissible values of current, voltage, speed&load etc.

• Switch ‘ON’/switch ‘OFF’ the load gradually and not suddenly.

Viva Questions:

1. What are the different losses occurred in the transformer?

2. By conducting the o.c test, which loss can be determined?

3. By conducting the s.c test, which loss can be determined?

4. What is meant by power factor?

5. What is meant by efficiency? Result:

Thus the open circuit and short circuit are conducted and the efficiency is calculated.

% Efficiency = ------------------------- Iron loss = ------------------------- Copper loss = -------------------------


40

(0 – 50) mA

A A

(0 – 50) mA

RPS

DRB

(0 – 30) V

- -

-

+

+

+

Calibration of Ammeter:

Circuit Diagram:

Calibration of Voltmeter:

V V

+ + +

- - -

RPS

(0 – 30) V

(0 – 30) V (0 – 30) V

1 KΩ


41

8. CALIBRATION OF AMMETER AND VOLTMETER

Aim:

To calibrate the ammeter and voltmeter with the standard meter. Apparatus Required:

S. No Apparatus name Range Quantity

1 RPS (0-30)V 1

2 Resistor 1KΩ/1w 1

3 Ammeter (0-50) mA 2

4 Voltmeter (0-30) V 2

5 Bread board - 1

6 Connecting wires - -

Procedure:

1. The connections are made as shown in the circuit diagram

2. Switch ON the power supply.

3. The RPS is varied and the corresponding standard and test meter

readings are noted and tabulated.

4. Switch OFF the power supply.


42

Tabulation:

Calibration of Ammeter:

S. No. IS in

(mA) IT in (mA)

Error =(I T - IS) (mA) Correction=(I S - IT) in (mA)

Model Graph

Error Curve Correction Curve

CO

RR

EC

TIO

N in

mA

ER

RO

R in

mA

Is in mA

IT in mA


43

Graph:

Error Curve:

It is drawn by taking test meter voltage along X – axis and error along Y– axis. Correction Curve:

It is drawn by taking test meter voltage along X- axis and correction along Y – axis. Application:


44

Tabulation:

Calibration of Voltmeter:

S. No. VS in

(volts) VT in

(volts) Error =( V T - VS )

Volts Correction= (V S - VT) volts

Model Graph

Error Curve Correction Curve

CO

RR

EC

TIO

N in

vol

t

ER

RO

R in

vol

t

Is in volt

IT in volt


45

Result:

Thus the voltmeter and ammeter were calibrated with standard voltmeter and

ammeter respectively.

Viva questions:

1. What is calibration?

2. What is the used of calibration?

3. What do you mean by error?


46

Circuit Diagram:

Tabulation:

S. No. R1

(KΩ) R2

(KΩ) R3

(KΩ) R4 (KΩ) Theoretical Value

QQQQPSPSPSPSR

xRxRxRx

= KΩ

G

E = (0 – 30) V

Rx = QQQQPSPSPSPS

PS = QRx

Under Balanced Condition,

DRB

12kΩ

33kΩ

Q

P

b

d

Rx

a

S

+ -


47

9. WHEATSTONE’S BRIDGE Aim:

To determine the unknown resistance value using wheatstone’s bridge. Objective:

To find out the medium resistance value in the range of 1 Ω to 0.1mΩ Apparatus Required:

Theory:

A very important device used in the measurement of medium resistances is the wheat stone bridge. It is still an accurate and reliable instrument and reliable instrument and is extensively used in industry. The wheat stone bridge is an instrument for making comparison measurements and operator upon a null indication principle. This means the indication is independent of the calibration of the null indicating instrument or any of its characteristics. For this reason, very high degree of accuracy can be achieved using what stone bridge. Fig. Shows the basic circuit of a wheat stone bridge. It has four resistive arms, consisting of resistances P, Q, R and S together with a source of emf (a battery) and a null detector (galvanometers) or other sensitive current meter.


1. RPS (0-30)V 1

2. Resistors 12KΩ 33KΩ

1 1

3. DRB - 1

4. Galvanometer (30-0-30) V 1

5. Unknown resistance - 1

6. Bread board - 1

7. Multimeter 1

8. Connecting wires - -


48

Formula Derivation:

The bridge is said to be balanced when there is no current through the

galvanometer or when the pot. Difference across the galvanometer is zero. This

occurs when.

Vb - a = Va-d

or

Vd - c = Vb-c

For bridge balance, we can write: I 1, P= I2 R

For the galvanometer current to be zero, the follow ing conditions also exist.

( )2QP

EII 31 →

+==

( )3SR

EII 42 →

+==

By substituting (2) and (3) in (1)

RSR

EP

QPE

+=

+

SR

EQP

E+

=+

QRPRPSPR +=+

Un known resistance Q

PSR =

PS = QR


49

Procedure:

1. Connections are made as shown in the circuit diagram 2. By varying DRB, the voltage across the galvanometer is mode zero and R3 is

noted in DRB. 3. The unknown resistance value is found by using the formula.

Application:

It can be used for measuring low resistance value exactly. Result:

Thus the unknown resistance of the different resistors were found out by using Wheat stone’s bridge.

Viva Questions:

1. What is he bridge used for measuring inductance of the coil?

2. What is the bridge used for capacitance of capacitor?

3. What is accuracy?

4. What is precision?

5. What is sensitivity?


50

E

R2

R4

R3

R1 C1

C3

Detector

Wien Bridge Measuring Frequency:

Circuit Diagram:


51

10. WEIN BRIDGE Aim:

To determine the unknown capacitance value using wein bridge. Objective:

It can be used for measuring frequency but also used as a notch filter. Apparatus Required:

Wien Bridge: Wien Bridge is used as an AC Bridge. This is used to measure frequency. Wien Bridge is used as a notch filter in the harmonic distortion analyzer. Also used in audio and high frequency oscillators as the frequency determining element. The Wien Bridge used for the measurement of frequency is shown in this bridge has a series RC combination in one arm and a parallel RC combination in the adjoining arm. The impedance of arm 1 is Z1 and an admittance of arm 3 is Y3.

S. No Apparatus Name Range Quantity 1. Function Generator - 1

2. Resistors 1KΩ 2KΩ

2 1

3. Capacitor 1µF 1 4. DRB - 1 5. DCB - 1 6. Galvanometer (30-0-30) V 1 7. Bread board - 1 8. Multimeter - 1 9. Connecting wires - -


52

Tabulation:

S. No. Set Freq (Hz)

C1 (µF)

R3

(KΩ) Frequency =

3131 CCRR21

πHz


53

For the Bridge to Balance, Z1Z4 = Z2Z3

)1(ZZZ

Z3

412 −−−−−−=∴

1

12 wCJ

RZ −=∴

Z2 = R2

33

3 jwCR1

Z +=∴

Substituting for Z 1, Z2, Z3 & Z4 in Equ. (1) We get

+

−=

33

41

12

jwCR1

1R

wCj

RR

+

−= 3

31142 jwC

R1

wCj

RRR

1

34341

31

44

3

142 wC

wCRjwCRR

RwCjR

RR

RRR ++−=

Equating real and imaginary terms we have

)2(CRC

RRR

R1

43

3

412 −−−−−−++=

)3(0RRwCRwC

Rand 413

31

4 −−−−−−=−

From equ. (2) We get

)4(CC

RR

RR

1

3

3

1

4

2 −−−−−−+=∴

From equ. (3) We get

1331

RwCRwC

1 =

3311

2

CRRC1

w =∴


54


55

3131 RRCC

1w =

w = 2πf

)5(RRCC2

1f

3131

−−−−−−π

=∴

In this the components are chosen so that R1 = R3 & C1 = C3 then equ. (4) reduces to

2RR

4

2 =

Therefore Equ. (5) Reduces to

RC21

Fπ

=

This bridge is used for measuring frequency in the audio range. Capacitors C1 and C2 are normally of fixed values. Resistances R1 and R3 are having identical values. In the audio range (from 20-200-2k-20kHz), the resistances are used for range changing and capacitors C1 and C2 are used for the frequency control. Procedure:

1. Switch on the power supply.

2. Set the value of frequency in FG.

3. By varying the value of capacitance & Resistance,

4. Note down the unknown value.

5. Find the value of calculated. 3131 RRCC2

1f

π=

Uses:

1. Used for measuring frequency

2. Can be used for measuring capacitances.

3. Used in harmonic distortion analyzer as a notch filter.

4. Used as frequency determining element in audio frequency and radio

frequency oscillators.

5. Accuracy from 0.5% to 1% can be obtained.

Result:

Thus the unknown frequency were found out by using Wein’s Bridge.


56

Circuit Diagram:


57

11. PHOTO ELECTRIC TRANSDUCER Aim:

To determine the characteristics of photoelectric transducer (LDR). Apparatus Required:


1. RPS (0-30)V 1

2. Resistor 470Ω 1

3. Ammeter (0-10) mA 1

4. LDR - 1

5. Lamp 60W 1

6. Bread Board - 1

7. Wires - -

Theory:

The photoconductive materials used are Cadmium Sulphide, Cadmium Selenide or Cadmium Sulpho Selenide. These materials are very sensitive to light radiation. Procedure:


2. Switch ON the power supply and setting the fixed voltage.

3. Now the bulb is ON and it’s placed at certain distance.

4. The distance is increased or decreased and corresponding ammeter readings

are noted and tabulated.

5. Switch OFF the power supply. Graph:

It is drawn by taking distance along X – axis and current along Y – axis.


58

Tabulation:

S. No. DISTANCE IN cm CURRENT IN mA

Model Graph:

I in

mA

Distance in cm


59

Application:

1. Opto electronic devices are designed for the emission and absorption of

optical radiation.

2. Used to detection and measurement of radiation in spectro photometers.

3. Used in pyrometry also.

Result:

Thus the characteristic of photoelectric transducer (LDR) was determined and the graph was drawn. Viva Question:

1. What is photoelectric phenomenon?

2. What is photo emissive cell?

3. What is photoconductive cell?


60

To Measure the Phase Angle:

Circuit Diagram:

To Measure the Frequency:

DCB

1240Ω

FGR CRO

V

V

H H

Function Generator

CRO

230 V 50Hz AC

Supply

Step Down Transformer

DCB

1240Ω

FGR CRO

V

V

H H


61

12. MEASUREMENT OF FREQUENCY AND PHASE ANGLE

Aim: To measure the frequency and phase angle using lissajious figure. Apparatus required: S.NO Apparatus name Range Quantity

1. Function generator - 1 2. CRO - 1 3. Probe - 3 4. DRB - 1 5. DCB - 1 6. Bread board - 1 7. Connecting wires - 10 8. Transformer (6-0-6) V 1

Theory:

Frequency Measurement:

To measure a frequency, the waveform viewed by the oscilloscope must be periodic. For example, the period of the sine function is between any two alternate zero crossing. The period can also be measured between any two positive peaks or any two negative peaks. The frequency is determined by, Frequency = 1/period

Phase Angle Measurement

It is interesting to consider the characteristics of patterns that appear on the screen of a CRT when sinusoidal voltages are simultaneously applied to horizontal and vertical plates. These patterns are called ‘Lissajous patterns’. When two sinusoidal voltages of equal frequency, which are in phase with each other, are applied to the horizontal and vertical deflection plates, the pattern appearing on the screen is a straight line. Thus when two equal voltages of equal frequency but with 90° phase displacement are applied to a CRO, the trace on the screen is a circle. When two equal voltages of equal frequency but with a phase shift φ (not equal to 0° or 90°) are applied to a CRO we obtain an ellipse. The phase angle is either between 0° or 90° or between 270° to 360°. When the major axis of ellipse lies in second and fourth quadrants i.e. when its slope is negative, the phase angle is either between 90° and 180° or between 180°and 270°.


62

Frequency Measurement:

Tabulation:

S.NO. Frequency in Hz TH TV

=

V

HHV T

TFF


63

Calculation: Frequency:

V

H

H

V

TT

FF =

Phase Angle:

=α −

BA

Sin)( 1

Formula:

=α −

BA

Sin)(anglePhase 1

Procedure:

Measurement of Phase Angle:

• Connections are made as shown in the circuit diagram

• A sinusoidal voltage is applied to the horizontal and vertical input with same

magnitude.

• Press the X – Y button in the CRO. Now an ellipse is drawn on the CRO.

• From this ellipse, the value of A & B is noted and phase angle is measured. Measurement of Frequency:

• The connections are made as shown in the circuit diagram.

• A known frequency (FH) is applied to the horizontal input using step down

transformer.

• By varying unknown frequency, a pattern with loops is obtained.

• The number of lines which cut the horizontal input is noted as TH. Similarly the

number of lines cut the vertical input is noted as TV.

• From the values FH, TH, TV, the value of unknown frequency is calculated.


64


65

Graph:

It is drawn by taking TH along X – axis and TV along Y – axis.

Result:

Thus the Phase Angle and Frequency were measured using lissajious figure. Viva Questions:

1. What are the applications of CRO?

2. What is Lissajious pattern?

3. What is dual trace oscilloscope?


66

CIRCUIT DIAGRAM:

Tabulation:

Measurement of Frequency& Amplitude:

WAVEFORM

AMPLITUDE TIME FREQUENCY

IN KHz Amp in div.

No. of Box

Total Amp. (V)

Time in div.

No. of Box

Total Time (ms)

SINE WAVEFORM TRIANGULAR WAVEFORM SQUARE WAVEFORM


67

13. MEASUREMENT OF FREQUENCY AND

AMPLITUDE USING CRO Aim: To measure the frequency and amplitude using dual trace CRO for different circuit. Apparatus Required:

S.NO Apparatus name Quantity

1. Function generator 1

2. CRO 1

3. Probe 2

4. Bread board 1

5. Connecting wires 10

Theory:

The oscilloscope consists of one set of horizontal plates (X-plate) and one set of vertical plates (Y-plate). The horizontal plates are connected to the vertical input points. A ramp generator generates a time base sawtooth voltage. The input to the Horizontal plates (X-input) can be applied either internally from the time base generator or externally. The voltage or the signal, which is to be analyzed, is applied to the vertical plates (Y-input). The electrons emitted by the cathode towards a phosphor coated screen causes a luminous spot on the screen. The spot moves horizontally due to the electrostatic deflection caused by the X-plates. Procedure:


2. Switch “ON” the CRO.

3. The Function generator is connected to the CRO.

4. By varying the frequency, the readings are noted and tabulated.

5. Switch “OFF” the power supply.


68

Model Graph:

TIME in ms

Amplitude (V)

Amplitude (V)

Amplitude (V)

TIME in ms

TIME in ms


69

Application:

CRO is a very fast X-Y plotter, which displays an input signal with respect to another signal or time. The luminous spot moves over the screen in response to the input voltage. The CRO can present visual representations of any dynamic phenomena by means of transducers, which convert pressure, strain, temperature, acceleration, …etc, into voltages.

Result:

Thus the frequency and amplitude were measured by using CRO.


70

E

R2

R4

R3

R1 C1

C3

Detector

RLC BRIDGE: WHEATSTONE’S BRIDGE

WEIN BRIDGE CIRCUIT DIAGRAM


71

14. RLC BRIDGE Aim:

To measure the value of the Resistance, Inductance and Capacitance using RLC bridge. Apparatus Required:


1. Digital RLC Bridge 1

2. Unknown Resistor 2

3. Unknown Capacitor 2

4. DIB 1

5. Bread board 1

6. Connecting wires 10

Theory:

A simple bridge for the measurement of resistance, capacitance and inductance may be constructed with four resistance decades in one arm, and binding post terminals to which external resistors or capacitors may be connected, to complete the other arms. Such a skeleton arrangement is useful in the laboratory, since it permits the operator to set up a number of different bridge circuits simply by plugging standards and unknown units into the proper terminals. Procedure:

1. At first we can set the components in the digital bridge.

2. The dial is positioned in the corresponding resistance, inductance and the capacitance mode.

3. Now the value should be noted from the display of the segment.


72

Tabulation:

RLC bridge measurement

S.No. APPARATUS DIGITAL VALUE ACTUAL VALUE


73

Application:

This bridge is used for the measurement of resistance, capacitance and inductance

value by giving proper connections on the bridge arms

Result:

Thus the value of the Resistance, Inductance and Capacitance were measured using Digital RLC Bridge. Viva Questions:

1. What is the bridge used for measurement of inductance value?

2. What is the use of Schering Bridge?

3. What is the use of Hay’s bridge?


74

Strain Gauge Measurement:

SENSOR 5V DC

OFFSET

Tp2 Gain

Tp4

Tp3 Gain

(0-5) V o/p

P4

T4 T5

T2

T3

SG1 SG2

SG3 SG4

+

-

DPM

T6


75

15. STRAIN GAUGE MEASUREMENT Aim:

To measure the strain in the beam using Strain Gauge Trainer Kit. Apparatus Required:


1. Stain Gauge Trainer Kit 1

2. Connecting Pin 1

3. Multimeter 1

4. Load 100gm

5. Cantilever Beam 1

Theory:

The strain gauge is an example of a passive transducer that uses the variation in electrical resistance in wires to sense the strain produced by a force on the wires. It is well known that stress (force/unit area) and strain (elongation or compression/unit length) in a member or portion of any object under pressure is directly related to the modulus of elasticity. Since strain can be measured more easily by using variable resistance transducers, it is a common practice to measure strain instead of stress, to serve as an index of pressure. Such transducers are popularly known as strain gauges. If a metal conductor is stretched or compressed, its resistance changes on account of the fact that both the length and diameter of the conductor changes. Also, there is a change in the value of the Resistivity of the conductor when subjected to strain, a property called the Piezo –resistive gauges. When a gauge is subjected to a positive stress, its length increases while its area of cross – section decreases. Since the resistance of a conductor is directly proportional to its length and inversely proportional to its area of cross – section, the resistance of the gauge increases with positive strain. The change in resistance value of a conductor under strain is more than for an increase in resistance due to its dimensional changes. This property is called the Piezo resistive effect.


76

Tabulation: Strain Gauge Measurement

S. NO. LOAD in kg BRIDGE OUTPUT (T2, T3) mV

DISPLAY READING Volts

Model Graph:

Dis

play

Rea

ding

s In

vol

ts

LOAD in Kg


77

Procedure:

1. The connections are made shown in the circuit diagram.

2. Switch ON the Stain Gauge tutor.

3. The bridge output and display readings are noted without applying any load in the input.

4. Then the input load is applied and the corresponding readings are taken.

5. The load is increased in 100gm for each step and readings are tabulated.

6. Switch OFF the supply. Application:

• Strain gauge is used for measuring low input pressure or force value in industries.

Model Graph:

The graph is drawn by taking Load along X – axis and display reading along Y – axis. Result:

Thus the Strain in the beam was measured using Strain Gauge Trainer Kit and Cantilever Beam. Viva Questions:

1. What is hysteretic effect in strain gauge?

2. What are the types of strain gauge?

3. Define Gauge factor.

4. What is Piezo resistive effect?

5. What is the material used for making strain gauge transducer?

6. What is semi conductor strain gauge?


78

Load Cell Measurement:

SENSOR 5V DC

OFFSET

Tp2 Gain

Tp4

Tp3 Gain

(0-5) V o/p

P4

T4 T5

T2

T3

SG1 SG2

SG3 SG4

+

-

DPM

T6


79

16. MEASUREMENT OF LOAD CELL

Aim: To measure the load using Load Cell Trainer Kit and load cell panel. Apparatus Required:

S.NO Apparatus name Quantity 1. Load Cell Trainer Kit 1 2. Load Cell Panel 1 3. Multimeter 1 4. Load (0 - 5) Kg

Theory:

The load cell is an electromechanical sensor employed to measure static and dynamic forces. The device can be designed to handle a wide range of operating forces with high level of reliability, and hence is it one of the most popular transducer in industrial measurements. The load cell derives its output from the deformation of an elastic member having high tensile strength. Procedure:


2. Initially one Kg load is applied and the corresponding readings are noted.

3. Then the load is increased in step by step and the corresponding readings are noted and tabulated.

Model Graph:

The graph is drawn by taking load along X – axis and display reading along Y – axis. Application:

To measure high value of static and dynamic forces or pressure.


80

Dis

play

Rea

ding

s

In v

olts

LOAD in Kg

Tabulation: Load Cell Measurement

S. No. LOAD in Kg BRIDGE OUTPUT (T2, T3) mV

DISPLAY READING Volts

Model graph:


81

Result:

Thus the load was measured using Load Cell Trainer Kit & Load Cell Panel. Viva Question:

1. Is there any difference between sensor and transducer?

2. What is the transducer used to measure low-pressure measurement?

3. What is the use of Piezo resistive transducers?


82

LVDT Measurement:

Oscillation

OFFSET Tp6

Tp5 Gain

(0-5) V o/p

P4

TP3

DPM

T1

T8 T7

Buffer

T6

Non – Inverting Amplifier Non – Inverting

Amplifier

TP2 - OFFSET

Phase Reference Amplifier

T3

T4 T2

CORE

LVDT AC Amplifier

Half wave sync RC Filter


83

17. LVDT MEASUREMENT Aim:

To measure the displacement using LVDT Trainer Kit. Apparatus Required:

S.NO Apparatus name Quantity 1. LVDT Trainer Kit 1 2. Screw Gauge 1 3. Multimeter 1

Theory:

The differential transformer is a passive inductive transformer. It is also known as a Linear Variable Differential Transformer (LVDT). The transformer consists of a single primary winding P1 and two secondary windings S1 and S2 wound on a hollow cylindrical former. The secondary windings have an equal number of turns and are identically placed on either side of the primary winding. The primary winding is connected to an ac source. An movable soft iron core slides within the hollow former and therefore affects the magnetic coupling between the primary and the two secondaries. The displacement to be measured is applied to an arm attached to the soft iron core. (Ni –iron alloy) When the core is in its normal (null) position, eq ual voltages are induced in the two secondary windings. The frequency of the ac applied to the primary winding ranges from 50Hz to 20KHz. The output voltage of the secondary windings S1 is Es1 and that of secondary winding S2 is Es2. In order to convert the output from S1 to S2 into a single voltage signal, the two secondaries S1 and S2 are connected in series opposition. Hence the output voltage of the transducer is the difference of the two voltages. Therefore the differential output voltage E0 =Es1 ~ Es2. Procedure:

1. The connections are made as shown in the circuit diagram. 2. The power supply is switched ON. 3. The screw gauge is adjusted so that the LVDT reads 8mm. 4. The displacement of core is reduced by adjusting the Screw Gauge step

by step by 2mm and the corresponding readings are noted. 5. The Screw Gauge is adjusted up to the LVDT reads – 8mm. the Screw

Gauge reading is noted and display reading is noted across T1 and T8. 6. The power supply is switched OFF.


84

Tabulation:

LVDT Measurement:

S. No.

Screw guage Readings (mm) LVDT Display LVDT output Readings (v)

Model Graph:

LVDT Display Readings (mV)

LVDT Output Readings (V)


85

Model Graph:

The graph is drawn by taking LVDT reading along X – axis and display reading along Y – axis. Application:

• It is widely used for measurement of displacement where linear displacement from few mm to few cm.

• It is widely used in data systems to measure linear displacement, velocity, acceleration, pressure, force, level, and rate of flow of liquids.

Result:

Thus the displacement was measured using LVDT Trainer Kit. Viva Question:

1. Is the output voltage of LVDT linear?

2. How much is the power consumption of LVDT?


86

Measurement of Temperature:

Characteristics of Thermistor:

G

R2

A

R1

R3

Thermistor

C + -

D

(0-30) V

+

-

Temperature in oC

Platinum

Spe

cific

Res

ista

nce

(Ω c

m)

Thermistor


87

18. THERMISTOR Aim:

To study the construction, operation and characteristics of Thermistor. Thermistor:

It stands for thermal resistor. It is a bulk semiconductor device, which behaves as a resistor with a high positive and negative temperature coefficient of resistance. Sometimes its coefficient as high as – 60º%/ deg C rise in temperature. This high sensitivity of Thermistor is highly useful in precision temperature measurement, temperature control and temperature compensation. It is mostly used in lower temperature range of – 100ºC to 300ºC. The two types of Thermistor are

1. NTC (Negative Temperature Coefficient Thermistor) 2. PTC (Positive Temperature Coefficient Thermistor)

NTC Thermistor:

Thermistors are composed of a sintered mixture of metallic oxides such as Manganese, Nickel, Cobalt, Copper, Iron and Uranium. Their resistance at ambient temperature may range from 100Ω to 100KΩ. Thermistors are available in a wide variety of shapes and sizes such as bead, probe or rod. Bead Thermistor:

It is a smallest Thermistor. It has a diameter of 15mm to 1.25mm. Beads may be sealed in the tips of solid glass rods to form probes. The glass probes are used to measure the temperature of liquids. Disc Thermistor:

This is used when greater power dissipation is required. These Thermistors are made by pressing Thermistor material under high pressure Thermistor material into cylindrical shape. It has 1.25 – 2.5mm diameter and 0.25mm to .75mm thickness. These are sintered and coated with Silver on two flat surfaces. Whasher Thermistor:

They are just like disc Thermistor but they have a hole in the centre. This hole is suitable for mounting on a bolt. Washer can be placed in series or parallel to increases power dissipation rating.


88

V-I Characteristics of NTC:

V-I Characteristics of PTC:

V

I

V

I


89

ROD Thermistor:

They are usually like long cylindrical units with 4.25mm diameter and 12.5 to 50mm long. Leads are attached to the ends of the rods. The advantage of this type is they produce high resistance under moderate power. Working:

The resistance of a Thermistor changes appreciably with a small change in temperature. These characteristics of a Thermistor permit to use for the accurate temperature measurement. For this purpose, Thermistor forms one of the four arms of Wheatstone bridge. When there is no change in temperature the bridge is balanced and the Galvanometer reads zero. When the Thermistor is exposed to a medium whose temperature is to be measured, its resistance changes. This makes the bridge is unbalanced and current flows through the Galvanometer. The change in resistance of Thermistor i.e.) current through the Galvanometer is a measure of the magnitude of temperature. PTC Thermistor:

They are usually made from Barium Titrate. It is made from small crystal, which is bonded to form inner cry stalling boundaries. The characteristics of PTC are more complex than the NTC Thermistor. Here the temperature increases, the resistance increases and this give a positive temperature coefficient. After some threshold voltage, further increase in voltage decreases current. This exhibits negative temperature coefficient. Applications:

1. Thermistors are well suited for precision temperature measurement, temperature measurement and compensation.

2. It is used for the measurement of the liquid level, liquid flow and pressure of liquid.

3. Used for the measurement of composition of gases. 4. Used for providing time delay. 5. Used for Vacuum measurements. 6. It can be used where linearity is not important because of its non linear

characteristic 7. It is not used for wide temperature range.

Result:

Thus the construction, operation and characteristics of Thermistors were studied. Viva Question:

1. Where Thermistor is applied? 2. What is active transducer? 3. What is passive transducer? 4. What is negative temperature co-efficient?


90

Circuit Diagram:

(0 – 100) mA

A

A (0 – 50) mA (0 – 30) V

RPS

1KΩ

Rsh

DRB

+ +

+ -

- -


91

19. EXTENDING THE RANGE OF AMMETER Aim:

To extend the range of Ammeter and calibrate the Ammeter with the standard meter. Apparatus Required:

S. NO APPARATUS NAME RANGE QUANTITY 1. RPS (0-30)V 1

2. Ammeter (0-100) mA (0-50) mA

1 1

3. DRB - 1 4. Bread Board - 1 5. Wires - -

Formula:

Shunt resistance Im)I(Rm)(Im

Rsh−

=

)1m(

RmRsh

−=

Multiplication Factor ImI

m =

Theory:

The range of an electrical measurement is actually limited by the current. This current can be carried by the coil of the instrument safely. The moving coil and the spiral springs are used as coil connectors. These can be designed for a maximum current of only 50mA and a potential drop of above 50mV. So, far measuring large current or voltage, the range of the instrument has to be extended.

The common devices employed for extending the range of instruments are shunts and multipliers. When instruments are supplied with such external devices, the instrument is calibrated over the range of associated shunt or multiplier.

The basic movement of a DC ammeter is a permanent magnet moving coil galvanometer. The basic movement coil is small and light. So it can carry only a very small current. When large current is to be measured, it becomes necessary to bypass the major part of current through shunt resistance.

An ammeter shunt is merely a low resistance. This is placed in parallel with the instrument coil circuit to measure large current.


92

Tabulation: Extending the Range of Ammeter:

S.NO. IS in

(mA) IT = m * IT

(mA) Error =(I T - IS)

(mA) Correction=(I S - IT)

(mA)

Model Graph:

Error Curve Correction Curve Is in mA

IT in mA

CO

RR

EC

TIO

N in

mA

ER

RO

R in

mA


93

Procedure:

1. Connections are made as per the circuit diagram.

2. The power supply is switched ON.

3. RM is found by using Multimeter and find RSH.

4. By varying RPS test meter, standard meter readings are noted and

tabulated.

5. The power supply is switched OFF. Graph:

Error Curve:

It is drawn by taking Is along X – axis and error along Y – axis.

Correction Curve:

It is drawn by taking IT along X – axis and correction along Y – axis. Application:

The range of ammeter can be extended by using a suitable shunt across its terminals. By using this experiment, we can increase the measuring capacity of instrument. Result:

Thus the range of ammeter was extended and the ammeter was calibrated with the standard meter. Viva Question:

1. How do we extend the range of ammeter?

2. What is damping torque?

3. What is the use of controlling torque?

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