P.S.R ENGINEERING COLLEGE, SIVAKASI-626140. DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

YEAR: II

SEMESTER: III

LAB MANUAL (2012 – 2013)

EE 2208 MEASUREMENTS AND INSTRUMENTATION LABORATORY

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING EE 2208 – MEASUREMENTS AND INSTRUMENTATION LABORATORY LIST OF EXPERIMENTS

Sl. No.

EXPERIMENT NAME

1.

Study of DC Bridges (Wheatstone Bridge and Kelvin’s Double Bridge)

2.

Study of Schering Bridge

3.

Calibration of Single Phase Energy Meter

4.

Calibration of Current Transformer

5.

Measurement of Three Phase Power and Power factor

6.

Digital to Analog Converter

7.

Analog to Digital Converter

8.

Calibration of Three Phase Energy Meter

9.

Study of Pressure Transducer

10.

Study of Displacement transducer.

11.

Transient Response Of Series RC Circuit For DC Input

12.

Instrumentation Amplifier.

STAFF IN – CHARGE

H.O.D / EEE

STUDY OF DC BRIDGES A. STUDY OF WHEATSTONE BRIDGE AIM: To measure the unknown value of resistance of a resistor by using Wheatstone bridge. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPARATUS REQUIRED: Sl.No.

Name of the Equipment

Range 100Ω, 10Ω

Type

2 (each)

1.

Known resistances

2.

Unknown resistances

-

-

1

3.

Bread Board

-

-

1

4.

Galvanometer

30-0-30

Analog

1

5.

RPS

(0-30V)

Analog

1

6.

Connecting Wires

-

-

1

DRB

-

Quantity

1

FORMULA USED: Rx= (R1 * R3) / R2 (Ω) Where, R3 – Variable Resistance (Ω) R1 & R2 – Known Resistance (Ω) Rx – Unknown Resistance (Ω) THEORY: The DC bridges are used to measure the resistance while the ac bridges are used to measure the impedances consisting capacitances and inductances. The two types of DC bridges are 1.Wheatstone Bridge 2. Kelvin Double Bridge.

1

CIRCUIT DIAGRAM: Wheatstone Bridge

B R1 =10Ω

R2=100Ω

A

C

D RX

R3

D +

-

(0 – 30 V) RPS TABULATION: Sl.No. Supply Voltage (V)

R3 (Ω)

Rx = (R3 * R1)/ R2 (Ω)

2

The Wheatstone bridge consists of four resistance arms together with a source of e.m.f and a null detector. The galvanometer is used as a null detector. The arms consisting of the resistances R1 & R2 are called Ratio arms. The arm consisting of the resistor R4 is the unknown resistance value to be measured. The battery is connected between A and C while galvanometer is connected between B and D. PROCEDURE: 1. From the available standard resistances, select a suitable value for the arms R1 & R2. 2. Select the suitable value for the resistance as R3. 3. Make the connections as per the circuit diagram. 4. Switch on the supply. 5. Adjust the value of DRB for null deflection in the galvanometer detector. 6. Increase the DC supply voltage continuously in steps and for each setting, obtain null deflection.

DISCUSSION QUESTIONS: 1. What is a DC Bridge? 2. What are the types of DC bridges? 3. What are the applications of Wheatstone bridge?

RESULT: Thus the measurement of unknown resistances using Wheatstone bridge was performed. The values of unknown resistances are

3

4

B. STUDY OF KELVIN’S DOUBLE BRIDGE AIM: To measure the value of unknown resistance using Kelvin bridge.

REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPARATUS REQUIRED:

Sl.No.

Name of the Equipment

Range

Quantity

Type

10Ω, 100KΩ

Known resistances

2.

Unknown resistances

-

-

1

3.

Bread Board

-

-

1

4.

Galvanometer

30-0-30

Analog

1

5.

RPS

(0-30V)

Analog

1

6.

Connecting Wires

-

-

Req.

DRB

-

2(each)

1.

1

FORMULA: Rx= (P/Q) * S (Ω) Where, Q,P --- Upper bridge arm resistances(Ω) S--- Variable Resistances (Ω) Rx--- Unknown Resistances (Ω) THEORY: The bridge consists of another set of ratio arms hence called Double Bridge. The second set of ratio arms in the resistances ‘q’ & ‘p’ with the help of these resistances the galvanometer is connected to point 3. The galvanometer gives null indication when the potential of the terminal

5

KELVIN’S DOUBLE BRIDGE:

P = 10Ω

Q = 100Ω

G

p = 10Ω

q = 100Ω

RX

DRB S RPS (0 – 30V)

TABULATION: Sl.No.

P

Q

S

RX Actual

RX = (P / Q) * S

(Ω)

(Ω)

(Ω)

(Ω)

(Ω)

6

’3’ is same as the potential of the terminal ‘4’. The important condition is that the ratio of the resistance of ratio arms must be same the ratio of the resistances of the second ratio arms. When both the contacts are switched to select the proper value of standard resistance the voltage drop between the ratio arm connection points is changed but the total resistance around the battery circuit is unchanged. With this arrangement, any contact resistance can be placed in series with the relatively high resistance values of the ratio arms. Due to this, the effect of the contact resistance becomes negligibly small. The ratio of R1 & R2 ie., R1 & R2 selected in such a way that the larger part of the variable standard resistance is used and Rx is determined.

PROCEDURE: 1. Connections are given as per the circuit diagram. 2. Supply is switched ON. 3. Galvanometer is connected in the deflector (mentioned) terminal and the zero deflection value is obtained by varying the value of potentiometer. 4. The value of Rx is calculated by using the formula.

DISCUSSION QUESTIONS: 1. What is Kelvin’s double bridge? 2. What are the advantages of bridge circuits? 3. State the main differences between AC and DC bridges?

RESULT: Thus the unknown value of resistance was measured by using Kelvin’s Double Bridge. The unknown values of resistances are

7

8

STUDY OF SCHERING BRIDGE AIM: To measure the unknown value of capacitance of a capacitor by using Schering Bridge. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPARATUS REQUIRED: Sl.No.

Name of the Equipment

Range

Type

Quantity

0.1 μF

-

1

1.

Known capacitance

2.

Unknown capacitance

-

Box

1

3.

Bread Board

-

-

1

4.

Multimeter

-

Digital

1

5.

AFO

-

Digital

1

6.

Connecting Wires

-

-

Required

FORMULA USED: Cx= (R1 * C2) / Rm (Ω) Where, Rm – Multiple Resistances (Ω) R1 – Variable Resistance (Ω) Cx—Unknown Capacitance (μF) C2— Fixed Capacitance (μF) THEORY: Schering Bridge is one of the most widely used AC Bridge for measurement of unknown capacitance, dielectric losses and power factors. It can be used for low voltages. The perfect capacitor Cx is to be measured. The Rx is series resistance C2 is standard air capacitor having very stable value.R3 and R4 are non inductive resistance where C4 is variable capacitor.

ωCx=(R4 / R3) * ωC2 ;

Cx=(R4 / R3) * C2 9

CIRCUIT DIAGRAM:

C1 R1

RM

1MΩ

100KΩ

10KΩ

1KΩ

100Ω

1Ω

To Detector

C2 0.1μF

CX

TABULATION: SL.NO. 1.

R1 (Ω)

RM (Ω)

C2 (μF)

CX (μF)

2. 3. 4. 5.

DISCUSSION QUESTIONS: 1. What two conditions must be satisfied to make an AC bridge balance? 2. What is Schering Bridge? 3. What are the advantages of Schering Bridge?

10

PROCEDURE:  Set the potentiometer to the initial position as mentioned above.  Connect the unit to mains supply 220V AC through power cord.  Switch ON the unit. The neon lamp will glow indicating that the unit is ready for operation.  Using patch cord feed the sine wave signal from the built-in oscillator to the bridge circuit.  Connect the unknown capacitance , whose value is to be determined , across sockets marked ‘Cx’  Connect a digital multimeter having a range of AC 0-200mV/0-2V across the sockets marked ‘TO DETECTOR’ and ‘GROUND’  Using a patch cord , connect the topend of the bridge circuit to the multiplex resistor (Rm) of value in the mid-range (like 1K Ω)  Read the bridge output in the Digital multimeter.  Change the multiplex resistor to successive higher or lower values, such that the unbalanced output drops towards zero  By selecting the appropriate value of Rm for minimum unbalance ,Vary the resistance R1 to obtain the final balance point  Correct balancing is obtained when the output drops almost to zero  Disconnect all patch cords from the bridge circuit  Using a digital multimeter , measure R1  Substitute the values of Rm, R1,and C2 in the formula and evaluate the unknown capacitance

RESULT: Thus the unknown value of capacitance of a capacitor was measured using Schering Bridge. The unknown capacitance value of the Capacitor is …………….. 11

12

CALIBRATION OF CURRENT TRANSFORMER AIM: To study the working principle of current transformer and to calibrate the same. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRARATUS REQUIRED: Sl.No.

Name of the Equipment

1.

Ammeter

2.

Current transformer

3.

Resistive load

4.

Voltmeter

5.

Connecting wires

Range

Type

Quantity

(0 – 10A)

MI

1

(0 – 500mA)

MI

1

200 / 5 A

1

3 kW

Single phase

1

(0 – 300V)

MI

1 Required

PRECAUTIONS:  The secondary of the current transformer should not be open circuited while primary winding is energized. FORMULA USED: % ratio error = [(Nominal ratio – Actual ratio) / Actual ratio] * 100 Nominal ratio = Rated primary current of CT / Rated secondary current of CT Actual ratio = Primary current (reading) of CT / Secondary current (reading) of CT THEORY: The calibration is the procedure for determining the correct values of measurand by comparing with the standard ones. The instrument with which comparison

13

CIRCUIT DIAGRAM: 10 A

P 230 V 1 Φ, 50Hz Supply

(0 – 10A) MI

Current Transformer (200 / 5A)

A D P S T S

N

V

(0 – 300V) MI

A

L O A D

(0 – 500mA) MI

10 A

Resistive Load 3 KW / 230V

1 Φ Variac (0 – 230/270V)

TABULATION: Sl.No.

Primary Current Ipy (A)

Secondary Current Isy (mA)

Nominal Ratio Actual Ratio % error

Nominal Ratio

Secondary Current

MODEL GRAPH:

Primary Current

Secondary Current 14

is made is called as a standard instrument. The instrument which is unknown and it is said to be calibrated is called test instrument .Thus in calibration; test instrument is compared with the standard instrument. There are two fundamental methodologies for obtaining the comparison between the test instrument and standard instrument. These methodologies are 

Direct Comparison



Indirect Comparison

PROCEDURE: 1. Circuit connections are given as per the circuit diagram 2. Supply is switched ON and by adjusting the Variac the rated voltage is set in the voltmeter. 3. By increasing the load in steps, the primary current and secondary current ammeter readings are noted. DISCUSSION QUESTIONS: 1. What is calibration? 2. What are the different calibration methodologies? 3. What are the advantages of instrument transformers? 4. Give the main differences between CT and PT.

RESULT: Thus the working principle of the Current Transformer was studied and calibrated.

15

16

CALIBRATION OF SINGLE PHASE ENERGY METER AIM: To calibrate the single phase Energy meter by direct loading. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRARATUS REQUIRED: Sl.No.

Name of the Equipment

Range

Type

Quantity

1.

Ammeter

(0 – 10A)

MI

1

2.

Voltmeter

(0 – 300V)

MI

1

3.

Energy meter

10A/230V

Analog

1

4.

Stop watch

Analog

1

5.

Connecting wires

Required

FORMULA USED: Power = Voltage in Volts X Current in Amps True Energy = Number of revolutions / Energy meter constant Actual Energy = [(Power X Time taken for ‘n’ revolutions) / (3600 X 1000)] % of Absolute error = (Actual Energy – True Energy / True Energy) X 100 THEORY: The calibration is the procedure for determining the correct values of measurand by comparing with the standard ones. The standard of device with which comparison is made is called as a standard instrument. The standard instrument which is unknown and it is said to be calibrated is called test instrument .Thus in calibration; test instrument is compared with the standard instrument. There are two fundamental methodologies for obtaining the comparison between the test instrument and standard instrument. These methodologies are 17

CIRCUIT DIAGRAM: 10 A

P 230 V 1 Φ, 50Hz Supply

(0 – 10A) MI A

D P S T S

N

Energy Meter C1

C2

P1 V

10 A

P2 L O A D

(0 – 300V) MI

Resistive Load 3 KW / 230V

1 Φ Variac (0 – 230/270V)

TABULATION: Sl.No.

Voltage

Current

Power

Time

No. of

Actual

True

%

(V)

(A)

(W)

(Sec)

revolutions

Energy

Energy

error

18



Direct Comparison



Indirect Comparison The calibration offers a guarantee to the device or instrument that is operating with

required accuracy under the stipulated environmental conditions. It creates the confidence of using the properly calibrated instrument, in user’s mind. The periodic calibration of instrument is very much necessary. The calibration procedure involves the steps like visual inspection for various defects, installations according to the specifications, zero adjustment, etc…. PROCEDURE: 1. Circuit connections are given as per the circuit diagram 2. Supply is switched ON by closing the DPSTS. 3. By increasing the load in steps, the voltmeter, ammeter and wattmeter readings are noted. Also the time taken for the energy meter disc to rotate for ‘n’ revolutions is noted down. 4. Using the formula the percentage error is calculated for each set of readings.

DISCUSSION QUESTIONS: 1. What is creeping? 2. Which torque is absent in energy meter? Why? 3. Define energy meter constant.

RESULT: Thus the calibration of the single phase Energy meter was done and the Absolute error was calculated. 19

CIRCUIT DIAGRAM:

R

RESISTIVE LOAD

10 A

(0 -10A) MI 600V, 10A, UPF M L A C V

T 415V 3Φ

Y

P S

50 Hz

SUPPLY

V

10 A

(0 – 600V) MI

LOAD

T S

B

R

Y 10 A

C

V

M

L 600V, 10A, UPF

3 Φ Variac TABULATION: M.F…….. W1 VL

M.F……. W2

IL

Sl.No. (V) (A)

Observed

Actual

Observed

Actual

Reading

Reading

Reading

Reading

M.F. – Multiplication Factor 20

Total Power

Phase angle

W1 + W2

Φ

Watts

Power factor CosΦ

B

MEASUREMENT OF THREE PHASE POWER AND POWER FACTOR AIM: To measure the 3 phase power using two single element wattmeter with 3 phase resistive and inductive load. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRARATUS REQUIRED: S.No.

Name of the Equipment

Range

Type

Quantity

1.

Ammeter

(0 – 10A)

MI

1

2.

Voltmeter

(0 – 600V)

MI

1

3.

Wattmeter

( 150 / 300 / 600V) (5 / 10A)

Single element UPF

1

4.

Connecting wires

Required

FORMULA USED: Phase angle, Φ = tan- 1 3 [Higher reading – lower reading] [Higher reading + lower reading] Total Power = W1 + W2 (watts) Power factor = Cos Φ THEORY: Three phase power measurements can be done by the following methods, i. By using three phase wattmeter. ii. By using 3-single element wattmeter i.e., three wattmeter method. iii. By using 2-single element wattmeter i.e., two wattmeter method. iv. By using 1-single element wattmeter i.e., one wattmeter method.

21

CIRCUIT DIAGRAM:

R

INDUCTIVE LOAD

5A

(0 -5A) MI 600V, 5A, UPF M L A C V

T 415V 3Φ

Y

P S

50 Hz SUPPLY

V

5A

A1 C2

(0 – 600V) MI B1 A2

T S

B

5A

C

V

M

L

C1 B2

3Phase Induction Motor

600V, 5A, UPF

3 Φ Variac TABULATION: M.F…….. W1 VL

M.F……. W2

IL

Sl.No. (V) (A)

Observed

Actual

Observed

Actual

Reading

Reading

Reading

Reading

M.F. – Multiplication Factor 22

Total Power

Phase angle

W1 + W2

Φ

Watts

Power factor CosΦ

Among the above four methods, the most commonly used three phase power measurement techniques are, two wattmeter method and three wattmeter method. PROCEDURE: 1. Circuit connections are given as per the circuit diagram 2. Supply is switched ON by closing the TPSTS. 3. By adjusting the Variac rated voltage is set in the voltmeter. 4. By switching ON the load (resistive / inductive) and increasing the load in steps, the voltmeter, ammeter and wattmeter readings are noted. 5. Using the formula the power factor is calculated.

DISCUSSION QUESTIONS: 1. Define power factor. 2. Explain why it is necessary to potential coil circuit purely resistive in wattmeters? 3. Give the expression for 3phase power. 4. What is LPF Wattmeter?

RESULT: Thus the 3 phase power was measured by using two single element wattmeters and the power factor was calculated. 23

CIRCUIT DIAGRAM: (+5V) MSB

LSB

B0

20 KΩ

B1

B2

B3

B4

B5

B6

B7

20 KΩ

20 KΩ

20 KΩ

20 KΩ

20 KΩ

20 KΩ

20 KΩ

10 KΩ

10 KΩ

10 KΩ

10 KΩ

10 KΩ

10 KΩ

10 KΩ

20 KΩ

10 KΩ

47 KΩ 7

2

47 KΩ

6

3

7

2

6

3

4 TABULATION: DIGITAL INPUT LSB B7

B6

ANALOG OUTPUT (V)

MSB B5

B4

20 KΩ

B3

B2

B1

24

B0

Practical

Theoretical

Vo

DIGITAL TO ANALOG CONVERTER AIM: To convert the given digital signal input to analog output. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRARATUS REQUIRED: S.No.

Name of the Equipment

Range

Type

Quantity

1.

Digital to Analog Converter Kit

-

-

1

2.

Patch cards

-

-

Required

FORMULA USED: V0 = VR x RF / Rin{ Bo /2 + B1 /4 + B2 /8 + B3 /16 + B4 /32 + B5 /64 + B6 /128 + B7 /256 } Volts PROCEDURE: 1. Circuit connections are given as per the circuit diagram 2. Supply is switched ON. By adjusting RPS V1 values are set and corresponding output voltage V0 are noted down. 3. Using the formula the gain is calculated. DISCUSSION QUESTIONS: 1. What are the different methods of D/A Conversion? 2. What are LSB and MSB? 3. Give the pin specifications of IC 741.

RESULT: Thus the performance of the D/A converter was studied.

25

26

ANALOG TO DIGITAL CONVERTER AIM: To convert the given analog signal input to digital output. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPARARATUS REQUIRED: S.No.

Name of the Equipment

Range

Type

Quantity

1.

Analog to Digital Converter Kit

-

-

1

2.

Patch cards

-

-

Required

PROCEDURE: 1. Circuit connections are given as per the circuit diagram. 2. Supply is switched ON. For different values of analog input the corresponding digital output values are noted down. 3. The digital output values are tabulated.

DISCUSSION QUESTIONS: 1. What are the different methods of A/D conversion? 2. What is IC 7408? 3. What is a clock signal?

27

TABULATION: DIGITAL OUTPUT ANALOG INPUT (V)

MSB B6

ANALOG VOLTAGE (V)

LSB B5

B4

INCREMENT

B3

B2

B1

CALCULATION

28

B0

RESULT: Thus the performance of the instrumentation amplifier is studied and gain is calculated. 29

CIRCUIT DIAGRAM:

30

CALIBRATION OF 3 PHASE ENERGY METER AIM: To calibrate the 3 phase Energy meter by direct loading. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRARATUS REQUIRED: Sl.No.

Name of the Equipment

Range

Type

Quantity

1.

Ammeter

(0 – 10A)

MI

1

2.

Voltmeter

(0 – 600V)

MI

1

3.

Energy meter

3Φ

1

4.

Stop watch

Analog

1

5.

Connecting wires

Required

FORMULA USED: Power = Wattmeter reading x Multiplication Factor(M.F) True Energy = Number of revolutions / Energy meter constant Actual Energy = [(Power X Time taken for ‘n’ revolutions) / (3600 X 1000)] % of Absolute error = (Actual Energy – True Energy / True Energy) X 100 THEORY: Energy is the total power delivered and consumed over a time interval by an electrical system. Energy=Power * Time Electrical energy is expressed as W= VIt Kwh V is expressed in volts, I is expressed in ampere and t is in seconds 31

TABULATION: Multiplication Factor:………….. Energy meter constant=…………… Wattmeter Voltage Current Time Number of Actual True % Reading Sl.No. (V) (A) (Sec) revolutions Energy Energy error Observed Actual

MODEL GRAPH:

%Error

Current

32

Unit for energy is joules or watt second. If the unit of time is taken as hour, energy is then expressed in watt hours, for larger units: energy may be expressed in kilo Watt Hour PROCEDURE: 1. Circuit connections are given as per the circuit diagram 2. TPSTS is closed and the load is applied gradually. 3. Voltmeter, Ammeter and wattmeter readings and time taken for energy meter disc to rotate ‘n’ revolutions are noted. 4. Percentage error is calculated for various load currents.

RESULT: Thus the calibration of the 3Φ Energy meter was done and the Absolute error was calculated. 33

CIRCUIT DIAGRAM: 7 (+Vcc) 2

6

Micro Controller RAM

3

Display

EPROM

4 (-Vcc) Differential Amplifier (Op-Amp)

+

Mircro Controller (Calibration)

Strain Gauge TABULATION: Increasing Pressure Sl.NO. APPLIED PRESSURE (Kg / Cm2) Output Voltage (mV)

Decreasing Pressure Sl.NO. APPLIED PRESSURE (Kg / Cm2) Output Voltage (mV)

MODEL GRAPH:

Vo (mV)

Increasing pressure (Kg/ Cm2)

Decreasing Pressure (Kg/ Cm2) Pressure

34

Output (LED Display)

STUDY OF PRESSURE TRANSDUCER AIM: To study the performance characteristics of Pressure Transducer. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRATUS REQUIRED: Sl.No. 1.

Name of the Equipment Pressure Transducer kit with Foot pump

Range

Type

Quantity

-

-

1

THEORY: Pressure is the basically a physical parameter is defined as the force acting per unit area measured at a given point or over a surface. Most pressure measuring devices use plastic members for sensing pressure at primary stage. These elastic members convert the pressure into mechanical displacement which is later converted into electrical form using a secondary transducer. The principle of working of these devices can be explained as, the fluid or gas whose pressure is measured is made to press the pressure sensitive element and since the element is a elastic member it deflects causing a mechanical displacement. The displacement is proportional to the pressure applied. The displacement is then measured with a help of electrical transducer is proportional to the displacement and hence to the applied input pressure. The commonly used pressure sensitive devices are  Diaphrams  Capsule  Bourdon tubes  Bellows 35

36

PROCEDURE: 1. 230 V AC Main Supply is switched ON. 2. By pressuring the pump, Pressure into the air cylinder is increased. 3. The pressure and output voltage in the front panel of the trainer kit is noted. 4. The pressure from the air cylinder is decreased in steps and the values of pressure and voltage are tabulated. DISCUSSION QUESTIONS: 1. How the transducers are classified? 2. Give the factors to be considered in selecting a transducer? 3. What is an active transducer? 4. What is a passive transducer?

RESULT: Thus the characteristics of Pressure Transducer were studied and the readings are tabulated. 37

CIRCUIT DIAGRAM: A.C. Input

Primary of the transformer

Displacement CORE

Secondary of the transformer Es1

Es2

VO TABULATION: Positive Displacement Sl.No. MSR VSC

TR = MSR +VSC Sensor Output (mV) Sensor Displacement (mm) x error

Negative Displacement Sl.No. MSR VSC

TR = MSR +VSC Sensor Output (mV) Sensor Displacement (mm) x error

MODEL GRAPH:

Sensor Output (mV)

Negative Displacement

Positive Displacement

Displacement (mm) 38

SYUDY OF DISPLACEMENT TRANSDUCER AIM: To study and determine the performance characteristics of LVDT. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRATUS REQUIRED: Sl.No. 2.

Name of the Equipment LVDT kit

Range

Type

Quantity

-

-

1

THEORY: The most widely used inductive transducer to translate the linear motion into electrical signals is the linear variable differential transformer(LVDT).LVDT is a differential transformer consisting of a single primary winding P and two secondary windings S1 and S2 wound over a hollow bobbin of non-magnetic and insulating material. The secondary windings S1 and S2 have equal number of turns and are identically placed on either side of the primary winding. A movable soft iron core is placed inside the transformer. The displacement to be measured is applied to the soft iron core. In order to overcome the problem of eddy current losses in the core, nickel-iron alloy is used as core material and is slotted longitudinally. Primary winding is connected to an AC source of voltage varying from 5 to 25V and of frequency ranging from 50Hz to 20kHz.Since the primary winding is excited by an alternating current source, it produces an alternating magnetic field which in turn induces alternating voltages. The output voltages of secondary winding S1 and ES1 and that of secondary winding S2 is ES2.Inorder to convert the output voltage from S1 and S2 into a single voltage signal, the two secondaries S1 and S2 are connected in series opposition as shown in figure. Therefore the output voltage of the transducer is the difference of the two voltages.

Differential output voltage E0=Es1-Es2

39

40

When the core is at its normal (NULL) position, the flux linking with both he secondary windings are equal and hence equal emfs are induced in them. Thus at null position Es1=Es2.Since the output voltage of the transducer is the difference of the two voltages, the output voltage E0 is zero at null position. Now if the core is moved to the left of the NULL position, more flux links with winding S1 and Less wit winding S2.Hence output voltage Es1,of the secondary winding S1,is more than Es2,the output voltage of secondary winding S2,The magnitude of output voltage is,thus,E0=Es1-Es2 and the output voltage is in phase with the primary voltage. Similarly, if the core is moved to the right of the null position,the flux linking with winding S2 becomes larger than that linking with winding S1.Hence output voltage Es2 of the secondary winding is more than Es1,the output voltage of the secondary winding S1.The magnitude of output voltage is thus ,E0=Es2-Es1 and is 180 out of phase with the primary voltage. Thus the LVDT output voltage is a function of the core position. The amount of voltage change in either secondary winding is proportional to the amount of movement of core. Hence, we have an indication of amount of linear motion. By noting which output voltage is increasing or decreasing, we can determine the direction of motion .Any physical displacement of the core causes the voltage of one secondary winding to increase while simultaneously reducing the voltage in the order secondary winding. The amount of output voltage may be measured to determine the displacement

PROCEDURE: 1.

Circuit connection is given as per the circuit diagram.

2.

The core is slowly moved and the displacement value and output voltage is noted

down. DISCUSSION QUESTIONS: 1. What is a transducer? 2. Mention some advantages of LVDT. 3. List out the disadvantages of LVDT. 4. Mention the applications of LVDT.

RESULT: Thus the characteristic of displacement Transducer was studied and the graph was drawn. 41

CIRCUIT DIAGRAM:

(0-25mA)MC 10KΩ + A (0-30V)MC

+

RPS (0-30V)

V

DPSTS

+ -

TABULATION: Sl.No.

CHARGING V(volts)

DISCHARGING

T(sec)

V(volts)

42

T(sec)

C 4700 μF

TRANSIENT RESPONSE OF SERIES RC CIRCUIT FOR DC INPUT AIM: To obtain transient response of RC circuit for DC input. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRARATUS REQUIRED: Sl.No.

Name of the Equipment

Range

Type

Quantity

1.

Resistors

10 KΩ

-

1

2.

Capacitor

4700μF

-

1

3.

RPS

(0 – 30V)

Analog

1

4.

Ammeter

(0-25mA)

MC

1

5.

Voltmeter

(0-30V)

MC

1

6.

Bread Board

-

-

1

7.

Stop watch

-

-

1

8.

DPSTS

-

-

1

9.

Connecting Wires

-

-

Required

THEORY: In series RC circuit shown in figure, the switch ‘S’ is in open state initially. There is no charge on the capacitor and no voltage across it. At the instant t=0, switch ‘S’ is closed. Immediately after closing the switch, the capacitor acts as a short circuit path, so current at the time of switching is high. The voltage across the capacitor is zero at t=0 as the capacitor acts as a short circuit, the current is maximum and is given by I=V/R amperes. This current is maximum at t=0+ which is called charging current. As the capacitor starts charging, the voltage across capacitor Vc starts decreasing. After some time, when 43

MODEL GRAPH:

Capacitor charging

capacitor Discharging

44

the capacitor charges to V volts, it achieves steady state. In steady state, it acts as an open circuit, so the current will be zero finally. Transient current, i= [V/R] X [e–t / RC] So at time t=0, i=V/R is maximum and in steady state it becomes zero. PROCEDURE: 1. Circuit connections are given as per the circuit diagram 2. Supply is switched ON and capacitor is charges to its rated voltage in steps with a time interval. 3. The corresponding voltmeter readings and time interval are noted down. 4. By discharging the capacitor from its rated voltage, in same steps the voltmeter readings and time intervals are noted down. 5. Graphs are plotted for charging and discharging of capacitor separately. DISCUSSION QUESTIONS: 1. What is transient? 2. What is the time constant for RC series circuit? 3. Define transient time?

RESULT: Thus the transient response of series RC circuit for DC input was obtained and the graph was plotted. 45

CIRCUIT DIAGRAM: 2 7 3 + 12V

+ VCC 7 6 4 - VCC

56 KΩ

12 KΩ

2

12 KΩ

3

7 6

3.9 KΩ 1 KΩ

1 KΩ

0.4 KΩ 1 KΩ

4

56 KΩ

1 KΩ 3.9 KΩ 2

7 6

3

4

TABULATION: Sl. No.

Input Voltage (mV) V1 V2

Output Voltage (Vo)

46

Gain Ad = Vo / Vin

Gain in dB = 20 log (Ad)

Vo

INSTRUMENTATION AMPLIFIER AIM: To construct and study the performance of instrumentation amplifier and to obtain the gain. REFERENCES: 1. A.K.Sawhney,’A Course in Electrical & Electronics Measurements & Instrumentation’, Dhanpat Rai and Co, 2004 2. J.B.Gupta,’ A Course in Electronic and Electrical Measurements’, S.K.Kataria & sons, Delhi, 2003 APPRARATUS REQUIRED: Sl.No. 1.

Name of the Equipment

Range

Type

Quantity

IC 741

3

-

Each 2

(0 – 30V)

-

1

Op – amplifier 1 KΩ, 3.9 KΩ,

2.

Resistors

0.4 KΩ, 12 KΩ, 56 KΩ

3.

RPS

4.

Bread Board

-

-

1

5.

Connecting Wires

-

-

Required

FORMULA USED: V0 = { (V1 – V2) x R2 / Rf [1 + (2R1 / Rg)] } Volts Ad = (V0 / [V1 – V2]) Theory: Physical quantities like temperature, humidity. Light intensity, water flow etc., are usually measured with the help of transducers. The output of transducer has to be amplified, so that it can be drive the display system of control system. This function is performed by an instrumentation amplifier. The important features of an instrumentation amplifier are

47

48

 High input impedance.  High gain accuracy  High CMRR  High gain stability with low temperature coefficient  Low output impedance PROCEDURE: 1. Circuit connections are given as per the circuit diagram 2. Supply is switched ON. By adjusting RPS V1 values are set and corresponding output voltage V0 are noted down. 3. Using the formula the gain is calculated. DISCUSSION QUESTIONS: 1. What is an instrumentation amplifier? 2. List the important characteristics of operational amplifier. 3. What are the applications of instrumentation amplifier? 4. What is CMRR?

RESULT: Thus the performance of the instrumentation amplifier was studied and gain was calculated. 49