Exp

Ex. No: Date:

1. TEMPERATURE MEASUREMENT USING DIFFERENT SENSORS

AIM:

To measure the temperature using sensors like Thermocouple, Thermistor and RTD.

REFERENCE:

1. A.K. Sawhney : A course in Electrical and Electronics Measurements and Instrumentation, Dhanpat Rai & Sons, 1984.

2. H.S. Kalsi: Electronic Instrumentation, TMH, 1995.

BASIC KNOWLEDGE REQUIRED:

Working principle and operations of different types of temperature

measurement sensors.

APPARATUS REQUIRED:

Sl.No. Particulars Quantity1 Temperature

measurement kit1 No.

2 Thermometer 1 No.3 Multi meter 1 No.

FORMULAE USED:

% Error = (Actual reading – True reading) / Actual reading

THEORY:

Thermistors:

Thermistor means Thermal Resistor.Thermistor is a semiconductor device

which behaves as thermal resistor having negative temperature coefficient (NTC) in

which their resistance decreases as temperature increases. The NTC is as large as

several percent per degree Celsius. This allows the thermistor circuits to detect very

small changes in temperature which could not be observed with RTD or

Thermocouple. In some cases the resistance of thermistor at room temperature may

decrease as much as 5% for each one degree Celsius rise in Temperature. This high

sensitivity to temperature changes makes thermistors extremely useful for precision

temperature measurements control and compensation

Thermocouples:

When two metals having different work functions are placed together, a

voltage is generated at the junction which is nearly proportional to the temperature.

This junction is called a thermocouple.

CIRCUIT DIAGRAM:

MODEL GRAPH:

OBSERVATION:

Room Temperature =

Sl. No

Thermometer Reading(Degree Celsius)

Thermocouple Reading (Degree Celsius)

% Error

12345678

RT

D

Th

erm

isto

r

Th

erm

ocou

ple

RTD

Thermocouple

Thermistor

DC output voltage

Fe Constantan

+5V

-5V

This principle is used to convert the heat energy to electrical energy at the

junction of two conductors. The heat at the junction is produced by the electrical

current flowing in the heater element while the thermocouple produces an EMF at its

output terminals which can be measured with the help of a PMMC instrument. The

EMF produced is proportional to the temperature and hence to the RMS value of the

current. Thermocouple types of instrument can be used for both ac and dc.

Resistance temperature detector:

Electrical resistance of any metallic conductor varies according to temperature

changes. The sensor for measurement of temperature by utilizing this phenomenon is

called resistance thermometer. It is the basic element for resistance temperature

detector.

PROCEDURE:

1. The heat source box is connected to the socket provided on the back side of

the main unit.

2. The leads from the Transducers are connected to the input socket of main unit.

3. Single phase supply is given to the main unit

4. The glass mercury thermometer is placed (to measure the temperature) in heat

source through the window hole.

5. Thermometer reading and digital display readings are noted down.

6. The knob of phase controller is adjusted to select the temperature level for

experiment.

7. For various temperatures, thermometer reading and display reading are noted.

DISCUSSION QUESTIONS:

1. What is a thermocouple?

2. What is Seeback effect?

3. What is Peltier effect?

4. What are the merits of thermocouple?

5. What are the demerits of thermocouple?

6. What are the applications of temperature sensors?

7. What are the various methods of measuring the thermocouple output?

RESULT:

Thus the temperature measuring transducer (Thermocouple) is studied.

WHEATSTONE BRIDGE

KELVIN’S DOUBLE BRIDGE

Ex. No: Date:

A

B

D

C

E

P Q

RS

D

R-Unknown ResistanceD- Galvanometer

A

D

++

Rb

RS

c

bRX

R2

R4

R1

DRB

R3

DRB

aA B

C

C

2. DC BRIDGES

AIM:

To determine the value of the given low resistance using

(i) Wheat stone’s Bridge(ii) Kelvin’s Bridge

REFERENCE:

1. A.K.Sawhney: A course in Electrical and Electronics Measurements and Instrumentation, Dhanpat Rai & Sons, 1984.

2. H.S.Kalsi : Electronic Instrumentation, TMH, 1985.


Principle and operation of bridge circuits.

APPARATUS REQUIRED:

Sl.No: Apparatus Range Quantity

1. RPS (0-30 V) 1 2. Ammeter (0-300 mA) 1 3. Decade Resistance Box (0-100 KΩ) 2 4. Resistor 1 KΩ 2 5. Rheostat 1180 Ω / 0.6 A 1

THEORY:

The bridges are used not only for the measurement of resistance but also used

for measurement of various component values like capacitor and inductor etc. Bridge

circuit in its simplest form consists of a network of four resistance arms forming a

closed circuit. A source of current detector is connected to the two junctions. The

bridge circuit uses the comparison measurement methods and operates on null-

indication principle.

The bridge circuit compares the value of an unknown component with that of

an accurately known standard component. Thus the accuracy depends on the bridge

component without the null detector. Hence high degree of accuracy can be obtained.

In a bridge circuit when no current flows through the null detector which is generally

a galvanometer, then the bridge is said to be balanced.

TABULATION:

Kelvin’s Bridge:

Sl.No R1 (Ω) R3 (Ω) RX (Ω) % Error

Wheat stone’s Bridge:

SL.No R1 (Ω) R2 (Ω) R3 (Ω) RX (Ω) % Error Actual works (Ω)

Wheatstone bridge:

A very important device used in the measurement of medium resistances is

the Wheatstone bridge. A Wheatstone bridge has been in use longer than almost any

electrical measuring instrument. It is still an accurate and reliable instrument for

making comparison measurements and operates upon a null indication principle. The

well known expression for the balance of Wheatstone bridge is follows

QR = PS If three of the resistance is known then the fourth may be determined from the

eqn,

R = S*(P/Q)Where R is the unknown resistance, S is called the standard arm of the bridge

and P and Q are called the ratio arms.

Kelvin’s double bridge:

The Kelvin Bridge is a modification of the Wheatstone bridge and provides

greatly increased accuracy in measurement of low value resistances. An

understanding of the Kelvin bridge arrangement may be obtained by a study of the

difficulties that arise in a Wheatstone bridge on account of the resistance of the leads

and the contact resistances while measuring low valued resistors.

PROCEDURE: Make the Connections as per the circuit diagram.

1. Give supply and adjust Decade Resistance Box to get null deflection.

2. Note the values and calculate unknown resistance using the formula.

By increasing DC Voltage source, note different readings and repeat the calculation

FORMULAE: Kelvin’s Bridge:

RX = (RSR1) / R2 + R4 r (R1 / R2 – R3 / R4) / (R3 + R4 + r) (Ω)

Wheat stone’s Bridge:

R = P * S / Q (Ω)

Where,

RS – Standard resistance, r - Load resistance, RX – unknown resistance

% Error = ((Actual Value – Obtained Value) / Actual Value) * 100

MODEL CALCULATIONS:


1. What is the range of low, medium and high resistances?

2. What are the methods of measuring medium resistances?

3. What are the advantages of Wheatstone bridge method?

4. What are the methods of measuring high resistances?

5. What are the precautions to be followed while measuring low resistance?

6. What are the factors involved in measurement of high resistance?

7. What are the advantages of bridges?

8. What is meant by Kelvin’s bridge?

9. What is Kelvin double bridge?

10. What is meant by balanced condition for Wheatstone bridge?

RESULT:

Thus the value of given resistance was determined using Wheatstone bridge &

Kelvin bridge.

The value of the given resistor = _________ (Using Wheatstone bridge) _________ (Using Kelvin’s double bridge)

INSTRUMENTATION AMPLIFIER

Ex. No: Date:

3. INSTRUMENTATION AMPLIFIER

AIM:

R’

R’

V0

V1

+

-

A1

R3

V2

R1

R2

R4

+

-

-

A3

A2

+

R

To design and determine the performance characteristics of Instrumentation Amplifier.

REFERENCE:

1. A.K. Sawhney : A course in Electrical and Electronics Measurements and Instrumentation, Dhanpat Rai & Sons, 1984.

2. H.S. Kalsi : Electronic Instrumentation, TMH, 1995.


Principle of working of Instrumentation amplifier.

APPARATUS REQUIRED:

THEORY:

In a number of industrial and consumer applications, one is required to

measure and control physical quantities. Some typical examples are measurement and

control of temperature, humidity, light intensity, water flow etc. These physical

quantities are usually measured with the help of transducers. The output of

transducers has to be amplified so that it can drive the indicator. So that it can display

system. This function is performed by an instrumentation amplifier.

Many of the input specification of an Op-amps employed directly determine

the input specifications of the instrumentation amplifier.

An analysis of the circuit gives the following equation:

Let R1 = R2 = R3 = R4

Considering the basic differential amplifier shown in the figure, the output

voltage V0 is given by

V0 = - R2/ R1 V2 + 1/1 + R3/R4 V1 (1+ R2/R1)

Or,

V0 = R2/ R1 (V2 – 1/1 + R3/R4 (R1/ R2+1) V1V1)

V0 = -R2/R1 V2 + 1/ 1+R3/R4 V1 (1+ R2/R1)

V0 = - Rf / Rin (V1 – V2)

TABULATION:

Sl.No Apparatus name Quantity

1. Regulated Power Supply 1 No.2. Resistors As reqd

3. OP-Amp IC 741 3 Nos.4. Connecting wires As reqd

Sl.No Input Voltage (V1) V2 Output Voltage (V0)

MODEL CALCULATIONS:

The Op-amp A1 and A2 have differential input voltage as Zero. For V1 = V2

that is, under common mode condition, the voltage across R will be zero. As no

current flows through R and R1 the non-inverting amplifier A1 acts as voltage follower

having output V11 and V1. However, If V1 ≠ V2 current flows in R and R2 and (V2-

V1).

The gain of an instrumentation amplifier can be varied by changing R1 alone.

High gain accuracy can be obtained by using precision metal film resistors for all the

resistances.

Because of the large negative feedback used, the amplifier has good linearity

typically about 0.01% for a gain less than 10. The output impedance is also low being

in the range of milliohms.

The input bias current of the instrumentation amplifier is determined by that of

the amplifiers A1 and A2.

FEATURES:

The important features of an instrumentation amplifier are

1. High gain accuracy and linearity

2. High CMRR

3. High gain stability with low temperature coefficient.

4. Low dc offset

5. Low output impedance

The instrumentation amplifier is also called as Data amplifier.

The expression for its voltage gain is generally of the form,

A = (V0/V2) – V1

Where V0 = output of the amplifier

V2-V1 = differential input is to be amplified.

REQUIREMENTS OF A GOOD INSTRUMENTATION AMPLIFIER:

1. Finite, accurate and stable gain

2. Easier gain adjustment

3. High input impedance

4. Low output impedance

5. High CMRR

6. Low power consumption

7. Low thermal and time drift

8. High Slew rate

PROCEDURE:

1. Circuit connections are made as per the circuit diagram.

2. V1 & V2 are connected together & the input voltage is set at 7V.The output

voltage V0 is measured.

3. Common mode gain is calculated Ac = V0/((V1+V2)/2)

4. V1 & V2 are given different voltages & the output voltage V0 is measured.

5. Differential gain is calculated Ad = V0/(V1~V2)

6. CMRR= Ad / Ac

DESIGN:

An analysis of the circuit gives the following equation:

Let R1 = R2 = R3 = R4

Considering the basic differential amplifier shown below, the output voltage V0 is given by

V0 = - R2/ R1 V2 + 1/1 + R3/R4 V1(1+ R2/R1)Or,

V0 = R2/ R1 (V2 – 1/1 + R3/R4 (R1/ R2+1)V1V1)

V0 = -R2/R1 V2 + 1/ 1+R3/R4 V1 (1+ R2/R1)

V0 = -Rf / Rin (V1 – V2)


1. What is instrumentation amplifier?

2. What are the important features of instrumentation amplifier?

3. What is an op amp?

4. What are the properties of an ideal op amp?

5. What are the characteristics of voltage amplifier?

6. What is CMRR?

7. What is bandwidth?

8. What is the need of instrumentation amplifier?

9. What are the advantages of instrumentation amplifier?

10. What are the applications of Op-Amp?

RESULT:

Thus an instrumentation amplifier is designed and analyzed.

CMRR of the Instrumentation Amplifier is determined.

R-L circuit:

For a series RL circuit,

V L

Circuit Equations:

V (t) = R i (t) + L di (t) dt

di (t) = V (t) - R i(t)dt L L

i (t) = ( V(t) - R i(t)) dt L L

R-L Circuit Simulation:

V /

Ex. No: Date:

4. STUDY OF TRANSIENTS

AIM:

To study the transients of DC circuits and AC circuits.

V/ L

R/L PRODUCT

+ S U M

_

INTEGRATOR SCOPE

R/ L

V(t)R2

I (t)

To obtain the Transient Response Curve of R-L circuit and R-C circuit using

MATLAB.

REFERENCE:

1. M.Arumugam and N.Prem Kumar – Electrical circuits Theory, Khanna

Publishers, Newdelhi.

2. B.L. Theraja – Fundamentals of Electrical and Electronics, S.Chand and

Company Ltd, New Delhi.


Basic concepts of DC and AC circuits.

Basic concepts of RL, RC transients and MATLAB.

THEORY:

Transient phenomenon is a periodic function of time and doesn’t last

longer. The duration of which they last is very significant as compared with

operating time of the system. But they are very important because depending upon

the reversibility of the transients, the system may result in block out condition.

REQUIREMENT OF TRANSIENT IN THE CIRCUIT:

1. Either inductor or capacitor or both should be present.

2. A sudden change in the parameter as the form should occurs as a fault or any

switching operation.

a) The following are the simple 3 facts which are the fundamental to the

phenomenon of transients in electrical power systems.

b) The current can’t change instantaneously through any inductor.

c) The voltage across a capacitor can’t change instantaneously.

3. The law of conversion of energy should hold good.

R-C circuit:

For a series RC circuit,

R C

Circuit Equations:

V (t) = R i(t) + 1 i(t) dt C

R i (t) = V (t) – 1 i(t) dt C

i (t) = V(t) /R – 1 i(t) dt RC

R-C Circuit Simulation:

SIMULATION PROCEDURE:

1. To work with Matlab-Simulink, first type simulink in the command

window. A library file and untitled notepad appears in the window.

2. Double click on each icon to get different blocks.

3. Drag each component from library block and place in untitled.

V(t)R2

i(t)

1/ RC

V/ R

INTEGRATORPRODUCT

SCOPE

+ S U M

_

4. Dragging the mouse between two components draws lines.

5. After completing the circuit, select start from the simulation menu.

6. Double click on the scope to view the response

PROBLEM:

R-L circuit

R=10; L=1H and V=10 V. Choose simulation time as 5 sec.

R-C circuit

R=10; C=1f and V=10 V. Choose simulation time as 5 sec.

RESULT:

Thus the transient response curve for the given R-L circuit and

R-C circuits have been obtained.

Ex. No: Date:

5. CALIBRATION OF SINGLE-PHASE ENERGY METER

AIM:

To calibrate the given single-phase energy meter by direct loading and

phantom loading.

REFERENCE:

1. A.K. Sawhney : A course in Electrical and Electronics Measurements and

Instrumentation, Dhanpat Rai & Sons, 1984.



Working principle and operation of single phase energy meter, loading

arrangements and method of calibrating the energy meters.

APPARATUS REQUIRED:

Sl.No. Particulars1 Voltmeter 1 No.2 Ammeter 1 No.3 Wattmeter 1 No.4 Test energy meter 1 No.5 Phase shift transformer 1 No.6 Connecting wires As reqd.

THEORY:

Direct loading:

In this method, precision grade indicating instruments are used as reference

standard. These indicating instruments are connected in the circuit of meters under

test. The current and voltage are held constant during the load test. The number of

revolutions made by the meter disc and the time taken during the test are recorded.

Phantom loading:

When the current rating of a meter under test is high. A test with actual

loading arrangements would involve a considerable waste of power. In order to avoid

this, phantom or fractious loading is done. The calibration procedure involves the

steps like visual inspection for various defects, installation according to the

specifications, zero adjustment etc.

PRE CAUTIONS:

1. Auto transformer is kept at minimum position at the time of starting.

2. Rheostat is kept at minimum position in phantom loading.

3. Phase shaft transformer is kept at UPF position

PROCEDURE:

Direct loading:1. Make the circuit connection as per the circuit diagram.

2. Close the DPST switch.

3. Adjust single phase auto transformer till the voltage connected across the primary

winding reads rated primary voltage.

4. Vary the resistive load to vary the load current.

5. Note down readings of time taken for the Energy meter for 5 revolution,

Wattmeter, ammeter and voltmeter.

6. Repeat the same procedure for various load conditions.

7. Calculate percentage error and draw the graph between percentage error and load

current.

Phantom loading:1. Make the circuit connection as per the circuit diagram.

2. Close the DPST switch 2.

3. Give the supply to energy meter circuit which energies the pressure coils in energy

meter and wattmeter.

4. Vary the single phase variac up to rated current in ammeter there by energising the

current coil.

5. Note down the time taken for five revolutions for various load at UPF.

6. Rotate the phase shifting transformer and note down the readings for lagging

power factor and leading power factor.

7. Calculate the true energy, actual energy and % error.

8. Draw the graph between % error Vs load current.

FORMULAE:

MODEL GRAPH:

TABULATION:

Direct loading

Sl.No. Voltage(Volts)

Current(Amps)

WattmeterReading (Watts)

Time taken for 5 revolutions

Actual Energy

True energy

%Error

Phantom loading:

Power factor

Voltage(V)

IL

(A)Wattmeter Reading

Time for 5 revaluations

Actual energy

True energy

%error

UPF

Lagging

Leading

Direct loading

IL (A)

% Error

IL (A)

% Error

Phantom loading

UPF

Lag

Lead


1. What is creeping in energy meter?

2. What is Phantom Loading?

3. What is energy meter?

4. What are the types of energy meter?

5. What are the advantages of two element polyphase meter? What is the provision

available in energy meter for adjusting creeping?

6. What is the provision available in low power factor measurement energy meter?

7. What is calibration and why it is needed for instruments?

RESULT:

Thus the single phase energy meter was calibrated using direct and phantom

loading methods and the graph is drawn.

.

Ex. No. Date:

6. MEASUREMENT OF THREE PHASE POWER AND POWER FACTOR

AIM:

To measure the power and power factor in three-phase circuit star connected, Delta

connected load & to check the relationship between line and phase quantity.

REFERENCE:

1. A.K.Sawhney : A course in Electrical and Electronics Measurements and




1. Basics of three-phase power and power factor

2. Basics of Star and Delta connections.

APPARATUS REQUIRED:

Sl.No. Particulars Quantity1 Voltmeter 2 Nos.2 Ammeter 2 Nos.3 Wattmeter 2 Nos.4 Rheostat 3 Nos.5 Connecting wires As reqd.

THEORY:

In a three phase, three wire system, we require three elements. But if we make the

common points of the pressure coils coincide with one of the lines, then we require only

two elements. Instantaneous power consumed by load =V1i1+V2i2+V3i3.

Star Connection:

Instantaneous reading of P1 wattmeter W1 and the instantaneous reading of P2 is

W2.Sum of instantaneous readings of two wattmeter =W1+W2.Sum of instantaneous

readings of two watt meters = V1i1+V2i2+V3i3.Therefore, the sum of the two wattmeter

reading is equal to the power consumed by the load. This is irrespective of whether the

load is balanced or unbalanced.

Delta Connection

Here also, by means of Kirchhoff’s voltage law, hence sum of instantaneous

readings of two watt meters = V1i1+V2i2+V3i3. Therefore the sum of the two wattmeter

readings are equal to the power consumed by the load. This is irrespective of whether the

load is balanced or unbalanced.

TABULATION:Sl.No Voltage (V) Current (V) Wattmeter reading Power

factor W1 (W) W2 (W)

M.F =

FORMULA:

3-phase power P = W1+W2 (Watts)

Power factor Angle = tan-1 [3 (W1 ~W2) ] (W1+W2)

MODEL CALCULATION:

PROCEDURE:

1. Make the circuit connection as per the circuit diagram.

2. Close the TPST switch.

3. Note down the Wattmeter readings W1 and W2.

4. By knowing the Multiplication factor, calculate the power.

5. Note down the line voltage and phase voltage using voltmeters.

6. Note down the line current and phase current using ammeters.

7. By using the above all the readings calculate the power and power factor.


1. What is energy?

2. What are the advantages of three phase system?

3. What is the relation between the line and phase quantities in delta connection?

4. What are the methods for measuring power?

5. What do you meant by power factor?

RESULT:

Thus the relationship between phase & line quantities for star and delta connected

load are verified in three phase connection and the power and power factor is measured.

LINEAR VARIABLE DIFFERENTIAL TRANSFORMER

Ex. No Date:

7. STUDY OF DISPLACEMENT TRANSDUCER(Linear Variable differential Transformer)

DifferenceVoltage

CORE

1 ACExcitation

AFO

CRO

Sy1

Sy2

+

+

_

_

Py

AIM:

To obtain the performance characteristics of Linear Variable differential Transformer

(LVDT) and to measure the displacement made by the given object using LVDT.

REFERENCE:





Principle of working of Linear Variable Differential Transformer and different

transducers.

THEORY:

Linear Variable Differential Transformer (LVDT):

The linear variable differential transformer (LVDT) is a type of electrical

transformer used for measuring linear displacement. The transformer has three solenoidal

coils placed end-to-end around a tube. The centre coil is the primary, and the two outer

coils are the secondaries. A cylindrical ferromagnetic core, attached to the object whose

position is to be measured, slides along the axis of the tube.

An alternating current is driven through the primary, causing a voltage to be

induced in each secondary proportional to its mutual inductance with the primary. The

frequency is usually in the range 1 to 10 kHz.

As the core moves, these mutual inductances change, causing the voltages induced

in the secondary coils to change. The coils are connected in reverse series, so that the

output voltage is the difference (hence "differential") between the two secondary voltages.

When the core is in its central position, equidistant between the two secondary coils, equal

but opposite voltages are induced in these two coils, so the output voltage is zero.

When the core is displaced in one direction, the voltage in one coil increases as the

other decreases, causing the output voltage to increase from zero to a maximum.

TABULATION:

Sl.No Micrometer Reading (mm)

Actual Displacement

(mm)

Display reading (Volts)

Indicated displacement

(mm)

%Error

1234567

MODEL GRAPH:

SPECIFICATION OF LVDT:

Four Stage range : 20mm

Excitation : Upto 5V, 3 KHz AC

Sensitivity : 5mV, rms at 3 KHz

Body Diameter : 22mm

Resolution : Infinite Resolution

This voltage is in phase with the primary voltage. When the core moves in the

other direction, the output voltage also increases from zero to a maximum, but its phase is

opposite to that of the primary. The magnitude of the output voltage is proportional to the

Displacement (mm)

Output voltage (mV)

distance moved by the core (up to its limit of travel), which is why the device is described

as "linear". The phase of the voltage indicates the direction of the displacement because

the sliding core does not touch the inside of the tube, it can move without friction, making

the LVDT a highly reliable device. The absence of any sliding or rotating contacts allows

the LVDT to be completely sealed against the environment.

PRECAUTIONS:

In all the arms of the bridge the resistance values one kept at Maximum position

to reduce current through the detector circuit.

PROCEDURE:

For plotting the Characteristics of LVDT:

1. Make the connection as per the circuit diagram.

2. Vary the frequency and the LVDT core.

3. Measure the output Voltage.

4. Plot the Graph between displacement and output voltage.

To measure the displacement made by the given object:

1. The LVDT module is connected to main unit.

2. Initially the unit is set at ‘0’ at 40mm in vernier.

3. The power supply is given to the unit.

4. The zero adjust is varied to obtain a correct zero value on output display.

5. Vernier position is adjusted using the screw provided towards right hand side.

6. Now core of LVDT wire will move towards positive position.

7. For 10mm movement towards right, the display will indicate 1V. For further

5mm movement the display will indicate 1.5V and so on.

8. Now the given object is placed in Vernier scale. The reading shown by the

display and Vernier scale are noted.

9. By using noted value, error is calculated.

FORMULAE:

% Error = (Actual Displacement – Indicated Displacement)/Actual Displacement

FORMULAE:

(i) V0 =V01-V02

Where, V0 = Output voltage

V01 = Voltage across secondary SV1

V02 = Voltage across secondary SV2

(ii) Displacement = MSR + (RSR x 0.01)

MODEL CALCULATION:


1. Mention some of the transducers.

2. What is LVDT?

3. State the advantages of LVDT.

4. What are the disadvantages of LVDT?

5. What are the applications of LVDT?

6. What is RVDT?

7. What is Synchro?

8. What are the types of synchro systems?

RESULT:

Thus the performance characteristic of LVDT is studied.

SCHERING’S BRIDGE

DAFO

R3

C1 C2

R4

C3

MAXWELL’S BRIDGE

Ex. No Date:

8. A.C. BRIDGES

AIM:

To determine the value of the unknown capacitance and loss angle (δ) using low

voltage Schering’s bridge.

To measure unknown value of inductance using Maxwell’s Bridge.

E

D

RX

LX

R2

R3

R4

C4

REFERENCE:

1. A.K.Sawhney: A course in Electrical and Electronics Measurements and


2. H.S.Kalsi : Electronic Instrumentation, TMH, 1985.


Principle of bridge circuits, loss angle, low voltage Schering bridge for

measurement of capacitance and low frequency and high frequency inductance

measurements using Maxwell’s Bridge.

APPARATUS REQUIRED:

Sl.No: Particulars Quantity

1. Capacitor 3 Nos.2. Decade capacitance Box 1 No.3. Decade Resistance Box 2 Nos.4. Resistor 1 No.5. AFO 1 No.6. Galvanometer 1 No.

THEORY:

Schering’s Bridge:

A very important bridge used for the precision measurement of capacitors and their

insulating properties is the Schering Bridge. The standard Capacitor C2 is a high quality

mica capacitor (low-loss) for general measurements or an air capacitor (having a very

stable value and a very small electric field) for insulation measurement.

Under balance condition,

R1+[1/jωC1]R4/[1+jωC4R4] = I/jωC2R3

R1+1/jωC1R = R3/jωC2[1+jωC4R4]

R1R4-[jR4/ωC1] = -[jR3/ωC2]+ [R3C4R4/C2]

C1=C2R4/R3

TABULATION: (Schering’s bridge)

SL.No.

CapacitorC2 (µf)

R4

(Ω)C4

(µf)R3

(Ω)C1

Actual Value (µf)

C1

Obtained

Value (µf)

% Error

FORMULAE:

C1= C2 ( R3 / R4) cos2δ Farad Where,

R3 – Variable resistance (Ohm)

R4 – Standard resistance (Ohm)

C1 – unknown Capacitance (Farad)

C2 – Standard Capacitance (Farad)

C4 – Variable Capacitance (Farad)

Loss angle δ = tan-1(ω C4 R4)

% Error = ((Actual Value – Obtained Value) / Actual Value) * 100

MODEL CALCULATION:

Equating real and imaginary terms,

R1= R3C4/C2

Two independent balance equations are balanced if C4&R4 are chosen are the variable

element.

Dissipation factor D1= tan δ=ωC1R1

= ω[C2R4/R3][R3C4/C2]

= ωC4 R4

This bridge is widely used for testing small capacitors at low voltages with very

high precision.

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Vary the DRB and DCB.

3. When the detector shows null position, note the corresponding readings.

4. Using the formula find the value of unknown capacitance.

Maxwell’s bridge:

Maxwell’s bridge measures an unknown inductance in terms of a known capacitor.

The use of standard arm offers the advantage of compactness and easy shielding. The

capacitor is almost a loss-less component. One arm has a resistance R1 in parallel with C1,

and hence it is easier to write the balance equation using the admittance of arm 1 instead of

the impedance.

The general equation for bridge balance is

Z1Zx = Z2Z3

Zx = Z2Z3/ Z1 = Z2Z3Y1

Where, Z1=R1 in parallel with C1; i.e. Y1=1/Z1

Y1=1/R1 + jωC1

Z2=R2

Z3=R3

Zx=Rx in series with Lx=Rx + jωLx

From these equations we have,

Rx + jωLx = R2R3(1/R1 + jωC1)

Rx + jωLx = R2R3/R1 + jωC1R2R3

TABULATION: (Maxwell’s bridge)

Sl.No R2(Ω) R3(Ω) R4(Ω) RX(Ω) LX(Ω)

Actual Practical Actual Practical

FORMULAE:

RX = R2 R3 / R4(Ώ)

LX = R2 R3 C4(H)

Q factor=ω LX / RX

Where,

LX = unknown Inductance

RX =Effective resistance of inductance LX

R2, R3, R4 = Known non – Inductance resistance

C4 = Standard capacitance

MODEL CALCULATION:

Equating real terms and imaginary terms we have

Rx = R2R3/R1 and Lx=C1R2R3

Also, Q = ωLx/Rx = (ωC1R2R3 * R1)/R2R3 = ωC1R1

Maxwell’s bridge is limited to the measurement of low Q values (1-10). The

measurement is independent of the excitation frequency. The scale of the resistance can be

calibrated to read inductance directly.

The Maxwell’s bridge using a fixed capacitor has the disadvantage that there is an

interaction between the resistance and reactance balances. This can be avoided by varying

the capacitances, instead of R2 and R3, to obtain a reactance balance. However, the bridge

can be made to read directly in Q.

This bridge is particularly suited for inductances measurements, since comparison

with a capacitor is more ideal than with another inductance. Commercial bridges measure

from 1-1000 H, with + 2% error. (If the Q is very large, R1 becomes excessively large and

it is impractical to obtain a satisfactory variable standard resistance in the range of values

required)

PROCEDURE:

1. Make the connections as per the circuit Diagram.

2. Give supply and adjust Decade Resistance Box to get null deflection.

3. Note the values and calculate unknown Inductance using the formula.


1. How can we eliminate the error?

2. Applications of Schering’s bridge?

3. What is the use of vibrational glanvanometer?

4. List out commonly used detectors for A.C. Bridge.

5. What are the types of A.C.bridges?

6. How do you measure capacitance?

7. What are the advantages of Maxwell Wein Bridge?

8. What are the disadvantages of Maxwell Wein Bridge?

9. What are the advantages of electronic oscillator?

RESULT: Thus the value of the unknown capacitance and loss angle (δ) using low voltage

Schering’s bridge was determined.

Thus the unknown value of inductance using Maxwell’s Bridge was determined.

Ex. No Date:

9. A/D CONVERTER AND D/A CONVERTER

AIM:

(i) To obtain the analog output voltage from digital Input.

(ii) To obtain the digital output voltage from Analog Input.

REFERENCE:





Basic theory and operation of A/D & D/A and its types.

APPARATUS REQUIRED:

1. VSTM 003 experiment unit and channel ADC kit.

2. VSTM 003 experiment unit and channel DAC kit.

THEORY:

DIGITAL TO ANALOG CONVERSION:

It involves conversion of digital information into equivalent analog information.

Digital to analog converter (DAC) acts as a decoding device since it operates on the output

of the system. DAC are of two types, Binary weighted resistor type & R-2R ladder type.

R-2R ladder DAC:

In this type, the reference voltage is applied to one of the switch position and the

other switch position is connected to ground. The typical value of resistors ranges from

2.5kΩ to 10kΩ. Let us consider 3 bit R-2R ladder DAC with binary input 001. The output

voltage will be VR/ 8, is equivalent to binary input 001.

ANALOG TO DIGITAL CONVERSION:

The analog information is converted into equivalent binary number in the digital

form. Analog to digital converter (ADC) acts as an encoder.

The types of ADC are 1) single slope, 2) Dual slope, 3) successive approximation,

4) Flash type, 5) Delta modulation and 6) Adaptive delta modulation.

In this type most frequently used method is successive approximation

Successive approximation:

In this type the basic idea is to adjust the DAC’s input code such that its output is

within ±1/2 LSB of the analog input Vi. The circuit uses Successive Approximation

Register (SAR) to find the required values of each bit by trial and error.

PROCEDURE:

D/A Conversion:

1. Switch on the Power supply.

2. The jumpers J9 to J16 should be in the s/w (right) position.

3. The switches sw1 through sw8 are placed approximately to represent the

desired output.

4. For example if the input is 496 V then the switch positions are as follows.

SW1 SW2 SW3 SW4 SW5 SW6 SW7 SW8 Hex Value

1 1 1 1 1 1 1 0 (FE) H

5. The output voltage can be observed by using CRO.

A/D Conversion:

1. Switch on the supply.

2. The Variable terminal of the potentiometer is given to analog input channel 2.

3. To select the analog input channel 2, the channel select switch position is as

follows.

SW1 SW2 SW3

0 1 0

4. The start of conversion button (soc) is pressed. Once to start the Conversion

from analog signal to digital form. The LED 9 glows on pressing start of

Conversion button.

5. The Address latch enable button is also pressed once so as to enable the digital

data to be sent to the output.

TABULATION:

Digital to Analog Conversion:

Sl.No

B7 B6 B5 B4 B3 B2 B1 B0Hex

ValueAnalog

O/p

Analog to digital Conversion:

Sl.No

Analog I/p

B7 B6 B5 B4 B3 B2 B1 B0Hex

Value

DISCUSSION QUESTION:

1. What are the types of D/A converter?

2. What are the advantages of R-2R ladder D/A converter?

3. What are the uses of D/A converter?

4. What are the types of A/D conversion?

5. What is the use of A/D conversion device?

6.What is sample and hold circuit?

7.What is resolution?

8.What are the advantages of successive approximation converter?

9.What are the disadvantages of Dual slope converter?

RESULT:

Thus the analog output voltage from digital input and digital output from analog

input were obtained.

Ex. No Date:

10. CALIBRATION OF THREE-PHASE ENERGY METER

AIM:

To calibrate and hence draw the characteristics curve for the given 3Φ energy

meter by direct loading.

REFERENCE:





Working principle and operation of Three-phase energy meter, loading

arrangements and method of calibrating the energy meters.

APPARATUS REQUIRED:

THEORY:

In a 3φ four wire system, the measurement of energy is carried out by a three phase

energy meter. In a 3φ three wire system, the measurement of energy is carried out by 2

element energy meter. This meter consists of 3 elements. The construction of an individual

element is similar to that of a single phase energy meter. The current coils are connected in

series with line and denoted as C1, C2, C3, while pressure coils are connected along line &

neutral and denoted as P1, P2, and P3. The coils are connected in such a manner that the

net torque produced is the sum of the torques due to all the three elements. These are

employed for 3φ four wire systems where the fourth wire is a neutral.

To have a zero error, the actual energy consumed by load for time corresponding to

two revolutions must be same as εr. This energy is actual energy consumed or true energy

denoted as εr. The graph is calibration curve for the energy meter.

Sl.No Apparatus Quantity Range

1 Ammeter M.I 1 0 – 10A

2 Wattmeter 1600 V,

10A,UPF

3 Three-Phase energy meter 1 -

4 Voltmeter M.I 1 0 - 600 V

MODEL GRAPH:

TABULATION:

Sl.NoIL

(Amps)

WattmeterReadings

(W)ActualEnergy(kWhr)

Time Takenfor 5

revolutions(sec)

TrueEnergy(kWhr)

% error =(AE-TE)/ TE x

100W1 W2

Load Current (A)

% Error

PRECAUTIONS:

1. Auto transformer should be kept at minimum position at the time of starting.

2. Resistive load should be kept at minimum position.

PROCEDURE:

1. Make the circuit connection as per the circuit diagram.

2. Close the TPST switch.

3. Adjust three-phase auto transformer till the rated voltage.

4. Vary the resistive load to vary the load current.

5. Note down readings of time taken for the Energy meter for 5 revolution, Wattmeter

and ammeter.

6. Repeat the same procedure for various load conditions.

7. Calculate the percentage error and draw the graph between percentage error and

load current.

FORMULA:

% Error = (Actual energy – True energy) / True energy X 100 Actual energy (kWhr) = No of revolutions by energy meter / Meter Constant

True energy (kWhr) = (Watt meter readings X Time taken) / (3600 X 1000)


1. What is Creeping?

2. What is Phantom Loading?

3. What is energy meter?

4. What is calibration?

5. What are the types of energy meter?

6. What are the methods of testing the energy meter?

7. What is the reason for rotation of disc?

8. How can the creeping be eliminated?

9. Which torque is absent in energy meter. Why?

RESULT:

Thus the given 3 φ energy meter was calibrated by direct loading & the graph was

plotted.

CALIBRATION OF CURRENT TRANSFORMER

Ex. No Date:

V

A

V

30 V AC Supply

P

N

11. CALIBRATION OF CURRENT TRANSFORMER

AIM:

To study and calibrate current transformer parameters

REFERENCE:





Principle of working of current transformer.

APPARATUS REQUIRED:

SNO Apparatus Range Quantity1 Current Transformer

Trainer1 No.

2 Rheostat 500 Ω,3A 1 No.3 Loading rheostat 700 W 1 No.4 Patch cords As reqd.

FORMULAE:

Ratio error or Current error (%) = 100( KN IS -IP) IP

KN = Primary winding current Secondary winding current

Phase Angle error ө =

Im =

THEORY:

A current transformer is an instrument transformer specially designed and

assembled to be used in measurement control and protective circuits. Its primary consists

of few turns and is connected in series with the circuit whose current is desired to be

measured and the secondary is connected to the current measuring instrument. The

secondary circuit is closed through the typical low impedance of the instruments

connected to it.

TABULATION:

Sl No SupplyVoltage

(V)

Primary Current

( IP)

Secondary Current

( IS)

Ratio ErrorKN

Phase angle Error

ө

MODEL CALCULATION:

In ideal CT the secondary current is inversely proportional to the ratio of turns and

opposite in phase to the impresses primary current. The exciting current must be

subtracted phasorially from the primary current to find the amount remaining to supply

secondary current. This value will be slightly different from the value that the ratio of

turns would indicate and there is slight shift in phase relationship. This results in

introduction of ratio and phase angle errors when compared to ideal CT.

PROCEDURE:

The calibration of current transformer operation is under two modes (ie.Low

voltage and high voltage)

Low Voltage : (ie.30 V)

1. Connect the circuit as per the circuit diagram

2. Switch on the kit with rheostat at minimum position.

3. Load the CT by using 500 Ω, 3A rheostat.

4. Now note down the primary (IP) and secondary current (IS) of transformer.

5. Tabulate the readings and calculate calibration parameters.

High Voltage : (ie.230 V)

1. Connect the circuit as per the circuit diagram

2. Switch on the kit and switch on the MCB.

3. Keep the rheostat maximum position.

4. Load the CT by using loading rheostat 700 W.

5. Now note down the primary (IP) and secondary current (IS) of transformer.

6. Tabulate the readings and calculate calibration parameters


1. Define current transformer

2. How is current transformer designed?

3. Mention the uses of current transformer.

4. Mention precautions to be followed while using current transformer.

5. What is calibration? Mention the need for calibration.

6. Mention calibrated parameters of current transformer

RESULT:

Thus the calibration of current transformer was studied and calibrated.

The calibrated parameters are ratio error & phase angle error .

MEASUREMENT OF IRON LOSS

GAC

R4

R

R3

A

L

Ex. No Date:

12. MEASUREMENT OF IRON LOSS

AIM:

To determine the iron loss in magnetic material using bridge method.

REFERENCE:





Concept of hysteresis and eddy current loss.

APPARATUS REQUIRED:

SNO Apparatus Range Quantity1 Ring Specimen 1 No.2 Ammeter 0-2A, M.I 1 No.3 AFO 1 No.4 Patch cords As reqd.

PROCEDURE:

1. Measure the resistance value of ring specimen by using multi meter in ohm.

2. Connect the galvanometer and ammeter with ring specimen.

3. Also connect variable inductor with the Maxwell’s bridge.

4. Switch on the power supply and adjust the variable inductance and potentiometer

till the galvanometer reads to zero.

5. Observe ammeter reading.

6. Switch off the power supply and measure the resistance value of potentiometer.

Iron loss Pi = I2[R4/(R3+R4)].[Rs-Rw]

Rs = (R3/R4).(R2+R2)

RESULT:

Thus the Iron loss of the given magnetic material is determined using bridge method.

Exp

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