G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
Department of Electrical and Electronics
Engineering
Electrical Measurements Lab Manual
R-13 Regulation
Prepared by
D.Gowthami
Assistant Professor
DEPT OF EEE
Page 1
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
ELECTRICAL MEASUREMENTS LAB
LIST OF EXPERIMENTS
1. Calibration of single phase energy meter.
2. Calibration of single phase power factor meter.
3. Power measurement by 3-Ammeter method.
4. Power measurement by 3-Voltmeter method.
5. Schering Bridge.
6. Strain-gauge transducer.
7. Measurement of Unknown Capacitance by using Desauty‟s Bridge.
8. Kelvin‟s Double Bridge.
9. Measurement of Unknown Resistance by using Wheatstone‟s bridge.
10. Anderson‟s Bridge.
11. Capacitive Pick-Up.
12. Linear Variable Differential Transformer (L.V.D.T).
13. Measurement of three phase reactive power with single phase watt
meter.
14. Crompton type DC potentiometer.
15. Measurement of three phase power using single phase wattmeter and
two C.Ts.
DEPT OF EEE
Page 2
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-1
CALIBRATION OF SINGLE PHASE ENERGY METER
AIM: To determine the error and percentage error at 5%, 25% and 125% of
full load current for the given single phase energy meter.
NAME PLATE DETAILS:
Meter constant = 1200 rev/KWH
Rated Current = 10A
Rated Voltage = 240V
Rated frequency = 50Hz
APPARATUS:
1. Voltmeter – (0-300V) MI
2. Ammeter – (0-20A) MI
3. 1-Ф variac – (230V / 0-270V)
4. Rheostats – 350Ω / 1.2A, 29Ω / 4.1A, 10Ω / 1.2A
5. Stop watch
6. Connecting wires
CIRCUIT DIAGRAM:
Single phase energy meter
THEORY:
Energy meter mainly consists of 4 parts of the operating mechanism.
They are
1. Driving system
2. Moving system
3. Breaking system
4. Registering mechanism
The driving mechanism of the meter consists of two electromagnets. The core
of these electromagnets is made up of steel laminations. The coil of the
electromagnets is excited by load current. This coil is called the current coil.
DEPT OF EEE
Page 3
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
The coil of second electromagnet is connected across the supply voltage. This
coil is called the pressure coil. Consequently the two electromagnets are known
as series and shunt magnets respectively. Copper shading bands are provided
on the central limb.
The position of these bands is adjustable. The function of these bands is
to bring the flux produced by the shunt magnet exactly in quadrature with the
applied voltage. Moving system consists of an aluminum disk system. The „Al‟
disc moves in the field of this magnet and thus provides a breaking torque. The
position of the permanent magnet is adjustable and therefore rotor shaft devices
a series of 5 or 6 pointers. These rotate on sound dials which are marked with
10 equal divisions.
PROCEDURE:
1. Connect the circuit as shown in figure.
2. Connect the load rheostat 350 Ω/1.2A in series with load.
3. Keep the variac in minimum output voltage position.
4. Keep the load in maximum position.
5. Adjust the variac output equal to the rated voltage of energy meter.
6. Adjust the load till rated current of energy meter passes through it. Note
down the voltmeter and ammeter readings.
7. Note down the time taken for 2 revolutions of disc in the energy meter.
8. Switch off the supply.
9. Replace 29 Ω / 4.1A instead of 350 Ω / 1.2A and switch on the supply.
10. Adjust the load current of 27% of rated current of energy meter and note
down the time taken for revolutions.
11. Now switch off the supply and replace 29 Ω / 4.1A and switch on the
supply.
12. Adjust the load till % of load current of energy meter and note down the
readings of voltmeter, ammeter.
13. Note down the time for revolutions with stop watch.
TABULAR COLUMN:
S.No
Voltage
in volts
DEPT OF EEE
Current
in amps
Time taken for
revolutions (S)
No. of
revolutions
Actual
Energy
Wa (W)
Energy
registered
by energy
meter WR
(W)
Error
WR - Wa
(W)
%Error
Page 4
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
THEORITICAL CALCULATIONS:
Actual energy consumed during „n‟ revolutions
Wa = V*I*t / 3600 watt-hour
where V= Voltage (V)
I= Current (A)
t = Time (S)
Energy registered by energy meter
WR = n / meter constant
Error = WR - Wa
% Error = [(WR - Wa) / Wa] * 100
RESULT:
The error and percentage errors are determined for single phase energy
meter at 5%, 25% and 125% of full load current.
DEPT OF EEE
Page 5
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-2
CALIBRATION OF SINGLE PHASE POWER FACTOR METER
AIM: To calibrate single phase power factor meter with various inductive and
capacitive loads.
APPARATUS:
1. Ammeter (0-10A) MI
2. Voltmeter (0-300V) MI
3. Wattmeter (300V, 10A,UPF)
4. 1-Ф variac 230V / 0-270V
5. 1- Ф power factor meter (300V, 10A)
6. Variable inductive / capacitive loading
7. Connecting wires
CIRCUIT DIAGRAM:
THEORY:
Power factor meter consists of a fixed coil which acts as the current coil,
the two pressure coils are connected across the voltage of the circuit. The
values of R, L are so adjusted that two coils carry some value of current at
normal frequency. The current through one coil lags it by any phase (Δ=90º).
The deflecting torques acting on coils are same but opposite.
Therefore the torque deflection of the instrument is a measure of the
phase angle of the circuit. Therefore the scale of the instrument can be
calibrated directly in terms of power factor.
PROCEDURE:
1. Connections are made as per the circuit diagram.
2. Keep the variac in the minimum output voltage position.
3. The inductance / capacitance are kept constant in maximum position.
DEPT OF EEE
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
4. Vary the variac till the rated voltage 230V is obtained in voltmeter.
5. The inductive load is also varied to get power factor between 0.5 lag and
near unity.
6. At every power factor setting, note down the voltmeter, ammeter and
watt meter readings in addition to power factor reading.
7. The above procedure for capacitance load is repeated so that power
factor varies between 0.5 lead and near unity.
8. Calculate the error by using appropriate formula.
FORMULAE:
Power factor cosФt = Active Power (KW) / Apparent Power (KW)
Error
%Error
= Wattmeter reading / (VI)
= PF meter reading – true PF = cosФm -cosФt
= [(cosФm -cosФt) / cosФt] * 100
TABULAR COLUMN:
INDUCTIVE LOAD
S.N
o
Supply Ammeter Wattmeter
Voltag reading
reading
e (V)
(A)
(W)
True
PF
cosФt=
W/(VI)
Measure
d PF
cosФm
Error
cosФmcosФt
%
Error
CAPACITIVE LOAD
S.No
Supply Ammeter
Voltage reading
(V)
(A)
Wattmeter
reading
(W)
True PF Measured
cosФt= PF cosФm
W/(VI)
Error
cosФmcosФt
%
Error
RESULT:
Single phase power factor meter is calibrated with various inductive and
capacitive loads and graph was drawn.
DEPT OF EEE
Page 7
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-3(A)
POWER MEASUREMENT BY 3- AMMETER METHOD
AIM: To determine the power consumed by the load by using 3- ammeter
method.
APPARATUS:
1. Ammeter (0-10A) MI -1
2. Ammeters (0-5A) MI -2
3. Voltmeter (0-300V) MI -1
4. Resistive load
5. Inductive load
6. Single phase variac (230V / 0-270V)
CIRCUIT DIAGRAM:
THEORY:
The power can be measured using 3-voltmeters, 3-ammeters and so on.
In this experiment of measurement of power, we use 3-ammeters in series
resistor, inductor and supply. By this readings various parameters, the power
factor which is true power was calculated. The power of inductive is the
product of voltage across the inductance. By this the power of the inductance
load was calculated and the power is calculated by the product of voltage
across the resistance and current following through resistive load only. Thus
the power of resistor was calculated, the addition of obtained power of the
circuit can be calculated by this 3- ammeter method.
PROCEDURE:
1. Connections are made as per the circuit diagram.
2. Variac is kept at minimum output voltage position.
3. Supply is given to the circuit by varying the variac, adjust the voltage
across the voltmeter as 230V.
DEPT OF EEE
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
4. Keep the resistance in maximum at starting.
5. For different values of inductive load note down the 3-ammeter readings
and voltmeter readings.
TABULAR COLUMN:
S.No
.
Supply
Voltage
(V)
Current
through
resistor (A)
Current
through
inductor
(A)
Total
Current
I (A)
Power
Factor
(cosФ
)
Power
consumed
by
inductance
PL=
VI3cosФ
(W)
Total
Power
P=
PR+
PL
(W)
Resist
ance
R (Ω)
Induct
ance L
(H)
Power
consu
med
by
Resist
ance
(W)
THEORITICAL CALCULATIONS:
V= Supply Voltage
I1= Current in the circuit
I2= Current through the resistive load
I3 = Current through the inductive load
By parallelogram law
I12= I22+ I32 +2 I2 I3 cosФ
cosФ= (I12- I22- I32) / (2 I2 I3)
Power consumed by inductive load is
PL= V I3 cosФL
Power consumed by resistive load is
PR= I2R (watt)
Total power consumed by load, P= PR+PL (watt)
r = PL / I32 (ohm)
ZL= V / I3 (ohm)
XL=√ (Z2 – r2) (ohms)
L = XL / 2πf H
RESULT:
The power consumed by the load is determined by using 3-ammeter
method.
DEPT OF EEE
Page 9
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-3(B)
POWER MEASUREMENT BY 3-VOLTMETER METHOD
AIM: To determine the power by using 3- voltmeter method.
APPARATUS:
1. 1-Ф variac (230V/0-270V)
2. Rheostat (350Ω/1.2A)
3. Voltmeters (0-300V) MI – 3
4. Ammeter (0-10A)MI -1
5. Inductive load
CIRCUIT DIAGRAM:
THEORY:
Generally in the case of A.C circuits as power factor is involved in the
expression for power, wattmeter must be used for the measurement of power.
But power in such circuits can also be measured by using 3- voltmeter method.
In this experiment load comprising of resistance and inductance is use. Power
consumed by load is determined by using voltmeter as follows. One voltmeter
is connected across resistance and other is connected across inductance. The
phasor sum of these two voltmeter readings fives the total voltage applied to
the circuit. From the above calculations power factor of the circuit is
determined. Hence, the sum of power load gives the total power consumed by
the load.
PROCEDURE:
1. Connect the circuit as per the circuit diagram.
2. Keep the variac in minimum output voltage position.
3. Keep the rheostat in maximum position.
4. Switch on the supply.
DEPT OF EEE
Page 10
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
5. Note down the readings of all meters for different values of inductive
loads.
TABULAR COLUMN:
S.N
o.
Supply
Voltag
e (V1)
Voltag
e
across
resistor
(V2)
Voltag
e
across
inducto
r (V3)
Current
I (A)
Pow
er
Fact
or
cosФ
L
Power
across
resistan
ce PR=
V2I
(W)
Power
across
inductor
PL=
V3IcosФ
L (W)
Total
Pow
er P=
PR+
PL
(W)
Resis
tance
RL
(Ω)
Indu
ctanc
eL
(H)
Induc
tive
Resis
tance
rL
(Ω)
THEORITICAL CALCULATIONS:
V1= Supply Voltage
V2= Voltage across resistive load
V3= Voltage across inductive load
I = Current in the circuit
By parallelogram law
V12= V22+ V32 +2 V2 V3 cosФω
cosФω= (V12- V22- V32)/(2 V2 V3)
Power consumed by inductive load is
P*ω= V2 I cosФL
Power consumed by resistive load is
PR= V2 I (watt)
Total power, P= PR+Pω (watt)
Impedance in the circuit = V3 / I (ohms)
Resistance = V2 /I (ohms)
Reactance = √ (Z2 – R2) (ohms)
Inductance in the circuit L= XL / (2πf) H
RESULT:
The power consumed by load was measured by using 3- voltmeter
method
DEPT OF EEE
Page 11
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-5
SCHERING BRIDGE
AIM: To determine the capacitance of a capacitor and its dissipation factor.
APPARATUS:
Schering Bridge
Head Phones
Probes
CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as shown in the figure, using AC supply of 1KHZ
and head phones.
2. Connect one unknown capacitor.
3. Set the capacitor dial C2 and resistance dial R at zero positions.
4. Adjust R1 to some value.
5. Vary R2 to minimize the sound in the head phone.
6. Note the values of R1, R2 & C1.
7. Calculate the value of unknown capacitor using the formula.
C = C1R2/R1
EXAMPLE:
C1 =0.01µF
R1=2100 OHMS
R2=2100OHMS
C = C1R2/R1
=0.01µF
DEPT OF EEE
Page 12
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
To find the dissipation factor of a capacitor:
1. Without disturbing the setting of the bridge inductance some resistance
„R‟ say 500Ω.
2. Now adjust the capacitor C2 to minimize the sound in the head phone.
3. Calculate the dissipation factor using the formula
Dissipation factor D = ωCR
Where ω = 2Πf
f = frequency of the oscillator
R = series resistance of a capacitor representing the loss in
the capacitor
C = Capacitance of the capacitor
4. Repeat the experiment with different values of resistance „R‟.
EXAMPLE:
Dissipation factor D = ω*C*R
=2Π*E+3*0.01*E-6*R
=2Π*E+3*0.01*E-6*600
=0.077
TABULAR COLUMN:
R1 (ohms)
R2(ohms)
C1(microfarad) C(microfarad) D= ω*C*R
RESULT:
Thus unknown capacitance and its dissipation factor were found using
Schering Bridge.
DEPT OF EEE
Page 13
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-6
STRAIN-GAUGE TRANSDUCER
AIM:
To measure strain due to applied loads, using resistance strain-gauge
transducer.
APPARATUS:
1. Strain gauge module
2. Weights
3. Multimeter
CIRCUIT DIAGRAM:
THEORY:
Resistance strain-gauge transducers are bonded to the surface of
structured members under list to sense the elongation/strain under applied
loads. It depends upon the fact that the resistance (R = ρ.L/A) changes under
elongation. But the change in resistance is small. For this reason, strain-gauges
are connected in the arms of a bridge. The detector used in the bridge will show
null deflection with out load. But under loads, the resistance changes which
result in deflection in the detector. Deflection in the meter is a measure of
change in resistance.
In this equipment, on a mild steel flat, two single element bakelite base
strain-gauges with nominal value of resistance 120Ω are mounted with the help
of adhesive cement. One of the gauges is on the top surface of mild steel is on
the bottom surface.
DEPT OF EEE
Page 14
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
PROCEDURE:
1.
2.
3.
4.
5.
Ensure that the instrument is switched off.
Connect the transducer to panel by cable provided.
Potentiometer marked Ex. Adjustment may be any where.
Switch on the main supply of the instrument.
Adjust the excitation voltage using Multimeter and Ex. Adj. trimpot to 5
volts. Measure this voltage between Red and Black terminals on panel.
6. Select 2 arm/4 arm configuration using switch provided.
7. Now with the help of Coarse and Fine potentiometer adjust meter
reading to zero.
8. Now apply gentle pressure by hand on the cantilever beam. The meter
will show some reading. If you apply force in upward direction, the
meter will show negative reading.
9. Now the setup is ready for experiment.
10. Put weight of 500gm. in weight pan. Note down the reading. Add
weights in the weight pan in steps of 500gm. and note down
corresponding readings.
OBSERVATION:
S.n
o
Weight
(load)g
ms
Eout
Ascendin
g
Eout
Desce
nding
Average
Eout
Stres
s
Strai
n
*E-5
Eout
Erro
(Calcu.)
r
CALCULATIONS:
1. Length of the cantilever from center of Gauge to the loading hook center
= L =19cms.
2. Thickness of the cantilever = t =0.4cms
3. Width of the cantilever = b =3cms.
4. Modulus of Elasticity for Mild steel = 2*106 Kg / Cm2
5. Gauge factor = 2
Now
Stress = M/Z, where M= Length of cantilever (L) * Applied load (Kg)
Z= 1/6 bt2
Strain = Stress / Modulus of Elasticity
= Stress / 2*106
DEPT OF EEE
Page 15
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
ΔR / R = Gauge factor * Strain
EOutput = EExc.* (ΔR / R) Volts
Note that, this calculations is for 4 Arm Bridge and when we are using 2 arm
bridge configurations, whatever theoretical answer, is to be divided by 2.
PRECAUTIONS:
1. Ensure cantilever assembly is properly fixed on the table.
2. Disconnect the transducer from the panel after completing experiment.
3. Do not tamper strain gauge on cantilever.
RESULT:
Thus the measurement of strain due to applied loads, were found using
resistance strain-gauge transducer.
DEPT OF EEE
Page 16
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-7
MEASUREMENT OF UNKNOWN CAPACITANCE
BY USING DESAUTY’S BRIDGE
AIM: To measure the unknown capacitance by using Desauty‟s bridge.
APPARATUS:
1. Head phones
2. Desauty‟s bridge circuit
3. Patch cards
CICUIT DIAGRAM:
PHASOR DIAGRAM:
DEPT OF EEE
Page 17
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
THEORY:
The bridge is the simplest method of comparing two capacitances. The
balance can be obtained by varying either R3 or R4 in this bridge. The
advantage of this bridge is its simplicity. But this advantage is nullified by the
fact that it is impossible to obtain balance if both the capacitors are not from
free dielectric loss. Thus with this method on loss less capacitor like air
capacitors can be compared. In order to make measurements on imperfect
capacitors i.e. capacitors having dielectric loss. The modified Desauty‟s bridge
is used. By using this modified bridge if the dissipation factor of one of the
capacitors is known, the value for the other can be determined. This method
doesn‟t give accurate results for dissipation factor since its value depends on
difference of quantities R1R4 / R3 and R2.
PROCEDURE:
1.
2.
3.
4.
5.
Connections are made as per the circuit diagram.
Supply is given across „a‟ and „c‟.
Set capacitance of C1 to a particular value.
Vary the resistances such that no sound is heard in detector.
Repeat the same for different settings of C1.
THEORITICAL CALCULATIONS:
Z1Z4 = Z2Z3
E1 = E 2
E3 = E 4
[1/ (-jωC1)] * R4 = [1/ (-jωC2)] * R3
C2 = (R3 / R4)
TABULAR COLUMN:
S.NO.
C1 (µF)
R3 (Ω)
R4 (Ω)
Unknown capacitance
Average
C2 = (R3 / R4)* C1 (µF) Capacitance
(µF)
RESULT:
DEPT OF EEE
Page 18
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
The unknown capacitance has been measured by using Desauty‟s
bridge.
EXPERIMENT-8
KELVIN’S DOUBLE BRIDGE
AIM: To determine the unknown resistance of a resistor (low resistance) using
Kelvin Double Bridge.
APPARATUS:
1.
2.
3.
4.
Kelvin‟s Double Bridge
Sensitive Galvanometer
Battery (or) DC source
Four terminal resistors, Two terminal resistor, cable
CIRCUIT DIAGRAM:
PROCEDURE:
1. Give supply to the terminals marked by „Battery‟ from the D.C source
(or) battery.
2. Connect the galvanometer to the terminal marked “Galvanometer”.
3. Connect the unknown resistor to the standard arm.
4. Press the galvanometer key marked „INITIAL‟ and notes the deflection.
If the deflection is high adjust the variable arm. If the deflection is small,
release „INITIAL‟ key and press FINAL key adjust slide wise dial until
the deflection is zero.
5. The unknown resistance can be calculated using the formula,
X = (milliohm decade value + slide wire milliohm value) *
Range Multiplier
DEPT OF EEE
Page 19
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
RESULT: Thus the resistance of an unknown resistor by using Kelvin‟s
Double Bridge was found.
DEPT OF EEE
Page 20
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-9
MEASUREMENT OF UNKNOWN RESISTANCE
BY USING WHEATSTONE’S BRIDGE
AIM: To determine the resistance by using the Wheatstone‟s bridge.
APPARATUS:
1. Resistors (200 Ω / 1.5A) – 1
(350 Ω / 1.2A) – 1
(29 Ω / 4.1A) – 2
2. Voltmeter (0-300V) MC – 1
3. Ammeter (0-10A) MC – 1
CIRCUIT DIAGRAM:
THEORY:
Wheatstone bridge is used for measuring medium resistance (1 Ω - 0.1M
Ω). It has four sensitive arms, consisting of resistances together with a source
of EMF and a null detector usually a galvanometer or other sensitive current
meter. It contains two fixed arms called ratio arms. One is known resistance
and other is standard resistance which can be varied.
The current through the galvanometer depends on the potential
difference between points „b‟ and„d‟. The bridge is said to be balanced when
there is no current through the galvanometer or when the potential difference
across the galvanometer is zero.
PROCEDURE:
1. Make the connections as per the circuit diagram.
2. Keep the resistance in maximum position.
3. Switch on the supply.
DEPT OF EEE
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
4. Vary the resistance „S‟ till zero current flows in the ammeter.
5. Measure the effective resistance „S‟ with multimeter.
THEORITICAL CALCULATIONS:
When bridge is balanced,
I1 P = I2 R --------------→ (1)
I1 = I3 = E / (P+Q) -----→ (2)
I2 = I4 = E / (R+S) -----→ (3)
From (1), (2) & (3)
I1P = EP / (P+Q)
I2R= ER / (R+S)
EP / (P+Q) = ER / (R+S)
R= PS / Q
RESULT:
The unknown resistance has been determined by using the Wheatstone‟s
bridge.
Resistance(Ω)
DEPT OF EEE
Theoretical Values (Ω)
Practical Values (Ω)
Page 22
G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-10
ANDERSON’S BRIDGE
AIM: To determine the self inductance of a coil by Anderson bridge
APPRATUS: Anderson Bridge
Head Phones
Galvanometer
Probes
CIRCUIT DIAGRAM:
PROCEDURE: D.C balance
1. Make the connections as shown in the figure, with DC supply,
Galvanometer and one unknown inductance.
2. Adjust „r‟ dial to 0Ω.
3. Now, adjust „R‟ to same value and press the galvanometer.
4. Use resistance dial S only for fine balance in the galvanometer and note
the value of R.
AC balance with head phones:
1. Replace the DC supply with AC supply of 1KHZ.
2. Replace galvanometer with head phones.
3. Set the standard capacitor „C‟ at position 0.1μFand adjusts the resistance
dial „r‟ to minimize the sound in the head phone.
4. Note the value of r, R and C.
5. Now calculate the value of unknown inductance using the formula
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
L = CR (Q+2r)
6. Repeat the experiment with another value of unknown inductance and
Capacitor C.
EXAMPLE:
R=46 OHMS
S=0.2 OHMS
P=Q=1000 OHMS
C=0.1µF
R=4400 OHMS
L=C*R(Q+2r)
=0.1E-6*46*9800
=45mH
RESULT:
Thus the self inductance of a coil was determined by using Anderson‟s
Bridge.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-11
CAPACITIVE PICK-UP
AIM: To calibrate capacitive pick-up.
APPARATUS: Capacitive Transducer
CIRCUIT DIAGRAM:
PROCEDURE:
1. Connect the capacitive pick-up to the input socket on front panel.
2. Keep the input angular displacement to zero position.
3. Check for zero reading on meter. Otherwise by operating potentiometer
marked MIN, obtain zero reading for zero angular position of the shaft.
4. Now turn the shaft of the capacitive pick-up full clockwise position in a
gentle manner corresponding to 170º by operating knob MAX, if
required again check zero reading.
5. Note down the readings corresponding to input angular displacement,
and indicated angular displacement on the meter. Enter the readings in
the table.
6. Plot the input and output readings on X-axis and Y-axis on graph. The
following points should be noted.
(a) There is a lot of non-linearity of the indicated Vs actual reading.
The reason is the non-linearity of 0 and C of the ganged
condenser.
(b) This method of angular displacement is free from mechanical
friction (neglecting the friction in the ball bearings of the shaft).
This is a advantage over potentiometer method.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
(c) The effect of the cable capacitance can be observed by playing
with the wires leading to the capacitive transducer. When wires
are taken away from each other„t‟ meter reading increases
indicating that effective „C‟ has decreased.
PRECAUTIONS:
1. If you touch the metallic plate on which the capacitor is mounted the
oscillations will stop and meter reading will negative.
2. Keep the pick-up free from dust particles etc.
3. If in any way the stator and rotor plates are shorted together, the
oscillations will not start. Under this condition check for a short between
stator & rotor plate by means of multimeter. Remove the short and then
circuit will be ready for use.
OBSERVATIONS OF WAVEFORMS:
1. Connect terminal TP-1 to live terminal of C.R.O and ground of the
instrument to ground of C.R.O. Then at terminal TP1 you can observe a
square waveform variable in frequency as the shaft rotates.
2. At terminal TP-2, output of the amplifier is observed. Again square
wave form is observed.
3. At terminal TP-3, constant pulse width, constant height pulses variable
in frequency are observed. This output is fed to meter finally.
TABULAR COLUMN:
S.No.
Input Angular
Displacements
(deg)
Meter
Reading(deg)
% Error
RESULT: Capacitive Transducer is calibrated and waveforms at different
terminals were observed.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-12
LINEAR VARIABLE DIFFERENTIAL TRANSFORMER
AIM:
1. To determine the characteristics of LVDT.
2. To calibrate LVDT.
APPARATUS:
1. Excitation power source.
2. LVDT kit.
CIRCUIT DIAGRAM:
PROCEDURE:
1. Connect the transducer to the input socket on front panel.
2. The magnetic core may be displaced using thumb wheel, so that the
pointer on the brass rod coincides to zero, using potentiometer marked
MIN on panel.
3. Now if the core is displaced by a known amount and the meter readings
can be entered in the table.
4. Plot the graph of input displacement (X-axis) Vs output indication (Yaxis).
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
TABULAR COLUMN:
S.No.
Input
Displacement Xaxis (mm)
Meter Reading
%Error
PRECAUTIONS:
1. Initial zero linearity of the output variations Vs input variations.
2. Move the core gently.
RESULT: LVDT was calibrated and the waveforms at different terminals are
observed.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-13
MEASUREMENT OF 3-Φ REACTIVE POWER
WITH 1-Φ WATTMETER
AIM: To measure three phase reactive power with single phase wattmeter.
APPARATUS:
1. Three phase supply
2. Three phase variac
3. Three phase Inductive load (415V, 10A)
4. Single phase wattmeter (300V, 10A,LPF)
5. Voltmeter (0-300V)
6. Ammeter (0-10A)
CIRCUIT DIAGRAM:
PROCEDURE:
1.
2.
3.
4.
5.
Make the connections as per the circuit diagram.
See that the variac is in the minimum output voltage position.
Switch on the supply with the help of TPST.
Vary the variac such that the voltmeter shows some reading (say 120V).
Note down the reading of wattmeter.
Wattmeter reading W = Vbc Ia cos (90-Φ)
= VL IL sinΦ
Reactive Power
= √3 W= √3 VL IL sinΦ
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
PHASOR DIAGRAM:
Vab
Vb
90-Φ
Ia
Va
Φ
Vc
RESULT:
Multiplying the wattmeter reading with √3 gives you the reactive power
consumed by the load.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-14
CROMPTON TYPE DC POTENTIOMETER
AIM: To calibrate PMMC ammeter & PMMC Voltmeter using Crompton type
DC Potentiometer.
APPARATUS: DC Potentiometer
PMMC Ammeter
PMMC Voltmeter
Volt Ratio Box
Standard cell
Battery
CIRCUIT DIAGRAM:
STANDARDISING THE POTENTIOMETER
PROCEDURE:
1. Connect the Galvanometer, standard Cell and Battery to their
appropriate terminals on the Standard Cell and Battery.
2. Set the potential dials to the exact voltage of the standard cell.
3. Press the STANDARDISE key and obtain a balance on the
galvanometer by rotating the battery rheostats (Coarse and Fine).
4. Galvanometer should no deflection with STANDARDISE key pressed.
Then the potentiometer has been standardized for use.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
CALIBRATION OF PMMC VOLTMETER
1. Connect the RPS, voltmeter to the primary of the Volt Ratio Box, with
proper polarity.
2. Connect the secondary terminals (marked 1.5V) to the „TEST‟ terminals
of the potentiometer. Other connections need not be disturbed.
3. Adjust the RPS to a position such that voltmeter reads say 4V.
4. Press the TEST key and obtain the balance on the galvanometer by
changing the setting of the potential dials.
5. Note the readings of the potential dials.
Ex. Input terminals used for volt ratio box E & 150V
Potentiometer reading
= 0.042V
Input voltage
=
(150/1.5)0.042 = 4.2v
TABULAR COLUMN:
S.NO
Measured
value
Actual value=measured
value/actual value
Error
%error
CALIBRATION OF PMMC AMMETER
CIRCUIT DIAGRAM:
PROCEDURE:
1. Connect the circuit as per the circuit diagram.
2. Make other connections as usual.
3. Vary the RPS such that ammeter shows some readings say (7.5A).
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
4. Standardize the potentiometer and measure the unknown potential
across the shunt potential terminals as usual.
5. The value of current flowing is then found by dividing the measured
potential in volts by the resistance of shunt in ohms.
Ex. By using potentiometer shunt of 0.1Ω
Potentiometer reading = 0.7545V
Current flowing = 0.7545/0.1 = 7.545A
%Error = 6.66
RESULT: PMMC Ammeter and PMMC Voltmeter were calibrated using DC
Potentiometer.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
EXPERIMENT-15
MEASUREMTNT OF 3-Ø POWER WITH 1- Ø WATTMETER & 2 C.Ts
AIM: To measure 3-Ø power with 1-Ø wattmeter & 2 CT‟s.
APPARATUS:
2 CT‟s
Ammeter
Ammeter
3 Rheostats
Wattmeter
Voltmeter
- (0-100)/5A
- (0-10) A
- (0-2) A
-10Ω/9A
- (150V, 10A, UPF)
- (0-200) V
CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as per the circuit diagram.
2. By varying the variac, apply voltage (say 100V).
Power consumed by the load = C.T ratio * wattmeter reading (watts)
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
PHASOR DIAGRAM:
Vb
Ia
Ia-Ib
Ib
Va
Φ
Vc
-Vb
Vab
VERIFICATION:
Power consumed by the 3-Ø load = √3 * VL * IL = 288 watts
Reading on the wattmeter, W =150 watts
Power as per the wattmeter reading = W * C.T.R
=150*2= 300 watts
RESULT: Thus the measurement of 3-phase power with single phase
wattmeter and 2 C.Ts.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
GLOSSARY
CALIBRATION OF ENERGY METER
1. CALIBRATON: Comparing with the reference meter, so that we can
try to reduce the losses.
2. CREEPING: It is a error, in some meters a slow but continuous rotation
is obtained even when there is no current flowing through the current
coil & only pressure coil is energized. This is called creeping.
3. CAUSES FOR CREEPING:
a. Over compensation
b. Over Voltage
c. Vibrations
4. 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 loading
(or) fictitious loading is done. Phantom loading consists of supplying the
pressure circuit from a circuit required normal voltage & current from a
separate low voltage supply. Phantom loading is to test meters having a
large current ratings for which loads may not be available in laboratory.
This also reduced power losses during testing.
5. METER CONSTANT: The number of revolutions made per KWH.
6. EMF GENERATED IN THE DISC:
e=K*Ф*n
Ф=flux of the permanent magnet
K=constant
n=speed of the rotation
7. In induction type energy meter, compensation for static friction is
provided by shading bands which are actuated by to provide a constant
torque irrespective of load.
8. In induction type wattmeter, the meter can be reversed by reversing the
potential coil terminals or current coil terminals.
9. If an induction type energy meter runs fast, it can be slowed by adjusting
the position of braking magnet and making it more away from the centre
of the disc.
CALIBRATION OF SINGLE PHASE POWER FACTOR METER
1. Power factor cosФ=P/(VI)
2. Power factor meters also having current coil and potential coil like
wattmeter.
3. The current circuit carries the current in the circuit in the power factor is
to be measured.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
4. Pressure circuit is connected across the circuit whose power factor is to
be measured and is split into two parallel paths. One is inductive and
other is non-inductive.
5. The direction of the instrument depends upon the phase difference
between main current and currents in the two paths of potential coils. i.e.
phase angle.
6. There are two types of power factor meters
a. Electrodynamometer type PF meter
b. MI type PF meter
ELECTRODYNAMOMETER TYPE PF METER:
There are two identical pressure coils (A, B), A is a pure resistance coil
and B is high inductive coil.
This is high accurate.
MI Type PF meter:
There are two categories depending on whether the operation of
instrument upon a rotating magnetic field or number of alternating fields.
ADVANTAGES:
a. Working forces are large as compared to electrodynamometers
b. Scale can extended over 360°
c. Simple & robust in construction and is cheap
DISADVANTAGES:
a. Errors are introduced in these meters owing to losses in iron parts. The
losses are depends upon the load, frequency.
b. Less accurate than electrodynamometer type meter.
c. Calibration of these instruments is appreciably affected by variations in
supply frequency and voltage waveform.
MEASUREMENT OF 3-Ф REACTIVE POWER
WITH 1-Ф WATTMETER
1. Reactive power Q = VI sinФ
2. Reactive power serves as a check on power factor measurements. Since
ratio of reactive power to active power is tanФ= Q/P
3. Varmeter is volt ampere reactive meter. (Electrodynamometer type).
4. Varmeters don‟t read correctly if harmonics are present or if the
frequency is different from that used when calibrating the instrument.
5. In measurement of 3-Ф reactive power with 1-Ф wattmeter, the current
coil of the wattmeter is connected in one line and pressure coil the other
two lines. Current through the current coil is I2 and voltage across the
pressure coil is V13.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
6. Reading of the wattmeter is V13 I2 cos(90+Ф) = √3 * VI cos (90+ Ф)=
- √3VI sin Ф.
7. Total reactive volt amperes of the circuit Q= 3VI sin Ф
8. Phase angle = Ф=tan-1(Q/P).
CROMPTON TYPE D.C POTENTIOMETER
1. The Crompton type potentiometer is also called laboratory type
potentiometer.
2.
Basically a potentiometer is a null type instrument and it is an
instrument designed to measure an unknown voltage by corresponding it
with a known voltage. (Supplied by a standard cell or reference source).
3.
Since a potentiometer measures voltages, it can also be used to
determine current simply by measuring the voltage drop produced by the
unknown current passing through a known standard resistance.
4.
STANDARDISATION: This is a process of adjusting the
working current so as to match the voltage drop across a portion of
sliding wire against a standard reference source is known as
standardization.
5.
Standardization of potentiometers is done in order that, they
become accurate and direct reading.
6.
Potentiometer is extensively used for a calibration of voltmeters,
ammeters and wattmeters. Also used for measurement of current, power
and resistance. Since it is a D.C device, the instruments to be calibrated
must be D.C MI or electrodynamometer type.
7.
The potentiometer method of measurement of resistance is
suitable for measurement of low resistances.
CALIBRATION OF VOLTMETER:
The fore most requirements in this calibration process is that a
suitable stable D.C voltage supply is available since any changes in the
supply voltage will cause a corresponding change in the voltmeter
calibration.
2.
For accuracy measurements, it is necessary to measure voltages
near the maximum range of the potentiometers, as far as possible.
1.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
3.
Two rheostats are used one for coarse adjustments and another
for fine adjustments.
CALIBRATION OF AMMETER:
1.
A standard resistance of suitable value and sufficient current
carrying capacity is placed in series with the ammeter under calibration.
2.
The voltage across the standard resistor is measured with the help
of potentiometers and the current through the standard resistance can be
computed.
I = V/R
LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT)
1. Mostly widely used inductive transducer to translate the linear motion
into electrical signals in LVDT.
2. This transformer consists of one primary and two secondary (having
equal no. of turns) winding.
3. The two secondary windings are identically placed on either side of the
primary winding.
4. The primary winding is supplied from A.C source and the output voltage
of secondary-1 is ES1 and the output voltage of secondary winding-2 is
ES2.
5. The output voltage of the transducer =E0 = ES1~ES2, at null position
ES1=ES2.
ADVANTAGES:
1. High range for measurement of displacement (1.25mm to 250mm)
2. Friction less (between coil and core), having infinite mechanical life.
3. Electrical isolation
4. For outputs no need of amplification and high sensitivity.
5. Rugged construction, low hysterisis, low power consumption.
DISADVANTAGES:
1. Sensitive to stray magnetic fields.
2. Performance affected by vibrations.
3. Dynamic response is limited mechanically by the mass of the core &
electrically by frequency of applied voltage.
4. Temperature affects the performance.
CAPACITIVE PICK-UP
1. Pick-up is also called transducer. Transducer is a device which converts
the non electrical quantity into electrical quantity.
2. Principle in the capacitive pick-up is the change of capacitance which
may cause by
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
a. Change in overlapping area (A).
b. Change in distance between plates (d).
c. Change in dielectric constant.
C = ЄA/d = (Єr*Є0*A)/d
Є = Єr*Є0 = permittivity of medium
Єr= relative permittivity of medium
Є0= permittivity of free space = 8.85 * 10-12
3. These changes caused by physical variables like displacement, force &
pressure, dielectrical constant (in liquids and gases).
4. Capacitive transducer used for measurement of linear displacement.
5. Output impedance of a capacitor transducer is high, so a careful design
of the output circuitary.
XC = 1/(2ΠfC)
ADVANTAGES:
1. Require extremely small forces to operate.
2. Extremely sensitive.
3. Having good frequency response.
4. Having high input impedance & therefore loading effects are minimum
resolution of order 2.5*10-3 mm.
5. Applications where stray magnetic fields render the inductive
transducers useless.
6. Force requirement is very small & hence small power to operate them.
DISADVANTAGES:
1. Metallic parts must be insulated from each other in order to reduce the
effects of stray capacitances, the frames must be earthed.
2. Non-linear behaviour, therefore guard rings must be used to eliminate
this effect. The guard rings are also must in order to eliminate the effect
of stray electric fields, especially when the transducers have a low value
of capacitance of the order power factor.
3. The output impedance of capacitive transducers tends to be high on
account to their small capacitance value.
4. The capacitance of a C.T. may changed on account of presence of
extraneous matter like dust particles & moisture.
5. It is a temperature sensitive.
6. Instrumentation circuitary used with these transducers is very complex.
STRAIN GAUGE TRANSDUCER
1. If a metal conductor is stressed or compressed, its resistance changes.
On account of this fact that both length and diameter of conductor
change. Also there is a change in the value of resistivity of the conductor
when it is strained & its properity is called piezoresistive effect.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
2. The change in the value of the resistance due to change in resistivity.
Therefore resistance strain gauges are also called piezoresistive gauges.
3. Strain gauges are used for measurement of strain and associated stress in
experimental stress analysis.
Resistance of Unstrained gauge R = ρ*L/A
4. Gauge factor Gf = (ΔR/R)/(ΔL/L) , where ΔL/L is strain (Є)
Types of strain gauges:
a. Unbounded metal strain gauges.
b. Bonded metal wire strain gauges.
c. Bonded metal foil strain gauges.
d. Vaccum deposited thin metal film strain gauges.
e. Sputter deposited thin metal strain gauges.
f. Bonded semiconductor strain gauges.
g. Diffused metal strain gauges.
5. Strain gauges are broadly used for two major types of applications:
a. Experimental stress analysis of machine & structures.
b. Construction of force, torque, pressure, flow & acceleration
transducers.
ANDERSON’S BRIDGE
1. This is a method is used to measure self inductance of a coil in terms of
standard capacitor.
2. The other bridges used for finding self inductances are
a. Maxwell‟s Inductance Bridge-Measures inductances by
comparison with a variable standard self-inductance.
b. Maxwell‟s Inductance Capacitance Bridge-Measures inductance
by comparing with a standard variable capacitance.
c. Hay‟s Bridge
d. Anderson‟s Bridge-Self inductance in terms of standard
capacitor.
e. Owen‟s Bridge-Measures inductance in terms of capacitance.
3. Balance condition for the Anderson‟s Bridge is I1 = I2 and I3 = IC + I4.
DESAUTY’S BRIDGE
1. Desauty‟s Bridge is used to measure the unknown capacitance by
comparing two capacitors (loss less capacitors like air capacitor).
2. The other bridges used for measuring the capacitance are
a. Schering Bridge-Measuring Capacitance & its dissipation factor.
This is used for measuring relative permittivity of dielectric
material.
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G. PULLAIAH COLLEGE OF ENGINEERING & TECHNOLOGY, KURNOOL
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINERING
b. High Voltage Schering Bridge-the supply is obtained from
transformer at supply frequency, here we are using vibration
galvanometer as detector.
3. The balance condition for Desauty‟s Bridge is I1 R1 = I2 R2
4. Relation between capacitors C1, C2 is C1 = C2 * (R2/R1)
WHEATSTONE BRIDGE
1. Wheatstone Bridge is used for measuring the change in resistance by
precise measurement of low resistance.
2. By using Wheatstone Bridge we can measure the resistances in the
medium range.
3. The change in the resistance gives the direct measurement of strain (if
meal conductor is stressed or compressed, then change in resistivity of
conductor due to strains).
4. We are going to measure the medium resistance by using these methods,
a. Ammeter-Voltmeter Method.
b. Substitution Method
c. Wheatstone Bridge Method
d. Carry Forster Bridge method
5. In Wheatstone Bridge these is no deflection meters.
KELVIN’S DOUBLE BRIDGE
1. Kelvin‟s Double Bridge method is used for measurements of low
resistances.
2. In the Kelvin‟s Double Bridge we are using the deflecting meter.
3. There are some methods used for measuring low resistance.
a) Ammeter Voltmeter method.
b) Kelvin‟s double bridge method.
c) Potentio meter method.
SCHERING BRIDGE
1. Schering Bridge is used for finding the capacitance of a capacitor and its
dissipation factor.
2. The balanced condition for Schering Bridge is Z1Z4 = Z2Z3
3. Schering Bridge is also used for measuring the leakage resistance.
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