AB-11
MAXWELL’S CAPACITANCE BRIDGE
ANALOG LAB
EXPERIMENT BOARD
Ver. 1.0
QUALITY POLICY
To be a Global Provider of Innovative and Affordable
Electronic Equipments for Technology Training by
enhancing Customer Satisfaction based on
Research, Modern manufacturing techniques and
continuous improvement in Quality of the products
and Services with active participation of employees.
An ISO 9001: 2000 company
94-101, Electronic Complex, Pardesipura INDORE-452010, India.
Tel.: 91-731-2570301 Fax: 91-731-2555643
AB-11
Email: info@scientech.bz Web: www.scientech.bz
Scientech Technologies Pvt. Ltd.
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AB-11
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AB-11
MAXWELL’S CAPACITANCE BRIDGE
AB-11
TABLE OF CONTENTS
1.
Introduction
4
2.
Theory
6
3.
Experiment
10
To study the operation of Maxwell’s Capacitance
Bridge and to measure the value of unknown
Inductance and Q factor.
Datasheet
12
4.
Warranty
14
5.
List of service Centers
15
6.
List of Accessories with AB-11
16
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AB-11
INTRODUCTION
AB-11 is a compact, ready to use MAXWELL’S CAPACITANCE
BRIDGE experiment board. This board is useful for students to understand
the working and operation of A.C. Bridges. It can be used as stand alone
unit with external DC power supply or can be used with SCIENTECH
Analog Lab ST-2612 which has built in DC power supply, AC power
supply, function generator, modulation generator, continuity tester, toggle
switches, and potentiometer.
List of Boards :
Model
Name
AB-01
AB-02
AB-03
AB-04
AB-05
AB-06
AB-07
AB-08
AB-09
AB-10
AB-14
AB-15
AB-16
AB-17
AB-18
AB-19
AB-21
AB-22
AB-23
AB-25
Diode characteristics (Si, Zener, LED)
Transistor characteristics (CB NPN)
Transistor characteristics (CB PNP)
Transistor characteristics (CE NPN)
Transistor characteristics (CE PNP)
Transistor characteristics (CC NPN)
Transistor characteristics (CC PNP)
FET characteristics
Rectifier Circuits
Wheatstone Bridge
Darlington Pair
Common Emitter Amplifier
Common Collector Amplifier
Common Base Amplifier
Cascode Amplifier
RC-Coupled Amplifier
Class A Amplifier
Class B Amplifier (push pull emitter follower)
Class C Tuned Amplifier
Phase Locked Loop (FM Demodulator & Frequency
Divider / Multiplier)
Multivibrator ( Monostable / Astable)
F-V and V-F Converter
V-I and I-V Converter
Zener Voltage Regulator
Transistor Series Voltage Regulator
Transistor Shunt Voltage Regulator
Differential Amplifier (Transistorized)
AB-28
AB-29
AB-30
AB-31
AB-32
AB-33
AB-41
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AB-42
AB-43
AB-44
AB-45
AB-51
AB-52
AB-53
AB-54
AB-56
AB-65
AB-66
AB-67
AB-68
AB-80
AB-81
AB-82
AB-83
AB-84
AB-85
AB-88
AB-89
AB-90
AB-91
AB-92
AB-93
AB-96
AB-97
AB-101
AB-102
AB-106
Operational Amplifier (Inverting / Non-inverting /
Differentiator)
Operational Amplifier (Adder/Scalar)
Operational Amplifier (Integrator/ Differentiator)
Schmitt Trigger and Comparator
Active filters (Low Pass and High Pass)
Active Band Pass Filter
Notch Filter
Tschebyscheff Filter
Fiber Optic Analog Link
Phase Shift Oscillator
Wien Bridge Oscillators
Colpitt Oscillator
Hartley Oscillator
RLC Series and RLC Parallel Resonance
Kirchoff’s Laws (Kirchoff’s Current Law & Kirchoff’s
Voltage Law)
Thevenin’s and Maximum power Transfer Theorem
Reciprocity and Superposition Theorem
Tellegen’s Theorem
Norton’s theorem
Diode Clipper
Diode Clampers
Two port network parameter
Optical Transducer (Photovoltaic cell)
Optical Transducer (Photoconductive cell/LDR)
Optical Transducer (Phototransistor)
Temperature Transducer (RTD & IC335)
Temperature Transducer (Thermocouple)
DSB Modulator and Demodulator
SSB Modulator and Demodulator
FM Modulator and Demodulator
………… and many more
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AB-11
THEORY
Alternating current Bridge methods are of outstanding importance for
measurement of electrical quantities measurement of inductance,
capacitance, storage factor, loss factor may be made conveniently and
accurately by employing a.c. bridge networks.
An a.c. bridge, in its basic form, consists of four arms, a source of
excitation and a balance detector. In an a.c. bridge each of four arms is
impedance, and the a.c. source and a detector sensitive to small alternating
potential differences.
The usefulness of a.c. bridge circuits is not restricted to the measurement of
unknown impedances and associated parameters like inductance,
capacitance, storage factor etc. These circuits find other application in
communication system and complex electronics circuits. Alternating
current bridge circuits are commonly used for phase shifting, providing
feedback paths for oscillators and amplifiers, filtering out undesirable
signals ad measuring the frequency of audio signals.
For measurement at low frequencies, the power line may act as the source
of the supply to bridge circuits. For higher frequencies electronic
oscillators are universally used as bridge source supplies. These oscillators
have the advantage that the frequency is constant, easily adjustable and
determinable with accuracy .The waveform is very close to a sine wave,
and their power output is sufficient for most bridge measurements.
Detectors most commonly used for a.c. bridges are:
a.
Head phones
b.
Vibration galvanometers
c.
Tuneable amplifiers detectors
Headphones are widely used as detectors at frequencies of 250 Hz and up
to 3 or 4 kHz. They are most sensitive detectors for this range
When working at a single frequency a tuned detector normally gives the
greatest sensitivity and discrimination against harmonics in the supply.
Vibration galvanometers are extremely used for power and low audio
frequency ranges. Vibration galvanometers are manufactures to work at
various frequencies ranging from 5 Hz to 1000 Hz but are most commonly
used below 200 Hz as below this frequency they are more sensitive that the
head phones.
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AB-11
Tuneable amplifiers detectors are the most versatile of the detectors .The
transistors amplifiers can be tuned electrically and thus can be made to
respond to a narrow bandwidth at the bridge frequency .The output of the
amplifier is fed to a pointer type instrument this detector can be used, over
a frequency range of 10 Hz to 100 kHz.
General equation for bridge balance:
Basic a.c. bridge circuit is shown below in fig.1
The four arm of the bridge are impedance Z1, Z2, Z3, Z4.
Basic A.C. bridge network
Fig.1
The condition for balance of bridge require that there should be no current
through the detector .This requires that the potential difference between
points b and d should be zero. This will be the case when the voltage drop
from a to b equals the voltage drop from a to d, both in magnitude and
phase. In complex notation we can, thus, write:
Also at balance,
E1 = E2
…………….(1)
I1Z1 =I2Z2
…………….(2)
I1=I3 =E/Z1+Z2
…………….(3)
I2=I4=E/Z2+Z4
…………….(4)
Substituting the value of I1and I2 in eq.2, we get
Z1Z4=Z2Z3
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…………….(5)
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AB-11
Eq.5 states that the product of impedances of one pair opposite arms must
equal the product of impedance of the other pair of opposite arms in
complex notation .This means that both magnitude and phase angle of the
impedance must be taken into account.
Two conditions must be satisfied simultaneously when balancing the a.c.
bridge
1.
2.
The first condition is that the magnitude of impedances satisfies the
relationship:
Z1 Z4=Z2Z3
…………….(6)
The second condition is that the phase angles of impedance satisfy
the relationship:
θ1+θ4=θ2+θ3
…………….(7)
The phase angles are positive for inductive impedance and negative for
capacitance impedance.
Measurement of self inductance by Maxwell’s capacitance bridge:
In this bridge, an inductance is measured by comparison with a standard or
variable capacitance.
Maxwell’s Capacitance Bridge
Fig.2
L1 =unknown inductance
R1 =effective resistance of inductor L1
R2, R3, R4= unknown non-inductive resistances
C4= standard capacitor
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AB-11
And writing the eq. for balance
(R1+jωL1)(R4/1+jωC4R4)=R2R3
………….(8)
R1R4+jωL1R4=R2R3+jωR2R3C4R4
…………….(9)
or
Separating the real and imaginary terms, we have
R1 =R2R3/R4
……………(10)
L1=R2R3C4
……………(11)
Q=ωL1/R1=ωC4R4
……………(12)
and
The expression for Q factor
Advantages of this bridge are :
1.
The frequency does not appear in any of the two equations i.e value
of L and R independent of the frequency.
2.
The Maxwell’s capacitance bridge is very useful for measurement of
a wide rage of inductance at power and audio frequencies.
Disadvantages :
The main disadvantage is the bridge is limited to measurement of low Q
coils (1<Q<10) thus for values of Q>10 the Maxwell’s bridge is unsuitable.
The Maxwell’s bridge is also unsuited for coils with a very low value of Q
(i.e. Q<1). Q value of this magnitude occur in inductive resistors or in R.F.
coil if measured at low frequencies .The difficulty in measurement occurs
on amount of labour involved in obtaining balance. Only medium Q coils
measurements are suited with the Maxwell’s capacitance bridge.
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AB-11
EXPERIMENT 1
Object :
To study the operation of Maxwell’s Capacitance Bridge and to
measure the value of unknown inductance and Q factor.
Apparatus Required :
1.
Analog board AB-11.
2.
DC power supply +12V from external source or ST-2612 Analog
Lab.
3.
Function Generator ST- 4064.
4.
Oscilloscope.
5.
Multimeter.
6.
2mm patch chords.
Circuit Diagram :
Circuit used to study the operation of Maxwell’s Capacitance Bridge and to
measure the value of unknown inductance is shown in fig3.
Fig.3
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AB-11
Procedure :
•
Connect +12V,-12V power supplies and gnd at their indicated position
from external source or ST-2612 Analog Lab.
1.
Adjust the pot in the minimum position so that the resistance R3
between the arm is minimum by measuring it with help of multimeter.
2.
Connect 10Vp-p, 1 KHz sine wave signal at the input Vin
(positive and negative terminal) of Maxwell’s Capacitance Bridge AB11 board.
3.
Connect the unknown inductor with 2mm patch cord with arm
consisting resistance R2.
4.
Now vary the resistance R3 with the help of pot till the null
position (or the first minimum sound position) is achieved.
5.
Now switch off the power supply and remove all the patch cord
and measure the resistance R3 with the help of multimeter.
6.
Calculate the value of unknown inductor using eq.11
7.
Calculate the value for Q factor by using eq.12
8.
Verify the result for calculation of Q factor using both the
formula in eq.12
9.
Verify the result for unknown value of resistance Rx1 by
measuring it with help of multimeter and calculating it using eq.10
10.
Repeat the process for different values of inductors.
Result :
The unknown value of Inductor L1, Resistance Rx1 and Q factor are ……
The unknown value of Inductor L2, Resistance Rx2 and Q factor are ....….
The unknown value of Inductor L3, Resistance Rx3 and Q factor are …….
Note :
1.
The value of inductor L1, L2 and L3 are 10mH, 20mH and 58.8mH.
2.
Small amount of error would be there due to component variations
and also due to human error.
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AB-11
DATASHEET
Scientech Technologies Pvt. Ltd.
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AB-11
Scientech Technologies Pvt. Ltd.
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AB-11
WARRANTY
1.
We guarantee the instrument against all manufacturing defects
during 24 months from the date of sale by us or through our dealers.
2.
The guarantee covers manufacturing defects in respect of indigenous
components and material limited to the warranty extended to us by
the original manufacturer, and defect will be rectified as far as lies
within our control.
3.
The guarantee will become INVALID.
a. If the instrument is not operated as per instruction given in the
instruction manual.
b. If the agreed payment terms and other conditions of sale are not
followed.
c. If the customer resells the instrument to another party.
d. Provided no attempt have been made to service and modify the
instrument.
4.
The non-working of the instrument is to be communicated to us
immediately giving full details of the complaints and defects noticed
specifically mentioning the type and sr. no. of the instrument, date of
purchase etc.
5.
The repair work will be carried out, provided the instrument is
dispatched securely packed and insured with the railways. To and
fro charges will be to the account of the customer.
DISPATCH PROCEDURE FOR SERVICE
Should it become necessary to send back the instrument to factory please
observe the following procedure:
1.
Before dispatching the instrument please write to us giving full
details of the fault noticed.
2.
After receipt of your letter our repairs dept. will advise you whether
it is necessary to send the instrument back to us for repairs or the
adjustment is possible in your premises.
Dispatch the instrument (only on the receipt of our advice) securely packed
in original packing duly insured and freight paid along with accessories and
a copy of the details noticed to us at our factory address.
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AB-11
LIST OF SERVICE CENTERS
1. Scientech Technologies P. Ltd.
90, Electronic Complex
Pardesipura,
INDORE – 452010
2. Scientech Technologies P. Ltd.
First Floor, 14, Uday Park,
NEW DELHI – 110049
3. Scientech Technologies P. Ltd.
New no.2, Old no.10, 4th street
Venkateswara nagar, Adyar
CHENNAI – 600025
4. Scientech Technologies P. Ltd.
202/19, 4th main street
Ganganagar,
BANGALORE- 560032
5. Scientech Technologies P. Ltd.
8,1st floor, 123-Hariram Mansion,
Dada Saheb Phalke road,
Dadar (East), MUMBAI –400014
6. Scientech Technologies P. Ltd.
988, Sadashiv Peth,
Gyan Prabodhini Lane,
PUNE – 411030
7. Scientech Technologies P. Ltd
SPS Apartment, 1st Floor
2, Ahmed Maooji Street,
Behind Jaiswal Hospital,
Liluah, HOWRAH-711204
W.B.
Scientech Technologies Pvt. Ltd.
Ph: (0731) 5202959
Email: info@scientech.bz
Ph.: (011) 26513912, 26864943
Fax: (011) 26864943.
Email: ndel@scientech.bz
Ph.: (044) 52187548, 52187549
Fax: (044) 52187549
Email: chennai@scientech.bz
Ph.: (080) 51285011
Fax: (080) 51285022
Email: bangalore@scientech.bz
Ph.: (022) 56299457
Fax: (022) 24168767
Email: stplmum@vsnl.net
Ph.: (020) 24461673
Fax: (020) 24482403
Email: pune@scientech.bz
Ph. +913355266800
E mail : kolkata@scientech.bz
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AB-11
LIST OF ACCESSORIES
1.
2mm patch cord (red)................................................................ 3 Nos.
2.
2mm patch cord (blue).............................................................. 2 Nos.
3.
2mm patch cord (black)............................................................ 3 Nos.
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