Electrical & Electronic Measurements : AC & DC Bridges

By Yash Bansal|Updated : July 13th, 2021

 In this article, you will find the study notes on Bridges which will cover the topics such as Maxwell’s inductance bridge, Maxwell’s inductance-capacitance bridge, Hay’s bridge, Anderson’s bridge, Owner's bridge, De-Sauty Bridge, Wein’s Bridge, D.C Potentiometer & A.C Potentiometer etc.

AC Bridges: AC bridges are used to measure self-inductance, mutual inductance, capacitance and frequency.

                                                                         

In this article, you will find the study notes on Bridges  which will cover the topics such as Maxwell’s inductance bridge, Maxwell’s inductance-capacitance bridge, Hay’s bridge, Anderson’s bridge, Owne’s bridge, De-Sauty Bridge, Wein’s Bridge, D.C Potentiometer & A.C Potentiometer etc.

AC Bridges: AC bridges are used to measure self-inductance, mutual inductance, capacitance and frequency.

Types of Sources

  1. At low frequency, the power line is used as a source.
  2. At high frequency, the electronic oscillator is used as a source

Types of Detectors

  1. Vibration galvanometer at low power frequency and audio frequency (up to 1000 Hz)
  2. Headphones at an audio frequency (250 Hz to 4 kHz)
  3. Tunable amplifier for frequency range (10 Hz to 100 kHz)

General Bridge Circuit

At balanced bridge 01-Bridges-and-potentiometers (1)

Magnitude condition 01-Bridges-and-potentiometers (2)

Angle condition 01-Bridges-and-potentiometers (3)

For balanced bridge both the magnitude

Measurement of Self Inductance

  • Maxwell’s inductance bridge
  • Maxwell’s inductance-capacitance bridge
  • Hay’s bridge
  • Anderson’s bridge
  • Owne’s bridge

Maxwell’s Inductance Bridge

Where, L1 = Unknown inductance of resistance R1

L2 = Variable induactance

R2 = Standard variable resistance

R3, R4 = Fixed non-inductance resistance

Maxwell’s Inductance - Capacitance Bridge

Q-factor, 01-Bridges-and-potentiometers (9)

Q-factor range 1 < Q < 10, for medium Q-coils

Where, R4 = Variable non-inductive resistance

C4 = Standard variable capacitance

Note: If C4 is fixed, then balanced bridge obtained as

  • Either by varying R2 and R4.
  • Put a resistance in series with L1 and varying R4.

Hay’s Bridge

01-Bridges-and-potentiometers (11)

Where, C4 = Standard capacitance

Q-factor 

for Q > 10 i.e., high Q-coils

L1 = R2R3C4

Anderson’s Bridge

01-Bridges-and-potentiometers (14)

Where, L1 = Unknown self-inductance with an internal resistance R1

R2, R3, R4 = Fixed standard non-inductive resistance

r = A variable resistance

C = A fixed capacitance

  • Anderson’s bridge is suitable for small Q-factor i.e., Q < 1.
  • It can also be used for the measurement of capacitance in terms of inductance.

Key Points

  • Maxwell’s bridge is used to measure the inductance of a low Q-inductor.
  • Hay bridge is used to measure the inductance of a high Q-inductor.
  • Inductance is measured in terms of capacitance, resistance by Anderson’s bridge.

Owen’s Bridge

01-Bridges-and-potentiometers (15)

Where, L1 = Unknown self-inductance with internal resistance R1

R2 = Variable non-inductive resistance

R3 = Fixed standard non-inductive resistance

C2 = Standard variable capacitor

C4 = Fixed standard capacitor

Measurement of Capacitance

The capacitance can be measured with the help of the following bridges

De-Sauty Bridge

01-Bridges-and-potentiometers (17)

01-Bridges-and-potentiometers (18)

Where C1 = Unknown capacitor

C2 = Standard capacitor

R3, R4 = Fixed non-inductive resistance

The de-Sauty bridge can be used for the measurement of either air-cored or gas-filled capacitance only (lossless capacitor).

Schering Bridge

Dissipation factor D1 = tan δ = ωC1r1 = ωC4 R4

Where C1 = Unknown capacitor with loss component r1

C2 = Fixed standard capacitor

R3 = Fixed standard non-inductive resistance

C4 = Variable capacitor

R4 = Variable non-inductive resistance

Key Points

  • High voltage Schering bridge is used for the determination of capacitance of insulators, capacitor bushings and insulating oil and other insulating materials.
  • Schering bridge is also used to measurement of relative permittivity of dielectric materials.
  • The Schering bridge is one of the most widely used AC bridges.
  • In order to measure the low value of capacitance Schering bridge is used.

Measurement of Frequency

Frequency by Wein’s bridge.

Wein’s Bridge

01-Bridges-and-potentiometers (21)

01-Bridges-and-potentiometers (22)

Frequency, 

For R1 = R2 = R

and C1 = C2 = C

and C1 = C2 = C

01-Bridges-and-potentiometers (23)

  • Wein’s bridge used as a notch Filter in harmonic distortion analyzer.
  • A frequency isolator in high-frequency oscillator and amplifier circuit.
  • A notch filter in a harmonics distortion analyzer where it is used to isolate and eliminate the fundamental frequency component from the output of the amplifier under test.

Comparison between Different Types of Bridges

 01-Bridges-and-potentiometers (25)

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Yash BansalYash BansalMember since Nov 2018
Content Manager (GATE)
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