# Electrical & Electronic Measurements : AC & DC Bridges

By Yash Bansal|Updated : November 21st, 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

Magnitude condition

Angle condition

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,

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

Where, C4 = Standard capacitance

Q-factor

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

L1 = R2R3C4

Anderson’s Bridge

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

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

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

Frequency,

For R1 = R2 = R

and C1 = C2 = C

and C1 = C2 = C

• 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

You can avail of BYJU’S Exam Prep Online classroom program for all AE & JE Exams:

## BYJU’S Exam Prep Online Classroom Program for AE & JE Exams (12+ Structured LIVE Courses)

You can avail of BYJU’S Exam Prep Test series specially designed for all AE & JE Exams:

## BYJU’S Exam Prep Test Series AE & JE Get Unlimited Access to all (160+ Mock Tests)

Thanks

Team BYJU’S Exam Prep

Download  BYJU’S Exam Prep APP, for the best Exam Preparation, Free Mock tests, Live Classes.