BEng (Hons) in Electrical and Electronic Engineering

1. EEEC6430312
Measurements and Instrumentation
Faculty of Engineering and Computer Technology
Laboratory Manual
Lecturer: Ravandran Muttiah BEng (Hons) MSc MIET
Year/Semester: Year 2 / Semester 1
Academic Session: 2020/2021
The information in this documentis important and should be noted by all students undertaking the
Bachelor of Engineering (Honours) in Electrical and Electronic Engineering
Approved by Coordinator: Endorsed By Dean:
------------------------------------------ __________________

2. AIMST University Faculty of Engineering and Computer Technology
BEng (Hons) in Electrical and Electronic Engineering Measurements and Instrumentation 1
Mini Project 2 - Wien Bridge Oscillator
Theory
Wien bridge oscillator is one of the most popular types of oscillators used in audio and
sub-audio frequency ranges from 20 Hz to 20 KHz. This type of oscillator is simple in
design, compact in size, and remarkably stable in its frequency output. Furthermore, its
output is relatively free from distortion and its frequency can be varied easily. However,
the maximum frequency output of a typical Wien bridge oscillator is only about 1 MHz.
This is also, in fact, a phase-shift oscillator.
The Wien bridge oscillator uses a feedback circuit consisting of a series RC circuit
connected with a parallel RC of the same component values producing a phase delay or
phase advance circuit depending upon the frequency. At the resonant frequency 𝑓r the
phase shift is 0
o
. Consider the circuit as shown in figure 1.
Figure 1: Wien bridge
A Wien bridge oscillator is a type of electronic oscillator that generates sine waves. It can
generate a large range of frequencies. The oscillator is based on a bridge circuit originally
developed by Max Wien in 1891 for the measurement of impedances. The bridge
comprises four resistors and two capacitors. The oscillator can also be viewed as a
positive gain amplifier combined with a bandpass filter that provides positive feedback.
Automatic gain control, intentional non-linearity and incidental non-linearity limit the
output amplitude in various implementations of the oscillator. The circuit shown in figure
2 depicts a once-common implementation of the oscillator, with automatic gain control.
𝑅1 𝐶1
𝑅2 𝐶2
𝑅1 = 𝑅2 𝐶1 = 𝐶2
High Pass Filter Stage
Low Pass
Filter Stage
𝑉in
𝑉out

3. AIMST University Faculty of Engineering and Computer Technology
BEng (Hons) in Electrical and Electronic Engineering Measurements and Instrumentation 2
Under the condition that 𝑅1 = 𝑅2 = 𝑅 and 𝐶1 = 𝐶2 = 𝐶, the frequency of oscillation is
given by,
𝑓r =
1
2π𝑅𝐶
and the condition of stable oscillation is given by,
𝑅b =
𝑅f
2
Objectives
The objective of this experiment is to become acquainted with Wien bridge oscillator
circuit. Demonstrate your ability to design and construct the Wien bridge oscillator
circuit and to view the function of the circuit.
The Wien bridge oscillator circuit diagram is shown in figure 2 to how you can make an
oscillation circuit. A Wien bridge oscillator circuit is required to generate a sinusoidal
waveform of 5.2 KHz.
Figure 2: Wien bridge oscillator
+
−
A
𝑅1
10.2 KΩ
𝐶1
3 nF
𝑅3
𝑅4
47 KΩ
𝑉out = 5.2 KHz
100 KΩ
𝑅2
10.2 KΩ
𝐶2
3 nF
Op Amp

4. AIMST University Faculty of Engineering and Computer Technology
BEng (Hons) in Electrical and Electronic Engineering Measurements and Instrumentation 3
Specification
Operational Amplifier 741
2 Capacitors 3 nF
2 Resistors 10.2 KΩ
Resistor 100 KΩ
Resistor 47 KΩ
It must be able to measure the audio frequency and must able to designs the long range of
frequencies.
The Function of Wien Bridge Oscillator Circuit
Then for oscillations to occur in a Wien bridge oscillator circuit the following conditions
must apply:
• With no input signal a Wien bridge oscillator produces continuous output oscillations.
• The Wien bridge oscillator can produce a large range of frequencies.
• The Voltage gain of the amplifier must be greater than 3.
• The RC network can be used with a non-inverting amplifier.
• The input resistance of the amplifier must be high compared to R so that
the RC network is not overloaded and alter the required conditions.
• The output resistance of the amplifier must be low so that the effect of external
loading is minimised.
• Some method of stabilizing the amplitude of the oscillations must be provided. If the
voltage gain of the amplifier is too small the desired oscillation will decay and stop. If
it is too large the output will saturate to the value of the supply rails and distort.
• With amplitude stabilisation in the form of feedback diodes, oscillations from the
Wien Bridge oscillator can continue indefinitely.
Report
Write a laboratory report on this project.
(1) Explain in detail about the theory and their method of calculations of Wien bridge
for the designed circuit with the component values.
(2) Discuss the obtained results of oscillations and how it was achieved and state if any
improvements can be made.
(3) Prepare slides for presentation and demonstration of this project.