Lab manual Notes of emft, Lab Reports of Electronics

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EE

Instrumentation & Measurements

Name: ______________________________________

Student ID: ______________________________________

Semester: Spring 2020

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Contents

Course Learning Outcomes........................................................................................................................vii Rules and Guidelines.................................................................................................................................viii List of Experiments......................................................................................................................................ix

Course Learning Outcomes A student who successfully fulfills the lab work requirements will have demonstrated the ability to: S. No. CLO Bloom’s Taxonomy Level Corresponding PLO

1. Use different type of sensors,

transducers, and electronic

measuring instruments.

P

Guided

Response

PLO-

Engineering Knowledge

2. Analyze different bridge circuits for

measurements of unknown values

of components.

P

Mechanism

PLO-

Investigation

3. Apply operational and

instrumentational amplifiers to

manipulate signals for

measurements.

P

Mechanism

PLO-

Investigation

4. Interface sensors to a digital system. P 3

Guided

Response

PLO-

Modern Tool Usage

5. Design and develop a project

according to given specifications.

P

Mechanism

PLO-

Design/Development of

Solutions

6. Effectively work in a team project. A

Valuing

PLO-

Individual and Teamwork

vii

Rules and Guidelines

1. Treat the instruments with care.
2. There must be at least two (2) people in the laboratory while working on live circuits.
3. Shoes must be worn all the times.
4. Report any damages to the equipment, hazards and potential hazards to the lab instructor.
5. Keep fluids, chemicals and meal away from the instruments and circuits.
6. Read the lab manual documentation prior to each lab meeting
7. Return the components to the correct shelf when used.
8. Before leaving the place the stools under the lab bench.
9. Before leaving the lab, turn off the power to all instruments.
10. Follow the lab instructions carefully. viii

Lab Rubrics for Non-Programming Courses  Lab Performance (5 Marks) 0 1 - 3 4 5 Student was unable to perform the required tasks. There was no attempt to make any arrangements to make up the lab. Student has partially implemented the required tasks. Student was able to perform the task but not very cleanly and precisely. Student performed the tasks cleanly and precisely.  Quality of Lab Report (3 Marks) 0 1 2 3 Student report is so incomplete and/or so inaccurate that it is unacceptable Student turned in an incomplete lab report with incomplete post-lab exercise. Student submitted a complete report and post-lab exercises with some lack of clarity. Student submitted a complete, neat and clean report with correct post-lab exercises.  Viva (2 Marks) 0 1 2 Student did not appear in the viva or has no idea of the theoretical concept of the experiment and its implementation. Student has unclear and weak concepts. Student has the required knowledge of the theoretical concepts along with the practical implementation. x

1 Lab 1-Measuring Unknown Resistance Using Wheatstone bridge 1.1 Objective

To study and implement the balanced and unbalanced Wheatstone bridge by using galvanometer.

1.2 Theory 1.2.1 Bridge Circuits Bridge circuits are used to convert impedance variations into voltage variations. One of the advantages of the bridge for this task is that it can be designed so the voltage produced varies around zero. This means that amplification can be used to increase the voltage level for increased sensitivity to variation of impedance. Another application of bridge circuit is in the precise static measurement of impedance. A basic type of bridge circuit is shown in figure 1, where four resistances are connected. A galvanometer or voltmeter is used to compare the potentials of points a and b of the circuit. If the current through the galvanometer is zero OR the potential difference across points a and b is zero then the bridge circuit is known as Balanced bridge circuit. In balanced bridge circuit the relation among the resistances is given as:

R 1 R 4 = R 2 R 3

1.2.2 Balanced Wheatstone bridge Wheatstone bridge is a simple bridge circuit of resistors, consisting of four resistors, with two branches in parallel and each branch with two resistors in series as shown in the figure below: Figure 1 -1: Wheatstone bridge Where, R1, R2 are resistors, R and Rs are also resistors and G is a galvanometer. The Wheatstone bridge is the most widely used circuit for precisely measuring resistance by the comparison method. Wheatstone bridge is actually invented by Samuel Hunter Christie during 1833 and Wheatstone bridge is named after Charles Wheatstone who popularized it in 1843. The Wheatstone bridge circuit is nothing more than two simple series-parallel arrangements of resistors connected between a voltage supply terminal and ground producing zero voltage difference when the two parallel resistor legs are balanced. A Wheatstone bridge circuit has two input terminals and two

Then a resistor Rs of known value is placed on the branch DC; whose is tuned, such that the bridge is balanced or no current flows through the galvanometer G. Now,

Let: Current flowing through the branch ABC = I^ 1 and through the branch ADC = I^ 2

Then, when the bridge is in balanced condition or no current flows through “G”: The Points B and D are in same potential or Voltage drop across the branch AB and AD is same, and also the voltage drop across the branch BC and DC is the same thus:

I 1 X R 1 = I 2 X R 1

And

I 1 X R 2 = I 2 X RS

Dividing the first equation by second we get:

R 1

R 2

R

RS

Thus the value of the unknown resistor R can be calculated using the formula:

R =

R 1

R 2

X RS

1.3.4 Application of Wheatstone bridge A Wheatstone bridge is also called Differential Resistance Measurer and is mainly used for measuring the value of an unknown resistor. It is also used in various electrical sensors like temperature sensor, light sensor etc. A Wheatstone bridge can also be supplied AC power and can be used to measure Inductance, Capacitance and Frequency when AC source is used with Wheatstone bridge. Figure 1-4: Application of Wheatstone bridge 3

1.3.5 Wheatstone bridge Light Detector A simplified Wheatstone bridge circuit is shown in Figure 1. In the figure, R1, R2 and R3 are precision, adjustable resistances and X is the unknown resistance. You are required to measure the unknown resistance X. Figure 1-5: Simplified Wheatstone bridge

R 1 X = R 2 R 3

X =

R 2 R 3

R 1

R 1 R 2 RX X

1. Connect the power supply and resistances as shown in figure 1.
2. Now vary resistances R3 until the volt-meter deflection is zero.
3. Now using the following formula, the unknown resistance X can be determined: 1.4 Equipment
   1. Galvanometer 4 Figure 1-6: Balanced Wheatstone bridge

1.7 Conclusion

1. Discuss different types of Bridges?

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2. What is the basic working principle of Wheatstone bridge?

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3. Why Wheatstone bridge is so commonly used?

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4. What is the main advantage of Maxwell Wien Bridge?

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5. Write down any three applications of Wheat stone bridge?

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Admittance: It is defined as the inverse of impedance. The SI unit of admittance is the siemens (symbol S). where, Z is the impedance, measured in ohms. Figure 2-2: Circuit diagram of Wheatstone bridge Accurate measurements of complex impedances and frequencies may be performed by using impedance measuring AC Bridges. There are number of bridges, which are called usually by their inventor’s name, to measure different types of impedances and frequencies.

Lx = R 2 R 3 C 1

Dissipation Factor D = w C 1 R 1

Where, w = 2πff

Lx  Unknown inductance

2.2.2 Maxwell Bridge The Maxwell Bridge is a complex impedance bridge to measure an unknown inductance in terms of a known capacitance. The complex balance equation yields two real equations. Using these two equations the unknown inductance and the resistor in series with it can be calculated as:

Rx =

R 2 R 3

R 1

Lx = R 2 R 3 C 1

2.3 Working principle of Maxwell Bridge The Maxwell Bridge measure an unknown inductance in terms of a known capacitance. One of the ratio arms has resistor and a capacitor in parallel, and it may now prove somewhat easier to write the balance equations using the admittance of arm 1 instead of its impedance.

ZX= Z 2 Z 3 Y 1 ------------- (1)

Where,

Z 2 = R 2

Z 3 = R 3

And

Y 1 = 1/ R 1 + jωCωCC 1

Substituting of these values in above equation (1)

ZX = RX + jw LX = R 2 R 3 ¿ + jw C 1 )

Separation of the real and imaginary terms

RX =

R 2 R 3

R 1

, LX = R 2 R 3 C 1

Figure 2-3: Maxwell Bridge for inductance measurement 2.4 Equipment

1. Galvanometer
2. DC Power Supply
3. Function Generator
4. Resistors
5. Variable capacitor
6. Inductor
7. Connecting wires 2.5 Procedure
8. Connect the circuit as shown in figure
9. Set the AC voltage supply to 10 Volts and frequency at 1 kHz.
10. Adjust the variable resistor and variable Inductor until current through the volt-meter/Galvanometer becomes zero. 3