Engr 261 – Circuits and Devices Lab
Experiment # 2 – Superposition, Thévenin Equivalent Circuit, Node Voltage and Mesh
Current Analyses
Purpose: This experiment exposes the students to simple DC circuits, with emphasis on the
experimental verification of Thévenin’s theorem, the principle of superposition, and the nodal
and mesh analyses. It also provides essential practice on using the MultiSIM program to
analyze DC circuits, and circuit analysis by applying the mesh current and node voltage
methods.
Experimental Procedure:
1. Node Voltages and Mesh Currents
Set up the oscilloscope. Calibrate the two oscilloscope probes using both Channels 1 and 2.
For the circuit shown in Figure 1:
Figure 1
a. Measure the actual values of the resistors. Compare with nominal values.
b. Construct the circuit shown in Figure 1, with a sinusoidal voltage source
V s (t ) = 5 cos( 2π 1000t ) . Use the built-in function generator with a sinusoidal input of
frequency 1kHz and amplitude of 5 V. Note: Period = 1/Frequency.
c. Display the node voltages of nodes 1 and 2 on the oscilloscope Channels 1 and 2. Make
use of what you observe to draw sketches and write equations for the two node voltages
as functions of time.
d. Set up and solve the nodal equations needed to determine the node voltages at 1 and 2.
e. Compare your results from parts c and d above.
f. What is the current in the 2-kΩ resistor?
g. Set up and solve the mesh current equations to determine the current in the 2-kΩ resistor.
h. Using Multisim calculate the node voltages of nodes 1 and 2, and the current in the 2-kΩ
resistor.
2. Superposition
Construct the following circuit in the laboratory:
Figure 2
a. Measure the actual values of the resistors. Compare with nominal values. (You may have
to combine resistors in parallel and/or series connection to obtain resistance values
needed in the circuit.)
b. Measure the magnitude and direction of the current in the 600-Ω resistor using the digital
multimeter.
c. Determine the same current by experimental measurements applying the superposition
principle (that is, measuring the current twice with each of the voltage sources “turned off,”
and “superposing” the results from these separate measurements of the current to
determine the resulting current when both sources are applied.)
d. Compute the current in the 600-Ω resistor using superposition.
e. Using Multisim, nodal analysis and mesh analysis, calculate the current in the 600-Ω
resistor.
f. Compare results from b, c, d, and e. Compute relative errors of measured currents and
explain discrepancies.
2. Thévenin Equivalent Circuit
Figure 3
a. Construct the circuit shown in Figure 3, with a source voltage V s (t ) = 5 cos( 2π 1000t ) . Use
the function generator with a sinusoidal input of approximate frequency 1kHz.
b. Measure the amplitude of the Thévenin Equivalent voltage VTH (the open circuit voltage
across the terminals.)
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c. Compute the Thévenin Equivalent voltage VTH.
d. Compare the measured and computed amplitudes of VTH.
e. Measure RTH by measuring the equivalent resistance across the open terminals with Vs
suppressed (replaced by a short).
f. Measure the Norton Equivalent current IN by measuring the short-circuit current (Isc) shown
in Figure 4.
Figure 4
Compute the Thévenin resistance as the ratio of the measured open circuit voltage to the
measured short circuit current.
h. Compute the theoretical value of RTH using any method.
i. Compare the values of RTH determined from parts e, g and h.
j. Draw the corresponding Thévenin Equivalent circuit.
k. Make use of your Thévenin Equivalent circuit to predict the voltage across the load resistor
for RL=500 Ω, 800 Ω, 1 kΩ, 1.5 kΩ, 1.6 kΩ, 1.7 kΩ, 1.8 kΩ, 2.0 kΩ, 3 kΩ, 4 kΩ, 5 kΩ, 6
kΩ, 7 kΩ and 8 kΩ. (See Figure 5.) You may use a decade box for RL.
g.
Figure 5
Measure the actual voltage across the load resistor in the circuit shown in Figure 5 for
each of the resistor values given in part k.
m. Prepare a graph of the power delivered to RL versus the value of RL. For what value of the
load resistor is the power maximum?
l.
LAB REPORT: Prepare a formal lab report following the required format. Please refer to
Evaluation Sheet on the next page.
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Engr 261 – Circuits and Devices
Lab Report #2 Evaluation Sheet*
Name:
Due Date:
Date Submitted:
Group Number: ______
Note: Lab reports will be prepared and submitted individually.
Organization and Structure
1. Introduction
2. Theoretical Background
3. Procedure
4. Results
5. Conclusion
6. Appendices
Content
Part 1: Nodal and Mesh Analyses
1. Experimental results
2. Computations
3. PSPICE Simulations
4. Comparison and error analysis
Part 2: Superposition
1. Direct Measurements and Superposition
2. Computations
3. Multisim, nodal and mesh analyses
4. Comparison and error analysis
Part 3: Thevenin’s Equivalent Circuit
1. Experimental Thevenin voltage and resistance
2. Computed Thevenin voltage and resistance
3. Results for different RL values
4. Graph for maximum power
5. Comparison and error analysis
Mechanics
1. Free of grammar, spelling and punctuation errors
2. Appropriate sentence structure
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Subtotals
Grand Total: ____________ out of 60.
Final Grade: ____________ out of 30.
*This evaluation sheet should be included in your lab report.
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Grading of Lab Reports
The following is a detailed description of the grading criteria for the lab report. For each category, a
description of the fulfilled elements is summarized for each assigned grade.
ORGANIZATION AND STRUCTURE:
Introduction
3 - Report has a title page with name of the student and name of group members, includes an evaluation
sheet, an introduction that clearly establishes the objectives of the experiment and describes of the
general approach of solution.
2 – Missing an appropriate title page, or missing an evaluation sheet, or has incomplete objectives and
general approach of solution.
1 – Missing two of the three items required above.
0 – Missing all the items required for this section.
Theoretical Background
3 – Gives a complete and concise discussion of all theoretical background of the experiment.
2 – Minor points missing in the discussion, or discussion not concise.
1 – Major/important points missing in the discussion of the theoretical background.
0 – No discussion of theoretical background, or discussion was copied verbatim from the handout or the
textbook.
Procedure
3 – Complete and concise description of procedure, including the apparatus and equipment used.
2 – Minor omissions in the procedure or list equipment used.
1 – Procedure is not clear, or contains incorrect steps.
0 – No procedure described, or procedure was copied verbatim from the handout
Results
3 – All observations and results are neatly summarized and presented using the most appropriate format
(tables, line graphs, etc.)
2 – Format used in summarizing some results not appropriate.
1 – Format used in summarizing most results not appropriate.
0 – Results not presented.
Summary and Conclusions
3 – Gives a concise description of how the experiment achieved, or did not achieve, the stated
objectives; Discusses sources of error and how they affect the results.
2 - Gives a concise description of how the experiment achieved, or did not achieve, the stated
objectives; Discusses sources of error but not how they affect the results.
1 – No discussion of how the experiment achieved (or did not achieve) the stated objectives, or the
sources of error not discussed.
0 – No summary and conclusions
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