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UNIVERSITY JF PJRTLAND
SchJJl Jf Engineering
EE271 Electrical Circuits Laboratory
Spring 2004
Dr. Aziz S. Inan and Dr. Joseph P. Hoffbeck
Lab Experiment #7: Transient Response of First-Order RL
and Second-Order RLC Circuits
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Transient Response of First-Order RL and Second-Order RLC Circuits | EE 271, Assignments of Microelectronic Circuits
Material Type: Assignment; Professor: Inan; Class: Electrical Circuits Laboratory; Subject: Electrical Engineering; University: University of Portland; Term: Spring 2004;
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UNIVERSITY J F P J RTLAND
Sch JJ l J f Engineering
EE271 Electrical Circuits Laboratory
Spring 2004
Dr. Aziz S. Inan and Dr. Joseph P. Hoffbeck
Lab Experiment #7: Transient Response of First-Order RL
and Second-Order RLC Circuits
Transient Response of First-Order RL and
Second-Order RLC Circuits
I. Objective
In this experiment, the students will make measurements and observations on the transient step response of simple RL and RLC circuits.
II. Procedure
PART 1: Step Excitation of First-Order RL Circuits
Pre-lab Assignment 1: A first-order inductive circuit is excited by a periodic pulse train as shown in Fig. 1. The values of the elements are given by R 1 =1 kΩ and L coil=15 mH respectively. Assuming the inductor to be ideal, calculate the time constant τ of this circuit. Approximately how long does it take for the inductor of this circuit to fully charge or discharge under pulse excitations? (Fully charge or discharge means the time it takes for the inductor current to reach approximately 99% of its final value.)
Fig. 1. First-order RL circuit connected like a L ow- P ass F ilter ( LPF ).
VR 1
2.5 V 2.5 V
V S
Scope Channel Output Signal
Scope Channel Input Signal
R 1 =1 kΩ
LPF
L coil=15 mH
Practical inductor coil
Ideal inductor coil R coil=?
L ideal=15 mH
Low-frequency equivalent circuit for a practical inductor coil
PART 2: Step Excitation of Second-Order RLC Circuits
Lab Experiment 2: Construct the second-order series RLC circuit shown in Fig. 3 using L coil=15 mH and C 1 =10 nF. Measure and record the actual value of the capacitor used. Set the function generator to provide the rectangular pulse train represented with the source voltage V S( t ) which oscillates between −2.5 V and 2. V with frequency of oscillation f = 1/ T = 1 kHz. Use the oscilloscope channels to observe the two voltage waveforms V S( t ) and VC 1 ( t ) simultaneously. Explain the difference between the voltage waveform VC 1 ( t ) observed in this circuit versus in a first-order RC circuit (like the one used in Lab Experiment # 6). Measure the damping frequency ωd of the under-damped oscillations observed in the VC 1 ( t ) waveform by measuring the damping period Td and using fd = 1 Td. Repeat this experiment at 5 kHz, 10 kHz, and 20 kHz. Explain what you observe happen.
Fig. 3. Second-order series RLC circuit.
VC 1
2.5 V 2.5 V
V S
Scope Channel Output Signal
Scope Channel Input Signal
C 1 =10 nF
LPF
L coil=15 mH
Practical inductor coil
Ideal inductor coil R coil
L ideal=15 mH
III. Discussions & Conclusion
- In this section, discuss the various aspects of Experiment # 7 and make some conclusions. In your write-up, you should at least address the following questions:
- What was the objective of this experiment and was the objective achieved?
- Explain how the output resistance of the function generator affected some of the waveforms observed on the scope and why. Why was this effect not observed in the first-order RC experiment (i.e., Experiment # 6)?
- Did any of your measurements have more than 5% error? What was your maximum % error?
- What sources of error may have contributed to the differences between the theoretical values and the measured values?
- Other comments relevant to this experiment.