ECEN214 Laboratory Manual, Lab 7
Lab 7: First Order RC and Second Order RLC Circuits
Objective:
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To study the step response of a simple RC circuit.
To understand the rise and fall times and explore the concept of time constant.
To learn how to use an oscilloscope to make such measurements.
To study the step response of a simple RLC circuit.
Lab Components:
Qty.
Value
One each
100, 220, 470 Ω resistors
One each
1, 2.2, 6.8, 22 KΩ resistors
One each
0.01,10 µf capacitors
One
120mH inductor
Jumper wires
Pre-Lab: (Due at start of lab period)
I. Calculations
Do not use any simulator for this part. Read through the entire lab before the start of the lab period.
1. For the circuit of Figure 1, use KVL and the linear models to set up the differential equation
for Vc(t). Use the resulted equation to calculate the capacitor voltage for t =0 and ∞.
2. Write the differential equation for a series RLC circuit, then find the roots of the equation in
terms of α and Ѡo.
3. For the circuit of Figure 2, if L = 120mH and C = 0.01 µF, calculate the ranges of resistor R for
over damped, critically damped and under damped responses.
II. Simulations
1. Use MultiSim program to simulate the RC circuit shown in Figure 1 using nominal resistor
value of 100Ω and 10uF capacitors. Set up the function generator for: square wave,
frequency 20Hz, duty cycle 50%, offset 1V, and amplitude 1V. Use Tektronix scope to display
the input source and the capacitor voltage waveforms on the same display.
2. Print out your schematics and print an output showing Channels A and B.
3. Use the scope cursors to measure simulated τ.
4. Change the resistor to a nominal 220Ω, 470Ω, and 1kΩ resistor and repeat the above step
for each resistor value.
5. Use MultiSim program to simulate the RLC circuit shown in Figure 2. Set up the function
generator for: square wave, frequency 400Hz, duty cycle 50%, offset 1V, and amplitude 1V.
Use Tektronix scope to display the input source and the capacitor voltage waveforms on the
same display.
6. Print out your schematics and print an output showing Channels A and B.
7. Change the resistor to 6.8kΩ and 22kΩ and repeat the above step for each resistor value.
Lab 7 page 1 of 4
ECEN214 Laboratory Manual, Lab 7
Procedure: (In Lab work)
This lab experiment is divided into two main parts:
• RC Circuit.
• RLC Circuit.
Procedures for each part are provided in this section. The results, as required, should be
documented in your lab report as presented in the following section.
Part I: RC Circuit:
1. In your component kit, find the resistors 100Ω, 220Ω, 470Ω, and 1kΩ and the capacitor
10µf. Use the DMM or RLC to measure their values.
2. Predict the values of τ = RC, using your measured values and record them in table 2.
3. Build the RC circuit shown in Figure 1 using 100 Ω resistor.
4. Set the function generator to High Z: press the output menu button
Load Impedance
High Z then press the
twice).
5. Set up the function generator to 20Hz square wave. with amplitude of 2 V pp.
6. View the input and output signals simultaneously on the oscilloscope screen, which is
accomplished by using CH1 to measure the function generator voltage and CH2 to
measure the voltage across the capacitor. Hint: make sure that ground level is at the
center of the screen for both channels.
7. Record the resulting waveforms.
8. Calculate the time constant from this waveform using the time is equal the time constant
when the voltage across the capacitor reachs 0.632 Vc and compare with the theoretical
predicted value above.
9. Replace the resistor by 220Ω, 470Ω, 1kΩ and repeat the above steps for each value.
Physically, the voltage across the capacitor rises more slowly as the resistance is
increased because the flow of charge (i.e. current) is reduced.
Figure 1: RC Circuit
Lab 7 page 2 of 4
ECEN214 Laboratory Manual, Lab 7
Part II: RLC Circuit:
1. In your component kit, find the resistors 2.2kΩ, 6.8kΩ and 22kΩ, the capacitor 0.01µF
and the inductor 120mH. Use the DMM to measure their values.
2. Build the RLC circuit shown in Figure 2 using 2.2kΩ resistor. Set up the function
generator to 400Hz square wave, with amplitude of 2 Vpp.
3. View the input and the capacitor signals simultaneously on the oscilloscope screen,
which is accomplished by using CH1 to measure the function generator voltage Vs
and CH2 to measure the voltage across the capacitor Vc. Hint: make sure that ground
level is at the center of the screen for both channels.
4. Record the resulting capacitor waveform and indicate whether the response is over
damped or under damped.
5. Replace the resistor by 6.8kΩ, 22kΩ and repeat the above steps for each value.
Figure 2: Series RLC Circuit
Lab 7 page 3 of 4
ECEN214 Laboratory Manual, Lab 7
ECEN214, Lab 7 Data Sheet
Station # __________
Date: ___________
Team Members:
Names (printed)
Signatures
1. ___________________________
_____________________________
2. ___________________________
_____________________________
3. ___________________________
_____________________________
In Lab Work:
Table 1: Measurement of step 1 for Part I
Nominal Value
100Ω
220Ω
470Ω
1KΩ
10uF
Measured Value
Tables 2: Calculations and Measurements for Part I
Nominal Resistor Value
100Ω
220Ω
470Ω
1KΩ
Predicted value of τ
Measured value of τ
Table 1: Measurement of step 1 for Part I
Nominal Value
Measured Value
2.2kΩ
6.8kΩ
22kΩ
0.01uF
120mH
Lab 7 page 4 of 4