EE 201
Lab 2
Time-varying signals: the function generator, RMS measurements, and the
oscilloscope
Note: Bring a flash drive to lab for recording oscilloscope traces.
0. Prior to lab
Read through the lab and do as many of the calculations as possible. Learn and understand the
material in the short classroom lecture covering sinusoidal signals and RMS values. Read
through the tutorials for the function generator and the oscilloscope.
1. Function generator
Work through the tutorial describing the operation of the Tektronix 3021B function generator.
2. Oscilloscope
Work through the tutorial describing the operation of the Agilent DSO-X-2024A oscilloscopes.
3. Measurements on resistive circuits
For each of the simple divider circuits shown below in Figures 1 and 2:
a. Build the resistor network as shown in each figure.
b. Use the function generator as the source, set to provide a 1000 Hz (1-kHz) sine wave with
amplitude of 5 VRMS (= 14.14 V peak-to-peak).
c. Calculate the expected voltages across each resistor, using the nominal values of the
resistors. (These circuits should be familiar – they were used in lab 1.)
d. Use the voltmeter, set to measure ac voltage, to measure the source voltage, and then
measure the ac voltage across each resistor. Remember that the voltmeter, when set to
measure AC voltages, gives RMS values. Here’s an important thing to note: AC
measurements have no polarity – it makes no difference which way you arrange the
probes.
e. Use Ohm’s law to calculate the AC current in each resistor.
f. Measure the current in each resistor using the ammeter. (Again, it must be set to measure
AC current.)
g. Use channels 1 and 2 of the oscilloscope to observe the source voltage and the voltage
across resistor R3 simultaneously. Adjust the traces so that the axes correspond (lie on top
of each other) and the vertical scales are the same. Record a screen shot of the two traces
together.
h. Change the input from sinusoidal to a square-wave and observe the waveforms on the
oscilloscope. Then change the input to a triangle wave and observe the waveforms on the
scope. Record a screen shot of the two triangle traces together for the report.
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EE 201
Lab 2
+ vR1 –
b
R1 1 k!
Fig. 1. The source voltage is a sinusoid with
frequency of 1000 Hz and amplitude of 5 VRMS
(14.14 V peak-to-peak).
VS
–
2.2 k!
R3 3.3 k!
–
Fig. 2. The source voltage is a sinusoid
with frequency of 1000 Hz and amplitude
of 5 VRMS (14.14 V peak-to-peak).
VS
+
c
1 k!
–
a
vR3 +
R1
iS
+
vR2
–
R2
+
R3
R2
2.2 k! i 3.3 k!
R2
R4
4.7 k!
iR3
4. Measurement of a circuit with a reactive element.
a. Build the simple resistor - capacitor circuit as shown in figure 3. A 0.1-µF capacitor is
labeled “104”. (The lab instructor can help you identify the correct capacitor.)
b. Use the function generator as the source, set to provide a 1000 Hz (1-kHz) sine wave with
amplitude of 5 VRMS (= 14.14 V peak-to-peak).
c. Use the voltmeter – set to measure AC voltage – to measure the source voltage, and then
measure the AC voltage across the resistor and then the voltage across the capacitor.
d. Use Ohm’s law to calculate the ac current in the resistor.
e. Measure the ac current using the ammeter.
f. Remove the ammeter from the circuit. Use channels 1 and 2 of the oscilloscope to observe
the source voltage and the voltage across the capacitor simultaneously. Adjust the traces so
that the axes correspond (lie on top of each other) and the vertical scales are the same.
Record a screen shot of two traces together. Use the cursor function to measure the time
delay between the source voltage and the capacitor voltage sinusoids. (Measuring zero
crossings is probably more accurate than looking at peaks of valleys.)
g. Repeat parts a - f above with the source frequency set to 100 Hz.
h. Repeat parts a - f above with the source frequency set to 10,000 Hz (10 kHz)
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iR4
EE 201
Lab 2
Note the significant differences in the voltages and currents at the different frequencies.
(Inductors have a similar effect. We will learn how to calculate these effects when we study AC
circuit analysis in the second half of EE 201. You don’t need to try to find the expected values
for the current and voltages in this section of the lab.)
+
Fig. 3. The source voltage is a sinusoid with initial
frequency of 1000 Hz and amplitude of 5 VRMS (14.14 V
peak-to-peak). In subsequent measurements, the source
frequency is changed to 100 Hz and then 10 kHz.
iS
VS
vR –
R 1.5 k!
+
–
+
vC
–
C
0.1 µF
5. Design it
Design a circuit that uses a 5-V DC power supply, a 10-kΩ potentiometer and some resistors to
provide a variable output voltage across some combination of the potentiometer and resistors.
The design requirements are that that when the potentiometer is adjusted fully in one direction,
the output voltage should be 1.67 V and when adjusted fully in the opposite direction, the output
voltage should be 3.33 V. The measured voltages should be correct to within 5% of the design
goals given above. Demonstrate the operation of the circuit to your lab supervisor. In your
report, include an analysis of the circuit (i.e. equations) that describe how the circuit behaves.
Then show that your circuit works just as well with AC voltages by replacing the DC source with
a 5-VRMS sinusoidal source (f = 1 kHz). Measure the AC output with the multimeter and show
that it amplitude varies betweens the two limits as you adjust the potentiometer. Then use the
oscilloscope to observe the input and output together simultaneously. Observer the change in the
output amplitude as the potentiometer is adjusted.
Fig. 4. Block diagram of the circuit
design. You need to fill in the box
with a circuit that meets the
specifications given above.
VS = 5 VDC +
or 5 VRMS –
+
vout
–
Reporting
Each lab group should prepare a report for the work done in this lab. A template for the report
can be downloaded from the web site. Be sure to fill in all of the measured data, calculated
values, attach screenshots, and answer all of the questions. To complete the report, add an
introduction and a conclusion (about one paragraph each). The report is due in one week.
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