ECE207 Electrical Engineering
Fall 2011 - 2012
Lab 2
Phasor Measurements
Objectives:
At the conclusion of this lab, students should be able to:

use the NI myDAQ to measure phasor voltage

use the NI myDAQ to measure phasor current

use a shunt to measure the current through a capacitor
Equipment:
Laptop with NI myDAQ software installed
NI MyDAQ
breadboard
1 - 1 k resistor
1 - 2 k resistor
1 - 10  resistor
1 - 33 mH inductor
1 - 0.1 F capacitor
Procedure
Part 1: Voltage Measurements
1. In this part, you will use the oscilloscope to measure AC voltages. If you need a refresher on
using the NI my DAQ instruments, please review the documentation in the box and the
tutorials at the following links:
Introduction to NI myDAQ:
http://decibel.ni.com/content/docs/DOC-13041
DMM – ohmmeter:
http://decibel.ni.com/content/docs/DOC-12880
Analog Output and Input:
http://decibel.ni.com/content/docs/DOC-12884
2. Use the LCR meter provided in the classroom to measure the inductor and capacitor and
record their values on the table in the worksheet.
3. Launch the NI ELVISmx Instrument Launcher from the National Instruments folder and you
should see the toolbar appear on your desktop.
4. Use the ohmmeter to measure each of the resistors and record their values on the table in
the worksheet.
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ECE207 Electrical Engineering
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5. Use nodal analysis, to find each of the labeled values on the circuit in Figure 1. Make sure
that you use the measured values of the components in your calculation. Show the
calculations on the space in the worksheet and record the values in the table. Express your
answers as phasors with the magnitude in RMS and the phase angle in degrees.
Figure 1: Phasor Circuit
6. Make sure that the breadboard is horizontal with the red buss across the top. Build the
circuit in Figure 1 with the ground on the blue buss at the bottom of the breadboard.
7. Connect the NI myDAQ function generator (AO 0, 1) to the left side of the 1 k resistor and
the ground buss. Connect Ch. 0 of the oscilloscope (AI 0+, 0-) to measure the function
generator on the circuit.
8. Connect Ch. 1 of the oscilloscope (AI 1+, 1-) to measure v1, across the 0.1 F capacitor.
9. Click on FGEN to open the function generator on the NI myDAQ and set it to 8.5 Vpp, 1.0
kHz sine wave. Click run on the function generator
10. Click on Scope button to open the NI MyDAQ oscilloscope. Set both channels to 1 V/div,
100 s/div, trigger type Edge, Chan 0 Source, positive slope. Make sure the source on
Channel 0 is AI 0 and the source on Channel 1 is AI 1. Click run on the oscilloscope.
11. If you have set up the circuit and instruments correctly, your system should look similar to
Figure 2. If it does not, please do not move on until you check your work and solve the
problem.
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Figure 2: Oscilloscope and function Generator Settings
12. Use the voltmeter to measure the magnitude of the node voltages in V rms and record the
values on the table in the worksheet. Recall that the percent error formula is
13. Use the cursors and time axis crossings to estimate the phase angle similar to what you did
in Lab 1. Please go back and review Lab 1 if you don’t recall how to do this. Record the
measured phase angles on the table in the worksheet. Note that the error for a phase angle
is a difference not a percent so use the following:
Part 2: Current Measurements
1. In this part, you will measure phasor current. Since the oscilloscope only measures voltage, you will
use voltages and measured resistor values to find current.
2. Use the measured voltage of the source and V1 to find the voltage drop across the 1 k resistor
using the following formula:

3. Use the measured values of V1 and V2 to find the voltage drop across the 2 k resistor. Use the
voltage across the resistor to find the current, I2, using the following formula:

4. Record the current magnitudes and phase angles on the table in the worksheet and perform the
error analysis.
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ECE207 Electrical Engineering
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5. It is necessary to do a little bit more work to find the current through the capacitor. It is necessary
to put a 10 resistor as shunt in series with the capacitor as shown in Figure 3.
Figure 3: Capacitor with shunt resistor
6. Use the oscilloscope to measure, Va, the voltage across the resistor. Note that this signal will be
very small and you will have to turn Channel 1 up to 10 mV/div. Finally, use the following formula to
find I3:

7. Record the magnitude and phase of I3 on the data table and perform an error analysis.
8. You have now completed Lab 2 and should confirm that you have included all of the required
information on the worksheet. Submit the worksheet to the instructor by the end of the lab session.
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ECE207 Electrical Engineering
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Lab 2
Phasor Measurements
WORKSHEET
NAME:
________________________________________________________
NAME:
________________________________________________________
Part 1: Voltage Measurements
Table 1: Component Values (include all units)
element
measured
nominal
% error
Nodal Analysis calculation on Figure 1:
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ECE207 Electrical Engineering
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Table 2: Voltage Measurements (include all units)
component
measured
nominal
error
| V1|
V1
| V2|
V2
Part 2: Current Measurements
I1 calculation from measured voltage and resistance:
I2 calculation from measured voltage and resistance:
I3 calculation from measured voltage and resistance:
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Table 3: Curent Measurements (include all units)
component
measured
nominal
Fall 2011 - 2012
error
| I1|
I1
| I2|
I2
| I3|
I3
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