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EE 215
Lab 4
24 Jan 2005
Power Factor and Power Factor Correction
Objectives:
 Practice magnitude and phase measurements with the oscilloscope.
 Practice average power determination.
 Practice power factor correction calculations.
 Practice using Multisim virtual wattmeter to simulate measured results.
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Work in pairs for this lab.
Construct the circuit shown in Figure 1. The source represents the function generator. The series
combination of the 1K resistor and the inductor represents an inductive load.
Connect Channel A (or 1) of the scope to measure the voltage at node 2.
Connect Channel B (or 2) of the scope to measure the node voltages at node 3, i.e., the voltage
across the 1K resistor.
Set the function generator to generate a sinusoid of about 1.7KHz frequency and peak amplitude
of 5V with no DC offset. Record the value of the peak amplitude.
Measure and record the amplitude of the voltages at nodes 2 and 3 and the phase of the voltage at
node 3 relative to that of node 2.
Use your measurements to determine the power factor of the voltage and current at the load and
the average power supplied to the load. Be sure to include a determination of the current supplied
by the function generator.
Calculate the value of the capacitance required in parallel with the load (i.e., between nodes 2 and
0 in Figure 1) to correct the power factor to 1. Connect a capacitor of approximately this value in
your circuit.
Now measure the voltage between nodes 2 and 0 and the voltage across the 100 ohm resistor. To
measure the voltage across the 100 ohm resistor, reverse the function generator connections to
make node 1 the reference (ground) node and connect the oscilloscope ground there. The voltage
measured at node 2 will then be the voltage across the 100 ohm resistor. Ask for help if you need
it to make this measurement. Use the voltage across the 100 ohm resistor to determine the current
supplied to the “corrected” load and use your result to determine the average power supplied to the
load and the corrected power factor, which should be near 1.
Use the Multisim wattmeter instrument to make simulated measurements and compare to your
results.
Discussion:
Measure the resistance of the inductor and include its effect in your simulation. Does this make any noticeable
difference in the simulated results?
R1
V1
1
100 Ohm
5 V
1.7kHz
0Deg
2
L1
0.1 H
3
R2
1kOhm
0
Figure 1