ECE 213 Electrical Circuits Lab II
LAB #5
Fall 2013
Name ___________________
Section ______________
The Phasor Lab
OBJECTIVE:
The objective of this experiment is to measure the complex voltages and the current in a series
resistive-capacitive-inductive circuit and draw a phasor diagram showing all the node voltages
and the current. Kirchhoff's voltage law will also be checked for the same circuit.
COMPONENTS AND EQUIPMENT:
1. Oscilloscope
2. Function Generator
3. Digital Multimeter
BACKGROUND:
In an alternating current(AC) circuit containing reactive elements, currents and voltages are
complex with a magnitude and a relative angular position. Actually, the angular position
represents a difference in time between sinusoids (a phase difference). This can be clearly seen
on a two channel oscilloscope. The period of a sinusoid is the time to complete one cycle or 360⁰
of the wave. The relationship between the complex currents and voltages in a circuit can be
shown on a phasor diagram. This relationship allows the time between the two sinusoids to be
expressed in degrees by the equation:
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ECE 213 Electrical Circuits Lab II
LAB #5
Fall 2013
Figure 1 - Phase angle measurement
PROCEDURE:
1. Turn on all equipment to be used in this experiment as early as possible and leave it on.
This will allow the instruments to warm up and stabilize.
2. In figure 2, the voltage source is 3Vrms operating at 1200Hz. Calculate the voltage
magnitude and phase at Node 1 (use node 1 as the reference voltage), Node 2, and Node
3 on a blank sheet or space below. Use voltage divider to solve the circuit. Make sure you
submit your calculation.
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ECE 213 Electrical Circuits Lab II
LAB #5
Fall 2013
V1 = node 1 voltage set to 3VRMS at 1200 Hz.
C1= 224nF
L1 = 210mH
R2 = The internal alternating-current resistance of the inductance (measure by DMM)
R3 = 1kΩ
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ECE 213 Electrical Circuits Lab II
LAB #5
Fall 2013
3. Set up the circuit shown in Figure 2. The nominal values of the components are given
under the figure. As usual in this course these values need not be matched exactly but
they will be measured closely. Place the measured values in Table D1.
4. With the circuit connected to the function generator adjust the terminal voltage of the
function generator to 3.00 volts rms. Use the oscilloscope to set the frequency to 1200
Hz.
5. Use a digital multimeter to measure the potential at nodes 1, 2, and 3 with respect to
ground. Determine the current from the potential at Node 3. Also measure the potential
from node 1 to node 2 and the voltage from node 2 to node 3. Place the results in Table
D-2.
6. Using an oscilloscope, and again using node 1 as the reference node, measure the peakto-peak potential at nodes 1, 2, and 3. Also determine the current. Assuming the voltage
at Node 1 is at zero degrees (i.e. this will be the reference phasor and will be placed at
zero degrees on the phasor diagram), measure the phase angle of the potential at Nodes 2
and 3 and the phase angle of the current. Place the raw data in Table D-3.
7. Exchange Cl and R3 and measure the magnitude and phase angle of the potential across
Cl still using the node 1 voltage as the reference. Replace C 1 and exchange the
inductance (L 1 and R2) with R3. Measure the magnitude and phase angle of the potential
across the inductance. Place the results of these measurements in Table D-3.
Result and Analysis
1. Using the raw data in Tables D-2 and D-3 find the measured values of the voltages and
current in Figure I. The magnitudes measured with the digital multimeter are probably
more accurate than those measured with the oscilloscope.
Potential
Measured
Calculated
Magnitude Phase
Angle
Magnitude
Percent Error
Phase
Angle
Magnitude
Phase
Angle
Node 1
Node 2
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ECE 213 Electrical Circuits Lab II
LAB #5
Fall 2013
Node 3
Voltage
Across C
(VC)
Voltage
Across L
(VL)
2. Draw a phasor diagram for the circuit of Figure 1 for Node 3 voltage. Label the title,
magnitude, and angle including unit. Label the axis (real and imaginary).
KirchhofPs Voltage Law states that the sum of the voltages around a closed loop must
add to zero. In direct-current circuits this sum is algebraic. In an alternating current
circuit the sum must consider the phase of each potential. This means that the sum of all
the real parts, and the sum of the imaginary parts, of the voltages around a closed loop
must each add to zero.
Potential across
Real Part volts
Imaginary Part volts
Function Generator
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ECE 213 Electrical Circuits Lab II
LAB #5
Fall 2013
C1 (from Step 7)
L1 (from Step 7)
R3
KCL Sum (VS-VL-VC-VR)
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ECE 213 Electrical Circuits Lab II
LAB #5
Fall 2013
Data Sheet
Normally when doing an experiment the data is placed on a data sheet which has been prepared
in advance such as this one. It should be recorded in a notebook for future reference. This data is
taken and recorded in such a way as to reduce the chance of error and generally is not in the best
form to be included in a report.
List the equipment used in this experiment. Give the manufacturer and model for each
instrument. The exact unit can be identified by giving the station number. The equipment is
listed in such a way that the experimenter can find the exact instrument used for each
measurement. If the data is not as expected, the instruments used can be checked to see if they
are appropriate ( ie does it have the proper frequency range) or if they are out of calibration.
1. _______________________________________________________
2. _______________________________________________________
3. _______________________________________________________
4. _______________________________________________________
5. _______________________________________________________
Table D-1 Measure value of the component:
Component
Measured Value
C1
L1
R2
R3
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ECE 213 Electrical Circuits Lab II
LAB #5
Fall 2013
Table D-2 Magnitude of the Node Potentials and the Current In Figure 1. Measured with a
DMM
Reading (indicate if this is RMS value)
Terminal Potential – Node 1
Potential at Node 2
Potential at Node 3
Potential at N1 to N2
Potential at N2 to N3
Current
Table D-3. Circuit Potentials and Currents in Figure 1. Measured with an Oscilloscope
Voltage
magnitude
Phase shift time
Scale (1X, 10X,
100X)
Node 1
Node 2
Node 3
Potential across
C1 (step7)
Potential across L
(Step 7)
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