Download ECE 211 Electrical Circuits Lab I

ECE 213 Electrical Circuits Lab II
LAB #6
Spring 2015
Name ___________________
Section ______________
The Phasors II
OBJECTIVE:
The objective of this experiment is to determine the characteristics of a parallel-series
alternating-current (AC) circuit. Kirchhoff's voltage law will also be checked for the same circuit
COMPONENTS AND EQUIPMENT:
1. Oscilloscope
2. Function Generator
3. Digital Multimeter
BACKGROUND:
DMM vs Oscilloscope
A digital multimeter (DMM) will probably give better accuracy than an oscilloscope when
measuring the magnitude of potentials. Digital multimeters have another advantage over
oscilloscopes in that both of the terminals of the DMJ\1 are isolated from ground. This means the
DMM can be connected anywhere in the circuit without being concerned about grounding the
circuit at two or more different points. Grounding the circuit at more than one point would
connect those points together. The oscilloscope also has some advantages. First, the wave shape
can be seen. Problems such as distortion of the expected wave form by overloading, component
failure, or noise can be detected. Second, the oscilloscope can measure phase shift.
Current Measurement
When measuring currents with an oscilloscope a current probe can be used to transduce the
current into a voltage. Current magnitude can also be measured with a DMM that has an AC
current capability.
Alternately, the voltage across a resistor (of known resistance) in the circuit can be measured
with either a DMM or an oscilloscope and the current calculated. Also the phase of the current in
the resistor is the same as the phase of the potential across the resistor. If there is no resistance
that can be used as current to voltage transducer existing in the circuit, a small resistor can be
added. This added resistor should be small when compared to other impedances in the circuit,
but it should be large enough to allow accurate measurement.
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ECE 213 Electrical Circuits Lab II
LAB #6
Spring 2015
PROCEDURE:
The following circuit will be created and tested in this lab.
Figure 1 - RLC Parallel Circuit
V1 = the internal generated voltage of the Function Generator set it to 3Vrms at 500 Hz.
C1= 480nF
L1 = 210mH
R1 = 4.7kΩ
RL = The internal alternating-current resistance of the inductance (measure by DMM)
R3 = 510Ω
Component Measurement
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 the table below.
Component
RS
(Function
generator
resistance)
C1
C2
R1
RL (internal
resistance of
L1)
R3
Value
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ECE 213 Electrical Circuits Lab II
LAB #6
Spring 2015
Circuit Analysis
Calculate the magnitude and phase at Node 1, Node 2, and Node 3 in Figure 1 using only the
measured value of the terminal voltage of the function generator 3Vrms shown in Figure 1.
Please show all the calculations.
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ECE 213 Electrical Circuits Lab II
LAB #6
Spring 2015
Experiment
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 1, set the voltage source to 3Vrms operating at 500Hz.
3. Construct the circuit shown in Figure 1.
4. Use a digital multimeter to measure the potential at nodes 1, 2, and 3 with respect to
Node 1.
5. Using an oscilloscope, and again using Node 1 as the reference node, measure the peakto-peak potential at nodes 1, 2, and 3. Also, measure the phase angle of the potential at
Node 1, Nodes 2 and 3.
6. Measure voltage across C1, R1, and C2. For VC2, it should be the same as node 3. For
VR1, exchange the C2 and R1 and measure node 3 again. For VC1, remove the C1 and
place it between ground and those parallel components (one side is grounded and the
phase can be measure the phase of the C1) shown in Figure 2.
Figure 2 - Circuit for measuring C1
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ECE 213 Electrical Circuits Lab II
LAB #6
Spring 2015
Result Analysis
1. Fill out 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
Node 3
Voltage Across
C1 (VC1)
Voltage Across
R1 (VR1)
Voltage Across
C2(VC2)
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).
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ECE 213 Electrical Circuits Lab II
LAB #6
Spring 2015
3. Kirchhoffs 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 Gen
C1 (from Step 6)
R1 (from Step 6)
C2
KVL Sum (VS-VC1-VR1-VC2)
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