ECE 213 Electrical Circuits Lab II
LAB #6
Spring 2015
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
1.
Oscilloscope
2.
Function Generator
3.
Digital Multimeter
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
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 3V rms
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
Value
RS
(Function generator resistance)
C1 C2 R1 RL (internal resistance of
L1)
R3
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ECE 213 Electrical Circuits Lab II
LAB #6
Spring 2015
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
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 3V rms
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 V
C2
, it should be the same as node 3. For
V
R1
, exchange the C2 and R1 and measure node 3 again. For V
C1
, 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
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 Percent Error
Magnitude Phase Angle Magnitude Phase Angle Magnitude Phase Angle
Node 1
Node 2
Node 3
Voltage Across
C1 (V
C1
)
Voltage Across
R1 (V
R1
)
Voltage Across
C2(V
C2
)
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 (V
S
-V
C1
-V
R1
-V
C2
)
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