Circuit Theory II – Cheap Research Essays

ELEC153 Circuit Theory II
M5A3 Lab: AC Thevenin Circuits
Introduction

In this experiment we take a look at finding the Thevenin equivalent for an AC circuit with two output terminals.

Procedure

1. Setup the following circuit in MultiSim.The voltage source is 10 volts peak at 1000 Hz.
Figure 1: AC Circuit for finding its Thevenin equivalent
2. There are two measurements that are important in a Thevenin analysis: (1) the open circuit voltage Vab, which is the
Thevenin voltage, and (2) the short circuit current between the terminals a and b, which is the Norton current. Recall that
dividing the Thevenin voltage by the Norton current gives you the Thevenin/Norton impedance.

First, we will measure the open circuit voltage Vab. Connect an oscilloscope to the circuit and measure the voltage of the
source and the voltage between the nodes a and b. The circuit should look like the following circuit:

Figure 2: Circuit of figure 1 connected to oscilloscope

Start the simulation and run it for several seconds, open the oscilloscope and adjust its settings for the scales of the
timebase and channels A and B. You should get a plot similar to the following graph:
Figure 3: Source volatage (red) and Vab (green) waveforms

This plot is the combined plot of the source voltage (red trace) against the voltage between terminals a and b, or Vab (green
trace).

3. Measure the amplitude and phase shift of Vab and record them here:

Measured Voltage
Measured Phase Shift

4. Perform the manual calculations needed to find the open circuit voltage and phase shift. Record the calculated values
here. Do they match the measured values within reason?

Calculated Voltage
Calculated Phase Shift
5. Now we want to get the short circuit current. Add a 1 Ohm resistor in series with R2 and add a wire between the output
terminals as shown here:

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Figure 4: Scheme to measure the short-circuit current between terminals a and b

The current through R3 is precisely the short circuit current we want to determine. By measuring the voltage across R3 and
dividing it by the value of R3 we get the current. Connect an oscilloscope to the circuit. Your circuit should look like the
following circuit
Figure 5: Connecting the oscilloscope to the scheme of figure 4
6. Start the simulation, open the oscilloscope and set the scales as indicated in the following oscilloscope plot
Figure 6: waveforms of the source voltage (red) and short-circuit current (blue)
7. Measure the short circuit current and phase shift and record them here:

Measured Current
Measured Phase Shift

8. Perform the manual calculations needed to find the short circuit current and phase shift. Record the calculated values
here. Do they match the measured values within reason?

Calculated Current
Calculated Phase Shift
Write-up and Submission

In general, for each lab you do, you will be asked to setup certain circuits, simulate them, record the results, verify the
results are correct by hand, and then discuss the solution. Your lab write-up should contain a one page, single spaced
discussion of the lab experiment, what went right for you, what you had difficulty with, what you learned from the
experiment, how it applies to our coursework, and any other comment you can think of. In addition, you should include screen
shots from the MultiSim software and any other figure, table, or diagram as necessary.

ELEC153 Circuit Theory II
M2A4 Lab: AC Parallel Circuits
Introduction

In this experiment we work with AC parallel circuits. As we did in the AC series circuits lab, the results obtained through
Transient Analysis in MultiSim will be verified by manual calculations.

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Procedure

1. Figure 1 is the circuit we want to analyze.The voltage source is 24 volts peak at 1000 Hz.
Figure 1: AC parallel circuit used for analysis using MultiSim
Unlike the series circuit, there is no resistor in series with the voltage source that allows us to plot the current by
taking advantage of its in-phase relationship. So, in order to measure the current produced by the source (total current) add
a 1 Ohm resistor in series with the source. This small resistor will not affect the calculations.
Figure 2: Arrangement for analyzing the current waveforms
2. Run the simulations and with the oscilloscope measure both the source voltage and the voltage across the resistor. You
should get a plot similar to the following graph:
Figure 3: Source voltage (red) and source current (blue) waveforms

3. From the resulting analysis plot, determine the peak current. Record it here.

Measured Peak Current

4. Determine the peak current by calculation. Record it here. Does it match the measured peak current? Explain.

Calculated Peak Current
5. Calculate the phase-shift. Using the method presented in the last lab, measure the time difference at the zero-crossing of
the two signals. Record it here.
Time difference

6. From the resulting calculation, determine the phase shift by using the following formula

Record it here.

Measured Phase Shift

7. Determine the phase shift by calculation. Record it here. Does it match the measured phase shift? Explain.

Calculated Phase Shift

8. Change the frequency of the voltage source to 5000 Hz. Re-simulate and perform a Transient Analysis to find the new
circuit current and phase angle. Measure them and record them here:

Measured Current
Measured Phase Shift