ece 231 elements of electrical engineering laboratory manual
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ECE 231 Elements of Electrical Engineering
Laboratory Manual
Prepared by R. Frank Smith
California State Polytechnic University, Pomona
Reference Text – Student Reference Manual for Instrumentation Laboratories, Wolf and Smith, Prentice Hall, 2004
Revised 09/01/16
i R. Frank Smith, Cal Poly Pomona University, 2016
Table of Contents
Exercise 1 - Ohm's Law 1
Exercise 2 - Kirchhoff's Laws 7
Exercise 3 - Oscilloscope/Function Generator Operation 11
Exercise 4 - Thévenin's and Norton Theorems 16
Exercise 5A - Diode Characteristics 22
Exercise 5B - Diode Characteristics 28
Exercise 5C - Diode Characteristics 32
Exercise 6 – Frequency/Time Response of RL and RC Circuits 35
Exercise 7 - Resonant Circuits
Exercise 8 – Time Domain Response of 2nd Order Circuits
42
47
ECE 231 Laboratory Exercise 1 Ohm’s Law
1 R. Frank Smith, Cal Poly Pomona University, 2016
ECE 231 Laboratory Exercise 1 – Ohm’s Law
Laboratory Group (Names) ________________________ _______________________ ________________________
OBJECTIVES
Verify Ohm’s Law
Learn to read resistor color codes
Learn to use ohmmeter, voltmeter, and ammeter
Learn to calculate power loss in resistors
EQUIPMENT REQUIRED
ECE 231 Circuit Board (In Stock room)
One banana cable
One lot of colored clip leads (students must supply their own clip leads)
DMM (digital multimeter)
DC power supply
BACKGROUND
Resistors are used for many purposes such as electric heaters, voltage, and current dividing elements, and current-
limiting devices. As such, their resistance values and tolerances vary widely. Resistance tolerances may range
from +0.001 to +20%. The most common types of resistors are carbon composition, wire wound, metal film,
carbon film, steel, and liquid. Their ratings can range from microwatts to megawatts. Variable resistors are called
either potentiometers or rheostats. When used as a potentiometer their output is a variable voltage. When used
as a rheostat they are used to control current. A good reference source is
http://en.wikipedia.org/wiki/Electronic_color_code. Review this website before you come to the laboratory.
Many types of resistors do not have a color code such as resistors made to military specifications and surface
mount resistors. You might remember the following mnemonic to remember the color versus number code: Bad
(0) Boys (1) Race (2) Our (3) Young (4) Girls (5) But (6) Violet(7) Generally (8) Wins (9).
Black Brown Red Orange Yellow Green Blue Violet Grey White
Most resistors use either 4 or 5 bands of colors. The 5 band color is usually used for 1% and 0.1 % resistors. This
band represents 5% if gold, 1% if brown, and fire resistant if yellow.
When you observe a resistor it is not always possible to predict its wattage by just observing its size. There are
many variables that affect a resistor’s wattage. Some such parameters are size, mounting, encapsulation, and
ECE 231 Laboratory Exercise 1 Ohm’s Law
2 R. Frank Smith, Cal Poly Pomona University, 2016
cooling. There are three ways you can calculate the power being dissipated in a resistor in this laboratory. See
Eq.1. In a thermodynamics' laboratory you could measure the rise in temperature of water in a calorimeter to
determine the power being dissipated by a resistor. Consider the following design problem. What size (ohms and
wattage) resistor would you use for the heating element in a coffee maker or toaster? Assume 120 VAC and 300
watts.
𝑃 =𝑉2
𝑅= 𝐼2𝑅 = 𝑉∆𝑅𝐼𝑅 (1)
The resistance of a resistor can be approximated by equation (2):
Resistance (R)= 𝜌𝐿
𝐴 (2)
Where 𝜌 =resistivity of the material; L = length of material; and A is the area of the material. The material may
be solid, liquid, or gaseous. Each of these parameters is often functions of temperature and stress. Liquid is often
used for low resistances rated in the megawatts.
Part 1. There are 7 resistors and one potentiometer on the BOARD. Determine and record the values of the 7
resistors and the potentiometer and their associated color code if appropriate. See your text or the internet for
the color code. Measure each resistor with an ohmmeter then see how that relates to the color code. We will
assume the color code is the Theoretical Value. See Figure 1.
ECE 231 Laboratory Exercise 1 Ohm’s Law
3 R. Frank Smith, Cal Poly Pomona University, 2016
Figure 1. Experimental board for ECE 231 experiments.
Table 1. Resistor color codes
Measured
Value
Color Code Theoretical
Value (Color Code)
% error
Experimental
Discrepancy
Part 2. Connect a variable voltage supply to three different resistors and vary the voltage from 0 to 10 volts. See
Figure 2. If the overload light is illuminated you may have tripped the overload protective device. Press the red
reset button to reset the overload device.
ECE 231 Laboratory Exercise 1 Ohm’s Law
4 R. Frank Smith, Cal Poly Pomona University, 2016
Figure 2. Variable voltage supply. Use cable with banana plug. Notch side goes to black.
Plot the current versus the voltage in Figure 4 for each resistor. Label each curve with its resistance value. There
is both a Fluke and Beckman multimeter that can be used to measure the current. See Figure 3. How does the
plot verify Ohm’s Law? What can you say about the slope of the plots? Calculate the slopes and show that they
are equal to 1/R.
Hint: All of the curves go through zero so only one additional point for each resistor is required to generate the
Ohm’s Law curve. Simply set the voltage supply at one voltage (for example 10 volts) for all the resistors and
then measure the current in each resistor. Verify the current using Ohm’s Law.
Figure 3. Laboratory bench equipment.
ECE 231 Laboratory Exercise 1 Ohm’s Law
5 R. Frank Smith, Cal Poly Pomona University, 2016
Figure 4. Plot for verifying Ohm's Law, (𝟏
𝑹=
∆𝑰
∆𝑽)
How does the plot verify Ohm’s Law? What can you say about the slope of the plots? Calculate the slopes and
show that they are equal to 1/R.
What are the possible ways to measure the current through a resistor? There are several ways. How do you
calculate the current through a resistor under test without using an ammeter? For a circuit board with surface
mounted resistors you would usually use the calculation method. Calculation of the measure of uncertainty for
each method is different. A good reference source for error analysis is the Reference text or
http://www.lhup.edu/~dsimanek/errors.htm.
Part 3. Connect a small resistor (less than 100 ohms) to the variable power supply. Gradually increase the voltage
and feel, using your finger, the increase in the temperature of the resistor. Only increase the voltage so that the
wattage lost in the resistor is less than 1/2 watt. What voltage created a ¼ watt loss? At what wattage does the
resistor get too hot to touch? Comment on how hot the resistor gets when it is dissipating 1/4, 1/3, and 1/2 watt.
Hint: Power = V2/R. Resistors are available on the 5th floor in the student work area and stock room.
CAUTION
ECE 231 Laboratory Exercise 1 Ohm’s Law
6 R. Frank Smith, Cal Poly Pomona University, 2016
Going beyond ¼ watt can cause the resistor to explode or ignite. A 100 ohm resistor will dissipate ¼ watt at 5
volts. You will usually see smoke or fire at ½ watt. Do NOT exceed 7 volts for a 100 ohm resistor.
Table 2. Wattage versus resistor temperature
Measured Test Value Temperature Check appropriate box
Comments
Resistance Voltage Wattage Ambient Warm Hot
1/4
1/3
1/2
Voltage
Part 4. Write a professional comprehensive laboratory report using a word processor. Show your
results, calculations, error analysis, and include a comprehensive conclusion. There are lots of sample
lab reports on the internet. Every figure must be sequentially numbered and referenced in the
preceding text. Your calculations may be handwritten and attached to the report if properly
referenced in the text. Number all pages.
On the cover page of your laboratory report include the number and tile of the experiment, date
performed, and laboratory partners.
Conclusion or comments.
___________________________________________________________________________________________
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