ECE 231 Elements of Electrical Engineering Laboratory Manual

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



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.



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.



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.



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



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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ECE 231 Elements of Electrical Engineering Laboratory Manual