ELC 131 Laboratory Report

Wake Tech Community College Electronics and Computer Engineering

ELC 131 Laboratory Report Requirements

Overview: The laboratory portion of this course is intended to prepare students for careers in the design, development, production, installation, maintenance, and repair of equipment related to electronics and computers. The technician must be able to communicate effectively. Regardless of your career path, the accurate completion of documentation is as important as the hands-on part of the job.

Due date and make-up labs: Every student must submit a laboratory report within one (1) week of the completion of the lab assignment. In the event of an unavoidable absence from a lab meeting, it is the student’s responsibility to complete the missed lab assignment. Work completed outside of the student’s regularly scheduled lab period must be signed and dated by the attending instructor or lab assistant.

Contents and Grading:

1. Presentation and Professionalism (10%): The report should follow the memorandum format as described in the Memorandum Report document. The report should free from grammatical errors, and the tone should be appropriate for a technical report.

2. Pre-lab (10%): Complete any pre-lab requirements before the lab meeting.

3. Data (40%) In the appendix, provide any data tables and graphs that are required in the lab. You may just copy the data tables from the lab word document. However, if there are a lot of calculations, you may find it is easier to create the data tables in Excel.

4. Abstract, Description of Work, and Results and Discussion (20%) The requirements of these sections should be met. The Results and Discussion section should show that the student has given some thought to the lab data and has made some educated statements regarding the lab activity and the data gathered.

5. Questions (20%) Complete the questions in the source document. These questions are to be attached to the memorandum report.

The Memorandum Report

The memorandum report is restricted to a single topic and rarely exceeds one to three typewritten pages. It contains only a few of the elements of the formal report. It is recommended for use between only two people: the author and a single reader who is reasonably acquainted with the subject and whose time should not be spent searching through non-essentials to find the results and conclusions that are of interest. Thus, the author omits materials that the reader is familiar with, such as description of standard tests and equipment.

Originally the term “memorandum” implied something of a temporary nature. This is no longer true, yet there are times when a memorandum is written to make immediately available some information that will later be included in a longer, more formal report. Some of the largest corporations in the nation make use of memoranda.

Printed forms, which vary from company to company, are often used for memoranda. If no form is provided then the report should include the following elements of information.

First Page Heading

The heading on the first page shows the reader at a glance the crucial data on the report. It should include:

a) The title of the report (often called the subject).

b) The serial number of the report, if the report is one of a sequence.

c) The name of the person who wrote the report or the organization that published the report, whichever is appropriate.

d) The person or organization for which the report was prepared, if the report goes to a certain person or organization.

e) The date of publication (or date of submission) of the report.

Abstract

Sometimes called a summary, it helps a busy reader decide whether or not to read the whole report. The abstract also helps in cataloging a report. Since the abstract gives a thumbnail sketch of the report, an abstract of a memo-report should run no longer than half a page; frequently one paragraph describing the entire report (100 words or less) will suffice. Also the abstract should indicate the conclusions of the work so that the reader will be able to evaluate the relevance of the work. In writing the rough draft of the abstract, a writer may ask himself, “What would I write if I had to sum up this report on a 3 x 5 index card?”

Description of Work

A brief, approximately one paragraph long description of the actual work performed which explains where and how the data in the report was obtained.

Results and Discussion

This section summarizes the data gathered in the lab activity. Do not restate information that can easily be found in the data tables, but do discuss the key results of the data and any implications that can be made from the data gathered. This section typically includes conclusions and recommendations.

Appendix

If an appendix is required, it should provide the data (preferably in a tabulated form), graphs, data sheets if available, sample calculations (as required by the instructor), and a list of references.

Data Tables

a) Every table should carry a description title at its top.

b) A table should fit onto a single page, if possible. If a table must spill over to the next page, that page should repeat the title and column headings.

c) A table should be numbered and always referred to in the results and discussion section.

d) A table should always show units in the column headings.

e) The independent variable usually, and logically, goes on the left; the dependent variables go in columns to the right.

Graphs

Only use graphs if they supplement, complement, simplify, or clarify the written work. Graphs are NEVER to be drawn freehand. Graphs should be computer generated. When you decide to plot a graph, you should consider the following:

a) Independent variables should be plotted on the horizontal axis (abscissa) while the vertical axis is only used for the dependent variables.

b) The axes should be labeled with the proper units on each. Use a convenient scale on each axis in such a way that the plot will fill the entire page if possible. The scales on the x- and y-axes may not necessarily be the same.

c) All data points should be included in your plot, even if you have some uncertainty regarding any of them. Points taken under the same test conditions should be identified using the same symbol. If you have to plot more than one curve on the same graph paper, use different symbols, one for each condition.

d) A legend box should accompany each graph, especially if more than one plot is included in the figure.

e) Each graph must be consecutively numbered and titled at the bottom.

Sample calculations

Include a sample calculation for each nontrivial type of calculation. Usually, the sample calculations called for on the data sheets are sufficient. If a data sheet is not included, make your own sample calculations in a labeled box and attach it to the appendix. Most important, show all units in your calculations. It should also be obvious where any number used in your sample calculations comes from i.e. data or graph.

Preparation the Report

1. Reports are to word processed on 8-1/2 x 11 paper. Use 12 point font. (Check with your instructor for preferred font style.)

2. Print on one side of the paper only.

3. Number the pages.

4. The report must be stapled.

If you need more information, you can consult the following references:

1. J.H. Earle, “Engineering Design Graphics,” Prentice Hall, 2004

2. T. A. Sherman and S. S. Johnson, “Modern Technical Writing,” Prentice Hall, 1975.

3. R. Hays, “Principles of Technical Writing,” Addison Wesley, 1965.

Examples are provided of two well-done memorandum reports which may be used as samples.

Memo Report No. I College of Engineering and Computer Science California State University, Northridge

To: I. A. Ibrahim

From: Jack Smith

Date: October 23, 2004

ABSTRACT

Hardness and tensile strength of a cartridge brass sample were measured as a function of percent cold work (0-60%CW). Both properties increased with the increased percentage of cold work. Recovery , recrystallization, and grain growth characteristics of a 50%CW brass was also investigated by measuring Rockwell Hardness (B Scale) of specimens annealed for 1/2 hour in the temperature range of 200- 700°C. A typical curve with the three distinct regions was obtained. The grain size was also determined for the four highest annealing temperatures and a dramatic increase in the average grain size with temperature was observed.

DESCRIPTION OF WORK

The initial hardness and tensile strength of 70/30 cartridge brass were measured using the Rockwell hardness tester (B scale) and the Instron machine, respectively. The thickness of the samples was successively reduced by rolling up to 60%, while hardness and ultimate tensile strength (UTS) measurements were determined at the different stages of cold work. A 50% CW brass strip was then cut into eight pieces, each was annealed at 200, 250, 300, 350, 400, 500, 600, and 700 °C for 1/2 hr., followed by water quench. The hardness of each sample was finally measured using the Rockwell tester.

Samples for the metallographic observation were polished, etched and observed in a light optical microscope at magnification x 100. The ASTM grain size number, n(l) was determined by comparing the microstructure with a standard ASTM grid, and consequently the average grain size was computed.

RESULTS AND DISCUSSION

The data on hardness and tensile strength as a function of the degree of cold work are shown in Table (1) and Figure 1. The hardness has increased from about 15 to 78 on the Rockwell B scale as a result of 60%CW. The tensile strength has also varied in a similar trend with the increased amount of cold work, The scatter of the data is very small since both properties were taken as the average of several readings under the same test conditions. Furthermore, the data obtained was in rather good agreement with those published in the literature(2,3).

Process annealing of the cold worked samples below 250 °C reduced the hardness very slightly. An abrupt decrease in hardness was observed in the temperature range 250-500°C. Above 500°C the hardness continued to decrease at a very small rate until 700oC has been reached. The three stages of the annealing process, namely recovery, recrystallization, and grain growth, have been established accordingly. This is shown clearly by plotting the data in Table 2 as in Figure 2. The hardness values at high temperatures exhibited greater scatter as is expected when approaching the lower limit of the B scale on the hardness tester.

The grain size of the completely recrystallized samples is also plotted in Figure 2 as a function of annealing temperature. Minor scatter in the values is observed as a result of the statistical errors involved in such measurements(3). However, the results in general are in good agreement with the literature(4).

APPENDIX

Table I. Rockwell Hardness and Tensile Strength of Cartridge Brass at Different Percentages of Cold Work**

% CW <RB>* UTSx10-7 (N/m2)
0

10

20

30

40

50

60

15

50

65

70

73

75

78

34

38

43

48

54

60

65

* Average of four hardness readings on Rockwell B scale.

Table 2. Hardness and Grain Size of 50%CW Cartridge Brass as a Function of Annealing Temperature

Temperature oC <RB>* Grain size (mm)
25

200

250

300

350

400

500

600

700

75

73

71

52

40

25

17

18

10

0.010

0.041

0.060

0.154

* Average of four hardness readings.

References

1. L. H. Van V lack, “Elements of Materials Science and Engineering,” Addison Wesley, Inc., 1975.

2. R. A. and P. K. Trojan, “Engineering Materials and Their Applications,” Houghton

Mifflin Co., 1975.

3. A.G. Guy, “Introduction to Materials Science,” McGraw Hill Book Co., 1972.

4. Metals Handbook, ASM, edited by T. Lyman, 1948.

Memo Report ELC 131 Lab 1 Electronics and Computer Engineering Wake Technical Community College

To: Bill Routt

From: John Smith

Date: August 21, 2011

ABSTRACT

Three basic quantities of electricity, voltage, current, and resistance, were examined. A simple electrical circuit was constructed. This circuit consisted of 1.5 V cells, an incandescent bulb, and a single-pole single-throw switch. A meter was used to measure the quantities voltage and current in the circuit. The values of carbon composition resistors were determined using the EIA/MIL color code scheme. A meter was used to measure the true value of the resistors.

DESCRIPTION OF WORK

A circuit was constructed with 1.5 V cells and an incandescent bulb. The brightness of the bulb with increasing numbers of cells was monitored. With the same circuit, the voltage across and the current through the bulb was measured as cells were added in a series-aiding configuration. The values of five resistors were measured and compared with the nominal value and stated range of the resistors.

RESULTS AND DISCUSSION

The brightness of the bulb with 1, 2, and 3 cells used the voltage source are shown in Table 1. The brightness of the bulb increased with the addition of each cell. This supports the idea that adding cells increases the energy supplied to the circuit.

The voltages across the bulb and the currents through the bulb with 1, 2, and 3 cells used the voltage source are shown in Table 2. The voltage across the bulb and the current through the bulb increased with the addition of each cell. This shows that as more energy is supplied, the potential difference across the bulb and the number of electrons flowing through the bulb increases.

The nominal values, the ranges of resistance as determined by the resistors’ tolerance, and the measured values of 5 resistors are shown in Table 3. Only two of the five resistors were within tolerance. All of the out of range resistors were higher than the maximum value allowed by the tolerance of the resistor. This is most likely due to the fact that the value of carbon resistors increase as the resistors age(1).

APPENDIX

Table 1. Brightness of an Incandescent Bulb with 1, 2, and 3 Cells

Number of series-aiding sources Observations
1 cell Barely lit. Nearly impossible to see with room lighting.
2 cells Slightly brighter. Still difficult to see.
3 cells Brighter, but not producing much light

Table 2. Bulb Voltage and Current with 1, 2, and 3 Cells

Number of series-aiding sources Voltage Current
1 cell 1.45 V 65.8 mA
2 cells 2.90 V 98.4 mA
3 cells 4.35 V 123.5 mA

Table 3. Calculated and Measured Resistor Values

Color code Nominal

value

Minimum

value

Maximum

value

Measured

value

Within

tolerance?

Red Black Red Gold 2 kΩ 1.9 kΩ 2.1 kΩ 2.04 kΩ yes
Orange Orange Brown Gold 330 Ω 313.5 Ω 346.5 Ω 348 Ω no
Brown Green Brown Gold 150 Ω 142.5 Ω 157.5 Ω 155 Ω yes
Gray Red Brown Gold 820 Ω 779 Ω 861 Ω 941 Ω no
Yellow Violet Red Gold 4.7 kΩ 4.46 kΩ 4.94 kΩ 4.99 kΩ no

Sample Calculations

Minimum value

2 kΩ – (2 kΩ x 0.05) = 1.9 kΩ

Maximum value

2 kΩ + (2 kΩ x 0.05) = 2.1 kΩ

REFERENCES

1. Jack Smith, Clifton Laboratories, http://www.cliftonlaboratories.com/carbon_composition_resistors.htm

ELC 131 Lab 4: Series-Parallel and Bridge Circuits

Introduction: Virtually all electronic products are filled with components that are connected both in series and in parallel to form circuits that are coupled, or combined, in order to perform a desired function. The key component to analyzing series-parallel circuits is the ablility to recognize which components are connected in series and which components are connected in parallel.

Objectives: Upon completion of this lab exercise the student will be able to:

1. Identify which components are connected in series and which components are connected in parallel in a series-parallel circuit; calculate the total resistance of a simple series-parallel circuit.

2. Calculate and measure the current flow through and the voltage dropped across any component in a simple series-parallel circuit.

3. Calculate the node voltages of a ladder network.

4. Recognize a circuit as being a bridge configuration; determine the value of resistance that will balance a bridge circuit when the resistance of three arms is given.

5. Describe an operation of a bridge circuit used to sense a change in temperature.

Parts and Equipment: variable DC power supply and leads

DMM and meter leads

resistors, 1 W minimum: 360 Ω, 470 Ω, 680 Ω, 1 kΩ, 2.2 kΩ, 5.1 kΩ, 10 kΩ,

18 kΩ.

potentiometer, 25 kΩ

NTC thermistor, R0=10 kΩ

resistance substitution box

spring board and wires as needed

Prelab: Complete Section 1 Step 1 and Step 2.

Complete Section 2 Step 1.

Complete Section 3 Step 1.

Section 1: Series-Parallel Circuits

Before beginning the analysis of a series-parallel circuit, you must recognize which components are connected in parallel and which components are connected in series. Refer to the circuit of Figure 1. Resistors R2 and R3 are connected in parallel. Resistor R1 is in series with both the parallel combination of R2 and R3 and the source.

The current supplied by the source, IT, flows through R1IT splits into two branch currents, IR2 and IR3, at node A. These two branch currents combine a node B and flow back into the source.

Figure 1: Series-Parallel Circuit Example

Calculating the total resistance is the first step in analyzing a series-parallel circuit. To find the total resistance of a series-parallel circuit, the circuit has to be simplified, one part at a time, until a simple series or a simple parallel circuit remains.

For the circuit of Figure 1, first the resistance of R2 in parallel with R3 is calculated as follows:

Now, the series-parallel circuit can be reduced to the simple series circuit shown in Figure 2.

Figure 2: Circuit of Figure 1 Reduced to a Series Circuit

The total resistance of the circuit of Figure 1 is calculated as follows:

The current supplied by the source is calculated using Ohm’s law as follows:

The voltage dropped across each of the resistors is calculated using Ohm’s law as follows:

The source current, IT, flows through R1.

The current through R2 is calculated using Ohm’s law as follows:

The current through R3 is calculated using Ohm’s law as follows:

Figure 3: Series-Parallel Circuit for Section 1

Step 1: Use the nominal values of the resistors to calculate the resistance of R2 in parallel with R3 and RT for the circuit of Figure 3. Record these values in Table 1.

Step 2: Calculate the current flow through each resistor and the voltage dropped across each resistor. Record these calculated values in Table 1.

Step 3: Use the DMM to measure the resistance of each resistor for the circuit of Figure 3. Record these measured values in Table 1.

Step 4: Connect resistors R2 and R3 in parallel. Measure the resistance of R2 in parallel with R3. Record this measured value in Table 1.

Step 5: Connect R1 in series with the parallel combination of R2 and R3. Measure the total resistance of the series-parallel configuration as shown in Figure 3. Record this measured value in Table 1.

Step 6: Construct the circuit in Figure 3. Measure the voltage dropped across each resistor and the current through each resistor. Record these measured values in Table 1. Turn off the power supply and disconnect the circuit.

Step 7: Calculate the percent error between the calculated values and the measured values. Record this data in Table 1.

Quantity calculated measured % error
R1 360 Ω 366
R2 470 Ω 470
R3 680 Ω 717
R2R3 277.91
RT 673.91
IT = IR1 18mA 18.20
IR2 11mA 11mA
IR3 7mA 7.2mA
VR1 6.41V 6.74V
VR2= VR3 4.95V 5.25V

Table 1: Data for the Circuit of Figure 3

Section 2: Series-Parallel Ladder Network

A resistive ladder network is a series-parallel circuit configuration that is used to divide or scale down voltages. The circuit of Figure 4 is an example of a series-parallel ladder network.

Figure 4: Series-Parallel Ladder Network

Step 1: Using the nominal value of the resistors, calculate the voltages at nodes A and B for the circuit of Figure 4. Record these calculated values in Table 2.

Step 2: Construct the circuit of Figure 4. Measure the voltages at nodes A and B. Record these measured values in Table 2.

Step 3: Calculate the percent error between the calculated and measured values in Table 2. Record these values in Table 2.

Quantity Calculated Measured % error
VA
VB

Table 2: Data for the Circuit of Figure 4

Section 3: Wheatstone Bridge Circuits

The Wheatstone bridge is used in the laboratory to make precision measurements of resistances. Also, the Wheatstone bridge is widely used in instrumentation circuits. The circuit of Figure 5 is an example of a Wheatstone bridge circuit. Frequently, a galvanometer is placed across the bridge. A galvanometer is an ammeter that can measure current flow in either direction.

A bridge circuit is considered to be balanced, or nulled, when the current through the galvanometer is zero. This occurs when the resistances in one arm (R1 and R2) of the bridge have the same ratio as the resistances in the other arm (R3 and R4) of the bridge. The bridge circuit of Figure 5 is balanced if:

Figure 5: Example of a Wheatstone Bridge Circuit

Unbalanced bridge circuits cannot be reduced to series-only or parallel-only circuits using the circuit reduction techniques described in Section 1. Unbalanced bridge circuits can only be analyzed by using a network analysis theorem, such as Thevenin’s theorem.

In this lab, instead of using a galvanometer, a DMM will be used as an ammeter. If the current through the ammeter is zero, the bridge is balanced.

Figure 6: Wheatstone Bridge Circuit for Section 3

Step 1: Use the nominal value of resistors to calculate the value of RX that will balance the bridge circuit of Figure 6. Record this value in Table 3.

Step 2: Construct the circuit of Figure 6 using the resistive decade box for RX. Set the resistive decade box to the value calculated in Step 1. Adjust the resistive decade box until the DMM reads 0.00 mA. Read the value of RX from the resistive decade box. Record this value in Table 3 as RX measured.

Step 3: Calculate the percent error between the calculated and measured values of RX and record this value in Table 3.

RX calculated RX measured % error
11124.12 Ω 11960Ω

Table 3: Data for the Circuit of Figure 6

Section 4: Wheatstone Bridge Application

Thermistors are widely used temperature sensors. The resistance/temperature relationship for NTC thermistors is described by the following equation:

where:

β values range from 1500 K to 7000 K. A typical β value is 4000 K. Figure 7 shows the response of an NTC thermistor, the A919a fluid temperature sensor.

Figure 7: A919a Fluid Temperature Sensor Resistance vs. Temperature

The circuit of Figure 8 shows a Wheatstone bridge circuit used as part of a temperature control system. The resistor labeled RT is an NTC thermistor.

Figure 8: Wheatstone Bridge Application

Step 1: Construct the circuit of Figure 8.

Step 2: Adjust the potentiometer, R2, until the voltmeter reads 0.00 V.

Step 3: Heat up the thermistor by holding it between your finger and thumb. Note the change in voltage.

Step 4: Cool the thermistor by holding it against a cold drink bottle (if available). Note the change in voltage.

Questions:

1. For the circuit of Figure 9, calculate the quantities listed below.

Figure 9

RT=

IT=

VR1=

VR2=

VR3=

IR1=

IR2=

IR3=

2. For the circuit of Figure 10, calculate the voltages at nodes A, B, and C.

Figure 10

VA =

VB =

VC =

3. For the circuit of Figure 11, calculate the values of R1R2, and R3 necessary in order to provide the stated voltages and currents to Load 1, Load 2, and Load 3.

Figure 7

R1 =

R2 =

R3 =

4. For the circuit of Figure 12, complete the following:

Calculate the value of RX that will balance the bridge.

Calculate the current supplied by the source if the bridge is balanced.

Calculate the voltage dropped across RX if the bridge is balanced.

Figure 12

RX =

IS =

VRX =

1