Evaluation and Presentation of Experimental Data

Lab 2a: Basic Mechanical Measurements

EXERCISE 1

Using the data in Table 1, which represents a standard weight value applied to a scale and the measurement obtained from a scale

a. Plot measurement vs. standard (hint: type in data and use scatter chart)
b. Label each axes and make sure the plot only goes from 0 to 70 lb. on the x axis and 0 to 80 lb. on the y axis
c. Find the linear trend line and the R squared value and include on chart
d. Make the plot lines thicker so they can project and print well
e. Include grid lines

EXERCISE 2

Given the data in Table 2,

a. Compute the average value and standard deviation of the population. In your Excel sheet, fill the average value cell with a red background and outline the standard deviation cell with a black border.

b. Plot the mean value and the data about the mean for each of the samples

i. The x axis should be labeled samples 1 thru 15
ii. The scatter should be points - not a curve
iii. Plot a straight line corresponding to the mean

iv. Label all axes and make lines dark enough to project
v. Place the legend at the bottom of the graph as shown

EXERCISE 3

Using the data of exercise 2, plot the histogram of the measured data. In this example, we used a total of 7 bins with the center bin having the mean value. Compare the number of points above and below the mean to the scatter plot of exercise 2.

EXERCISE 4

Let us revisit Exercise 2. In this case we will present the data as a column and name the columns. Then we will compute the average and standard deviation and also name the results.

To name a cell (or column or row of cells) select the cell(s), right click and choose Define Name from the pull down list.When you choose Define Name Excel will fill in the name if there is text such as "my_name" in the cell to the left or above the cell(s) highlighted. You have to click ok. You can also override the name Excel chooses if you wish. It is a good idea to include a column/row with the name of the variable to aid in documentation. In the following Excel spread sheet example seen in Table 3, the names of the columns are meas_no and in_data while the name avg_all is the average value of in_data and std_all is the population standard deviation.

You can then use the name of individual cells in computations such as was done in the highlighted cell. Here we entered "=3*std_all". Column names can be used as input to plotting and other functions. We will address how to access individual cells in a named column in a later lesson.

Lab 2b: Image Analysis with MATLAB

REPORT

The report format should follow that in the "ENGR202_Report_Grading.pdf" posted on the BbLearn site for the course. You are expected to present your methodology and results in a lab report/ narrative format. The lab report main body should contain: the equipment used; the methodology used for the measurements; and answers to questions posed in this lab manual.

Calculations (either hand calculations or Excel generated) should be provided in an Appendix. Show all calculations. At no time should you cut and paste text from your lab handout into your report. Only put graphs that you want to discuss in detail into the body of your report. The others can go into an appendix.

Here are some questions to that must be answered in the discussion of results and conclusions, but do not limit yourself to these:

a. If you needed a measurement to the nearest 0.1 inch, what instrument would you choose? How about 0.01 in, 0.001 in, or 0.0001 in?
b. How did your individual measurements compare to your team results?
c. Comment on the accuracy and precision of the measurements. The washers you have are stamped parts, and you would not expect them to have high precision. What size bolt do you think they are designed for? How do the sets of bolt measurements compare?
d. Which instrument produces the narrowest distribution of results? What shape do the distributions have?
e. Which standard deviation function did you use in your calculations? Why?
f. Discuss whether the histograms match a Gaussian distribution - why or why not.
g. How do your bolt measurement results compare to your mechanically measured results? Compare the errors.
h. What would cause error in your image analysis for counting and dimensional measurements of the objects?
i. What are some good applications using MATLAB's image analysis tool? What are the pros and cons?

Attachment:- Attachments.rar