Graphical Analysis Applications In An Electrical Engineering Technology Laboratory

Troubleshooting frequently focuses on the process of developing a systematic logical approach to the identification and solution of a problem. Identifying the problem, devising a hypothesis for its cause, postulating a test strategy that will identify the source of the fault, implementing tests to confirm the fault, and correcting the fault are some of the steps in this process. This paper describes the use of graphical analysis techniques that take the student beyond the point of fixing the immediate problem on a single unit to asking questions about the underlying causes for failures when several units are involved and proposing solutions that will prevent their recurrence. Introduction A learning tool called ALFRED (Amplitude Linear Frequency Related Educational Device) was developed in the mid 1980’s by the faculty and staff of the Electrical Engineering Technology Department of Purdue University to provide students in a sophomore-level course “with hands-on experience in electronic troubleshooting from the system level to the component level.” It is essentially a one octave music synthesizer that has served as a useful tool to teach troubleshooting for more than a decade. A supplementary board that monitors “six inputs—two thermometer calibration voltages, three single ended DC voltages, and one temperature dependent differential voltage—and displays them one at a time on a three and one-half digit display” was introduced by Aubrey and Brelage in 1995. 4 It functions as a temperature and voltage monitor for the rest of ALFRED. Hundreds of students have developed their troubleshooting skills to the point where they are able to locate and repair multiple faults at the component level in a complex electronic system. In an effort to address problems associated with the manufacturing environment, lectures on graphical analysis techniques, such as flowcharts, check sheets, run charts, Pareto charts, cause & effect (fishbone) diagrams, histograms, etc. , were added to the troubleshooting course (EET 276) in 1997. They provide methods of data analysis that relate to the solution of production problems where issues of reliability and quality control are concerned. Student Involvement A homework assignment is given in which the student uses a check sheet to tabulate the results of various test procedures conducted at different locations on several units of a fictitious electronic system. One is required to enter the data in a spreadsheet, construct histograms that show the frequency of each of the tests for several locations, analyze the results, determine what faults are present, and decide how significant they are. During a laboratory session, students analyze several ALFRED fault sheets to identify types of faults, how often they occur, on which board(s) they occur, and draw conclusions about possible causes for the failures. P ge 304.1 Homework Problem Stated The homework assignment is stated as if it is a preliminary report from tests conducted on several faulty units: During one 8-hour shift, 60 units were removed from the assembly line of a product due to failures. Each unit was placed on a bed-of-nails tester and several measurements were taken at 5 different test points (a-e). The 5 test points do not necessarily indicate a progression of signal through the unit! The assessments of the data from these measurements on each unit are listed in Table 1 below in the form of 5-digit numbers. For each of the digits the numeral interpretations are as follows: • Numeral 0 indicates acceptable AC and DC signals at the test point; • Numeral 1 indicates no AC or DC signal at the test point. • Numeral 2 indicates a DC quiescent current that exceeds the maximum specification at the test point; • Numeral 3 indicates a DC quiescent current that falls below the minimum specification at the test point; • Numeral 4 indicates a frequency that exceeds the maximum frequency specification at the test point; • Numeral 5 indicates a frequency that is less than the minimum frequency specification at the test point; • Numeral 6 indicates the presence of the +V supply at the test point; • Numeral 7 indicates the presence of the -V supply at the test point; • Numeral 8 indicates an AC voltage greater than the maximum specification at the test point; • Numeral 9 indicates an AC voltage less than the minimum specification at the test point; This assignment requires the student to analyze the data using various graphical techniques discussed in lecture. It focuses on the most-significant digit, the middle digit, and the least-significant digit in each number, and on all of the digits collectively in all of the numbers. In order to provide variation each semester, the 5-digit numbers are derived from the student identification numbers of the students enrolled in the course. Table 1. Test Measurement Results abcde abcde abcde abcde abcde abcde 69640 69983 71373 71681 80333 81045 22912 25082 25801 27346 27418 27908 49823 49927 61567 62751 63196 64294 64359 64525 65989 66899 66990 69051 81353 83188 83869 84414 85477 86455 43832 45251 45805 46678 46910 48402 87208 87416 87732 88836 88891 8897