5.6. Case Studies
5.6.1. Eddy Current Probe Sensitivity Case Study
The data for this case study is a subset of a study performed by
Capobianco, Splett, and Iyer.
Capobianco was a member of the NIST Electromagnetics Division and
Splett and Iyer were members of the NIST Statistical Engineering
Division at the time of this study.
The goal of this project is to develop a nondestructive portable device for detecting cracks and fractures in metals. A primary application would be the detection of defects in airplane wings. The internal mechanism of the detector would be for sensing crack-induced changes in the detector's electromagnetic field, which would in turn result in changes in the impedance level of the detector. This change of impedance is termed "sensitivity" and it is a sub-goal of this experiment to maximize such sensitivity as the detector is moved from an unflawed region to a flawed region on the metal.
The case study illustrates the analysis of a 23
full factorial experimental design. The specific statistical goals
of the experiment are:
|Software||The analyses used in this case study can be generated using both Dataplot code and R code. The reader can download the data as a text file.|
|Data Used in the Analysis||
There were three detector wiring component factors under
Y X1 X2 X3 Probe Number Winding Wire Run Impedance of Turns Distance Gauge Sequence ------------------------------------------------- 1.70 -1 -1 -1 2 4.57 +1 -1 -1 8 0.55 -1 +1 -1 3 3.39 +1 +1 -1 6 1.51 -1 -1 +1 7 4.59 +1 -1 +1 1 0.67 -1 +1 +1 4 4.29 +1 +1 +1 5Note that the independent variables are coded as +1 and -1. These represent the low and high settings for the levels of each variable. Factorial designs often have two levels for each factor (independent variable) with the levels being coded as -1 and +1. This is a scaling of the data that can simplify the analysis. If desired, these scaled values can be converted back to the original units of the data for presentation.