PROCESS CONTROL FOR ATTRIBUTES
P, NP, C, and U Charts
Attribute type data has noncontinuous values, namely “go” or “no-go,” “conforms” or “nonconforms,” “pass” or “fail,” “on time” or “not on time,” “small, medium, or large,” and so forth. For some inspections such as contamination, scratches, chip, and so forth, it might be difficult to define the difference between a conforming and a nonconforming or defective product unit, especially when an inspector’s judgment is involved. Precise operational specifications for attribute characteristics are a must. Thorough training of inspectors is also required. Attribute data versus time can be collected and analyzed using different types of attribute control charts. There are four main types of control ...