1. Conceptual Framework for Statistical Process Control
Based on Ch. 5 from Statistical Quality Design and Control Authors: Devor, Chang and Sutherland
Presented by Dr. Joan Burtner, Certified Quality Engineer
Associate Professor of
Industrial Engineering and Industrial Management
Mercer University

2. Origins and Nature of Variability
Outer Noise
External factors that affect the product when it is operating
Measured during field use under actual operating conditions
Inner Noise
Internal change in product parameters
Caused by such things as mechanical wear and aging
Variational Noise
Variation in product parameters from one unit to the next
Manufacturing imperfection
ISE 327 Chapter 5
Dr. Joan Burtner, Associate Professor of Industrial Engineering

3. Countermeasures to Functional Variation
Engineering design
Outer noise
Inner noise
Statistical process control
Variational noise
ISE 327 Chapter 5
Dr. Joan Burtner, Associate Professor of Industrial Engineering

4. Two Types of Process Variation
Common cause
Problems within the system that are ever-present
Correctable typically by management
Special cause
 Assignable sporadic problems
 Correctable locally
ISE 327 Chapter 5
Dr. Joan Burtner, Associate Professor of Industrial Engineering

5. Dr. Joan Burtner, Associate Professor of Industrial Engineering
Deming’s Observation
Common cause 80% -85%
Special cause 15%- 20%
Similar to the Pareto Principle which is also known as the Rule
80% of the complaints come from 20% of the customers
80% of the defects can be attributed to 20% of the faults
ISE 327 Chapter 5
Dr. Joan Burtner, Associate Professor of Industrial Engineering

6. Time Evolution of Process Behavior
When a system is subject to common causes, data collected over time may be used to develop a statistical model for the process.
The most common changes in process performance over time are changes in the process mean level and changes in the amount of variation in the process.
Through periodic sampling, it is possible to detect changes in the process model.
ISE 327 Chapter 5
Dr. Joan Burtner, Associate Professor of Industrial Engineering