Jeff Cawley, Northwest Analytical, and Dave Harrold, CONTROL ENGINEERING

Articles

Process Instrumentation and Sensors May 1, 1999

SPC and SQC provide the big picture about processing performance

Statistical Process Control (SPC) and Statistical Quality Control (SQC) methodology is one of the most important analytical developments available to manufacturing in this century. SPC has come to be known as an on-line tool providing close-up views of what's happening to a process at the moment. SQC provides off-line tools to support analysis and decision making to help determine if a process is stable and predictable from shift to shift, day in and day out, and from supplier to supplier. —SPC provides on-line tools that permit a close-up view of what's currently happening to a process. —SQC provides off-line tools to support analysis and decision making about process stability over time. When SPC and SQC tools work together, users see the current and long-term picture about processing performance. Before SPC, products were inspected after they were completed and defective products were discarded or reworked. The idea behind continuous improvement is to focus on designing, building, and controlling a process that makes the product correctly the first time (See CE , Jan.

By Jeff Cawley, Northwest Analytical, and Dave Harrold, CONTROL ENGINEERING