Method · reference manual

What is SPC?

Statistical Process Control

In 30 seconds

SPC monitors a process with statistical methods, especially control charts, to separate common-cause variation from special causes and to intervene in time.

How does it work?

  • A measurement plan is set for critical characteristics.
  • Data is plotted on a control chart; control limits are calculated from the process’s own data.
  • Points outside the limits and meaningful patterns signal a special cause, triggering the reaction plan.

Often confused with

Control limit and tolerance

Tolerance is the limit the customer wants; a control limit is the process’s natural behaviour. A process can be within tolerance and still out of control. Capability (Cp/Cpk) compares the two.

Common mistakes

  • Setting control limits equal to tolerance values.
  • Keeping the chart but not running the reaction plan when a signal appears.

From a QWorks perspective

SPC is part of the QWorks platform vision; the aim is for a signal to become work with an owner and a deadline.

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