Poisson Defect Monitoring
The c-chart models rare discrete nonconformities where opportunities for defects are very large, such as surface blemishes on an automotive panel, circuit board solder voids, or fabric flaws per 100 meters.
Foundational Category: Statistical Process Control (SPC) • ~5 min read
c Chart for Count of Defects
Monitor multiple defects per item on circuit boards, textiles, paint surfaces, or weld seams.
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Q:
When should a C-Chart be used in Statistical Process Control?
Use a c-chart when counting the total number of nonconformities (defects) across a constant sample inspection area or unit (Poisson model). Limits are: UCL = c̄ + 3√c̄, LCL = Max(0, c̄ - 3√c̄).
Average Defects (c̄)4.47Center Line
Upper Limit (UCL)10.81c̄ + 3√c̄
Lower Limit (LCL)0.00Max(0, c̄ - 3√c̄)
C-Chart (Poisson Count of Defects)c̄ = 4.47
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