AiVibeIndustry 4.0 & Manufacturing Operations
Control Chart
A control chart is a time-ordered plot of a process measurement with a centre line and upper and lower control limits calculated from process data, used to detect when a process has changed and whether it is in statistical control.
Each point on a control chart represents a measurement or a statistic from a subgroup, such as a mean, range, proportion or count, plotted in time order. The centre line is the process average, and the control limits are typically set three standard deviations of the plotted statistic above and below it. A point beyond a limit, or a non-random pattern such as a long run on one side of the centre line, signals a likely special cause.
Different charts suit different data. Variables charts, such as X-bar and R, X-bar and S, and individuals and moving range charts, are used for continuous measurements. Attribute charts, such as p, np, c and u charts, are used for counts of defective items or defects. Time-weighted charts such as CUSUM and EWMA detect small, sustained shifts more quickly than standard Shewhart charts. Control charts are used on production lines, in laboratories and in service processes.
Control limits should be calculated from data collected while the process is stable, and recalculated only after a deliberate, verified change. Drawing specification limits on a chart of subgroup means is misleading, because individual parts vary more than averages. Charts are useful only when someone reacts to signals using a defined reaction plan. ISO 7870-2 covers Shewhart control charts.
Key points
- Plots process data over time against a centre line and control limits.
- Limits are typically three standard deviations of the plotted statistic.
- Variables charts suit measurements; attribute charts suit counts.
- CUSUM and EWMA charts detect small sustained shifts sooner.
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory as the OEM: edge devices plus AI agents that let people talk to PLC, CNC and robot controllers in plain language. Existing lines are retrofitted with edge devices, and a trained operator confirms every change an agent proposes.
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Related terms
- Statistical Process Control (SPC)Industry 4.0 & Manufacturing Operations
- X-bar and R ChartIndustry 4.0 & Manufacturing Operations
- Attribute Control Charts (p, np, c and u Charts)Industry 4.0 & Manufacturing Operations
- Western Electric RulesIndustry 4.0 & Manufacturing Operations
- Common-Cause and Special-Cause VariationIndustry 4.0 & Manufacturing Operations