A time plot that includes a centerline and upper and lower control limits. The control limits are statistically calculated from the data in the plot. These limits allow you to quickly detect specific changes in a process. A control chart also helps quantify the current capability of a process and identify when special events interrupt usual operations.
(1) A graphic comparison between the process's performance and computed limits know as control lines. This statistical method is used to decide when to take action and when to leave a process alone. The charts can identify when statistically unnatural patterns occur so their cause can be investigated. Tool for monitoring process variation. (2) A plot of the process output against time or observation order. The variation observed is used to determine and plot the process average and the upper and lower control limits set at three standard deviation from the average. Observations outside the control limits and other patterns indicate the presence of special cause variation.
A graphic display of the results of a process over time and against established control limits. The dispersion of data points on the chart is used to determine whether the process is performing within prescribed limits and whether variations taking place are random or systematic.
A cumulative summary chart of results from QA tests with reference materials (e.g. reference toxicants). The results of a given QA test are compared to the control chart mean value and acceptance limits (typically 95% confidence limits, i.e. mean + 2 standard deviations) or warning limits (typically 99% confidence limits, i.e. mean + 3 standard deviations).
a graphic representation of a characteristic of a process that shows plotted values of statistical data gathered from that characteristic, a central line, and one or two statistically derived control limits. [EIA 557
A chart with upper and lower control limits on which values of some statistical measure for a series of samples or subgroups are plotted. The chart frequently shows a central line to help detect a trend of plotted values toward either control limit.
A chart that indicates upper and lower statistical control limits, and an average line, for samples or subgroups of a given process. If all points on the control chart are within the limits, variation may be ascribed to common causes and the process is deemed to be "in control." If points fall outside the limits, it is an indication that special causes of variation are occurring, and the process is said to be "out of control."
A tool for monitoring changes that occur within a process, by distinguishing variation that is inherent in the process (common cause) from variation that yield a change to the process (special cause). This change may be a single point or a series of points in time - each is a signal that something is different from what was previously observed and measured.
The control chart, also known as the 'Shewhart chart' or 'process-behaviour chart' is a statistical tool intended to assess the nature of variation in a process and to facilitate forecasting and management. A control chart is a more specific kind of a run chart.