control chart, quality control chart, process chart(redirected from p chart)
Also found in: Encyclopedia.
control chart, quality control chart, process chart or P (percent defective control) charta diagram used to plot variations in the size or other characteristic of a component or PRODUCT made by a machine and/or operative. Such charts are compiled by taking samples of items produced and measuring their sizes or characteristics. Where variations are small and fall within predefined normal or acceptable limits marked on the control chart, no action is necessary. However, where machine faults, worn tools or defective materials cause larger variations than the control limits then the cause of this variation must be investigated and immediate corrective action taken to avoid any further production of defective items. See QUALITY CONTROL.
Fig. 27 shows a typical control chart which depicts variations in the size of a machine component, and the upper and lower control limits at which the process would require correction.