Reducing variation in the process industries

Engineering control systems continually adjust processes online in order to counteract the effects of disturbances which, if uncorrected, would cause output to deviate ever further from target. Statistical process control (SPC) seeks to reduce this variation to an acceptable level by identifying the causes of extraneous disturbances so that they can be removed by appropriate online or offline action. If it is uneconomic or impossible to eliminate the cause of a particular type of disturbance then the production system should be modified so as to mitigate its effect