Literature Review about statistical process control (SPC) Term Paper

Literature Review about statistical process control (SPC) - Term Paper Example It can be employed in any production unit (which generates material or data as outputs) where the process can thus remain independent from constant supervision. Although there can be variety in products and the required steps necessary for the production process, the SPC analysis remains uniform. SPC is advantageous over other methods of control particularly since it ensures that the production is not affected to any significant degree due to interruptions since it requires no direct inspection. Only "Out of control" process can be covered by SPC. An â€Å"in-control-process† does not always refer to an acceptable and desirable output. This conceptual misunderstanding often results in misleading applications of SPC. If not properly perceived, SPC can lead to loss of production. The Control chart is the fundamental tool for SPC. It is a graphical representation defined by the plot of measured data (at least 15 observations) on the chart. Using control charts the changes in the inherent process from the accumulated data can be identified. This, in turn determines the ‘special’ cause that affects the results. In a control chart the ‘central line’, denoted by a solid line reflects the average of the accumulated data points and passes through the middle of the graph. Control limits are the lines (a specified distance is maintained from the central line) in the control chart which are calculated by using statistical tools and indicate the behavior of the process i.e whether the process is ‘out of control’ or ‘in-control’. There are two type of control limits- (i) the upper control limit (UCL) and (ii) the lower control limit (LCL). UCL and LCL are defined by the following rule: UCL = centre line + 3* SD †¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ equ.(1) Recall that a Percentile is given by the division of pointed data in hundred equally divided groups. The nth percentile Pn is defined as- n% of the data points are on or below this