Essay On Control Charts

Control charts refer to statistical tool used in quality control to determine process capabilities, monitor the effects of variables and analyze the variables on the difference between the target and real performance. The control charts often indicate the lower and upper control limits with medium to help in detecting the trend of the plotted values.
While interpreting control charts, it important to `consider the following: patterns (natural and unnatural patterns), test for the patterns, root assignable cause of the patterns and finally the statistical properties of the run tests. The natural and unnatural patterns show the plots on the control charts over time. The natural pattern occurs when points fluctuate in random manner while the opposite is for unnatural. It is important to test the patterns in unnatural patterns using a set of statistical tests. Once the patterns are tested, it is necessary to determine the cause of the patterns. Finally, the statistician may infer the statistical properties of the run tests. There are different causes of the out-of-control indicators in a control chart. These include; first, wrong setting, error in measurement and incomplete operation especially in significant shift patterns. Second, change in materials especially new tools, new operator and failure to recalculate limits when the process is a little-halted example, smaller sustained shift. Third, wearing out of tools, operator fatigue and gradual change in a person level of skill for example in trends. Finally, it is observed that, environmental changes such as temperature fluctuations that may result in a cycle.
In conclusion, control charts have the capacity to identify the causes of process variability, restriction and elimination of their influence on a given test.