19 Nov 2020
A process can be out of control even though all of the samples fall within the upper and lower control limits when there is an indication of non-random variations which is caused by definite, specific causes called assignable causes which makes the process go out of control or become statistically unstable. Once assignable causes are removed and only random variation due to common causes remains, the process will become stable and return to an in control condition.
According to our book statistical process control involves establishing standards, monitoring standards, taking measurements, and taking corrective action as a product or service is being produced, and control charts is a graphic description of data that has been collected and they help us created establish between the upper and lower limits of the data that we need to control. All the process that we need to control will always have variations, which can be natural and assignable, but the creation of the chart is with the purpose to help managers and employees to produce under an acceptable limit of variance. Since natural variables are out of the personal control, they will set a limit within these naturales variables that they can occur without affecting the production. The process can be out of control even if the limits remain within the acceptance, but being out of control means that is a non-random or assignable variables that is causing the process to go out of control, assignable variable are an specific cause that management and workers have to take to further investigation to find the assignable variable and eliminate what is causing it, once the assignable variable is identified and remove, the process can be back to the stay with the natural variable and go back to being in control.