Statistical Quality Control Essay Example | Topics and Well Written Essays - 500 words

Statistical Quality Control - Essay Example If one or more observations lie outside the control limits of the chart, the process is out of control. However, a process can be out of control even if all samples fall within the upper and lower control limits. A process can be out of control but may still fall within limits due to a false specification of limits. In such a scenario, the management will get an idea that the process is in control while actually it is out of control. This can be reduced by regular review of control limits. A process can be out of control but it may not be able to interpret the same from the control charts. The process may actually be following certain trend which is depicted in a better fashion by Run charts. The idea here is that there should not be too few or too many runs in a process. Run implies a series of observations on the same side of the centre line. The observations may lie within control limits but actually follow a zig-zag pattern (NHS). It is also possible that there may be a seasonality effect in the observations which has no explanation. Also, one or two observations may be quite distinct from others are can easily be identified to understand the fault in a process. In a real life scenario in a factory production line, it is possible that if the process variation is measured it is within limits. But if a day is broken into several hours and studied, possible trends are observed. These may be due to nature of working of machine at various times of the day, impact of wear and tear during the day, difference in the accuracy of tasks done by various workers, difference in availability of facilities such as light during various hours and so on. An experiment was conducted in a factory for two days to find out whether the process was in control. On the first day, it was noticed that during various hours in the day, the observations were within control limits. On the second day, when the process was studied after breaking the day