BS ISO 7870-5:2014 pdf free

BS ISO 7870-5:2014 pdf free.Control charts – Specialized control charts
This part of ISO 7870 establishes a guide to the use and understanding of specialized control charts in situations where commonly used Shewhart control chart approach to the methods of statistical control of a process may either be not applicable or less efficient in detecting unnatural patterns of variation of the process.
In certain cases of industrial production it takes considerable time to produce a new item or the tests are destructive in nature. As a result, it is inconvenient to sample frequently to accumulate sample of size n > 1. In the meantime process average or dispersion may have changed and this may incur some appreciable loss. Under such situations subgroups, each consisting of individual observations, are used for process monitoring.
Unlike the case of Shewhart control charts, here successive moving averages and moving ranges are not independent. Hence, in moving average and moving range control charts, runs on either side of the centre line do not have the same interpretation as is given by Shewhart control chart. However, a point beyond control limits here has the same significance as in case of Shewhart control chart. Cyclic pattern and/or increasing or decreasing trend in the moving range chart is indicative of potential for improvement. However, the assignable causes for the moving average chart and those for moving range chart may be different.
In some situations a control chart for moving average and moving range is more efficient. It gives a warning signal earlier than with usual (X,R) charts. It is not necessary to wait until an entire new sample is accumulated. This may be important if the product is either expensive or the rate of output is small.
Successive points are not independent. Since the probability of obtaining a run of any kind is much larger with control chart for moving average or moving range as compared to the Shewhart control charts, the traditional interpretation of runs is not valid for these control charts.BS ISO 7870-5 pdf download.