XbarS card
The XbarS card is a type of quality control card .
construction
The XbarS chart (mean and standard deviation chart, x- bar -s chart) contains sample data and two traces or graphs showing two sample parameters: the arithmetic sample mean ( ) (read "X bar", hence the name ; in German "x quer") and the sample standard deviation s.
In practice, a sample often consists of 5 measured values. This can be, for example, the measurement results for five parts manufactured in direct sequence. For each sample, the sample mean and sample standard deviation are then calculated and plotted in the respective graphs. The resulting curves give the worker information about the stability of his process.
The XbarS card can of course also be used in areas other than production. In the age of manual control chart management, the use of the XbarS card was seldom, as the manual calculation of the standard deviation was very laborious and error-prone; Instead, the XbarR map was primarily used , which only requires the calculation of range values. With the advent of computer programs for statistical process control , this was no longer an advantage worth mentioning, and the XbarS card is now the standard means of monitoring measurable features because of its greater statistical efficiency.
literature
- Edgar Dietrich, Alfred Schulze: Statistical procedures for machine and process qualification . Carl Hanser Verlag, Munich / Vienna 2005, ISBN 3-446-22894-2 .