Various rules

In addition to the use of the simple rule for the following settings:

  • Within the control limits: whenever a part is measured that falls within control limits the perfectly centered process hypothesis is completely verified. No futher action is required.
  • Outside of control limiits: whenever a part is measured that falls outside of the control limits the perfectly centered process hypothesis is not verified. The process must, therefore, be adjusted.

Using the rules defined above allows for variation detection in finer processes.

Graph Description Meanvalue chart decision Range chart decision
sous controle Controlled procedures

The curves and the oscillating R from each side of the mean.

2/3 of the points are in the central third of the chart.

Production Production
hors controle1 Points outside of the limits

The last point traced surpassed the control limits.

Adjusting the procedure

by the difference value that separates the point from the target value.

Upper limit case

The short-term capability deteriorates.  It is necessary to find the source of this deterioration and intervene.

There is a measurement error

hors controle2 Upper or lower trend

7 consecutive points are above or below the mean.

Adjusting the procedure

by the mean difference that separates the trend from the target value 

Upper trend case

The short-term capability deteriorates.  It is necessary to find the source of this deterioration and intervene.

Lower trend case

The short-term capability improves.  It is necessary to find the source of this improvement and maintain it.

hors controle3 Increasing or decreasing trend.

7 consecutive points show a regular increase or a regular decrease.

Adjusting the procedure

if the last point approaches the control limit of the difference that separates the last point from the target value.

Ascending series case

The short-term capability deteriorates.  It is necessary to find the source of this deterioration and intervene.

Descending series case

The short-term capability improves.  It is necessary to find the source of this improvement and maintain it.

hors controle 4 1 point is close to the limit.

The last traced point within 1/6 of the edge of the control chart.

 

 

Confirm

by taking another sample immediately. If the point reappears in the central third – production.  If the point is also close to the limits or outside of the limits, adjust the meanvalue of the two points

Upper parameter case

Monitor the capability

If several of the points on the chart are also close to the upper limits, the capability deteriorates.  It is necessary to find the source of this deterioration and intervene.