iSPCChart Alarms 
You can apply Western Electric Company (WECO) rules to SAP Manufacturing Integration and Intelligence (SAP MII) statistical process control (SPC) charts to evaluate control chart run alarms.
Features
You can customize the default behavior of the alarm evaluation on a template-by-template basis. The system applies the WECO rules on a subgroup level and does not indicate trends of points within a subgroup. You can enable alarms for upper and lower charts.
Alarm setup requires integer values for limit and length values. The length value (y) is the number of data points being evaluated, and the limit value (x) is the number of data points within the length that cause the alarm to be activated. When x of y consecutive data points exceeds a threshold, the system activates an alarm. For example, if 2 (limit value) of 3 (length value) points are beyond Zone A, the Zone A alarm rule is violated. Zones A, B, and C represent the 3, 2, and 1 sigma widths beyond the centerline, respectively.
The limit alarms are defined in the following table:
Limit Alarm | Violation Occurs When |
Control | Any point exceeds the control limit. Default value is one point. |
Specification | Any point exceeds the specification limit. Default value is one point. |
Alternating | X of y points move from one side of the centerline to the other. |
Run | At least x of y consecutive points appear on the same side of the centerline. |
Trend | X of y points indicate the variable continues in the same direction (either increasing or decreasing). |
Sigma Difference | The values of consecutive subgroup plot points vary by four sigma. |
Zone A | X of y points are in or beyond the zone (for example, 2 of 3 points are in Zone A or beyond). |
Zone B | X of y points are in or beyond the zone (for example, 2 of 3 points are in Zone B or beyond). |
Inside Zone C | All x of y points are inside the zone. |
Outside Zone C | All x of y points are outside the zone. |
For more information, see iSPCChart Alarm Properties.