Control Limit Alarm
Control limits are horizontal lines on SPC charts that are calculated and placed at a fixed distance (by default, +/- 3 standard deviations) above and below the centerline (mean). Alternatively, you can specify fixed control limits or calculate dynamic control limits using a query.
For alarm rule 1, the limit and length values are used for both the upper and lower charts and for both the upper and lower control limits. The data points plotted on the chart are compared to the specified control limits. For alarm rule 1, an alarm is triggered when there are <Limit> number of data points in the <Length> data point string, thereby taking the data points beyond either of the control limits. You can also use rules 20, 21, 22, or 23 with control limit alarm.
Features
Following are the alarm properties defined for Control Limit Alarm
:
Alarm Name | Property Name | Parameter | Data Type | Description |
|---|---|---|---|---|
Allow Upper Chart Control Limit Alarm |
| Boolean | Enables control limit alarm for upper chart | |
Allow Lower Chart Control Limit Alarm |
| Boolean | Enables control limit alarm for lower chart | |
Alarm 1 | Alarm Limit for Control Limit |
| Integer | Sets the limit and length values to be used to determine the alarm for the upper and lower charts and upper and lower control limits |
Alarm Length for Control Limit |
| Integer | ||
Alarm 20 | Alarm Limit for Upper Chart Upper Control Limit |
| Integer | Defines the limit and length for upper control limit of the upper chart |
Alarm Length for Upper Chart Upper Control Limit |
| Integer | ||
Alarm 21 | Alarm Limit for Upper Chart Lower Control Limit |
| Integer | Defines the limit and length for lower control limit of the upper chart |
Alarm Length for Upper Chart Lower Control Limit |
| Integer | ||
Alarm 22 | Alarm Limit for Lower Chart Upper Control Limit |
| Integer | Defines the limit and length for the lower control limit of the lower chart |
Alarm Length for Lower Chart Upper Control Limit |
| Integer | ||
Alarm 23 | Alarm Limit for Lower Chart Lower Control Limit |
| Integer | Defines the limit and length for the upper control limit of the lower chart |
Alarm Length for Lower Chart Lower Control Limit |
| Integer |
Example
If you use alarm rule 21 with limit and length values each as 1, the alarm rule is violated if any one point in any string of one adjacent point is beyond the upper control limit on the upper chart. A single point is marked below the lower control limit and is marked as a rule violation. The following is a graphical representation of Control Limit Alarms
:
