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Function documentationZone A Limit Alarm Locate this document in the navigation structure

 

Alarm rule 5 is triggered when multiple points (in a series) are in Zone A or beyond (upper or lower zone A).

The area between a control limit and the center line is divided into thirds, which are called Zones. Standard control limits are located 3 sigma away from the center line. For standard control limits, the distance from the center line to the control limit is divided into 3 equal parts of one sigma each.

Zone A, often referred to as 3-sigma zone, is closest to the control limit (typically between two and three standard deviations from the center line). Zone B is the middle zone (typically between one and two standard deviations from the center line). Zone C is closest to the center line (typically between the center line and one standard deviation from the center line).

For alarm rule 5, the limit and length values are used for both the upper and lower charts. The data points on the chart are checked for the specified number of points in zone A or beyond. For alarm rule 5, an alarm is triggered when there are <Limit> number of data points in the <Length> that are either in or beyond Zone A. You can also use other alarms, 32, 33, 34, or 35.

Features

General guidelines to detect instability in Zone A for different chart types are as follows:

Chart Type

Maximum Points to apply Rule

X-Bar

2 of 3 successive points in upper or lower Zone A or beyond

Individual Chart

Median

R-chart when the minimum subgroup size is 4

R-chart when the minimum subgroup size is less than 4

2 successive points in upper Zone A or beyond

S

1 point in upper or lower Zone A or beyond

Moving Average

Moving Range

P

NP

C

U

Following are the alarm properties defined for Zone A Limit Alarm:

Alarm Name

Property Name

Parameter

Data Type

Description

Allow Upper Chart Zone A Limit Alarm

UpperWEZoneAAlarmEnabled

Boolean

Enables Zone A limit alarms for upper chart

Allow Lower Chart Zone A Limit Alarm

LowerWEZoneAAlarmEnabled

Boolean

Enables Zone A alarm points for lower charts

Alarm 5

Limit of Zone A Limit Alarm

WEZoneAAlarmLimit

Integer

Sets the limit and length values to check data points within Zone A

Length of Zone A Limit Alarm

WEZoneAAlarmLength

Integer

Alarm 32

Limit of Upper Chart Upper Zone A Limit Alarm

WEUpperChartUpperZoneAAlarmLimit

Integer

Defines the limit and length values to check points in upper Zone A of the upper chart

Length of Upper Chart Upper Zone A Limit Alarm

WEUpperChartUpperZoneAAlarmLength

Integer

Alarm 33

Limit of Upper Chart Lower Zone A Limit Alarm

WEUpperChartLowerZoneAAlarmLimit

Integer

Defines the limit and length values to check points in lower Zone A of the upper chart

Length of Upper Chart Lower Zone A Limit Alarm

WEUpperChartLowerZoneAAlarmLength

Integer

Alarm 34

Limit of Lower Chart Upper Zone A Limit Alarm

WELowerChartUpperZoneAAlarmLimit

Integer

Defines the limit and length values to check points in upper Zone A of the lower chart

Length of Lower Chart Upper Zone A Limit Alarm

WELowerChartUpperZoneAAlarmLength

Integer

Alarm 35

Limit of Lower Chart Lower Zone A Limit Alarm

WELowerChartLowerZoneAAlarmLimit

Integer

Defines the limit and length values to check points in lower Zone A of the lower chart

Length of Lower Chart Lower Zone A Limit Alarm

WELowerChartLowerZoneAAlarmLength

Integer

Example

If you define alarm rule 32 with limit and length as 2 and 3 respectively, the alarm rule 32 is violated if only 2 points in a string of 3 adjacent points in the upper chart are lower than or beyond Zone A.

Graphical representation of Zone A Limit Alarm:

This graphic is explained in the accompanying text.