Control Tests

To assess ongoing control and stability, you test incoming sample data online against various statistical conditions. Each condition is represented by a control test that is applied to subgroups that are plotted on a control chart. Quality includes a set of 17 default control tests. Each test is based on a standard Shewhart pattern for identifying special causes of variability. Use the default test or create control tests from the industry-standard default prototypes.

You can selectively apply the tests to mean or variance charts, and control the sensitivity of each test by specifying the number of points to evaluate and the number of points in the pattern that are required for triggering a violation. If a data point (subgroup) violates one or more control tests, the system generates an alarm. The system identifies a test by a unique ID number and description.

Note:

Control tests 1 through 17 are supplied as industry-standard system defaults. You can't change the prototype fields for these tests.

Test ID Number	Description	Prototype	Chart	k of K
1	Specification limit violation.	1	1	1 of 1.
2	Control limit violation (mean).	2	1	1 of 1.
3	Control limit violation (variance).	2	2	1 of 1.
4	Trend - 7 pts (mean).	4	1	7 of 7.
5	Shift - 2 of 3 pts (mean).	6	1	2 of 3.
6	Shift - 4 of 5 pts (mean).	7	1	4 of 5.
7	Shift - 8 of 8 pts (mean).	3	1	8 of 8.
8	Mixture - 8 pts (mean).	9	1	8 of 8.
9	Systematic variable - 14 pts (mean).	5	1	14 of 14.
10	Stratification - 15 pts (mean).	8	1	15 of 15.
11	Trend - 7 pts (variance).	4	2	7 of 7.
12	Shift - 2 of 3 pts (variance).	6	2	2 of 3.
13	Shift - 4 of 5 pts (variance).	7	2	4 of 5.
14	Shift - 8 of 8 pts (variance).	3	2	8 of 8.
15	Mixture - 8 pts (variance).	9	2	8 of 8.
16	Systematic variable - 14 pts (variance).	5	2	14 of 14.
17	Stratification - 15 pts (variance).	8	2	15 of 15.

The standard Control Test Prototypes are defaults that are shipped with Quality. The prototypes illustrate the basic pattern that is evaluated. Control tests that you create are variations that are based on specific prototypes.

Illustration	Description
	Value < LSL or > USL.
	Current point beyond zone A.
	K consecutive points in zone C or beyond.
	K consecutive points steadily increasing or decreasing.
	K consecutive points alternating up and down.
	k of K consecutive points in zone A or beyond.
	k of K consecutive points in zone B or beyond.
	K consecutive points in zone C above and below the centerline.
	K consecutive points beyond zone C.