Specify conditions for the SQC pattern tests

Pattern tests are run on point data to determine if alarm conditions exist, based on your limit specifications.

Perform the following steps to specify conditions for the SQC pattern tests:

• Select the checkbox next to each pattern test you want to apply in the SQC alarm. Values that reach the specified limits of any active pattern test will place the SQC point in alarm state. By default only the 3 sigma limit test is applied.

• For selected pattern tests, specify the number of values (X) out of a number of sampled values (Y) that are Above or Below the corresponding pattern test limits.

• The Western Electric suggested patterns are shown by default, and by default tests are applied on both sides of the center line.

The following tests may be selected:

• OutsideControl: Counts the number of samples outside the control limit on one side of the center line.

• OutsideTwoSigma: Evaluates the sample against a limit drawn 2/3 of the way between the center line and the control limit.

• OutsideOneSigma: Evaluates the sample against a limit drawn 1/3 of the way between the center line and the control limit.

• OneSideofCL: Counts the number of samples on one side of the center line.

• Stratification: Counts the number of samples that fall within the upper and lower One Sigma limits on both sides of the center line.

• Mixture: This test counts the number of samples that fall outside the upper and the lower One Sigma limits on both sides of the center line.

• Trend: Counts the number of samples which are monotonically increasing or decreasing.

  Note: The term sigma generally refers to one standard deviation in a PI SQC alarm. SQC control limits are not limited to three times the standard deviation of process measurements. Control limits may be set to other values depending on process needs. Thus sigms, as used in the PI SQC alarm pattern tests is one-third the difference between the value of the center line and the control limits.