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Control Chart Setup

SPC Detail Setup

Access the Detail Setup by selecting SPC Edit from the Setup menu in Sigma. Then select a vaiable and press Edit. The SPC Detail Setup dialog box allows you to set up critical parameters about your table of data.

1. Select Setup | SPC Edit
2. Open samlpes\charts\rr.spc

The Detail Setup window. Click on a section for explanation.

Explanation of parts of Detail Setup:

Variable This is the name of the part measurement field in the table.  
Chart Type Control chart type Pull down list gives you choices
Sample Size The Sample Size is the number of table records that make up one plot point on a chart. It has a maximum value of 400.
Activated Check to include this setup info. May want to temporarily turn off without losing the settings.  


Your product specs go here. These may be left blank. Used for yield calculations and histograms


Decimal Places How many decimal digits to display. Internally all precision is kept.
Measurement Unit Text label on chart  
Control Chart Length Set the number of points to display on the control chart. Smaller is faster since less data to read.

Control Chart

Auto Scale Auto scales the Y-axis if on. X-axis is always the length of the chart you setup.
Auto Control Limits Calculates control limits based on data in the chart. Uses chart length number of points, so provides a moving window.
Screen Data If on, skips data that is out of a range you enter. Useful for ‘flyer’ data that is not possible.
Target Chart Used on Short run charts that have a target value subtracted off based on product type (or other) Uses a separate lookup table to determine the values to use. (Advanced)
Product Filter Used to filter out unwanted data with a SQL query The maximum length of the SQL query is 255 characters.

Chart Evaluation

Check Rules Turns on runs/trend checks Can toggle individually. Western Electric standards. See below.
Points To Include Number of plot points to include in the runs/trend testing A control chart may show more points than you want included in the analysis.
Set Rules... Toggle individual rules on / off. Modifies sensitivity of run/trend testing

Runs and Trends Tests

AT-Sigma SPC uses both standard tests and user defined rules for checking patterns in a control chart. The object in checking for patterns is to detect non-randomness which is clue to an assignable cause of variation. They enhance the sensitivity of the control chart.

The standard tests are the eight Western Electric (Western Electric Handbook 1956) rules. All the rules map the control chart area in to zones for ease of classification. The zones are one third on each side of the control chart center line. For 3 sigma limits, each zone is a 1 sigma width.

On each side of the center, the zones progress from Zone C, to B, to A. By selecting which run tests to use, you can tailor the sensitivity of the chart for the application.

When clicking on advanced: