When performing data acquisition, it is important to attach an assignable cause list to your product’s characteristics. Assignable causes are used to track potential causes of variation. Why would we want to track this? Because unless the special causes of variation are identified and acted upon, they will continue to affect the process output in unpredictable ways. Over time, if special causes of variation are present, the process output is not stable. Rather than relying on people’s memory of what made an occurrence different from all others, you should create assignable cause lists operators can use to document causes. If your characteristic is configured with an assignable cause list, you can assign a cause to individual subgroups from control charts in History or the active set work space. You cannot assign causes while viewing control charts in Alarms. In order to enter an assignable cause, select the subgroup on the control chart. Then, right click or press the F5 key and select Assignable Cause. The Sub Group Assignable Cause dialog box appears. Select an item from the list. Assignable cause lists are configured in public field definitions and attached to characteristics in statistics setup. If no assignable cause definition is attached to the characteristic, Assignable Cause is unavailable on the menu. The new assignable cause list should now appear in the Assignable Cause field. Now you need to set the rules for Assignable Causes and Comments. Click Red so that Operators are forced to enter an assignable cause when a Red, or state of alert, occurs. Note that the Red or Yellow option will prompt upon Alert or Warning state. If the data fails any statistical tests, you will receive a dialog box that looks similar to the one pictured.
When this box appears, it is mandatory to enter an Assignable Cause. Click the Enter AC button. When the Sub Group Assignable Cause box appears, select the appropriate cause and click OK. If the product is configured to have comments follow the assignable cause prompt, operators will receive a Sub Group Comment screen. They would enter comments regarding the problem or possible fix for the problem. Click OK when done.
Also see the video How Do I? - Adding Assignable Cause for more information.
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