Select Variables Plans for Defective Units Dialog Box

Select Variables Plans for Defective Units Dialog Box

Used to specify the information required to select variables sampling plans for defective units. In order to select such plans, it must be specified whether the standard deviation is known, how many spec limits there are and sometimes the value of Cp. The controls are:

Standard Deviation Radio Buttons: Specify standard deviation known or unknown. Specifying standard deviation known requires that historical data be available to demonstrate that the standard deviation is consistent over time and that can be used to estimate the standard deviation.

Specifications Radio Buttons: Specify 1 or 2 spec limits.

Cp: This control is only shown when the standard deviation is known and 2 specifications are specified. In this case only, further information about the standard deviation and spec limits are required in the form of Cp. You can enter a value or you can enter an expression like "(30 - 10) / (6 * 1,2)". The expression "(USL - LSL) / (6 * SD)" is initially displayed in this edit box which is the formula for Cp. Just substitute the three values USL = upper spec limit, LSL = lower spec limit and SD = standard deviation into this expression.

When done, click the OK button or press the Enter key. If an error is found, a message is displayed and you are given the chance to change your input. Clicking the Cancel button or pressing the Esc key instead results in no sampling plan of this type being selected.

This dialog box is displayed by clicking the Select button on the ~~Select New/Matching Sampling Plans~~ dialog box when a variables sampling plan for defective units with known standard deviation and 2 specification limits is checked in the list of types. An AQL was entered in this dialog box. If Cp is so small that it is not possible to achieve the this AQL, an error message is displayed.