Variables Single For Defective Units Dialog Box

Variables Single For Defective Units Dialog Box

Used to enter the parameters of a variables single sampling plan for defective units. Used to both specify a new plan and to edit an existing plan.

Form: Form 1 has parameters n and k and Form 2 has parameters n and M.

Sample Size (n): The sample size must be an integer. For standard deviation known, n³1 for Form 1 and for n³2 for Form 2. For standard deviation unknown, n³2 for Form 1 and for n³3 for Form 2.

Accept Constant (k or M): Parameter k for Form 1 and parameter M for Form 2. M must satisfy 0<M<100.

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.

For most Form 1 plans there is an equivalent Form 2 plan and visa versa. Press the Convert Form button to view the equivalent plan of the other form. When an equivalent plan is displayed, both forms give identical results for every lot inspected. One exception is when the standard deviation is unknown and there are 2 specs. In this case a similar plan of the other form is given instead. This plans has nearly the same OC curve but the two plans do not make the same decision for each lot inspected. Equivalent or similar plans exist only when n³2 for standard deviation known and n³3 for standard deviation unknown.

When done, click the OK button or press the Enter key to save the sampling plan and close the dialog box. Clicking the Cancel button or pressing the Esc key cancels the changes to an existing sampling plan or the creation of a new sampling plan.

For a new plan, this dialog box is displayed by selecting the characteristic Defective Units and the type "Variables Single" from the ~~Enter New Sampling Plan~~ dialog box. To edit a plan, double click on it in the ~~List Sampling Plans~~ window.