TECHNOLOGY OVERVIEW

Lot Tolerance Percent Defectives (LTPD) without Rectification Double Sampling Plan

The BIS.Net Team BIS.Net Team

Double sampling plans generally require less sampling than single sampling plans but are more complicated to use. For AOQL and LTPD with rectification sampling plans the expected number of items inspected can be considerably less. For LTPD without rectification sampling plans the savings in number of items inspected is very small because there is no rectification involved. Often sample size for the first sample is considerably larger than the second sample which may cause confusion. The sampling plan is only recommended when the cost of sampling is very high.

For a double sampling plans you take a first sample consisting of n items and each item is checked to see if it is defective. The number of defective items is then counted and compared with the first sample acceptance value for the sampling plan. If the number of defectives is less or equal to the first sample acceptance value the batch is rejected. If it exceeds the SECOND sample acceptance value the batch is rejected. If the number of defectives of the first sample are more than the first sample acceptance value and less or equal to the resample value the batch is resampled. If the total number of defectives of BOTH samples exceeds the second sample acceptance value the batch is rejected and accepted otherwise.

This type of sampling plan can be used on batches, or lots prior to shipping to a customer when rectification is not possible. For example, when testing cans of soft drink for composition, rectification is not possible because every can would have to be opened to test the composition and decide which cans needs replacing. More often the plan is used to screen incoming goods. Rejected batches are returned to the supplier.

The output includes an OC curve as shown below, which can be used to determine the probability that a lot will be accepted or rejected at a hypothetical quality level.

The sampling plan itself is displayed in a table which is used as explained above.

BIS.Net Analyst 2019 - Analysis As A Service