TECHNOLOGY OVERVIEW

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

BIS.Net Team

This type of sampling plan is normally 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. Another more common application is for testing incoming goods.

For this type of plan, you must specify the AQL and an associated producer’s risk and a LTPD and its associated consumer’s risk. The producer’s risk is the risk to whoever produces the product. It is the percent probability of REJECTING the lot at the AQL. If the LOT has percent defectives better or equal to the AQL it makes no sense to reject such a lot because the process cannot do better. But, because a limited number of samples are taken there will be a risk of rejecting a lot with defectives equal to the specified AQL. This risk is the producer’s risk. To design your sampling plan, you need to specify this risk with a reasonable value.

The consumer risk is the risk carried by whoever receives the product. It is the percent probability of ACCEPTING lots that are at the LTPD.

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. For example, at the an assumed 3.5% of defectives there is an equal chance of accepting or rejecting the batch.

The sampling plan itself is displayed in a table. The sample size and acceptance value define the plan. The Producer’s risk and Consumer’s risks are the actual risks for the sampling plan. Due to the discreteness of the sampling plan the exact values will not always equal the specified plan.