TECHNOLOGY OVERVIEW

Lot Tolerance Percent Defectives (LTPD) with Rectification Single Sampling Plan

BIS.Net Team

This type of sampling plan, as is the AOQL plan, is normally used on batches, or lots prior, to shipping to a customer ensuring that the outgoing quality matches the specified level for customer acceptance. Several samples are taken randomly, and the number of defectives counted. If the number of defectives exceed a certain number for that sample size the batch is rejected, and 100 percent inspection carried out. Defective items are then removed and replaced with good items ensuring.

For this type of plan, you must specify the AQL and a LTPD. This is the maximum percent defectives that you are willing to tolerate. Of course, the ideal is 0, but a realistic level is needed, or you will most likely reject every lot. You must also specify the maximum consumers risk associated with the LTPD. 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 algorithm used by BIS.Net Analyst will obtain the sample size and acceptance value which minimizes the total number of items to be inspected (taking into account those when 100% inspection is required) when the lot has defectives at the AQL level, whilst ensuring the consumer risk is less, or equal to the one specified for the specified 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 is the risk of falsely rejecting the batch at the AQL. The Consumer’s risk is the actual risk obtained as compared to the specified risk. Due to the discreteness of the sampling plan the exact values will not always equal the specified plan. The displayed values are the exact values.

The expected items inspected is the average number of items inspected when lots are at the AQL. This includes items inspected for lots rejected which are then 100 percent inspected.