In the 1930s, some smart statisticians at Bell Labs worked on an amazing amount of manual calculations to suggest sampling plans for product quality inspections. Over time, it became the topic of MIL STD standards and one of those plans … [Read more...]
Using the Limiting Quality Level (ISO 2859-2:2020) Instead of AQL
A reader asked me how he should do an inspection of a lot produced in isolation. In theory, he should work with the Limiting Quality Level (LQ), not the AQL, which is designed for inspections of a continuous stream of production. I shot … [Read more...]
Inspecting Productions with Very Few Defects: Dump the AQL
The topic of "do we really need to send inspectors to check productions" and "does that whole AQL concept even make sense" are frequently raised. In this article, I want to write about what it takes to get to a very low rate of defective … [Read more...]
How The AQL Inspection Levels In ISO 2859-1 Affect Sampling Size
This article introduces the different AQL inspection levels available to buyers. Those levels are mentioned in the ISO 2859-1 standard (or its American equivalent, ANSI/ASQC Z1.4). Let’s explore the different levels of random … [Read more...]
What Is the Confidence Level when Working with AQL Tables?
A reader wrote to me and asked the following question about sampling plans by attributes: What is the "Confidence Level" when using the AQL Tables? How can we determine what the confidence levels are, and are there formulas we can … [Read more...]
A Simple AQL Calculator To Prepare Your Product Inspections
One of our developers prepared this simple AQL calculator for Sofeast. You can use it instead of reading the AQL tables to quickly produce your sample size and permissible defect number. … [Read more...]
The Special Inspection Levels in the AQL Tables
A few years ago I wrote about the inspection levels, but I regularly notice that some people are confused about the "special" levels (S1, S2, S3, and S4). Here is what the ISO 2859-1 standard says (emphasis is mine): The inspection … [Read more...]
When To Do a Random AQL Inspection vs. Check 100% of the Goods
First, let me get one thing out of the way: not all batches need to be checked. If a manufacturer has great systems and processes, and if they have a history of complying with your quality standard, there is usually no reason to send … [Read more...]
When AQL Sampling Plans Can’t Find Defective Products
A reader sent me this interesting question: I would like to better understand AQL usage and more precisely whether inspections based on AQL are effective in situations where the distribution of defects is not homogeneous within the … [Read more...]
What is the “AQL” (Acceptance Quality Limit) in simple terms?
What Does AQL Mean? 'AQL' stands for 'Acceptance Quality Limit', and is a method used by many businesses to check a random sample from the production batch of their products and confirm that the risk of bad quality is relatively low. In … [Read more...]
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