2 sigma control chart2/18/2024 ![]() For example, you may expect changes to the chart if you swap in/out a tool. With the aid of the charts you should have an understanding if your operation that tells you if it is stable or not. Really there's no way to use the charts in the absence of process knowledge. ![]() Once you've had a period of time without any special causes, you can declare the process stable and freeze the limits. Others continue to revise the limits as they collect new data while continuing to identify and eliminate special causes. Some have the practice of calculating "theoretical limits" based on eliminating the special cause data. Calculate limits, find the special causes and eliminate them. If your process is unstable, then the limits are passing judgement alone -helping you identify and eliminate special causes.Īn unstable process may cause you to calculate substantial changes in the limits. If the process is stable, there's no need to revise the limits - they'd essentially give you the same limits you already have. So, to your questions about recalculating limits with the onset of new data. If not, then the second role they play is to predict where future output is likely to appear. First, they pass judgement as to whether there are any out-of-control conditions. In it he explains that the limits play two roles. Like others, I suggest you get Wheeler's book. ![]() If I can be of assistance to you with data analysis, my e-mail is some really good discussion here about the fundamentals of control charts. Keep thinking.you are on the right track. Ultimately, the questions are: Did the same system produce this data point as produced the previous data points? How do you know? Do you expect the change (signal) to be sustained? This takes years of practice and thought. Again, Wheeler treats this situation in his writings. Updating control limits at every succeeding data point is dangerous. Once you have established control limits and a succeeding point shows a lack of control, then you have a signal which can be investigated. The software package you are using can calculate anything you want, but utilizing your knowledge and experience about the process and data is where the real value of the control chart lies. This is why it is so important to have knowledge regarding the origin, collection, and definition of the data. None1, We have to be careful not to over-think or try to out-think the process behavior charts and the data.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |