Six Sigma: DMAIC; Y=f(x)Is it a Goal, a Measure, a Process, a

Tool or an expletive deleted?

Six Sigma

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I’m not conducting a typical gage R&R, but rather comparison to a standard by two different systems – test machines. A brief summary if I may to help you understand my problem if you will please: I work for an ice cream company and I our raw ingredients are milk, skim milk, cream and other substitutes like butter milk and whey. Unlike a discrete manufacturing industry this is a commodity driven process industry and we inventory our raw dairy fluid ingredients based on their butter fat and total solids content. The higher the BF and TS the more money it’s worth impounds of weight. We have two systems, actually test machines, one is made be accompany call Foss and the other is made by a company called CEM, both do the same thing to measure butter fat and total solids in a given sample of a dairy fluid product like milk or cream. However, they use completely different technologies to do the same thing and of course they each claim that their system is the most accurate to laboratory test standards.

It is algal requirement in the state of Iowa that milk be tested by a reputable, independent, unbiased third party tester. This is to ensure that the dairy farmer doesn’t get short-changed on his tanker load of milk. We pay the farmer based on the third party’s test results. We still create inventory on our side when we receive a tanker of milky our own BF and TS test results. Once a week our procurement department compares a report on our results with the third party’s test results and we've notice that over the course of a year our test results were testing higher than the third party’s results, so we were paying for less than we took in. In our unique business .5% shrink is an acceptable loss, but we recreating a financial paper loss of 2.5% this equated to over a million dollars loss.

I was assigned to see what was going on. My first investigation showed that despite the Foss testers had better repeatability the CEM testers; the CEM testers came closer in agreement with the third party’s test results. We took the Foss testers offline and are using the CEM testers for all raw dairy product testing. This has improved our financial reporting. The thing is the Contesters takes 7 minutes to test a sample, the Foss testers only takes 45seconds. With our high season approaching the CEMs will not be able to keep up with testing demands. So, to the end I’ve been investigating why the Foss testers went out of calibration. It didn’t take long for me to find out that the Foss testers had not been re-calibrated on over three years; someone dropped the ball on that one. I’ve been working hard with the Foss people to get the Foss testers back to their previous performance levels, plus a new feature they have is that these Foss testers can now be hooked up to the internet and Foss can condition monitor them remotely and warn us of any anomalies.

So, I now have the Foss testers re-calibrated. The re-calibration process has been extremely time and labor consuming as I have to have specially made to order from a dairy laboratory all our raw dairy product standard test sets across thebe and TS range 3.25%, 3.50%, 3.75% and so on. Run duplicates in both the calibration and temperature compensations at 39, 69 and 104 degree F –what a job this has been… Ultimately, I need to demonstrate that the Foss testers are accurate to the third party test results. I see this a boxing match with CEM in one corner and Foss in the other with DQCI (the third party tester)as the referee. The third party tester uses a very accurate wet chemistry method called Moonie for BF and TS testing, it’s an industry best practice.

I'm planning tomorrow to get the samples from the six dairy products and run them through both testers twenty four times and send the other same test sample vials to the third party for them to test twenty four times and send me their results. Typically we are looking for a standard deviation of not more than0.06.

To this end Dana, what would be a to the point statistical tool for me to use to compare these two systems (the Foss and CEM testers) BF and TS results with the third party’s using the same raw dairy test samples to see who is closer in agreement with the third party. I have attached my data collection sheet I plant use and have populated the cream test results from a previous investigation.

To try and keep this simple I will summarize. You can visualize what I am saying in the graphicsT2 vs. Master• The mean of the Data is not significantly Different• The variation between T2 and M is significantly differentT1 vs. Master• The mean of the Data is significantly different• The variation between T1 and M is not significantly different

I am going out on a limb using the word Significantly

With the little data I have to go on I cant provide much more than the data provided says that T1 and T2 are significantly different than M.

QuestionsWas the MSE Run 10 samples x 3 measurements by 3 Techs?Was the study randomized?Was it crossed or nested?If the Study was run again with the Master would it be similar?Can you provide the MSE Data

If you are wanting to assure your measurement system is accurate, repeatable, stable, and precise. The below will not answer that question. I guess I did not understand when I sent you the initial response. But let me try and clarify what I did and what an alternative is to that first even though I do not feel this will be the correct path for you to take now that I have more information.

I will have to stick by what I provided originally with just one question that you will have to take into account. To begin with if the samples you are taking are independent i.e. samples drawn from 2 different populations you would use a two-sample t-test as I did. What I did not know was if the samples were dependent. If they are dependent then a paired t-test would be appropriate. Both of these tests will tell you if there is a difference.

Here is the catch. These tests will only tell you if there is a difference between the samples. They will not give you any indication of where the sources of variation are coming from in your samples. It can come from within or between samples, your measurement system or other sources I am not aware of not being knowledgeable of your processes. This subject of variation within and between samples takes into account 4 questions that are based on time..

1 and 2 below is considered short term variation.

1 - What is changing within your samples?2 - What is not changing within your samples?3 and 4 below is considered long term variation?3 - What is changing between samples?4 - What is not changing between samples?

Now that I think I understand you want to evaluate your measurement system I would recommend you perform this study first. You can do this 2 ways. A crossed or nested study. Minitab explains this very well and has great examples as well to walk you through the process. It will also provide you with an interpretation of the examples. In summary a crossed study is used when your 3 appraisers measure the same 10 parts 3x each. For a crossed study your 3 appraisers never measure the same part more than once. This is normally done during a study that is destructive in nature or renders the sample no longer useable. There is no other way to move forward with comparing samples without knowing your measurement system is capable first. Once that is established then you can evaluate differences between your samples with confidence.I wish I was in a better position to get involved with the study but with the position I am currently in I have very little time to help except after hours. I really would like to give you the best I can and have to say you must do a true Measurement System evaluation first. If you cannot measure then your data from the testing will not give you an accurate account of the variation in the product you are trying to assess not matter how you analyze it.