$Account.OrganizationName
Measurement System Analysis
Are you using a rubber ruler?
March 2007 - Vol 4, Issue 2
In This Issue
Sign Up
Quick Links
Greetings!

Here in Vermont in late March with below freezing nights and above freezing days, the sap of maple trees starts running and sugaring season gets underway. Sap is collected and then heated to concentrate the liquid into pure maple syrup. It takes 40 gallons of sap to make 1 gallon of syrup!

While you will still see buckets hanging on trees to collect sap, larger sugaring operations in Vermont have gone high tech with vacuum piping systems and sophisticated measuring devices to assure the highest quality and most consistent maple syrup.

But, like any other production operation, the quality of the syrup is only as good as the quality of the measurements of those devices. So, it made sense this month to focus on the importance of good measurement systems. We hope it gets you thinking about your own measurements systems and how well they are working for you.

Not every organization is aware of the importance of understanding and quantifying the variation in measurement systems. Without a good measurement system, there is no way of knowing what the true output of a process really is! Based on measurements that are taken during manufacturing, an organization may think that it is producing good parts only to find out that the parts are seriously defective or out-of-tolerance because the measuring device used is inaccurate, out-of-calibration, or not stable. When that happens, you might as well be using a rubber ruler for measuring!

GR&R Studies are the most widely used techniques for evaluating the variation in a measurement system and determining if the measurement system is acceptable for use. Once a measurement system is found acceptable, it is equally important to institute a formal system to manage the measurement system to ensure that it continues to be reliable and dependable. Use of structured GR&R techniques with a comprehensive calibration system for measurement devices is the only way to avoid the rubber ruler syndrome.

Robin McDermott is director of Training for Resource Engineering, Inc. You can contact her at 800-810-8326 or 802- 496-5888 or by e-mail at robinm@reseng.com.
Our MSA course consists of two units: Unit 1, Analyzing Measurement System Variation and Unit 2, Managing Measurement Systems. In Unit 1, techniques for analyzing the variation within a measurement system, determining its suitability for use, and ways to improve measurement systems are explored. In Unit 2, approaches to managing measurement systems to ensure that they can be depended upon are covered. Each unit contains lessons to divide the content into manageable learning segments. At the end of each unit, learners have access to a Challenge to test their comprehension of the body of knowledge covered in the unit.

The GR&R analysis techniques presented in the MSA CBT Program are generally in compliance to those presented by the 3rd Edition of AIAG’s MSA Reference Manual.

Carolyn Burke is Sr. Customer Service Representative. She can be reached toll free directly at 866-791-1003 or by e-mail at carolynb@reseng.com.
The analysis of a measurement system involves understanding the uncertainties associated with taking a particular measurement and then, where possible, quantifying those uncertainties. The uncertainties that can be quantified (by statistical means) include issues of accuracy, linearity, stability, repeatability and reproducibility. They are known as Type A Uncertainties.

The variation from the test equipment is called Repeatability. A good way to think about repeatability is that it is the variation we get when we measure the same part a number of times with the same measuring device. Reproducibility variation is the uncertainty, or variation, we get between people who are measuring the same parts with the same gage. Many times this is the largest source of measurement system variation. GR&R (Gage Repeatability and Reproducibility) studies are used to evaluate the level of variation due repeatability and reproducibility.

There are a number of other uncertainties associated with measurement systems that cannot be evaluated as readily by statistical methods. These are termed Type B Uncertainties. A Type B Evaluation of Uncertainty is typically based on engineering and scientific judgment and not on statistical methods. Type B uncertainties may be temperature-related, can be related to part form (such as parallelism, concentricity, parting lines or even burrs), may involve variations related to fixturing and can be related to part or measurement equipment conditioning requirements.

Ray Mikulak is president of Resource Engineering, Inc. You can contact him at 800-810-8326 or 802- 496-5888 or by e-mail at raym@reseng.com.
Here are some links that will help broaden your knowledge and understanding of MSA.

  1. From the NIST Sematech Engineering Statistics Handbook, Measurement Process Charaterization, an exceptional resource on MSA techniques:  http://www.itl.nist.gov/div898/handbook/mp c/mpc.htm

  2. From StatPoint, Inc., a short explanation of measurement system analysis:  http://www.statgraphics.com/measurement _systems_analysis.htm

  3. An explanation on assessing measurement system variation from Minitab: http://www.minitab.com .mx/training/TrainingSampleMeasurementSystems.pdf

  4. An article on GR&R entitled “Measurement System Analysis and Destructive Testing” by Minitab printed in the August 2002 issue of the Six Sigma Forum Magazine: http://www.minitab.com/resources/articles/ MeasSysAnalysisDT.pdf

Data is critical to making a high quality product whether it is a precision part for an airplane or maple syrup. But we need to be sure that the data we are getting from our measurement system is giving us a true picture of the variation in our process. Measurement System Analysis is a set of techniques to help us understand the variation in our measurement system. So, the next time you pick up your measurement device, whether it is a ruler, a micrometer, or a hydrometer, ask yourself if you can trust what it is telling you.

Please enjoy some Vermont Maple Syrup next time you have the chance!
Robin McDermott
Resource Engineering, Inc.

phone: 802-496-5888 or 800-810-8326