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Measurement System Analysis
Are you using a rubber ruler?
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March 2007
- Vol 4, Issue 2
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In This Issue
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Quick Links
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Sugaring Season Greetings from Vermont!
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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.
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Are You Using a Rubber Ruler? by Robin McDermott
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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!
R&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.
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Training in MSA Techniques by Carolyn Burke
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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.
Want to try out a free MSA training lesson? Click here>>>
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Types of Measurement Error by Ray Mikulak
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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.
Visit our MSA Resource Center for more on measurement error>>>
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Helpful Links for Measurement System Analysis |
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Here are some links that will help broaden your
knowledge and understanding of MSA.
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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
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