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Reprinted from Modern Machine Shop Online
THE NEW METROLOGY STANDARDS
Confused about which ones apply to you? You're
not alone. Here's a report that will make sense of the alphabet soup
for those involved in gage calibration.
By Robert Edmunds III
Part of my daily routine includes fielding telephone calls and
retrieving e-mail from shops across the country involved in gage
calibration. Many of the inquirers pose questions like these:
"Is the standard we are working to still valid?"
"Which standard applies to our operation?"
"Which is the most current standard?"
With all the changes and revisions in standards over the past
five years, particularly the cancellation of the military standard
MIL-STD45662A in 1995, I can understand the confusion. Here is an
overview of the current metrology standards.
ISO 10012-1-1992, Quality Assurance Requirements for
Measuring Equipment
Part 1: Metrological Confirmation System for Measuring Equipment.
When you use a micrometer, for example, this standard assures that
it measures to the accuracy to which it was manufactured. ISO
10012-1-1992 is for companies working within one of the ISO 9000
quality management systems and who are performing gage calibrations
and gage control in-house. ISO 10012 is under revision at this time,
as all ISO standards must be reviewed every five years.
ISO-IEE Guide 25: 90, General Requirements for the
Competence of Calibration and Testing Laboratories.
If you are considering using an outside source, make sure your
calibration lab is certified to this international standard. It is a
document for calibration and testing laboratories to follow in the
development and implementation of their quality systems. It may also
be used by accreditation bodies, certification bodies and others
concerned with the competence of laboratories. Laboratory
accreditation bodies such as A2LA (American Association for
Laboratory Accreditation) and NVLAP (National Voluntary Laboratory
Accreditation Program) both use ISO Guide 25 as a foundation
document for accreditation because it has international acceptance.
ISO Guide 25 is also being revised at this time, and when it is
released it will be known as ISO Standard - 17025. Its release date
will be late 1999 or early 2000.
ANSI/NCSL Z540-1-94, American National Standard for
Calibration - Calibration Laboratories and Measuring and Test
Equipment - General Requirements.
This standard, sponsored by the National Conference of Standards
Laboratories, adds areas that ISO Guide 25 does not include, though
both documents are similar. Our American organization felt Guide
25:90 didn't cover equipment well enough. Like Guide 25:90, Z540-1
is intended for metrology labs performing calibration services for
outside customers. Part 1 establishes the requirements that a
laboratory must demonstrate to prove competence in performing
calibrations. Part 2 titled, Quality Assurance Requirements for
Measuring and Test Equipment, applies to the actual equipment used
in the calibration process and actually mirrors ISO10012-1-1992.
ANSI/NCSL Z540 - 2-97, American National Standard for
Expressing Uncertainty-U.S. Guide to the Expression of Measurement
of Uncertainty.
The subject of uncertainty is a complex one. It is difficult for all
the governing bodies to agree on the best way to determine a lab's
uncertainty, but we all need to realize that it is there.
Uncertainty should not be confused with accuracy. When we talk about
accuracy, we mean the accuracy of the equipment. When we talk of
uncertainty it's the entire gaging process, and many factors come
into play. An expert in this subject, Ted Doiron, says about
uncertainty, "the more we find we can measure, the more we find we
can't."
This new document, Z540-2-97, is the American version of what is
commonly known as the "GUM" or the ISO Guide to the Expression of
Uncertainty in Measurement. Any lab working on accreditation should
have a copy of both.
ISO - 14253-2, Geometrical Product Specifications (GPS) -
Inspection by Measurement of Work pieces and Measuring Equipment -
Part 2: Guide to the Estimation of Uncertainty in GPS Measurement,
in Calibration of Measurement Equipment and in Product Verification.
At this writing, this international standard is still in the draft
stage. The most recent one I reviewed is easy to understand and
includes concise examples of common dimensional gaging uncertainty
parameters.
ANSI/ASQC M1 - 1996 American National Standard for
Calibration Systems.
This standard was originally issued in 1987 and the reaffirmed in
1996. M1 provides guidance on two different methods for quality
assurance of calibrations. Though not as common as the ISO
standards, it is one of few documents that clarify the check
standards that should be in use in all metrology /calibration
laboratories.
For more information and where to purchase these standards
contact:
ANSI (American National Standards Institute)
11w. 42nd St.
New York, N.Y. 10036
1-800-THE-ASME
(212) 642-4980
Fax (212) 302-1286
ASQ (American Society for Quality)
Box #3005
Milwaukee, WI 53201
1-800-218-4916
(414) 270-8810
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