Connector magazine - Spring 2020

Page 18

MANAGEMENT

By Lee Pielaet

Building Blocks of Calibration Systems Key terms used in calibration

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hen it comes to measurements, calibration is how we know we are doing what we say we are doing. Calibration is an important quality control measure considered as part of the AISC certification process. AISC offers various certifications steel fabricators and erectors. When developing an effective calibration program, it is important to understand the terms, review examples of best practices, and determine the frequency needed for calibration. In the 1890s, a Swedish arsenal worker named Carl Edward Johansson discovered a system to make accurate measurements. The Jo Block was born! Made from a block of steel at a constant temperature of 68° Fahrenheit gave it accuracy within two-millionths of an inch, making it possible for the interchangeability of parts, which one could call the building blocks of mass production. A complete set of block gauges would have numbered over 100,000 blocks. Johansson discovered that all measurements were possible with a combination of 81 blocks with a range from one-tenth of an inch to four inches. In 1923, Johansson moved to the U.S. and met Henry Ford. The meeting resulted Lee Pielaet is the President of Pioneer Steel Services, Inc., Missoula, Mont., which helps companies achieve, manage, and upgrade their AISC Certifications. He is an ASQ-Certified Quality Auditor, AWS Certified Welding Educator, and AWS Certified Welding Inspector. Contact him at lpielaet@ pioneersteelservices.com.

in Johansson helping standardize the Ford Motor Co. Today we don’t need Carl Edward Johansson to help us with our calibration needs, but you will want to look for an outside calibration laboratory to help develop your program. It is important that the calibration lab you select is certified to International Organization for Standardization (ISO) and by the International Electrotechnical Commission (IEC), 17025, the leading standard used by testing and calibration laboratories. The calibration labs must meet the general requirements for the competence to carry out tests and calibrations, including sampling. The certification also covers testing and calibration performed using standard methods, non-standard methods, and laboratory-developed methods.

Critical terminology Before we discuss calibration best practices, the following terms should be made clear: Calibration/Verification, Traceability, Accuracy, Tolerances, and Welding Validation. Calibration and Verification—These terms can mean the same thing. Most believe that calibration includes the determination of measurement uncertainty (MU). MU is a must for the chain of traceability to national or international standards. If the MU is not known, it is thought by many to be only verification. The bottom line is that it is up to a company to determine the terminology which works best for them.

18 | THE STEEL ERECTORS ASSOCIATION OF AMERICA

Traceability is the ability to relate individual measurement results through an unbroken chain of calibration to a national standard, such as the National Institute of Standards and Technology (NIST) or National Bureau of Standards (NBS). Accuracy is the extent to which the measured value of a quantity. Does the measurement agree with the accepted value of a standard, including the MU? Tolerances are the permitted amount of deviation from the exact value specified and dictated by the manufacturer, standard, code, and specifications for calibrated items. Welding Validation—calibration and verification of welding machines can be confusing and has led many to use the new term “Welding Validation.” This term is not yet standardized, and currently, the American Welding Society provides no definition that is universally accepted.

Examples for erectors, fabricators These terms will help clarify the following best practices, and the principles applied to these examples will be the same through your specific calibration system. Steel Measuring Tapes: The following passage from NIST describes how they calibrate steel measuring tapes. “Calibration of metal tapes is made with the tape under tension and supported on a horizontal flat


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