Who Takes the Measurements? Does It Matter?

CMS study looks at how metrologists methods influence CMM data

An interactive measurement study conducted by the National Physical Laboratory (U.K.), on assignment for the Coordinate Metrology Society, and assisted by members of the CMS Certification Committee, examines the ways that measurement strategies and behaviors of coordinate metrologists influence CMM results. CMS conducted the study — its first large-scale interactive research effort — among more than 100 attendees at the 27th Annual Coordinate Metrology Systems Conference (CMSC), held in July of this year.

Metrology is the science of measurement, and it informs a wide variety of testing methods and protocols, including many used by manufacturers to determine design integrity and product quality. In 2009, the Certification Committee was formed to consider the need for professional certification in the field of metrology. After market research and an investigation of existing certifications, the group determined a properly structured certification program would be of value to the CMS.

Then, the committee began to develop a preliminary “body of knowledge.” In 2010, the committee performed a statistical study at CMSC to identify skill gaps in the general metrology community. At that 2010 event, hundreds of attendees at an open workshop tested their knowledge of core metrology principles based on a variety of ‘hand tools’ used in dimensional measurement.

The report of the interactive study conducted this year, How Behavior Impacts Your Measurement, is available for downloading at the CMS website. The authors are Keith Bevan of the National Physical Laboratory and Trevor Toman, metrology manager at England’s Coventry University. They performed statistical analysis of the study and compiled their conclusions for the report.

The criteria of the study’s measurement tasks allowed the authors to examine various training and assessment techniques, including the evaluation of a participant’s prior learning and experience level, questioning methods, practical task monitoring and demonstration. Almost 25% of those surveyed had less than three years of measurement experience, and 12% had 3-7 years of CMM working experience. Among those surveyed, 69 had more than seven years of practical working experience with various measurement systems.

Bevan stated: “The outcome of this study drives home the importance of defined best practices, and understanding measurement fundamentals that enable an individual to make informed judgments about a measurement… irrespective of the technology used, whether it is hand tools or 3D portable metrology systems."

The study was conducted over two days, and participants were asked to perform three tasks using portable, 3D CMM equipment for data acquisition:
1) Measure a door using a combination of a laser tracker, retro reflectors, and software;
2) Measure an engine compartment using a combination of an articulating arm, probe, and software; and
3) Measure a vehicle using a combination of a laser tracker, probing, and laser scanning system.

The final report reveals various results based on 3D measurement tasks executed with little or no instruction, versus the outcome of 3D measurement tasks completed using procedures, or a participant guiding an operator with methodology to collect the needed measurements.

“Clearly, questioning and planning the requirements of the measurement help reduce the possibility of making poor measurements,” Bevan concluded.

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