So You Think You Can Measure…

 

Forty or 50 years ago, when you sat down in front of, or picked up, a dimensional measurement tool, you immediately recognized that a certain amount of knowledge and skill was required to use it. The measurement operation was almost always completely manual, and even reading and interpreting the readings was an acquired skill. In addition, it was largely understood that precise measurements needed to be taken in a controlled environment on a stable surface. A skilled measurement specialist was half engineer, half craftsman (or half Houdini).

An interview with Randy Gruver Randy Gruver is a technical skills instructor with Boeing and chairman of the CMS certification committee. Composed of industry experts, the CMS certification committee represents manufacturing, original equipment manufacturers, service providers, and national standards measurement laboratories. The committee was chartered to investigate the need for a certification in portable, large-volume industrial measurement systems. In this interview Gruver describes the status of the CMS large-volume measurement certificate.     Quality Digest: Is there a certification process now for the metrology industry?  Randy Gruver: There are existing certification programs that support fixed, limited-volume equipment such as coordinate measurement machines. There are also programs for photogrammetry, but at the opposite end of the measurement spectrum, primarily geospatial applications. However, there are no programs for close-range industrial photogrammetry, laser trackers, laser radar, structured light scanners, and post-processing of data.     QD: Currently, how can an employer verify a measurement specialist’s level of expertise?   RG: If an employer wanted to verify an applicant’s level of 3-D expertise, he’d probably have to rely on a resume or validate references.     QD: Are there formal programs for a metrology degree?   RG: Yes, there are a few technical colleges and universities that have metrology programs. Often, metrology is included in an engineering degree curriculum but usually has limited emphasis on application processes with portable 3-D equipment.     QD: What was the catalyst for the CMS to begin its investigation into a certification program for the metrology industry?   RG: Industry has recognized, and in some cases required, certification or at least qualification of portable 3-D metrology technicians. CMS members have responded to industry’s call for a credential that demonstrates a level of competence to recognized standards in portable 3-D metrology systems.     QD: Last year at the CMSC, you conducted a session on metrology certification and polled the attendees. What were the results?   RG: The polls are a great way for us to gauge our success, determine direction, and validate data. Among those items that have been reinforced by polling membership is that it is important that this certification include a practical, or hands-on element, and that our partner is an accredited certifying body. The certifier must be certified!     QD: Please give us an update on your research and findings.   RG: The CMS certification committee has validated industry requirements by sector, as represented at the conference by attendees and personal networks. We have determined that the complexity of designing, developing, and administering a certification program is daunting, and as such our strategy has been to develop a relationship with a partner organization that has the infrastructure to support our requirements and is a good fit with our membership and areas of interest.     QD: Will there be another certification presentation at CMSC 2011?   RG: Absolutely. We have much to share, and our efforts have yielded what we hope will be a strong and mutually beneficial relationship with a much experienced, closely aligned, partner organization.

Today, when even the lowly micrometer or caliper can be tethered to a PC, and measurements and calculations done on the fly on the shop floor, it is easy to forget that there is still skill required for accurate and repeatable measurements. The problem gets worse when we move to large-volume 3-D measurement systems with their digital displays, touch screens, built-in temperature compensation, and, of course, the advertising that would seem to indicate that the tool does all the measurement work for you. This has led to an impression in industry that large-volume dimensional measurement is so simple even a college intern could do it.

Unfortunately, the truth is that as great as the latest tools are, it still takes a knowledgeable operator to get accurate, and more important, consistent results. In fact, one of the issues facing industries where precision measurement is critical, such as aerospace and nuclear, is the slow attrition of the “old timers,” the ones who understand not only the equipment, but also how to set up to take precision measurements. As these maestros of measurement retire, a lot of their knowledge goes with them. According to many people we have spoken to in the aerospace and nuclear industry, there’s a growing pool of young measurement specialists who may know how to use measurement equipment but don’t know how to measure.

This point was dramatically demonstrated at last year’s Coordinate Metrology Systems Conference (CMSC) in Reno, Nevada, where a mock gauge repeatability and reproducibility (GR&R) study was conducted to measure the influence that operator knowledge had on measurement results. The operators in this case were attendees of the show.

The study was sparked by a realization of Talion Edwards, the CMSC’s executive committee chairman, that basic measurement principles were not being practiced by many metrologists.

Early last year Edwards went to the UK’s National Physical Laboratory (NPL) to audit a training module the lab was putting together for large-volume measurement. The NPL is comparable to the National Institute of Standards and Technology (NIST) in the United States. The NPL first asked Edwards to go through its levels 1 and 2 measurement-foundation training.

That was an eye opener, says Edwards. “The exercises in the class showed me where the aging work force got its knowledge,” he recalls. “The guys who have been doing measurements for 30 years had to have background in first-principle measurements because when they started, that was all there was. Most practitioners with fewer than 15 years of experience started with CAMS equipment and therefore suffer some level of ignorance of these fundamentals, which was troublesome to me.”

Edwards thinks many of those people lack the basic knowledge on how to set up and take measurements using precision instruments. “I quickly realized that the software and hardware we have today make it so easy to measure that a lot of us in industry don’t realize how much impact that the user has on the measurement results,” he says.

Believing that his experience wasn’t unique, Edwards and the Coordinate Metrology Society (CMS) certification committee put together the [gauge repeatability and reproducibility] GR&R experiment in Reno. “The purpose of the study was to make it obvious to the technical community that this is a real issue,” says Edwards. “Our combined lack of experienced, first-principle measurement tools and our blind dependence on automated software has ramifications to our results.”

A booth was set up in the exhibit hall to conduct the study with attendees. During the first day, attendees were asked to take some simple measurements using basic measurement tools such as micrometers and calipers. No instruction was given other than what they were supposed to measure and with what tool. Keep in mind that attendees to the CMSC are, ostensibly, metrology specialists. At the end of the day, the examiners looked at the range of measurement variation amongst the participants.

During the second day, the same people were asked to take the same measurements again. This time, they were given a standardized procedure—steps that a person with a background in measurement should know. They measured the same parts with the same tool. The only difference was being instructed on how to do it properly. Again, the examiners looked at the range of measurement variation.

After the second round, the data between the two days were compared to see the difference in measurement variation. As expected, there was a much greater degree of variation amongst participants on the first day than there was on the second. “It was almost an order of magnitude change in the range of discrepancies in the measurement data,” says Edwards.

During a follow-up workshop, the results were shared with the study participants and other CMSC attendees. “The message was well received, and I believe that attendees had the same feeling I did,” says Edwards. “They are aware that there is missing knowledge but are not sure where that knowledge comes from.”

This year, the CMS will conduct the study again at the CMSC to be held July 25–29 in Phoenix. But where last year’s study used basic hand gauges, this year’s study will use large-volume tools such as a laser tracker. “The idea behind this year’s study will be to show not only user interaction but also how things like vibration, cleanliness, temperature, how you handle an SMR [i.e., whether it is clean, if you are breaking the beam] affect measurement,” explains Edwards.

The CMS wants to drive home the point that neither the hardware nor the software used for large-volume measurement is enough for an accurate and repeatable measurement. “If you don’t fully understand what the software is doing, you are really limited on how much you can improve the process,” says Edwards. “Even with trackers as accurate as they are, 0.001 in. over 100 ft, we need 10 times better than that to meet the specifications we need on aircraft. Most people in industry are completely reliant on the software. They don’t know how to better control the process.”

The overarching purpose of these two studies, says Edwards, is to generate interest and support for a portable, large-volume measurement certification program, something the CMS has been working on for the past three years. When complete, the certification program will teach existing or potential measurement specialists the basics of measurement theory and how to use specific types of equipment. A certification test will assess students’ knowledge, while a hands-on test will demonstrate their practical measurement skill. A certificate will be awarded by the CMS that certifies that person has met the minimum requirements.

The CMS is working on which organization outside of the CMS will provide the actual training and which body will accredit the program. The goal is have a national accredited program in large-volume measurement that will be recognized by industry.

The need is critical says Edwards. “Without a certification program and the training that goes with it, industries such as aerospace, which depend upon large-volume 3-D metrology, are going to be faced with a work force that lacks the necessary skills to do their jobs,” he warns.

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