MEASURE FOR MEASURE
Calibration: Who Does It?
by Graeme C. Payne
This column is the second of three that explore what calibration is, who does it and why it is important. The May 2005 column discussed the nature of metrology and calibration and the types of confusion that arise because of differences between the technical definitions and common usage of the words. This month’s column looks at how calibration is viewed in different ways by different groups.
Dedicated scientists and engineers make exacting measurements in the scientific, high level realm of calibration. They are often called metrologists and may spend years examining one particular measurement problem or physical characteristic that is subject to measurement, trying to transform theory into practical application.
Making measurements with the highest levels of precision and accuracy is routine. At this level, the sometimes abstract definitions of measurement units are realized as closely as possible, usually in terms of a reproducible method. New discoveries in fundamental physics, chemistry, mechanics and other sciences are often tested to see whether they can be used for measurements with lower uncertainty than previous methods provided.
For example, one of today’s current measurement challenges is to find methods that use natural phenomena to replace the international prototype kilogram artifact as the definition of the unit of mass. This work is important because the kilogram is the only unit of the International System of Units (SI) that is still defined by a physical artifact, and we know it changes slightly over time even though it was manufactured to be as perfect as possible.
Units based on fundamental physical phenomena, on the other hand, do not change. One method being studied is a watt balance that would use a magnetic field to determine mass; another method is to count the number of atoms in a crystal of pure silicon.1
The scientific view comprises metrologists with national metrology institutes such as the National Institute of Standards and Technology, international organizations such as the International Bureau of Weights and Measures, the corporate metrology standards laboratories of some major corporations and some other government laboratories.
The national metrology institutes (NMI) calibrate transfer standards from other calibration laboratories, and those calibrations are a vital link in the documented series of comparisons that provide traceability from a quality practitioner’s work to the SI units. In most countries, the SI units as maintained by the NMI are the basis of legal metrology—the measurements made in commerce and regulated industries.
End User’s View
The end user of calibrated tools has another view. A typical end user has a requirement to use calibrated inspection, measurement and test equipment. The requirement may be corporate policy, but it was likely derived from external sources such as ISO 9001, a regulatory body or a customer requirement.
Many end users view calibration as a nonvalue added expense that should be minimized. Given the parameters of fast service, high quality and low cost and asked to pick any two, they often want the fastest possible service and the lowest possible cost. They are more concerned about compliance with requirements than measurement quality. They also don’t always understand what calibration is, how poor measurements affect the quality of their products or why calibration is important.
Average Practitioner’s View
The majority of people who do the work of calibration have, by necessity, a more practical view of calibration. The biennial benchmark survey done by NCSL International2 indicates only 3% of calibration laboratories classify themselves as standards labs. That means they only calibrate measurement standards for other calibration laboratories. The other 97% have customers who use calibrated equipment for all types of jobs.
This is where results of NMI level science are applied to meet the needs of the end user, and the perfection of pure science is balanced against the demands of the customer paying the bills. The work has to be done quickly and at low cost to provide customer satisfaction, efficiently to generate enough profit to stay in business and accurately and precisely to maintain traceability and give confidence in the measurement results. These goals often conflict with each other, and it does not help that most calibration laboratories are small organizations.
One indicator of laboratory size is the NCSL International benchmark survey. The proportion of calibration laboratories that are in organizations of 50 or fewer people has increased from approximately 21% in 1999 to about 44% in 2003. A different NCSL International survey of the small and independent calibration laboratories in 2000 showed approximately 79% had 20 or fewer employees.3
Both surveys indicate most calibration labs are small businesses, which implies they have limited resources. As with any other small business, calibration practitioners and their companies have to continually balance the triad of speed, quality and cost while being mindful of each customer’s needs and desires.
There are many job titles applied to the practical worker in calibration. Calibration technician is one, but a recent check showed at least seven other common job titles that include calibration duties.4 The ASQ Measurement Quality Division is currently working jointly with NCSL International to update the calibration related standard occupational descriptions published by the U.S. Department of Labor.
Qualified calibration technicians must be educated in the relevant science to the extent necessary to perform the work for which they are responsible. Technicians must be adaptable because the lab probably supports hundreds of types and models of equipment, and the technicians are usually expected to become qualified to calibrate most or all of them. To keep up with advances in the measurement fields, calibration technicians should also partake in ongoing professional education.
Instead of seeking the “best possible” measurement, the practical view of calibration looks for efficient calibration procedures and measurements that are sufficient for the task.
If the measurement uncertainty is sufficient (a 4:1 to 10:1 ratio from the specification to the measurement standard), there is little incentive to seek out a better measurement standard or method. No matter how much the lab might want to approach the scientific ideal, the customers will probably not pay for the extra time or equipment. Instead, most labs will try to improve productivity by automating as many measurement systems and laboratory processes as possible.
Automation does not always—or even necessarily—increase speed. It does, however, improve repeatability of the procedure and may reduce the uncertainty of the method. If the unit under test is controlled by the measurement system, automation may nearly double productivity by allowing the technician to start a procedure on one system and then start calibrating another unit at another workstation.
Many calibration laboratories are exploring other ways to improve service and productivity and reduce overall costs. Within the past 10 years, for example, available technology has enabled the development of calibration applications for notebook or handheld computers, allowing on-site calibrations without the need for paper procedures or data recording and eliminating errors from manual data transfers.
At the same time, there has been a proliferation of calibration oriented laboratory databases and information systems. These systems typically manage inventory, data collection and recording, procedures and other documents, calibration recall systems and physical traceability from measurement standards to the workload items they have been used on.
Many systems also aid regulatory compliance or quality management system conformance with features such as user identification and data security, automatic data audit trails and authentication and digital signatures based on public-key encryption. Other improvements include applying barcode tags to equipment to speed laboratory check-in processes and using the laboratory database to print calibration labels to eliminate the problem of dates mismatched between the computer record and handwritten label.
Three Interdependent Layers
The essential measurements, the research and development to support them and the national and international standards of measurement that are a foundation of global commerce all exist in the high level, scientific view of calibration. Those who use calibrated inspection, measurement and test equipment to make the measurements essential to production, service and commerce see the end user’s side of calibration. In between those two groups are the organizations that perform the majority of calibrations and must balance the perfection of science with the realities of the competitive marketplace. Most of the time the end users do not see the high levels of science and engineering associated with calibration or the countless dedicated technicians, engineers, metrologists, scientists, managers and administrators who make the whole system work.
In the September 2005 column, I will discuss how calibration reduces variation in a production process, facilitates global commerce and affects the products you buy every week.
- Michael Shirber, “Time To Redefine the Kilogram, Scientists Say,” LiveScience.com, April 25, 2005, www.livescience.com/technology/050425_redef_kilo.html.
- J. Wade Keith III, “2003 NCSL International Benchmarking Survey,” proceedings of the NCSL International Workshop and Symposium, August 2003.
- Malcolm Smith and Carol Rake, “Small Business Issues,” proceedings of the NCSL International Workshop and Symposium, August 2004.
- Christopher L. Grachanen, “Metrology Job Description Initiative,” presentation to the NCSL International Board of Directors, January 2005.
GRAEME C. PAYNE is the president of GK Systems Inc., a technical consulting company near Atlanta. A Senior Member of ASQ, Payne has been working in electronic calibration and product testing since 1981. He is a certified quality engineer, calibration technician and quality technician. He is also the chair of the Measurement Quality Division and a member of NCSL International.