Is that measurement correct? Check it again! | Automation.com

Is that measurement correct? Check it again!

April 162012
Is that measurement correct?  Check it again!
Volts, Ohms, Temperature, Vibration, Pressure & Cubits?
 
April 2012
 
By Bill Lydon, Editor
 
On April 5, 2012, I visited Fluke’s corporate headquarters in Everett, Washington to attend presentations, tours and have hands on experience with their products. It became obvious that Fluke is passionate about reliable measurements. Accurate measurements are fundamental for automation and control systems to accomplish precise control.
 
Metrologist - What does weather have to do with automation?
 
Jeff Gust, Chief Metrologist for Fluke Corporation began his presentation noting that many people think a Metrologist’s job is forecasting the weather. Gust made it clear that Metrologists do not forecast weather - that is a Meteorologist!  Metrology is defined by the International Bureau of Weights and Measures (BIPM: www.bipm.org) as "the science of measurement, embracing both experimental and theoretical determinations at any level of uncertainty in any field of science and technology.” He described Metrology as the Science of Measurement, a sub-filed of physics, underpinning most other technologies.
 
 
Jeff Gust, Chief Metrologist, “Metrology as the Science of Measurement, a sub-field of physics, underpinning most other technologies.”
 
Jeff Gust oversees Fluke’s primary metrology laboratories in Everett, Washington; American Fork, Utah; Phoenix, Ariz.; and Houston, Texas.   Gust started his career in the US Marine Corps as a TMDE Technician (Test Measurement and Diagnostic Equipment Technician), and is a recognized member of the international metrology community, holding active roles with several leading professional organizations. He has authored numerous technical papers on various metrology topics, is a recognized authority in proficiency testing and has performed more than 50 laboratory accreditation assessments. He holds a B.S. in Physics from Purdue University.
 
Gust reviewed the reasons for measurements including fair trade, safety, interoperability, traceability, consistency and quality. He cited a quote from Galileo on the topic, “Measure what is measurable, and make measurable what is not so.” Accurate measurements date to early civilization and are fundamental for fair trade. Gust explained, “When we were trading an ounce of gold for a bushel of wheat, we wanted to insure we got the proper quantity.”   That is why measurement keepers of the United States, the National Institute of Standards and Technology (www.nist.gov), are under the department of commerce.
 
Measurements are important for many reasons. Safety standards are based on measurements, for example defining dangerous amount of voltage to physically approach. Legal requirements are becoming a bigger issue; in 2012 the European Union required homes to have an energy performance certificate before they are allowed to be put on the market. As a part of this certification, thermography scans are required. Interoperability is another important requirement for the global economy. For example, an electronic board builder needs to have consistency of components from all world sources. 100 ohm resistors from anywhere in the world needs to be within tolerance limits. Traceability is a key concept in standards, meaning all measurements need to be traceable to a stable reference.
 
Cubit
 
Gust used a model of an Egyptian Cubit to illustrate that value of standards. The Cubit was unit of measure that was used to build the pyramids and was based on the length of the forearm plus the width of the hand of the Pharaoh. He explained that the pyramids were built using a single cubit reference standard. The Egyptians had strict quality control standards with workers. Supervisors issued cubit sticks and on every full moon all cubits were returned to be checked against the master cubit. Failure to return your cubit was punishable by death or stated another way, “quality by death.” Gust pointed out that the pyramids were built with each side of the base within six inches, the relative accuracy is 0.05% or 500 parts per million. Gust noted that this illustrates the value of good measurements. The only catch was the standard changed with each new Pharaoh’s arm and hand.  More information on the Cubit.
 
Traceability
 
Gust also discussed traceability which refers to an unbroken chain of comparisons relating an instrument's measurements to a known standard. Calibration to a traceable standard can be used to determine an instrument's bias, precision, and accuracy. The standards are maintained by government agencies. 
 
 
Typical Traceability Hierarchy correlation with Fluke Groups - Calibration & Industrial Group (IG)
 
The basis for most of the standards can be created through fundamental physical constants. For example, for the triple point of water, that is a temperature and pressure at which the three phases (gas, liquid, and solid) co-exist in thermodynamic equilibrium. In contrast, the standard kilogram made in the 1880s is a bar of platinum-iridium alloy, kept in a vault near Paris, which is losing weight. Scientists are hoping to redefine the kilogram by basing it on standards of universal constants rather than on an artifact standard.
 
 
Hy Tran examines a kilogram sample in a mass comparator at Sandia’s Primary Standards Laboratory. (Photo by Randy Montoya)
 
 
Gust described a range of precise standards that Fluke has created and maintains to insure quality. Many standards labs use Fluke equipment. An example is the ISO/IEC 17025 standard used by testing and calibration laboratories to meet requirements for the competence of testing and calibration laboratories.
 
Pressure
 
Fluke Calibration also designed and manufactures the PG9607, a primary pressure reference for absolute and gauge pressures to 500 kPa (kilo Pascals). It supports the use of a 100 kg mass set to define gauge and absolute pressures from 11 to 500 kPa with a single piston-cylinder.   This piston gauge is designed for use as a true primary pressure reference in metrology and research institutes.   The PG9607 is the result of Fluke Calibrations' extensive work with national metrology institutes (NMIs) to minimize pressure measurement uncertainty and years of supplying PG7000 piston gauges to NMIs and other top pressure metrology labs worldwide. More information

Thoughts & Observations
 
Fluke people are obviously passionate about reliable measurements, the core of their business. In the field we take solid measurements for granted. You can relate to this if you have had experience troubleshooting a problem in the field with a faulty test device, such as a multi-meter.  If a faulty meter does read what you expect it to, it’s easy to think you are losing your mind. 
 
These are some quotes Fluke people used in presentations that illustrate how long people have been contemplating measurement:
 
“When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind. It may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science.”   Lord Kelvin
 
“Immersion in water makes the straight seem bent; but reason, thus confused by false appearance, is beautifully restored by measuring, numbering and weighing; these drive vague notions of greater or less or more or heavier right out of the minds of the surveyor, the computer, and the clerk of the scales. Surely it is the better part of thought that relies on measurement and calculation.” Plato (The Republic)
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