Metrology – the science of how measurements are made
Metrology is the science of measuring, and the name derives from the Greek words metron “measure” and logos, which have several meanings, including “science.” We can apply metrology to evaluate many different properties of objects, materials and substances, such as weight, length, temperature and pressure. In dimensional metrology, we are interested in measuring length and angle accurately. The main subject of analysis is also the position, shape and angular orientation of the object in three-dimensional space.
Metrology is particularly important in manufacturing, which cannot function without standardized parts. For example, a manufacturing company must assemble components to produce a car, and these components must be interchangeable. If a part needs to be replaced, the customer needs to be sure that the manufacturer can supply one that will fit and function the same as the original. Components for a specific car will be supplied by many companies around the world. This requires international agreement on units of measurement and value, so that, for example, 1 meter (length) measured by a company in France is the same as 1m in length measured by a company in China.
How long is one meter?
The photo shows a computer-generated image of the “International Prototype Meter” bar, made of a 90% platinum-10% iridium alloy. It was the length standard for the SI (metric system) from 1889 to 1960. Then the SI system changed the definition of length based on the wavelength of light emitted by krypton 86. The length of a meter was determined by the distance between two thin lines located on the center rib of the pattern near its ends, at freezing water temperature.
Researchers made a rod with an X-shaped cross-section to increase its stiffness-to-weight ratio, improve thermal accommodation time. This allowed the pitch lines to be placed on the “neutral” axis of the bar, where the change in length with deflection is minimal.
The French made a prototype in 1889, its length was equal to the earlier French standard “Metre of the Archives.” The researchers made twenty-nine identical copies simultaneously. They then calibrated them all against the prototype and distributed them to individual countries to serve as national standards.
The main problem with defining a unit of length by an artifact such as a pattern is that there is no reliable way to detect a change in its length due to age or misuse. People can compare it with other copies, but the same ones may have already had a different length. This motivated the change in 1960. for a definition based on light waves. The BIPM museum is now ensuring security for future generations.
How to divide metrology?
We can conventionally divide metrology activities into three general categories:
- Scientific metrology
Measurement science, including the development and delivery of measurement standards - Industrial metrology
Application of measurement science to manufacturing and other processes - Legal metrology
Measurement activities underpinning fair trade and consumer protection
What kind of metrology does our company do?
We provide services in the business of Industrial Metrology. We use portable 3D metrology measuring machines such as Laser Trackers and Measuring Arms. We are transporting these devices directly to where the measurements will take place and have checked the dimensions on site. We are also specialists in large-scale metrology services (large industrial facilities, furnaces, mills, cranes, machine bodies, etc.).
We use portable metrology equipment for tasks where typical lengths range from 1 meter to as much as 150 meters. During our services, achievable 3D accuracies range from parts of a millimeter to up to tens of microns. On average, this is the thickness of a human hair which averages about 75 μm (0.075 mm).
In this article, we wanted to share our perspective on the definition of the science of measurement that is metrology.