Everything about Metrology totally explained
Metrology (from
Ancient Greek 'metron' (measure), and 'logos' (study of)) is the
science of measurement. Metrology includes all theoretical and practical aspects of measurement.
Introduction
Metrology is defined by the
International Bureau of Weights and Measures (BIPM) as "the science of measurement, embracing both
experimental and
theoretical determinations at any level of
uncertainty in any field of science and technology."
(External Link
)
Metrology is a very broad field and may be divided into three subfields:
- Scientific or fundamental metrology concerns the establishment of measurement units, unit systems, the development of new measurement methods, realisation of measurement standards and the transfer of traceability from these standards to users in society.
- Applied or industrial metrology concerns the application of measurement science to manufacturing and other processes and their use in society, ensuring the suitability of measurement instruments, their calibration and quality control of measurements.
- Legal metrology concerns regulatory requirements of measurements and measuring instruments for the protection of health, public safety, the environment, enabling taxation, protection of consumers and fair trade.
A core concept in metrology is (metrological)
traceability, defined as "the property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of
comparisons, all having stated uncertainties." The level of traceability establishes the level of comparability of the measurement: whether the result of a measurement can be
compared to the previous one, a measurement result a year ago, or to the result of a measurement performed anywhere else in the world.
Traceability is most often obtained by
calibration, establishing the relation between the indication of a measuring instrument and the value of a measurement standard. These standards are usually coordinated by national laboratories:
National Institute of Standards and Technology (USA),
National Physical Laboratory, UK, etc.
Tracebility,
precision,
bias, evaluation of
measurement uncertainty are critical parts of a
quality management system.
Historical development
length,
time, and
weight. These standards were established in order to facilitate
commerce and record human activity.
Little progress was made with regard to proto-metrology until various scientists,
chemists, and
physicists started making headway during the
Scientific Revolution. With the advances in the sciences, the comparison of experiment to theory required a rational system of units, and something more closely resembling modern metrology began to come into being. The discovery of
atoms,
electricity,
thermodynamics, and other fundamental scientific principles could be applied to standards of measurement, and many inventions made it easier to quantitatively or qualitatively assess physical properties, using the defined units of measurement established by science.
Metrology was thus one of the precursors to the
Industrial Revolution, and was necessary for the implementation of
mass production, equipment commonality, and
assembly lines.
Modern metrology has its roots in the
French Revolution, with the political motivation to harmonize units all over
France and the concept of establishing units of measurement based on constants of
nature, and thus making measurement units available "for all people, for all time". In this case deriving a unit of length from the dimensions of the
Earth, and a unit of
mass from a
cube of
water. The result was
platinum standards for the
meter and the
kilogram established as the basis of the metric system on June 22, 1799. This further led to the creation of the Système International d'Unités, or the
International System of Units. This system has gained unprecedented worldwide acceptance as definitions and standards of modern measurement units. Though not the official
system of units of all nations, the definitions and specifications of
SI are globally accepted and recognized. The SI is maintained under the auspices of the
Metre Convention and its institutions, the
General Conference on Weights and Measures, or CGPM, its executive branch the
International Committee for Weights and Measures, or CIPM, and its technical institution the
International Bureau of Weights and Measures, or BIPM.
As the authorities on SI, these organizations establish and promulgate the SI, with the ambition to be able to service all. This includes introducing new units, such as the relatively new unit, the
mole, to encompass metrology in chemistry. These units are then established and maintained through various agencies in each country, and establish a hierarchy of measurement standards that can be traced back to the established standard unit, a concept known as metrological traceability. The U.S. agencies holding this responsibility is known as the National Institute of Standards and Technology, or
NIST; and the
American National Standards Institute (ANSI).
Industry-specific metrology standards
In addition to standards created by national and international standards organizations, many large and small industrial companies also define metrology standards and procedures to meet their particular needs for technically and economically competitive manufacturing. These standards and procedures, while drawing in part upon the national and international standards, also address the issues of what specific instrument technology will be used to measure each quantity, how often each quantity will be measured, and which definition of each quantity will be used as the basis for accomplishing the
process control that their manufacturing and product specifications require. Industrial metrology standards include dynamic control plans, also known as “dimensional control plans”, or “DCPs”, for their products.
In industrial metrology, several issues beyond accuracy constrain the usability of metrology methods. These include
1. The speed with which measurements can be accomplished on parts or surfaces in the process of manufacturing, which must match the
TAKT Time of the production line.
2. The completeness with which the manufactured part can be measured such as described in
High-definition metrology,
3. The ability of the measurement mechanism to operate reliably in a manufacturing plant environment considering temperature, vibration, dust, and a host of other potential hostile factors,
4. The ability of the measurement results, as they're presented, to be assimilated by the manufacturing operators or automation in time to effectively control the manufacturing process variables, and
5. The total financial cost of measuring each part.
Mechanisms
At the base of metrology is the definition, realisation and dissemination of units of measurement. Physical or chemical properties are quantised by assigning a property value in some multiple of a
measurement unit.
The basic 'lineage' of measurement standards are:
The definition of a unit, based on some physical constant, such as absolute zero, the freezing point of water, etc.; or an agreed-upon arbitrary standard.
The realisation of the unit by experimental methods and the scaling into multiples and submultiples, by establishment of primary standards. In some cases an approximation is used, when the realisation of the units is less precise than other methods of generating a scale of the quantity in question. This is presently the situation for the electrical units in the SI, where voltage and resistance are defined in terms of the ampere, but are used in practice from realisations based on the Josephson effect and the quantised Hall effect.
the transfer of traceability from the primary standards to secondary and working standards. This is achieved by calibration.
Theoretically, metrology, as the science of measurement, attempts to validate the data obtained from test equipment. Though metrology is the science of measurement, in practical applications, it's the enforcement and validation of predefined standards for precision, accuracy, traceability, and reliability.
Accuracy is the degree of exactness which the final product corresponds to the measurement standard.
Preciseness refers to the degree of exactness which a measuring instrument can determine accuracy (actually, inaccuracy).
Reliability refers to the consistency of accurate results over consecutive measurements.
Traceability refers to the ongoing validations that the measurement of the final product conforms to the original standard of measurement.
(Fundamentals of Dimensional Metrology, Ted Busch, Wilkie Bros Foundation, Delmar Publishers, ISBN 0-8273-2127-9)
These standards can vary widely, but are often mandated by governments, agencies, and treaties such as the International Organization for Standardization, the Metre Convention, or the FDA. These agencies promulgate policies and regulations that standardize industries, countries, and streamline international trade, products, and measurements. Metrology is, at its core, an analysis of the uncertainty of individual measurements, and attempts to validate each measurement made with a given instrument, and the data obtained from it. The dissemination of traceability to consumers in society is often performed by dedicated calibration laboratory with a recognized quality system in compliance with such standards. National laboratory accreditation schemes have been established to offer third-party assessment of such quality systems. A central requirement of these accreditations is documented traceability to national or international standards.
Some common standards include:
ISO 17025:2005 - General Requirements for Calibration Laboratories
ISO 9000 - Quality Systems Management
ISO 14000 - Environmental Management
21 CFR Part 210/211 - FDA Regulations concerning GMP (Good Maintenance Practices) Quality Systems
21 CFR Part 110 - FDA Regulations concerning Food Industry GMP'sFurther Information
Get more info on 'Metrology'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://metrology.totallyexplained.com">Metrology Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
