Lundi 22 Avril 2019  

N°124 - Quatrième trimestre 2018

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  M./Mr Andrew Wallard

The Metre Convention 130 years young  

By Prof. Andrew Wallard, Director of the Bureau International des Poids et Mesures

“Weights and Measures”? Does that evoke, for you, the notion of some esoteric or even anachronistic activity? Well, it shouldn’t! I hope, in this editorial, to convince you that Metrology – the science of measurement – and the work of the Bureau International des Poids et Mesures, just outside Paris, – has important and far-reaching economic and commercial implications world-wide, and that it is still enormously relevant to us all, as we reach the end of 2004.
I became BIPM's 10th Director in January, 2004, humbly conscious that I was following in the footsteps of many famous scientists who have been associated with the Bureau since it was created: Benoît, de Broglie, Cornu, Fabry, Kösters, Michelson, Sears, Siegbahn, Volterra, Zeeman, Mendéléev – all have served on the BIPM's Management and Advisory Committees. Many Nobel prizewinners – including one of my predecessors, Guillaume, – have also worked closely with the Bureau.  And why should Metrology have had such appeal for these scientific giants? Quite simply, scientists need to understand what limits their ability to measure, in order to advance our knowledge.  Steve Chu, the 1997 Nobel Physics Laureate, speaking at the 125th Anniversary of the BIPM and the Metre Convention, gave a succinct answer:  "Accurate measurement is at the heart of physics and, in my experience, new physics begins at the next decimal place."
Formally, the Convention du Metre was signed in 1875, during a diplomatic conference organised by the French Government, France being the holder of the Convention. This diplomatic conference survives as the General Conference on Weights and Measures (CGPM), which now meets every four years, in Paris, to debate a number of issues related to world metrology. It also approves the BIPM’s work-programme and sets its budget: – currently about €10 million a year. In between meetings of the CGPM, an International Committee for Weights and Measures (CIPM) of 18 individuals, nominated for their personal expertise, monitors the activities of
the BIPM.
On a daily basis, the BIPM works with over 80 National Metrology Institutes worldwide, and co-ordinates their international technical scientific work. The Bureau maintains the closest possible working relations with international and inter-governmental bodies, such as the International Organisation for Legal Metrology (OIML), the International Organisation for Standardisation (ISO), the International Electrotechnical Commission (IEC) and many other specialist technical bodies. The link between metrology and the application of written standards creates an essential and mutually dependent infrastructure recognised by the World Trade Organisation, as well as agencies such as UNIDO.
BIPM was created as the result of a worldwide appreciation that better measurement helps to create better products for the whole world. It was immediately clear that units, and standards of measurement, needed to be agreed internationally if they were to be relevant. The stage was set for the BIPM to begin its stewardship of the international system of measurement.
There is much more to "weights and measures" than pure science, though. At BIPM's inauguration, the Government representatives who signed the Convention were acutely aware of the impact of measurement standards on industrial companies making (what they hoped were) compatible products and components, in different locations. In earlier days, the lack of agreed and validated measurement standards and techniques led to those infamous stories about bullets which didn't fit guns, or couplings for fire hoses which didn't fit the hydrants! However, in general, the international infrastructure now works well and the vast majority of users take it for granted that the measurement standards they use are properly calibrated, traceable to internationally agreed reference, and are the same all over the world.
Few are aware of the complex and vital networks co-ordinated by the BIPM – for, as with other areas of "hidden" infrastructure, stories only hit the headlines when something goes wrong: a shipment of food rejected in one country, for instance, because their ways of measuring contamination levels differ from the source country; or an international trade dispute over conflicting whiteness standards which, when finally resolved, saved the Canadian paper industry several million dollars.  On the other hand, there are many success stories – the wings of the European Airbus are made in the UK and assembled onto the locally constructed fuselage in France, thanks to accurate dimensional measurement with laser standards, and the international time scale (Coordinated Universal Time) and satellite-based atomic clock standards are used throughout the world for accurate navigation.
Until about 10 years ago, National Metrology Institutes carried out informal comparisons of their standards. These comparisons were, however, generally driven by a scientific, rather than a commercial motivation, and the process lacked any formal basis. In 1999, therefore, the BIPM launched a Mutual Recognition Arrangement between the Members of the Convention, part of which involves a peer-review of the technical capabilities of all the national laboratories, as well as a technically robust series of comparisons between them. The end results give us confidence in the ability of all participants to make equivalent measurements and enable the provision of Calibration Certificates which, for the first time, are accepted by all signatories, thus helping to reduce technical barriers to trade (TBTs). The WTO's TBT Committee is now taking an interest in the CIPM MRA, noting that it is already cited as a suitable technical reference frame for a number of international trade agreements. An increasing number of regulators also regard it as providing the technical evidence they need for acceptance of non-national Calibration Certificates.
The Conference created a new category of Membership of the Metre Convention – the Associate of the CGPM. This category was specifically designed to encourage the widest possible participation in the CIPM MRA. In addition, it  is also possible for recognised economic groupings to sign the CIPM MRA as a single entity, so paving the way for the smaller economies to become involved. Currently, there are 51 Member States of the Metre Convention and 16 Associates of the CGPM. Many more emergent economies are now expressing interest in the work of the BIPM and, specifically, in the CIPM MRA as it enables them to demonstrate their measurement credentials at whatever level of measurement accuracy is appropriate to their stage of development. The Metre Convention is therefore responding to the fresh awareness of globalisation: it is, and must be, open to all.
BIPM today is still a small organisation with about 70 staff drawn from some 14 countries. Its headquarters on what is considered to be international territory granted by the French Government, lies above the banks of the Seine at Sèvres centred around a Pavillon originally constructed by Gobert for Louis XIV in 1672. It still holds the international prototype Kilogram; the last of the seven "base" units of the SI (the International System of Units) which is based on a physical artefact. The international prototype, copies of which are made for Member States, is rarely used, but still fascinates the makers of documentary television science programmes (!), and is inspected annually by the CIPM in a ceremony which involves the opening of a vault with keys held by three different individuals, the BIPM Director, the CIPM President and the Archivist of France. Its days are, however, numbered as various projects, including one at the BIPM itself, are poised to monitor it sufficiently well to give confidence in a new definition based on a fundamental constant of nature.
Where are the important areas for metrology in the 21st century? Of course there will continue to be a range of challenges from traditional areas in physics and engineering, and industrial demands for more and more precise measurement appear insatiable. Improved measurement standards and techniques will continue to be needed in areas like Ionising Radiation and Ultrasonics, for industrial and medical uses. New technologies, such as Nanoengineering, are beginning to create a whole new field of standards work for the measurement of the very small and the very fast, and BIPM will need to respond with studies and projects to deal with the implications of these developments at the international level. However, the greatest and most pressing demand for us in the next couple of years, is to satisfy the need for precise, traceable measurements in Chemistry, especially for those relevant to environmental issues, biotechnology, drug testing, food safety and medicine. The economic and societal benefits here are potentially enormous, and we have only just begun to scratch the surface of the growing need amongst professionals in the user communities for accurate measurement. A number of comparison projects have revealed some weaknesses in the current world system, as well as a degree of disparity amongst laboratories in different countries measuring the same samples.
Our aim is to bring these domains into the framework of the CIPM MRA or a similar arrangement, in order to continue our mission of seeking worldwide uniformity of measurement. I, and my successors, have much-needed work to do, for as far ahead as we can see.
All our work is, I believe, testimony to the wisdom of the founding fathers of the Metre Convention – they would have been surprised and, I hope, delighted to see their creation flourishing and continuing to serve today’s international community.


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