Skip to main content
RISE logo

SI system, The Meter Convention and international cooperation

Having access to an internationally accepted and uniform system of measurement units is a basis for modern society and a prerequisite for science, technological development and international trade.

Lenght

SI - International system of basic units 

In all countries around the world, there are designated organizations with the task of providing close and secure access to measurements with traceability to SI. The scope of the different nations' metrology resources is adapted to their own needs and is in all cases seen as an "offer" to their own society, part of the country's technical infrastructure.

The SI consist of seven basic units and a large number of derived units. The units of measurement are in many cases cross-linked to each other and in this way the necessary robustness is achieved.

The Meter Convention and its organization

The Meter Convention from 1875 is one of the oldest international agreements and Sweden was one of 17 signatories of origin. Today, the Meters Convention is ratified by 62 states and it covers all the world's industrial nations, www.bipm.org  

For many years, the work with traceable measurements was based on artifacts and comparisons of these, with the International Bureau of Weights and Measures (BIPM) as the center. International research has led to that all units of measurement today have definitions based on natural constants. The work of linking the units of measurement to natural constants has in several areas attracted attention with the Nobel Prize, which shows both the required research quality but also the importance of having a uniform and robust unit internationally accepted system of measurement units, SI.

A growing need for an open, transparent and comprehensive system to provide measurement service users with reliable quantitative information on the comparability of national measurement services led, in 1999, to the Meter Convention being supplemented by an MRA, Mutual Recognition Arrangement, www.bipm.org/en/cipm-mra/

The MRA means that National Metrology Institutes in each country as well as any designated Designated Institutes must:

  1. Report their Measurement and Calibration Capability, CMC Calibration and Measurement Capability in a public database managed by BIPM, http://kcdb.bipm.org/appendixC/default.asp
  2. Participate in international, key-comparisons, i.e. comparative measurements (to an extent agreed internationally at an overall level) and that the results of the comparative measurements are reported in a public database managed by BIPM http://kcdb.bipm.org/appendixB/KCDB_ApB_search.asp
  3. Conduct an operation in accordance with an internationally accepted quality standard, in most cases SS EN ISO / IEC 17025, General competence requirements for testing and calibration laboratories.

To confirm traceability of measurement quantities, international comparative measurements are carried out at different levels. The “highest” level of such key-comparisons is organized through BIPM´'s consultative committees, CC, and participation in these requires that each country/institute qualify as a member of a specific committee. The comparative measurements are continued at a “lower” level by regional metrology organizations e.g. EURAMET.

Participation at the “highest” level means that the measurement results are based on direct realizations in relation to the SI unit. The result thus also shows with what accuracy realizations can be made with different independent measurement setups and thus also forms the basis for a global “reference level” (that the reference level is determined by several independent realizations reduces the risk of systematic errors).

In some areas such as Electricity, Time and Frequency, Mass and related quantities as well as metrology in the Chemistry area, RISE is a member of the respective CC and, where applicable, their working groups.


Jan Johansson

Contact person

Jan Johansson

Senior forskare

+46 10 516 55 04
jan.johansson@ri.se

Read more about Jan