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Dynamic calibration of pressure sensors

Dynamic calibration of pressure sensors Pressure measurement in non-equilibrium conditions is required in many applications. For example, pressure must be monitored in the cylinders of an engine to study combustion phenomena, in an injection moulding press to study a moulding process, in a Pitot tube to determine the speed of an aircraft, or in a catheter to determine blood pressure. In applications like these the pressure quantity is in dynamic state, i.e. the measurand is constantly changing, including during measurement. In static state a sensor is characterized by its sensitivity for a given measurand, defined as the variation in output quantity divided by the corresponding variation in the measurand. The same calculation performed in dynamic state produces different sensitivity values. Determination of sensitivity as performed in static state is thus not sufficient for dynamic calibration, and a specific method is required. To design this calibration method, the characteristics of the sensor must first be defined. Specific references are then required to perform the calibration. Further studies and calibrations must also be carried out to take into account the specific characteristics of the measurement system (measurement line, recessed chamber, change of fluid, etc.).

Dynamic calibration of pressure sensors (pdf - 165 kB)

Metrology of the waveform of complex dynamic signals

Oscilloscope

Digital technologies used in telecommunications (WPAN*, WLAN*, WMAN*, WWAN* and DSL* networks, satellites, etc.) and in instrumentation are developing fast. The main trend today in telecommunications is towards systems operating in ever higher bandwidths and using modulated radio frequency signals with a complex waveform. This raises the problem of calibrating the waveform of these complex dynamic signals and ensuring their traceability to the International System of Units (SI). A number of different instruments are needed to generate, obtain and process the signals: modulated radio frequency sources, random waveform generators, broadband digital oscilloscopes, spectrum analysers, non-linear vectorial network analysers, etc. At present these instruments are not systematically calibrated in France.

Metrology of the waveform of complex dynamic signals (pdf - 314 Ko)

Gas flow measurement references

gas flow measurement references

This file presents the national references developed by LNE-LADG (Associate Laboratory for Gas Flow Measurement) to ensure the traceability of high-pressure gas flow measurements.

The main feature of the traceability chain maintained by LNE-LADG is the use of critical flow Venturi nozzles as transfer standards. The Laboratory has used these nozzles since the early 1970s to generate and measure reference flow on calibration and test benches operating with air or natural gas.

This technology is used today in defining the value of the reference high-pressure natural gas cubic metre, established under a harmonization agreement between PTB (Germany), NMi (Netherlands) and LNE-LADG.

Gas flow measurement references

Radiotherapy - Graphite calorimetry

Radiotherapy : graphite calorimetry

Since medical exposure is by far the most common source of artificial irradiation, there is a clear need to provide specific metrological references in this field. Radiotherapy in particular requires precise control of the doses administered in "target" volumes (for tumours), which in turn depends on highly accurate characterization of the doses produced by radiation sources (accelerators, cobalt).

To meet this need, metrologists must develop primary reference standards that represent as closely as possible the dose absorbed in biological environments, in irradiation conditions that are identical to those of human exposure.

Reference standards are defined in environments close to biological tissue, for their properties of interaction with matter (similar atomic number): air, water, graphite, etc.

Medical physicists thus characterize radiation beams in terms of absorbed dose to water.

Graphite calorimetry (pdf - 829 Kb)

Pesticides

Water pollution : pesticides analysis, traceability of measurements

Analytical chemistry - metrology in chemistry in particular - is currently undergoing major developments as a result of high demand from society for measurement of chemical compounds in the environment, health and agri-food sectors. In each of these fields, along with other industrial sectors, thousands of laboratories carry out millions of analyses every year. The metrological traceability of these measurements is not always adequately ensured in sensitive sectors such as environment and health. Pesticides are a prime example of a field where metrology in chemistry can play a significant role. The level of water pollution caused by these compounds is alarmingly high and numerous laboratories are analysing pesticides on a daily basis. Unfortunately, despite the implementation of sophisticated analysis techniques, traceability to the SI system is not always proved. This document covers the question of pesticides in general and reviews the analytical and metrological aspects.

Pesticides (pdf - 407 kB)

Chip-scaled atomic clocks

Chip-scaled atomic clocks

The Bose-Einstein Condensate, a new state of matter predicted in 1924 by A. Einstein then experimentally observed in 1995 by E.A. Cornell and C.E. Wieman on the one hand and W. Ketterle on the other hand, has aroused great interest from the scientific community. And Metrology was not lagging behind. As the LNE-SYRTE, the national metrology laboratory designated under the French metrology scheme to carry out the time and frequency activities, had embarked in a project based on the Bose-Einstein condensates, in collaboration with the Laboratory Kastler Brossel and the Ecole Normale Supérieure of Paris. The aim was to realize a chip-scaled atomic clock that will operate alternatively with the thermal atomic and degenerated gases.

Chip-scaled atomic clocks (pdf - 621 kB)

Balance du watt

Expérience française de la balance du watt

The kilogram is the unique unit among the International System (SI) that is still defined from a single artefact, in accordance with the definition that was adopted by the General Conference on Weights and Measures (CGPM) in 1889. It is equal to the mass of the international prototype kilogram, platinum-iridium material standard, kept by the International Bureau of Weights and Measures (BIPM), and named .

However, even if represents the mass unit by definition, the international prototype is not perfectly stable, owing to its interaction with the surrounding medium.

Encouraged by the 20th and 21th CGPM (1995-resolution 5 and 1999-resolution 7) and to contribute to the international effort, France has made the decision to realize an experiment called "Watt Balance" based on a principle devised in 1976 by B.P. Kibble (NPL).

It has a twofold objective :

If this determination can be carried out with a sufficiently low uncertainty, satisfying both objectives could allow obtaining an evolution in the definition of the mass unit based on a fundamental constant, as was the case for the metre in 1983 by setting the value of the light speed conventionally, and hence relate the metre to the second.

Watt balance