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**Mass and related quantities

Mass

Physico-chemical characterization of the materials used for the mass reference through X reflectometry and fluorescence

The general purpose of this study that was launched in 2004 and is lasting three years, is to allow determining, in a non destructive fashion, the physical or physico-chemical parameters that govern the exchanges between the active surface of a mass standard and the surrounding environment, and thus control its long-term stability.

Analysis of the surface activity of the mass standards

This study is aimed at the improvement and the implementation of reactivity analysis techniques and adsorbability measurement of surface to cover the needs of metrology (mass, temperature, nanometrology,...). More specifically, works carried out in 2006 were focusing on the improvement of one device for mass spectrometry via thermodesorption (improvement of the reproducibility of the results and their exploitation).

Definition of a metallic material for the realization of mass standard

The objective of this study launched in 2003 is to define and characterise a metallic alloy with high mass stability for the realisation of reference standards ranging from 1 g to 10 kg. Improvement made with these standards will be necessary to take advantage of the anticipated improvement in the maintenance of the mass unit deriving from the experiments made for linking the kilogram to fundamental constants of physics (experiments such as the watt balance currently under development in France).

Torque

Development of new torque references

The LNE has undertaken the renewal of its torque references. To date, two references of 5 N·m and 50 N·m are about to be finalized (figure 1).

Fig. 1. - View of the 50 N.m device undergoing construction
Fig. 1. - View of the 50 N.m device undergoing construction

Pressure

Implementation of the ultravacuum reference

The purpose is to realise a pressure reference up to 10-8 Pa through the dynamic expansion method for extrapolation towards the lowest pressures. This method requires the knowledge of the gaseous flux injected into the system using one gaseous fluxmeter which is currently undergoing development. It will allow the measurement of low pressures (below absolute 10-8 Pa absolus) and to carry out the primary connection of the reference leakages.

Improvement of the uncertainties in high pressure

Works carried out in this area focus on the improvement of the uncertainties. Said works cover the implementation of one pressure level at 50 MPa and the improvement of the piston-cylinder unit that constitutes the 200 MPa reference.

Expansion of the capabilities for dynamic pressure

Generally speaking, works carried out concerning dynamic pressure are aimed at the expansion of the capabilities beyond 10 bar (1 MPa), which corresponds to the highest pressure covered by the current reference shock tube. Works under way focus on the one hand, on the realisation of one quick aperture device of 40 bar (4 MPa) to ensure the transition between the low and high pressures in the area of low frequencies (cf. figure 2). And on a new high pressure reference shock tube to ensure the comparison of the different means on the other hand, one instrument is currently under development at the Brasilia University, Brazil, in collaboration with the LNE-ENSAM.

Fig. 2. - Rapid aperture device (DOR40)
Fig. 2. - Rapid aperture device (DOR40)

Flow

Primary calibration bench for the small sonic nozzles (gas flowrate)

If the calibration range of the sonic nozzles is currently ranging between 1,5 m3/(hbar) and 200 m3/(hbar) for upstream pressure ranging from 6 bar (0,6 MPa) to 55 bar (5,5 MPa), the LADG has undertaken the implementation of a second primary calibration bench in compressed air, using the PVTt method to cover a range extending between 0,1 m3/(hbar) and 5 m3/(hbar) for upstream pressure ranging from 6 bar (0,6 MPa) to 55 bar (5,5 MPa). Said primary installation will allow to fulfill the traceability needs regarding small sonic nozzles and to provide coherence between air and natural gas calibrations.

Development of a new diverting system (water flow)

Each measurement line of the Cetiat’s gravimetric calibration bench is using one diverter that directs the fluid towards one weighing tank at the start of measurement or, towards one storage tank at the end of measurement. A chronometer is engaged at the start of measurement and stopped when it is completed. Each of the transitory phases is the source of non negligible uncertainty. A rotating Double Wing diverter allowing minimizing this uncertainty is under development. It will be duplicated on the three measurement lines of the fluid (water) flowmetering reference.

Sound pressure

Development of a reference in the audiometry field

Pure sound audiometers, used for screening deafness are controlled by one artificial ear, a transducer that is supposed to have the same acoustic impedance close to the one of the average human ear, when used in conjunction with a super-aural headphone. The CEI 318 standard specifies the composition, the characteristics and tolerances of the different elements in the artificial ears, but to date, there is no method for accessing the measurement of these elements. This absence of traceability in measurement has led to important dispersion in the audiometry measurements.

The first step of the study consisted in taking the basis of acoustics theory back and defining the model of acoustical behaviour of one cavity, specifically from the thermoacoustic point of view. This section of the study was the source of one doctoral thesis defended in September 2005. Said thesis has led to question the model currently standardized to define the behaviour of one cavity and has proposed a new model. Works will now concentrate on partial validation of this new model by applying it to the experimental cavities.