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Australian Government: National Measurement InstituteAustralian Government: National Measurement Institute
National Measurement Institute
      

Mass and Related Quantities Facilities

1 kg mass comparatorMass
Metler HK1000 1 kg prototype balance
Various balances from max loads of 3 g to 20 kg
Platinum-iridium prototype kilogram number 44 (Australian national standard of mass)
Sets of E1 weights to 20 kg

Density
Hydrostatic weighing facility
Silicon sphere volume standard
ULE density standard artefacts
Hydrometer hydrostatic calibration facility

Flow (see below)
A 300 L bell prover
Five mercury sealed piston provers with volumes up to 12 L
Four critical flow Venturi nozzle arrays with nozzle diameters from 0.1mm to 22mm
A 670 L PVTt system

Force (see below)
Deadweight force machine to 5 kN
Deadweight force machine to 550 kN
Hydraulic Force Machine to 10 MN

Pressure (see below)
Hydraulic piston pressure balances to 500 MPa
Gas operated piston pressure balances to 7 MPa
Interferometric mercury manometer to 100 kPa
Water/mercury manometers
Bradshaw gauge
McLeod gauges

Viscometry (see below)
Glass capillary master viscometers

Volume
Volume calibration facility to several hundred litres

Force

550 kn force machineAustralia's Dead-weight Force Standard

NMI maintains force standardising machines, which allow all force measurements to be traceable to the Australian standards for mass, length and time. The main primary standard for force in Australia is a dead-weight force machine with a capacity of 550 kn. The uncertainty associated with the applied forces in the dead weight force standard is ±20 ppm. In order to maintain the stated uncertainty level, and to provide traceability of the weights to the international kg, periodic recalibration of the weights is necessary. The recalibrations are done using an in situ technique described elsewhere. The test results show that the calculated mass differences agree with the known mass differences to within 2 ppm.

NMI maintains dead-weight force standardising machines and a hydraulic force standardising machine.

The dead-weight machines, absolute machines by definition, operate in the range of 2 N to 550 kN in both tension and compression modes. The hydraulic machine covers the range from 0.5 to 10 MN in the compression mode and from 0.5 to 3.5 MN in the tension mode.

Although the latter machine is not an absolute force standardising machine, it is traceable to the dead-weight machine. These machines are used to characterise or calibrate force measuring instruments such as proving rings, load cells and aircraft weighing kits used as transfer standards in industry. The table below lists the principal capabilities of these machines.

Capabilities of force standardising machines
Force range
Minimum force increment
Uncertainty of applied force
2 to 100 N (compression and tension)
0.01 N
0.002%
50 to 5600 N (compression and tension)
1 N
0.002%
5 to 550 kN (compression and tension)
200 N
0.002%
0.5 to 2 MN (compression)
0.02%
2 to 10 MN (compression)
0.06%
0.5 to 3.5 MN (tension)
depends on application

Pressure

Standards for high pressure (100 to 5 000 kPa), primarily using hydraulic fluids and piston gauge technologies, are established, maintained and disseminated through the calibration of piston gauges (pressure balances or dead weight testers) and high precision pressure measurement devices, submitted by users in industry, regulatory authorities, research and academic institutions and the community.

At NMI, traceability of the SI unit of pressure is derived via two pistons that have been calibrated at the French national measurement laboratory. Pressures up to 500 MPa are derived by bootstrapping (calibrating and extrapolating) piston calibrations.

High-precision calibration of pressure standards requires the careful measurement and analysis of many physical parameters, such as load (hence mass and gravitational weight), air and density parameters, fluid parameters and of course temperature. The extensive use of measurement automation technologies, analytical techniques such as mathematical modelling, data visualisation, regression and statistical tools, combined with in-house development of sophisticated and powerful software algorithms, allows the maximum amount of useful information to be extracted from measurement data, including rigorous determination of the uncertainty of the measured quantities of complex physical systems.

Wika 380L with new weight setBarometric Pressure Standards

The primary standard for pressure in the region up to 7 MPa in gas is a mercury manometer. This instrument uses the interferometry of light of known wavelength to measure the difference in heights of the two columns. Because free mercury surfaces are subject to small ripples even under very good conditions floats that contain a very shallow mercury pool are used to provide the reflecting surface for the interferometer. This instrument is now being refurbished to take advantage of the advances in interferometers that have occurred in the 25 years since it was originally built.

Controlled Clearance Gauge

Controlled clearance gaugeNMI's controlled-clearance piston gauge is pictured at right. It operates on the principle of controlling the clearance between the piston and the cylinder by applying an auxiliary (jacket) pressure to the cylinder’s outer surface. In theory, as the jacket pressure increases, it will reach a point at which the cylinder will come into contact with the piston. This would correspond to a zero fall rate of the piston and the effective area of the assembly is defined as the effective area of the piston. In practice, this condition cannot be achieved and a flow model is required to relate the fall rate and the jacket pressure to estimate the point of zero clearance. A study is underway to optimise the use of the gauge.

Gas Flow

Currently, the services available at NMI cover a wide range of flows and pressures.

Calibration of critical flow Venturi nozzles for volume flowrate (normalised to atmospheric conditions and room temperatures) up to 250 m3 h-1 and upstream pressures up to 7 bars. NMI also provides services for calibration of nozzles at various pressures and relative humilities.

Calibration of flow measurement devices for flowrates ranging from 0.1 cc min-1 up to 7000 m3 h-1 (normalised to atmospheric conditions and room temperatures) using various gases.

Calibration of flow measurement devices at pressures up to 7 bars and flowrates up to 500 kg h-1. 

Viscometry

NMI maintains a set of master viscometers, but due to limited demand for viscosity standards, does not offer the routine distribution of viscosity-certified materials. Information on alternative sources of viscosity-certified materials is available from NMI.