To improve the consistency of 3-dimensional data describing the geometry of pressure-measuring piston-cylinder assemblies, a new approach, based on the leastsquares method, is proposed. It allows the results of diameter-, straightness- and roundness measurements to be linked with each other, with only minimum discrepancies between them. When processing the dimensional data, it is possible thanks to this new approach to weight them differently - according to their measurement uncertainties. The new approach was applied to three gas-operated piston-cylinder assemblies with nominal effective areas of 10 cm² and 5 cm² which are used at PTB as primary gas pressure standards for the range up to 2 MPa. The dimensional measurements were carried out by means of different instruments and the results were analysed. The discrepancies in the dimensional data sets obtained within the scope of the new approach are typically smaller than 16 nm, which agrees with the uncertainties claimed for each kind of dimensional measurement. The effective areas of the three piston-cylinder assemblies were calculated using the Dadson theory and then adjusted taking into account the results of both cross-float measurements carried out between them and pressure measurements carried out against a primary mercury manometer. Finally, relative standard uncertainties smaller than 2·10^-6 could be obtained.

This article is about a special type of pressure sensors usually labelled tactile sensors. After a short overview on the subject, two application examples, one in the medical domain developed by the authors for heart rate variability using an electretsbased pressure sensor, are presented.

Devices measuring pressure, temperature and humidity simultaneously are known as PTU devices. There are hardly any commercial calibration systems for the PTU devices available for low temperatures (< 0 °C). To obtain more comprehensive data on the performance of PTU devices, a new calibration system is developed at MIKES. In this PTU Apparatus, pressure, temperature and humidity can be controlled simultaneously so that all combinations over the ranges are possible. The nominal ranges of the system are the following: absolute pressure 500 hPa … 1200 hPa, temperature -52 °C … +80 °C and relative humidity 10 % … 95 %. The estimated uncertainties (k = 2) of the pressure, temperature and humidity are 10 Pa, 0,1 °C to 0,3 °C and 1 %RH to 3 %RH, respectively. The construction and operation as well as the results of operational tests of the PTU Apparatus are reported in this paper.

The present work illustrates the improvements made to the hydrometer calibration sys-tem of CENAM, the NMI of Mexico, making use of an image processing technique to align the scale mark of the hydrometer to the surface of the liquid where it is immersed, reducing the variability in the apparent mass determination during the hydrostatic weighing in the calibration process, decreasing the relative uncertainty of calibration (k = 2) from 1 x 10^-4 to 5 x 10^-5 or better.

The design and the expected performance of a new apparatus suitable to satisfy the traceability requirements in the density field is here presented. The apparatus is mainly intended to measure liquid density range between 500 kg/m³ and 3000 kg/m³ and to evaluate the performance of on-line densimeters during the actual use, i.e. the same process liquid under similar flow conditions. Details about the hardware components of the system and the software programs are also given. By using an instrument not specifically selected and calibrated for the intended working conditions, the value of u_instr(ρ) = 0.20 kg/m³ instr u is the lowest expected uncertainty of density measurements of fluids. However, higher accuracy can be established for the selected reference instrument by the use of the same fluids employed in the process at the usual operative conditions and whose densities are certified by national metrological institutes (NMIs) or accredited laboratories.