This paper focuses on the problematic of intraocular pressure (IOP) measurements, performed by non-invasive methods. More specifically, the devices that are connected with the presented finding are non-contact tonometers that use concentrated air stream and optical sensors to determine the IOP within a human’s eye. The paper analyzes various influential factors that have an effect on the determination of the IOP values originating from the patients themselves and from the non-contact tonometer devices. The paper furthermore elaborates on the lack of independent methods of calibration and control of these devices. In order to fill this gap a measurement standard device that is capable of calibrating and testing these devices with traceability to the basic SI unit is presented. A detailed characterization and the determination of the expected uncertainty of the device are provided. By introducing an independent and traceable calibration method and control of non-contact tonometers into the clinical practice, the reliability of the measured IOP that is the primary indicator of glaucoma can be improved.
In this work the thermodynamic behavior of a synthetic four-component biomethane-like mixture, composed mainly of methane (96.48%), with small amounts of carbon dioxide (2.00%), nitrogen (1.50%), and traces of oxygen (0.02%), is studied using accurate (p,ρ,T) experimental data. Two mixtures of identical nominal compositions were prepared by the gravimetric method at the Spanish National Metrology Institute (Centro Español de Metrología, CEM) and at the Slovak National Metrology Institute (Slovenský Metrologický Ústav, SMÚ). The composition was double checked by Gas Chromatography, at both NMI and at the beginning and end of the measurements. An additional test of the consistency of the given compositions was performed by measuring the density of both mixtures at selected points, with two different techniques, in two different laboratories. Accurate density measurements have been taken over a wide temperature range, from (240 to 350) K, and pressures up to 14 MPa, using a single-sinker densimeter with magnetic suspension coupling. Experimental data are compared with the densities calculated with the GERG-2008 and AGA8-DC92 equations of state. Deviations between experimental and GERG-2008-estimated densities are within a ±0.03% band at all temperatures, which shows the outstanding performance of the current reference equation for natural gases when describing a biomethane-like mixture. Deviations between experimental and AGA-8-estimated densities are higher than 0.04% at 250 K for pressures greater than 10 MPa and also at 240 K for pressures higher than 9 MPa. This work is part of the research project 'Metrology for Biogas' supported by the European Metrology Research Program.
To meet the needs of industries using high pressure technologies, in traceable, reliable and accurate pressure measurements, a joint research project of the five national metrology institutes and the university was carried out within the European Metrology Research Programme. In particular, finite element methods were established for stress-strain analysis of elastic and nonlinear elastic-plastic deformation, as well as of contact processes in pressuremeasuring piston-cylinder assemblies, and high-pressure components at pressures above 1 GPa. New pressure measuring multipliers were developed and characterised, which allow realisation of the pressure scale up to 1.6 GPa. This characterisation is based on research including measurements of material elastic constants by the resonant ultrasound spectroscopy, hardness of materials of high pressure components, density and viscosity of pressure transmitting liquids at pressures up to 1.4 GPa and dimensional measurements on pistoncylinders. A 1.6 GPa pressure system was created for operation of the 1.6 GPa multipliers and calibration of high pressure transducers. A transfer standard for 1.5 GPa pressure range, based on pressure transducers, was built and tested. Herewith, the project developed the capability of measuring pressures up to 1.6 GPa, from which industrial users can calibrate their pressure measurement devices for accurate measurements up to 1.5 GPa.
After the CCM Medium Pressure Working Group intercomparison indicated that the SMU primary mercury manometer differed by more than 20 ppm from other national standards, attention was paid to determining and eliminating the possible sources of these deviations. These efforts included replacing or redesigning some of the manometer components. The modified manometer design is presented in this paper. A piston gauge has been calibrated in the absolute mode using nitrogen as a pressure media, with the primary standard manometers at four national standards laboratories: Slovensky' Metrologicky' Ustav (SMU), Bratislava; Amt fir Standardisierung, Messwesen und Warenpriifung (ASMW), Berlin; Physikalisch-Technische Bundesanstalt (PTB), Braunschweig; and the National Institute of Standards and Technology (NIST), Gaithersburg; over a period of six years. Each of these manometers is of a different design. This has provided a basis from which to determine how the design changes affect the SMU manometer performance. The results indicate that the previous systematic deviations have been eliminated in the upper pressure ranges. The results for all four manometers agree to within their claimed uncertainties, however at the lowest pressures significant differences still exist and require further investigation.
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