Typicality rating of 10 red wine samples, using a non-structured scale, at left “very bad example”, at right “very good example” of what a panel of wine experts, professionals, initiated assessors and consumers, considered to be a typical Xinomavro Naoussa wine, was combined to physicochemical analysis (color characteristics, phenolic content) and GC analysis of volatile profile. Assessors were able to successfully identify the Xinomavro Naoussa samples and rate them as the most typical. Based on both physicochemical and sensory data, wines were successfully grouped according to composition and origin (monovarietal or blended, Naoussa or other PDO’s).

One of the methods to realize reference values for Volume of e.g. Natural Gas at increased pressures is via a calibration under a pressure difference (i.e. with expansion). In such a process, applied since the sixties in the Netherlands, the "un-known" meter or Meter-under-Test (MuT) is compared through expansion with the "known" meter or Reference Meter (RM) at low-pressure. In a "normal" calibration-process the difference in pressure between the two compared meters is relative small and the resulting difference between the compressibility at the Reference Meter Z_RM and the compressibility at the Meter-under-Test Z_MuT has hardly any effect on the ratio Z_RM / Z_MuT and can be neglected (the ratio is thus considered to have a value of 1). However, in a calibration under expansion a comparison is made of a gas-flow under significant differential pressure-conditions and one of the most important contributions of uncertainty stems from the real gas constant Z. So, the ratio Z_RM / Z_MuT is of importance, rather than the absolute values of the compressibility factor. The Z / Z-meter is one of the current technical developments at NMi VSL-Flow. The uncertainty contribution in the conventional method of calculation, described e.g. in M-GERG of 1991, is rather high (0,1% for the compressibility factor) and the resulting uncertainty of the Z_RM / Z_MuT ratio is 0,14%.
Therefore, a method leading to a lower contribution to this source of uncertainty offers advantages. In the presented approach is the ratio Z_RM / Z_MuT is considered to be the measurand. The ratio should then be measured more accurately than the one resulting from calculation of the absolute values of the compressibility factor. As a consequence, the impact of this source of uncertainty is reduced. NMi has developed a device that is able to measure the ratio Z_RM / Z_MuT directly.
In this paper, the development of a new measuring instrument is described that measures the Z₁ / Z₂ ratio of gases (at pressures P₁ and P₂ between 1 and 70 bar) with a maximum uncertainty of 0,03%. The measuring principle of the Z / Z ratio meter is based upon the accurate measurement of a piston-displacement. The piston is displaced by a controlled gas expansion from high-pressure to a low-pressure condition (or for compression, vice versa) in a measurement cell. The measurement cell with an adjustable volume is mounted inside a high-pressure vessel for an adequate control of temperature and pressure. The cell is constructed as a cylinder-piston combination together with small ball-valve actuators that can be opened and closed to connect or disconnect the chamber of the cell to the surrounding vessel and to fill or empty the system.
During its operation, measurements are taken of the piston-displacement, together with measurements of pressures and temperatures. For the calculation of the ratio Z₁ / Z ₂ basically only the ratio of the cell volumes at pressures P₁ and P₂ needs to be established.