The total quantity and energy delivered through a metering point in a gas grid is calculated using simple formulas that sum the increments measured at regular time intervals. These calculations are described in international standards (e.g., ISO 15112 and EN 1776) and guidelines (e.g., OIML R140). The uncertainty structure of the measurement results that enter in these calculations is quite complex and contains a lot of dependencies. These dependencies arise in part due to the fact that the same equipment is used throughout a metering point, and partly due to fluctuations in environmental conditions (e.g., flow rate, composition, pressure, temperature) give rise todependencies. The evaluation of the associated measurement uncertainty should thus appreciate these dependencies. In the project in the European Partnership for Metrology programme, “Metrology for the hydrogen supply chain”, the underlying assumptions of these uncertainty evaluations were revisited and reworked to be more adequate. The dependence of measurement results from, e.g., the same flow meter and gas chromatograph will be assessed for correlations, along with other effects such as the chosen mathematical approximation of the totalisation integral and fluctuations in flow rate and gas quality. This report illustrates methodological approaches for evaluating measurement uncertainties though selected case studies along the supply chain. The aim of this is to demonstrate how the extended methods for evaluating measurement uncertainty can be applied and how dependencies between measurement results can be evaluated and taken up in custody transfer.
Kjetil et al. (Fri,) studied this question.