A new 3-ton electromagnetic balance system was designed and built up for a high level mass-time primary standard of natural gas up to 60bar in CVB. The system is composed of a 3-ton electromagnetic balance, two tanks with thermal isolation, two platforms, two roller guide rails and two big weights which are used for special test. To achieve a lower uncertainty and the security application in natural gas measurement, several special methods were used in the system. Firstly, the tanks and platforms can be moved together steadily on the roller guide rail to be connected with pipeline system or to be weighted by the balance which also reduces the pipeline length between tanks and pipeline system. Secondly, the substitute weighing method is used for high accurate weighting. Finally, the whole system is located in a thermal isolated room with temperature and humidity controlling. Technical details, performance tests, uncertainty analysis and the future improvement ideas of the balance system are presented in the paper. The uncertainty analysis shows that the mass measurement uncertainty of gas can achieve less than 1.0g and the relative standard uncertainty of natural gas mass measurement can achieve less than 0.02%.

High level of public and legal interest concerning fuel dispensers’ measurements accuracy is always present. Surveillance of dispensers prior to 2013 reported undesired high error values. To limit possibilities of systematic favoring of single parties Slovenian national regulative was adapted. In year 2013 value of maximum permissible error at periodic verifications for higher flow rates of fuel dispensers was reduced. After one verification period passed Surveillance service of Metrology Institute of the Republic of Slovenia (MIRS) performed a surveillance of fuel dispensers seeking feedback information on implementation of modified requirements.
On over 150 petrol stations over 300 nozzles serving four different fuel types were controlled at two different fuel flow rates. More than 600 evaluated control results showed among others, that the average measured error at maximum flow rate Qmax amounted up to + 0,23 %, depending of the fuel type. Almost all measured errors were in line with the metrological requirements, 76 % of which however appeared to be in favor of the petrol station owner. Average deliveries at Qmax were less favorable to an end customer than deliveries at Qmin.
After another verification period surveillance was performed again. Average measured errors showed further reduction. Measurements also improved their symmetry.
Compliance of measuring instruments is not hindered by adapted regulative, while level of measurement fairness is apparently elevated.

The strange behaviors of the discharge coefficient of the critical nozzle were found when gradually changing the back pressure ratio (Pd/Pu) from the almost zero to the critical back pressure ratio in the nozzle to nozzle test method. When the test gas is Helium, the change amount of the discharge coefficients at these strange behaviors is quite large and seems significantly to influence to flow measurements. The causes of the strange behaviors are different in the ranges of Pd/Pu<0.1 and of Pd/Pu>0.1, and in either case are considered to be due to the measurement principle of the nozzle to nozzle test method that the mass flow rate through the system is constant. Under the condition that the mass flow rate is constant, the discharge coefficient of the critical nozzle on the downstream side in the nozzle to nozzle test method must definitely change in inverse proportion to its upstream pressure change. The flow models are suggested to explain the reason why the upstream pressure changes when changing the back pressure ratio. The more important point of the present results is that the equivalence of the discharge coefficient determined by the general calibration methods and by the nozzle to nozzle test method may be not always hold.

This paper presents the establishment and verification of a mercury-sealed piston prover, which is commonly used for low pressure gas flow calibration. The calibration gases could be dry air, nitrogen, argon, helium, oxygen and carbon dioxide. The flow capacity of the new system covers from 0.002 L/min to 40 L/min at 23 °C and 101.325 kPa, and some overlapped flows are between various columns. The relative expanded uncertainty of mass flow measurement is less than 0.08 % at 95 % confidence level.
We were also successfully altering the temperature sensor construction, temperature sensor placement, data logger system to real-time monitor the temperature difference of the entering gas. The data showed that the temperature difference between the entering gas and column could approximate in the calibration period.
The newly piston prover measurement result between different column was less than 0.01 %. A comparison between new-constructed and original CMC submitted piston prover that both are in CMS was conducted, and the En value was less than 0.4. The results indicate that the measurement capabilities of each column of newly piston prover were identical with expectation.

Multiphase flow meters are measurement instruments that simultaneously measure the flow rates of oil, natural gas and water flowing through a pipe line. Their traceability and the comparability of test results stemming from different multiphase test facilities is much less well established than that of single phase flow meters and single phase calibration facilities. In the (first) EMRP MultiFlowMet project an intercomparison for multiphase test facilities was organised to investigate the comparability of multiphase flow test facilities. Three facilities participated: NEL, DNV GL and OneSubsea-Schlumberger (OSS). VSL acted as independent partner auditing the uncertainty budgets, witnessing the tests and analysing the data. The outcome of this analysis was pairwise consistencies in the order of 80 %, taking into account the claimed uncertainties of the test facilities and the estimated meter reproducibility. This value was also found for the comparison with OSS, where a different inlet geometry was used. Open access to data and more extensive testing could provide means to get a better understanding of the reasons behind the inconsistency of a small part of the points.