The Mutual Recognition Arrangement (MRA) is framed by the International Committee of Weights and Measures in order to establish the degree of equivalence of national measurement standards via the key comparisons as well as the inter-comparisons of measurements. Based on this objective, the current work was performed in order to determine the degrees of equivalence among three laboratories in Korea Research Institute of Standards and Science (KRISS), National Metrology Institute of Japan (NMIJ) and HCT company for air speed over the range from 2 m/s to 40 m/s. In this inter-comparison of air speed, two AMCA type Pitot static tubes were considered as artifacts. The reference value (RV) and its uncertainty was calculated from all measurement results reported by the participants. The normalized deviations, En-number, were mostly smaller than 1. Consequently, the results of participants were mutually consistent.

Wind lidar systems have become a cost-efficient alternative to wind met masts in the recent years to measure and monitor the wind velocity in many applications in the fields of wind energy and meteorology. Conventional wind lidar systems work according to the monostatic measurement principle that is inherently accompanied by a spatial and temporal averaging procedure. This averaging procedure complicates the traceability of such systems as the uncertainty of the measured wind velocity depends on the homogeneity of the investigated wind fields. In contrast, the wind lidar system presented here works according to a bistatic measurement principle that measures the velocity vector of single aerosols in a spatially highly resolved measurement volume in heights from 5 m to 250 m with a resolution of about 0.1 m/s. The novel system has the potential for traceable wind speed measurements in homogeneous as well as in inhomogeneous wind fields as was proven by comparison measurements with a wind met mast. At PTB, the aim is to use the bistatic wind lidar as a traceable reference standard to calibrate other remote sensing devices, necessitating an in-depth validation of the bistatic lidar system and its measurement uncertainty. To this end, a new, specially designed wind tunnel with a laser Doppler anemometer (LDA) as flow velocity reference has been built up to validate the bistatic lidar in detail. First validation measurements in the velocity range from 4 m/s to 16 m/s are presented, showing an average deviation between the bistatic lidar and the LDA of 0.37 %.

Of all alternatives to gasoline fuels, hydrogen offers the greatest long-term potential to radically reduce many problems inherent in transportation fuel use. Hydrogen vehicles have zero tailpipe emissions and are very efficient. If it is made from renewable sources, nuclear power, or fossil sources with carbon emissions captured and sequestered, hydrogen use on a global scale could produce nearly zero greenhouse gas emissions and greatly reduce emissions of air pollutants.The aim of this work is to realise a traceability chain for hydrogen flow metering in the range typical for fuelling application in a wide pressure range with pressures up to 875 bar (for Hydrogen Refuelling Station HRS with Nominal Working Pressure of 700 bar) and temperature changes from - 40 °C (pre-cooling) to 85 °C (maximum allowed vehicle tank temperature) in accordance with the worldwide accepted standard SAE J2601.Several HRS have been tested in Europe (France, Netherlands and Germany) and the results show a good repeatability for all tests. This demonstrates that the testing equipment works well in real conditions. Depending on the configuration of installation, some systematic errors have been detected and explained. Errors observed for the stations of Configuration 1 can be explained by the difference of pressure, at beginning and end of the fueling, in the piping between the CFM and the dispenser: the longer the distance, the bigger the errors. For Configuration 2, as this distance is very short, the error is negligible.

Because the flow fluctuation can cause the deviation of flow measurement, flow stabilizing methods are used, in the most of the flow metering facilities. Two common flow stabilizing methods of water flow facilities are tested by a new flow stability measurement system which is consisted by a flowmeter and a pressure sensor.
The amplitude of fluctuation can be measured by flowmeter, and the frequency of fluctuation can be obtained by FFT (Fast Fourier Transform) analysis of the pressure signal. The direction of fluctuation source can be distinguished by correlation analysis of pressure and flow signals. Based on this method, the characteristics of the fluctuation source can be obtained by experiments under different flow rate and pipe pressure. An obvious fluctuation signal with a frequency of about 1.5Hz had been found in a test for a flow facility with a buffer tank. The amplitude of fluctuation increases with the decrease of flow rate. When the flow rate is less than 1/10 of the rated flow rate of the pump, the amplitude of fluctuation is about 1%. It is shown that the high frequency fluctuation produced by the pump can be effectively isolated by the buffer tank, but the low frequency fluctuation can be caused by the pump when it worked in a low efficiency range.
In another set of experiments, a flow facility with a constant head water tank and a buffer tank was tested, and two flow stabilizing methods were directly compared and analysed. The test results of the two methods are close under the similar working flow rate and pressure. And if it is under different operating conditions, the amplitude of fluctuation is closely related to the opening of the regulating valve which is installed downstream of the test bench. The fluctuation amplitude increases with the decrease of the valve opening. When the valve opening is less than 30%, the fluctuation amplitude is about 0.5%. Further, it is obtained that the cavitation is caused by the excessive local pressure loss of the regulating valve is the main reason of the facility with constant head water tank.
In summary, the buffer tank and the constant head water tank are both effective methods for stabilizing flow, and the optimal stabilization effect can be obtained by setting a reasonable range of operation for the pump and the regulating valve.

In order to attempt to mitigate the climate change, efforts to reduce the quantity of carbon emissions by actively seeking CO2 trading and carefully control the liability of the emission test monitoring system from the industrial factories are a current issue. Therefore, the quality of greenhouse gas (GHG) emissions measurement with a proper uncertainty needs to be firstly considered. Currently, GHG emissions are estimated by a continuous emission measurement (CEM). The U.S Environmental Protection Agency (EPA), has classified the measurement of GHG emissions by the CEM as the highest quality Tier IV with lowest uncertainty level. Relating to accuracy of the CEM, both knowledge of the uncertainty contributions on GHG concentrations and volumetric flow rates are necessary for achieving a credible result. In order to accurately evaluate the uncertainty of the CEM method, flow rate measurements in the stack as well as GHGs concentration measurements by gas analyzer are crucial due to various uncertainty factors. In this study, we concentrate on finding measurand inputs and their uncertainty estimates that affect volumetric flow rates in a heat and power generation plant. Both the law of propagation method and Monte Carlo method (MCM) are used to evaluate the uncertainty of the flow rate measurement in order to minimize the numerical approximation of the partial derivatives of the complex model with respect to the every input. Consequently, the result of MCM is consistent with the result that by the law of propagation of uncertainty. The relative expanded uncertainties at 95% confidence level with coverage factor k = 2 are 528.1 m³ and 527.2 m³, respectively.