Verifications of hydrogen refuelling stations have shown that variations in the station design and operation can greatly influence accuracy at the dispenser, and there are sources of error unrelated to the flow meter which if uncorrected make it difficult to achieve the accuracy requirements of OIML R-139. To improve dissemination of knowledge in this area, an interactive measurement uncertainty tool has been developed which allows the user to specify a range of different station configurations and filling scenarios to estimate the resulting errors at the dispenser. This is intended to serve as a basis for HRS manufacturers to improve HRS designs with respect to billing accuracy and to assist notified bodies in understanding uncertainty contributions from an HRS and the corrections required. This paper describes the initial version of the HRS uncertainty tool, explaining the inputs required from the user, the sources of measurement uncertainty considered, how the flow meter behaviour is modelled, and which calculations are implemented.

There are currently several mobile gravimetric standards for testing and calibrating hydrogen refuelling stations in operation. These standards are compliant for fuel delivery to light-duty vehicles according to the SAE J2601 protocol and provide measurement uncertainties that are low enough to use them for type-approval testing according to OMIL R139 recommendation. An international field comparison under real conditions is required to ensure a complete acceptance of test results by operators and notified bodies. In this paper, we will present details on a currently running comparison to settle this issue, and how it differs from standard comparisons. Specific strategies had to be adopted to make the experimental results consistent and comparable. The refuelling operating conditions can affect the outcome from the comparison and need to be taken into account. All these points are being addressed in this paper and are part of the comparison protocol. The aim is that in the end, based on the comparison results and the applied strategy, participants will be able to declare certified measurement capabilities to the BIPM.