Final report of the APMP water flow supplementary comparison (APMP.M.FF-S1)
Authors: Chun Sejong , Furuichi Noriyuki 
Published: January 2022

Main text
A supplementary comparison, entitled as APMP.M.FF-S1, has been undertaken between KRISS and NMIJ, AIST under the supervision by the Technical Committee for Fluid Flow (TCFF) in the Asia Pacific Metrology Programme (APMP). The purpose of this supplementary comparison was to prove the measurement equivalence between NMIJ, AIST and KRISS for water flow measurement standards from 300 m3/h to 1 200 m3/h. This supplementary comparison was meaningful because there has not been an international comparison for water flows greater than 300 m3/h. Previous key comparisons have been performed only from 30 m3/h to 200 m3/h [1]. Therefore, this supplementary comparison became the first inter-laboratory comparison to cover the flow range for large-capacity water flow measurement standards. In fact, the inter-laboratory comparison between NMIJ, AIST and PTB (Berlin) has been already done for such flowrate range [2], however, this inter-laboratory comparison has not been supervised by APMP or EURAMET, such that the result of inter-laboratory comparison is published in a research journal, not in the BIPM KCDB for inter-laboratory comparisons.
A turbine flow meter with the pipe diameter of 250 mm was chosen as a transfer standard in this supplementary comparison. A flow conditioner was used to define inflow conditions upstream of the turbine flow meter. The flow conditioner was a perforated plate with a well-known design. The turbine flow meter was calibrated in two ways: with or without the flow conditioner. The calibration of turbine flow meter with the flow conditioner was according to the revised test protocol for this supplementary comparison. The other calibration without the flow conditioner was performed to investigate the flow characteristics of the turbine flow meter.
K-factor was the measurand to evaluate the measurement equivalence between NMIJ, AIST and KRISS. The K-factor was corrected by considering the temperature change between the water temperature and the reference temperature of 20 oC [3]. The measurement uncertainty of the K-factor included uncertainty factors such as repeatability, day-to-day reproducibility, re-installation effect, long-term stability, and the influence by temperature change. Inconclusiveness test was also performed to see whether the K-factor was suitable for evaluating the number of equivalence between NMIJ, AIST and KRISS. The number of equivalence was found to be less than 1. The number of equivalence became better in the case without the flow conditioner than the case with the flow conditioner. The number of equivalence was found to be conclusive because the inconclusiveness index was less than 2. Therefore, the measurement equivalence between NMIJ, AIST and KRISS has been proven by this supplementary comparison.
To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.
The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).