Based on Pneumatic Photonic Structures, High-Accuracy Measurement Procedure for the Universal Gas Constant

Abstract

In this work, an approach is proposed to determine the universal molar gas constant R with approximately ten significant digit accuracy that is based on extra accurate volume controlling and highly sensitive pressure measurements in the framework of scale echeloning procedure. An essential moment of the method is uniting the results of two connected measurement scales with the relative standard uncertainty near 10 ⁻⁵ to obtain a higher precise level. A calibrated stable area of fixed temperature is used in the vicinity of the triple point of water. The gas-filled 1D elastic pneumatic photonic crystal is used as an optical indicator of pressure uniting several scales of pressure magnitudes. The pressure gauge includes layered elastic platform, optical fibers, and switching valves, all enclosed into a chamber. With this aim, we have investigated the pneumatic photonic crystal bandgap structure and light reflection changes under external pressure. At the chosen parameters, the two-scale device may cover the pressure interval (0, 10) bar with accuracy near 1 nbar. A self-consistent iteration procedure increasing initial accuracy of parameters and the molar gas constant to the level of volume and pressure accuracy measurements is proposed and tested.