By measuring the refractivity and the temperature of a gas, its pressure can be calculated from fundamental principles. The most sensitive instruments are currently based on Fabry–Perot cavities where a laser is used to probe the frequency of a cavity mode. However, for best accuracy, the realization of such systems requires exceptional mechanical stability. Gas modulation refractometry (GAMOR) has previously demonstrated an impressive ability to mitigate the influence of fluctuations and drifts whereby it can provide high-precision (sub-ppm, i.e., sub-parts-per-million or sub-${10}^{-6}$) assessment of gas refractivity and pressure. In this work, two independent GAMOR-based refractometers are individually characterized, compared to each other, and finally compared to a calibrated dead weight piston gauge with respect to their abilities to assess pressure in the 4–25 kPa range. The first system, referred to as the stationary optical pascal (SOP), uses a miniature fixed point gallium cell to measure the temperature. The second system, denoted the transportable optical pascal (TOP), relies on calibrated Pt-100 sensors. The expanded uncertainty for assessment of pressure ($\mathrm{k}=2$) was estimated to, for the SOP and TOP, ${[{(10\mathrm{mPa})}^2+{(10\times {10}^{-6}\mathrm{P})}^2]}^{1/2}$ and ${[{(16\mathrm{mPa})}^2+{(28\times {10}^{-6}\mathrm{P})}^2]}^{1/2}$, respectively. While the uncertainty of the SOP is mainly limited by the uncertainty in the molar polarizability of nitrogen (8 ppm), the uncertainty of the TOP is dominated by the temperature assessment (26 ppm). To verify the long-term stability, the systems were compared to each other over a period of 5 months. It was found that all measurements fell within the estimated expanded uncertainty ($\mathrm{k}=2$) for comparative measurements (27 ppm). This verified that the estimated error budget for the uncorrelated errors holds over this extensive period of time.

中文翻译：

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帕斯卡的光学实现——两种气体调制折射计的表征

通过测量气体的折射率和温度，可以根据基本原理计算其压力。目前最灵敏的仪器基于法布里-珀罗腔，其中激光用于探测腔模式的频率。然而，为了获得最佳精度，此类系统的实现需要出色的机械稳定性。气体调制折光率 (GAMOR) 先前已展示出令人印象深刻的减轻波动和漂移影响的能力，从而可以提供高精度（亚 ppm，即亚百万分之一或亚${10}^{-6}$) 气体折射率和压力的评估。在这项工作中，两个独立的基于 GAMOR 的折光仪被单独表征，相互比较，最后与校准的自重活塞计比较它们评估 4-25 kPa 范围内压力的能力。第一个系统称为固定光学帕斯卡 (SOP)，它使用微型定点镓电池来测量温度。第二个系统，表示为可移动光学帕斯卡 (TOP)，依赖于校准的 Pt-100 传感器。压力评估的扩展不确定度（$\mathrm{克}=2$) 估计，对于 SOP 和 TOP， ${[{(10\mathrm{毫帕})}^2+{(10\times {10}^{-6}\mathrm{磷})}^2]}^{1/2}$ 和 ${[{(16\mathrm{毫帕})}^2+{(28\times {10}^{-6}\mathrm{磷})}^2]}^{1/2}$， 分别。虽然 SOP 的不确定性主要受氮摩尔极化率 (8 ppm) 的不确定性的限制，但 TOP 的不确定性主要受温度评估 (26 ppm) 的影响。为了验证长期稳定性，系统在 5 个月的时间内相互比较。发现所有测量值都在估计的扩展不确定度范围内（$\mathrm{克}=2$) 用于比较测量 (27 ppm)。这证实了不相关误差的估计误差预算在这段长时间内保持不变。