Eckel S, Barker D S, Fedchak J, Newsome E, Scherschligt J, Vest R
Sensor Sciences Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
Metrologia. 2022;59(4). doi: 10.1088/1681-7575/ac7927.
We demonstrate operation of a constant-pressure flowmeter capable of generating and accurately measuring flows as low as 2 × 10 mol/s. Generation of such small flows is accomplished by using a small conductance element with ≈ 50 nL/s. Accurate measurement then requires both low outgassing materials (< 1 × 10 mol/s) and small volume changes (≈ 70 L). We outline the present flowmeter's construction, detail its operation, and quantify its uncertainty. The type-B uncertainty is < 0.2 % ( = 1) over the entire operating range. In particular, we present an analysis of its hydraulic system, and quantify the shift and uncertainty due to the slightly compressible oil. Finally, we compare our flowmeter against a NIST standard flowmeter, and find agreement to within 0.5 % ( = 2).
我们展示了一种恒压流量计的运行情况，该流量计能够产生并精确测量低至2×10⁻⁶摩尔/秒的流量。通过使用一个电导率约为50纳升/秒的小电导元件来实现如此小流量的产生。然后，精确测量既需要低出气材料（<1×10⁻⁸摩尔/秒），也需要小体积变化（约70皮升）。我们概述了当前流量计的构造，详述了其运行情况，并对其不确定度进行了量化。在整个工作范围内，B类不确定度<0.2%（k = 1）。特别地，我们对其液压系统进行了分析，并量化了由于油的轻微可压缩性导致的偏移和不确定度。最后，我们将我们的流量计与美国国家标准与技术研究院（NIST）的标准流量计进行了比较，发现二者的一致性在0.5%以内（k = 2）。
