Monitoring Air Moisture with Laser Absorption Spectroscopy

TL;DR

This paper proposes a laser absorption spectroscopy method to monitor air moisture, aiming to improve the accuracy of mass measurements by better understanding water vapour behaviour and reducing uncertainties in air density determination.

Contribution

It introduces a novel laser-based technique for precise air moisture measurement to enhance mass metrology accuracy, addressing limitations of traditional hygrometers.

Findings

Laser absorption spectroscopy effectively detects water vapour inside the chamber.

Water vapour behaviour varies with environmental conditions, impacting mass measurements.

The method offers higher sensitivity compared to conventional hygrometers.

Abstract

Determination of air density and the quantitative estimates of water vapour adsorbed or desorbed by the surface of mass standard, remain the principals sources of uncertainties when weighing mass standard made from stainless steel or super alloy. The classical method, for air density determination, use the so called CIPM-1981/91 formula and the measured air parameters. An other approach is based only on the results of comparisons, realized successively in air and in vacuum, between special artefacts. The distribution and the state of water molecules inside the chamber of mass comparator influence the results of weighing. Also, the instruments used for air moisture measurement are either, not very sensitive (capacitive hygrometer) or disturbing for environment (dew-point hygrometer). To control that, a proposal method is given and observations of water vapour behaviour inside the enclosure for different conditions are reported. Keywords. mass metrology, air density, water vapour