OPTICAL SENSOR FOR AIR MOISTURE MONITORING IN MASS METROLOGY

Capteur Optique pour le Contrôle de l’Humidité de l’Air en Métrologie des Masses

N. Khélifa1*, S. Guellati1, P. Kerviel2, M. Lecollinet1

1 BNM-INM : Conservatoire National des Arts et Métiers, 292, rue Saint-Martin F.75141, Paris Cedex 03, France

2 Office National d’Etudes et de Recherches Aérospatiales, B.P.72 – 92322, Châtillon Cedex, France

* Corresponding author.  E-mail: khelifa@cnam.fr

Received: 15 February 2003; revised version accepted: 21 December 2005

Abstract

In metrology, a mass is measured by comparison with a standard. The main uncertainty in the mass determination is associated with the measurement of air moisture inside the weighing chamber. The knowledge of this environmental parameter is required for the determination of the mass difference owing to air buoyancy. In practice, a chilled mirror hygrometer is used, with some precautions, for air humidity measurement. In this paper, we describe an experiment; based on molecular absorption in the near infrared, intended for monitoring water vapour contained in an enclosure chamber of about 2,5x10-2 m3 in volume. The performances of this optical sensor are demonstrated by the observation of the perturbations, induced by the dew-point hygrometer transients, on the water vapour amount in the chamber.

Keywords: Molecular absorption; Water vapour; Optical sensor; Air moisture; Air density and mass measurement.

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