Dew Point Measurement of High Purity Gas with Slab Optical Waveguide Technique

UCHIDA Naoko, TAKATSU Akiko, KATO Kenji

doi:10.2116/bunsekikagaku.54.205

A remarkable feature of the slab optical waveguide (SOWG) technique is internal multi-reflection in a thin core layer. It allows one to detect only samples on the surface of SOWG with high sensitivity. This technique has so far been applied to the detection of various samples, such as dye molecules and proteins. As a new application field, an experimental dew-point measurement system based on the SOWG technique was tested for moisture analysis in high-purity nitrogen (N₂) gas. The system consisted of both cooling and light-detection components. The former had a Peltier thermoelectric temperature controller and a platinum resistance probe to cool the SOWG, as do conventional chilled mirror hygrometers. The latter had a light source, optical fibers, a photo detector, and a slide glass-shaped quartz plate as the SOWG to detect light signals. While wet N₂ gas with a certain water concentration (approximately −60°C at the dew point) was introduced into the system, the analytical capability of the system was evaluated under various conditions, such as different sample gas flow rates, cooling speeds, thicknesses of the SOWG, and introduction times for wet N₂ gas. Since the evaluation provided satisfactory results, the system 1) was available for dew-point detection down to −65°C, 2) had higher sensitivity by utilizing a thinner SOWG, such as 0.1 mm thick, and 3) had a fast response time, compared with a conventional capacitance-type hygrometer. The SOWG technique was concluded to apply to trace moisture measurements in high-purity gas.<br>

Dew Point Measurement of High Purity Gas with Slab Optical Waveguide Technique

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