Abstract
To meet the many different requirements of gas humidity and water vapour measurement, a wide variety of measurement techniques has been developed. The criteria for deciding which technique to use are the range of concentration, the accuracy of measurement required, the sensitivity, and the pressure or even the corrosiveness of the gas sample. For measuring traces of moisture, sensors are used in which the admittance of an arrangement of electrodes changes with the partial pressure of the water vapour. Another method measures desorption due to Joule heat after absorption of the water by phosphorus pentoxide. Devices for measuring high humidities are equipped with capacitive, temperature-controlled sensing elements which measure the dew point. For special application, units have been developed which make use of the dielectric absorption of microwaves by the water. For hygrometrical problems requiring a high degree of accuracy, good discrimination and continuous measurement, a method is discussed below which uses the absorption of IR radiation by molecules in gaseous phase: Non-Dispersive Infra-Red Analysis.
Published Version
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