Tag: dew point meter

A dew point meter is an instrument that can directly measure the dew point temperature. A mirror is cooled in the humid air of the sample until the moment when dew droplets (or ice crystals) are looming on the mirror, and the average temperature of the mirror is measured, which is the dew point (frost) temperature. It has high humidity measurement accuracy, but requires a mirror surface with high smoothness, a temperature control system with high precision, and an optical detection system for dew droplets (ice crystals) with high sensitivity.

The dew point meter is an instrument that can directly measure the dew point humidity. Place a mirror in the sample of the humid air to cool down until the moment when dew droplets (or ice crystals) appear on the mirror. The dew point meter can measure the average temperature of the mirror, which is the dew point (frost) temperature.

Mirror contamination is a prominent problem in dew point meter. Its impact is mainly manifested in two aspects. One is the Raoul effect, and the other is changing the level of specular background radiation. The Raoul effect is caused by water-soluble substances. If this substance (usually soluble salts) is carried in the measured gas, dew condensation will occur on the mirror surface in advance, which will cause a positive deviation in the measurement result. If the pollutants are water-insoluble particles, such as dust and so on, the background scattering level will be increased, and the photoelectric dew point meter will have zero drift. In addition, it is needless to say that the vapour of some easily condensable substances (such as organic matter) having a boiling point lower than water will interfere with the measurement of the dew point. Therefore, for any type of dewpoint meter, measures should be taken to prevent contamination of the mirror surface. Generally speaking, the impact of industrial process gas analysis pollution is more serious. However, even in the measurement of pure gas, the pollution of the mirror surface will accumulate over time.

Dew point can be simply understood as the temperature at which the water vapor content in a gas reaches a saturated state. It is one of the ways to express the absolute humidity of a gas. It can be seen that the dew point temperature is a unit system for measuring the moisture content of a gas. The dew point meter is an instrument that measures the absolute moisture content of a gas based on this unit system.