Overview of the principle of chilled mirror dew point meters
Overview of the principle of chilled mirror dew point meters
A dew point meter is an instrument that directly measures the dew point temperature. It works by cooling a mirror surface in a sample of humid air until dew drops (or ice crystals) appear on the surface. The average temperature of the mirror at that moment is the dew (or frost) point temperature. It offers high accuracy in humidity measurement, but requires a highly polished mirror, a very precise temperature control system, and a highly sensitive optical detection system for dew drops (or ice crystals). When using it, the pipe that draws in the sample air must be kept clean; otherwise, impurities in the pipe will absorb or release moisture, causing measurement errors.

In winter, we observe a common phenomenon: due to the low outdoor temperature, the relatively warm and humid indoor air condenses on the window glass, making the window pane foggy. If we observe and study this further, we find that if we turn on a dehumidifier indoors to gradually remove the moisture, even though the outdoor temperature remains the same, the condensation on the window glass will slowly disappear, and the window glass will become transparent and clear again. If the outdoor temperature then drops, at a certain point, even though the dehumidifier has made the indoor air very dry, a layer of condensation will still appear on the window glass. This phenomenon shows that the condensation temperature on the glass is related to the water content of the surrounding atmosphere. Further research reveals that this is a one-to-one relationship; that is, each condensation temperature (which we call the dew point temperature) corresponds to a specific water content value in the surrounding atmosphere.
The dew point can be simply understood as the temperature at which the water vapor content in a gas reaches saturation. It is one way to express the humidity of a gas; therefore, the dew point temperature is a unit of measurement for the water content of a gas. A dew point analyzer is an instrument that measures the water content of a gas based on this unit of measurement.
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