Principle of dew point meter

1. Cold mirror dew point meter

Gases with different water content will come to the surface at different temperatures. The dew point is directly displayed by the photoelectric detection technology, which detects the dew layer and measures the temperature when the dew is exposed. The methods of mirror cooling are: semiconductor refrigeration, liquid nitrogen refrigeration and high pressure air refrigeration. The dew-point hygrometer with cold mirror is a direct measurement method. It can be used as a standard dew-point hygrometer under the premise of ensuring the accuracy of dew-point detection, high efficiency of mirror cooling and precise measurement of dew-point temperature.

2. Electric sensor dew point meter

A hydrophilic material or a hydrophobic material is adopted as a medium to form a capacitance or a resistance, and the dielectric constant or the conductivity of the water-containing gas is changed correspondingly after passing through the water-containing gas, and the capacitance value or the resistance value at the time can be measured, and the moisture content of the gas at the time can be known. This kind of sensor, which is designed on the dew point unit system, constitutes an electric sensor Dew Point Analyzer.

3.Electric method dew point meter

The electrochemical micromoisture analyzer based on absolute moisture content unit system was designed by using the characteristics of accumulation of charge on electrode by decomposing into polar molecules after absorbing phosphorus pentoxide and other materials. At present, the highest precision in the world can reach ±1.0°C (dew point temperature), and the general precision can reach ±3°C. This method requires high clean gas and can measure corrosive gas. One company in Germany has done this, and the domestic application is few.　

4.Crystal oscillation dew point meter

The oscillation frequency of the crystal after wetting can be changed. The oscillation dew point meter can be designed. This is a relatively new technology, which is still at an immature stage. There are related products abroad, but the precision is poor and the cost is high. Example like CI-PC36, GEN-25 of Chang'ai Co.

5.Infrared dew point

The infrared dew-point instrument can be designed by the absorption of moisture in gas to infrared spectrum. At present, it is difficult to measure the low dew point of the instrument, mainly because the peak detection rate of the infrared detector can't reach the level of micro water absorption, and the interference of other components in the gas on the absorption of infrared spectrum. However, this is a new technology, which is of great significance for the non-contact online monitoring of the moisture content of the environmental gas.

6. Semiconductor sensor dew point meter

Each water molecule has its natural vibrational frequency, when it enters the void of the semiconductor lattice, generates a resonance with the lattice subjected to charge excitation, whose resonant frequency is proportional to the molar number of water. The resonance of water molecule can make the semiconductor junction emit free electrons, thus increasing the conductivity of the lattice and reducing the impedance. The moisture content of -100°C dew point can be measured by a semiconductor dew point meter designed with this characteristic. 

Comprehensive assessment of technological progress

With the development of modern science and technology, people have applied photoelectric technology, new material technology, infrared technology, microwave technology, microelectronics technology, optical fiber technology, acoustic wave technology and even nano technology to the measurement of moisture in gas, which makes the old field of moisture measurement fresh.

The measurement of trace moisture in gas is a difficult technique. It can be said that up to now there is no mature and perfect technical means in the world to solve the problem of micro-water measurement under various working conditions. After the application of modern technology, it can only be said for a specific environment, the use of a certain technical means to solve a certain degree (including the range and precision) of micro-moisture measurement. Therefore, the development prospect of micro-moisture measurement technology is very broad, and the professional technicians still have a long way to go.