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What are the types of dew point meters?

1. Mirror type dew point meter
Gases with different moisture content will condense on the mirror surface at different temperatures. Using photoelectric detection technology, the exposed layer is detected and the temperature at the time of condensation is measured, and the dew point is directly displayed. The methods of mirror refrigeration include: semiconductor refrigeration, liquid nitrogen refrigeration and high-pressure air refrigeration. The mirror dew point meter adopts a direct measurement method. Under the premise of ensuring accurate dew detection, high efficiency of mirror cooling and precise measurement of the dew point temperature, this dew point meter can be used as a standard dew point meter. At present, the accuracy of Zgao in the world can reach ±0.1℃ (dew point temperature), and the general accuracy can reach within ±0.5℃.

2. Electric sensor type dew point meter
Hydrophilic or hydrophobic materials are used as the medium to form a capacitor or resistor. After the gas with moisture flows through, the dielectric constant or conductivity changes accordingly, and the current capacitance or resistance value can be measured. The moisture content of the gas at that time. This type of sensor designed on the basis of the dew point unit system constitutes an electric sensor type dew point analyzer. At present, the accuracy of Zgao can reach ±1.0℃ (dew point temperature) in the world, and the general accuracy can reach within ±3℃.
3. Dielectric method dew point meter
Using the characteristics of phosphorus pentoxide and other materials that absorb moisture and decompose into polar molecules, thereby accumulating charges on the electrode, an electrolysis micro-moisture meter based on the moisture content unit system is designed. At present, the accuracy of Zgao can reach ±1.0℃ (dew point temperature) in the world, and the general accuracy can reach within ±3℃.

4. Crystal oscillator dew point meter
Using the characteristic that the oscillation frequency changes after the crystal is wetted, the crystal oscillation dew point meter can be designed. This is a relatively new technology, and it is still at an immature stage. There are related products abroad, but the accuracy is poor and the cost is high.

5. Infrared Dew Point Meter
The infrared spectrometer can be designed by using the moisture in the gas to absorb the infrared spectrum. At present, it is difficult for this instrument to measure the low dew point, mainly because the peak detection rate of the infrared detector cannot reach the level of the absorption of trace water, and the content of other components in the gas interferes with the absorption of the infrared spectrum. But this is a very new technology, which is of great significance to the non-contact online monitoring of the moisture content of the ambient gas.

6. Semiconductor sensor dew point meter
Each water molecule has its natural vibration frequency. When it enters the gap of the semiconductor crystal lattice, it resonates with the crystal lattice excited by the charge, and its resonance frequency is proportional to the number of moles of water. The resonance of water molecules can release free electrons from the semiconductor junction, thereby increasing the conductivity of the crystal lattice and reducing the impedance. The semiconductor dew point meter designed with this feature can measure the trace moisture of -100 ℃ dew point.

7. Intelligent dew point meter (portable)
With large-screen LCD display and self-check and self-correction functions; it can directly measure atmospheric dew point and moisture. The instrument consists of a built-in fully compensated dew point sensor, a microcomputer-controlled measurement circuit, a large-screen dot-matrix liquid crystal display, a touch keyboard, HVAC pressure and temperature compensation algorithm data processing software, a built-in rotameter, and a miniature needle valve. For the integrated portable structure, the whole set of instruments are all installed in an instrument case, which is very convenient to carry and operate.

The detection component of the instrument is a complete set of dew point sensing detection system composed of imported thermal polymer capacitive dew point sensor and miniature platinum resistance, and has a temperature compensation function, which is calculated and corrected by a microprocessor to accurately compensate the dew point sensor Calibration makes the accuracy of dew point measurement better than ±2.0℃ and the resolution reaches 0.1ppm. It is suitable for the detection of trace moisture concentration in air, nitrogen, hydrogen, argon and other gases.

8. Online precision dew point meter
Online precision dew point meter, using imported alumina capacitive dew point sensor, with fast response speed and high sensitivity. Easy to use and operate. It can measure the trace moisture content in various gases, and is suitable for various online analysis occasions that have strict control requirements on moisture content. Application areas: petrochemical, natural gas, industrial gases, semiconductor industry, drying industry, food industry, power industry, machinery manufacturing, air separation industry, pharmaceutical industry.
Precautions for use of dew point meter
1. The influence of mirror pollution on dew point measurement
In dew point measurement, mirror pollution is a prominent problem, and its impact is mainly manifested in two aspects; one is the Raoul effect, and the other is to change the level of mirror background radiation. The Raoult effect is caused by water-soluble substances. If this substance (usually a soluble salt) is carried in the measured gas, the mirror surface will condense in advance, which will cause a positive deviation in the measurement result. If the pollutant is water-insoluble particles, such as dust, etc., it will increase the level of background scattering, which will cause the photoelectric dew point meter to have a zero drift. In addition, some vapors of easily condensable substances (such as organic substances) with a lower boiling point than water will obviously interfere with the measurement of the dew point. Therefore, regardless of any type of dew point meter, the mirror surface should be prevented from being polluted. Generally speaking, the impact of industrial process gas analysis pollution is more serious. But even in the measurement of pure gas, the contamination of the mirror surface will accumulate over time.
2. Selection of measurement conditions
In the design of the dew point instrument, various factors that directly affect the heat and mass exchange of the condensation process should be considered. This principle is also applicable to the selection of the operating conditions of the dew point instrument with a low degree of automation. Here we mainly discuss the problems of mirror cooling speed and sample gas flow rate.


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