High Quality H2s Analysis From Changai

The conference was successfully held
In order to promote the development of gas analysis technology, strengthen international standardization work, and serve the high-quality development of the national modern industrial system, the 27th plenary meeting of the International Organization for Standardization Technical Committee on Gas Analysis (ISO/TC 158) and the International Academic Seminar on Gas Analysis Technology were grandly held in Hangzhou, Zhejiang Province from October 18th to October 19th.







In this exhibition, Changai actively participated in exchanges and discussed the latest progress and international standardization trends of gas analysis technology with industry experts, further promoting the development and cooperation in related fields.
Changai has been rooted in the gas industry for 20 years and has promoted the continuous innovation and development of gas analysis technology. At this seminar, Changai exhibited high-precision chromatographs, mass spectrometers, sensors and other instruments, bringing the latest gas analysis methods, technologies and sample processing devices to the industry.





At this exhibition, Changai's star products include: CI-PC63-DP Portable Laser Dew Point Meter, CI-PC9200 gas chromatograph, CI-BM149-Puri high-purity gas dew point transmitter, CI-PC21 infrared gas analyzer, CI-PC931 portable trace Oxygen Analyzer and CI-PC832 Portable High-Content Oxygen Analyzer. With advanced high-tech, Changai has achieved efficient analysis of a variety of gases and provided users with customized optimal solutions for gas detection in different scenarios.
At the exhibition, customers showed strong interest in Changai's products. Changai's one-stop service meets users' needs for efficient and accurate detection. Whether in chemical industry, electricity or other fields, Changai instruments have shown great application potential.


With its outstanding technical strength and innovative spirit, Changai shines on the international stage, not only showing the latest research and development results and technical strength in the field of gas analysis, but also promoting in-depth exchanges and cooperation with domestic and foreign customers, injecting new vitality into the industry's technological innovation, and contributing more "Chinese wisdom" to promote the continuous progress and innovative development of global gas analysis technology.
I believe that in the future, we will continue to forge ahead and bring more high-quality products and solutions to our customers. Looking forward to seeing you next time!

Process flow and pollution generation analysis of polysilicon


Hydrogen preparation and purification process


Hydrogen is produced in an electrolytic cell by electrolysis desalination. The hydrogen produced by electrolysis is cooled and separated by liquid, then enters into deaerator, under the action of catalyst, the trace oxygen in the hydrogen gas reacts with the hydrogen gas to generate water and is removed. The deoxygenated hydrogen is dried by a set of adsorption dryers. The purified and dried hydrogen gas is sent to a hydrogen storage tank, and then is sent to the hydrogen chloride synthesis, trichlorohydrogen and silicon hydrogen reduction and silicon tetrachloride hydrogenation processes.


The oxygen produced by electrolysis is sent into an oxygen storage tank after cooling and separating the liquid. Put oxygen out of the tank and put it in the bottle.
The waste adsorbent discharged by the gas-liquid separator, the waste deoxidation catalyst discharged by the hydrogen deoxidizer and the waste adsorbent discharged by the dryer are all recovered and reused by suppliers.
Hydrogen chloride synthesis process


Hydrogen from the hydrogen preparation and purification process and circulating hydrogen returned from the dry separation process of the synthesis gas are respectively entered into the hydrogen buffer tank of the process and mixed in the tank. The hydrogen gas from the hydrogen gas buffer tank is introduced into the combustion gun at the bottom of the hydrogen chloride synthesis furnace. The chlorine gas from the liquid chlorine vaporization process is also introduced into the combustion gun at the bottom of the hydrogen chloride synthesis furnace through the chlorine gas buffer tank. The mixed gas of hydrogen and chlorine is ignited at the exit of the combustion gun, and the hydrogen chloride gas is generated by combustion reaction. The hydrogen chloride gas out of the synthesis furnace is sent to the trichlorosilane synthesis process after passing through the air cooler, the water cooler, the deep cooler and the fog separator.


In order to ensure safety, the device is provided with a hydrogen chloride gas absorption system which is mainly composed of two hydrogen chloride falling film absorbers, two hydrochloric acid circulating grooves and a hydrochloric acid circulating pump, and can absorb the hydrogen chloride gas discharged due to the load adjustment or emergency discharge of the device by water. The system maintains continuous operation and can receive and absorb hydrogen chloride gas discharged by the device at any time.


In order to ensure safety, the working procedure is provided with a set of chlorine-containing waste gas processing system which is mainly composed of an exhaust gas processing tower, an alkaline liquid circulating tank, an alkaline liquid circulating pump and an alkaline liquid circulating cooler. When necessary, the chlorine in the chlorine buffer tank and the pipeline can be sent into the waste gas treatment tower, and the chlorine can be washed and removed by sodium hydroxide aqueous solution. The waste gas treatment system is maintained in continuous operation to ensure that chlorine-containing gases are received and treated at any time.


Trichlorosilane synthesis process


The raw material silicon powder is suspended and discharged into the silicon powder receiving hopper through the silicon powder discharging hopper. The silicon powder is put into the lower middle hopper from the receiving hopper, the gas in the hopper is replaced by the hot hydrogen chloride and is boosted to be balanced with the pressure of the lower hopper, and the silicon powder is put into the lower silicon powder supply hopper. The silicon powder in the feeding hopper is fed into the feeding pipe of the trichlorosilane synthesis furnace by a star feeder installed at the bottom of the feeding hopper.


The hydrogen chloride from the hydrogen chloride synthesis process is mixed with the circulating hydrogen chloride from the circulating hydrogen chloride buffer tank, then the hydrogen chloride is introduced into the feeding pipe of the trichlorosilane synthesis furnace, the silicon powder in the feeding pipe is carried and conveyed from the silicon powder feeding hopper, and the silicon powder enters into the trichlorosilane synthesis furnace from the bottom.


In a trichlorosilane synthesis furnace, silicon powder and hydrogen chloride gas form a boiling bed and react to generate trichlorohydrogen silicon, and at the same time, products such as silicon tetrachloride, dihydrogen chloride silicon, metal chloride, polychlorosilane, hydrogen gas are generated, and the mixed gas is called trichlorohydrogen silicon synthesis gas. The reaction was exothermic. The outer wall of the synthetic furnace is provided with a water jacket, and the heat is taken away by the water in the jacket to maintain the temperature of the furnace wall.
The synthetic gas with silicon powder is placed on the top of the synthesis furnace, after the part of the silicon powder is removed by a dry dust removal system composed of a three-stage cyclone dust collector, the silicon powder is sent into a wet dust removal system, and the silicon tetrachloride liquid is washed, and part of the fine silicon dust in the gas is washed off. 


At the same time, wet hydrogen is introduced to contact with the gas, and part of the metal oxide contained in the gas is hydrolyzed and removed. The mixed gas purified by removing the silicon powder is sent to a synthesis gas dry separation process.
Synthetic gas dry separation process


The synthesis gas from the trichlorosilane hydrogen synthesis step is separated into chlorosilane liquid, hydrogen gas and hydrogen chloride gas in the step and is recycled to the device for use.


The synthetic gas stream of trichlorosilane is passed through a mixed gas buffer tank, then enters into a spray washing tower, and is washed by the low temperature chlorosilane liquid under the top flow of the tower. Most of the chlorosilane in the gas is condensed and mixed into the washing liquid. The chlorosilane at the bottom of the tower is pressurized by a pump, most of the chlorosilane is circulated back to the top of the tower after being cooled and cooled for gas washing, and the residual chlorosilane is sent to the hydrogen chloride analysis tower.


Most of the chlorosilane gas is removed from the top of the spraying and washing tower, compressed by a mixed gas compressor, cooled and cooled, is sent to a hydrogen chloride absorption tower, is washed by the chlorosilane liquid which is cooled and cooled and sent from the bottom of the hydrogen chloride analysis tower, most of the hydrogen chloride in the gas is absorbed by the chlorosilane, and most of the chlorosilane remaining in the gas is washed and condensed. The top gas of the tower is hydrogen gas containing trace hydrogen chloride and chlorosilane, and the hydrogen gas with high purity is obtained after the hydrogen chloride and the chlorosilane are further removed by a group of temperature-changing pressure-changing adsorbers. The hydrogen flows through the hydrogen buffer tank, and then returns to the hydrogen chloride synthesis process to participate in the reaction of the hydrogen chloride synthesis. The regenerated waste gas of the adsorber contains hydrogen, hydrogen chloride and chlorosilane, and is sent to the waste gas treatment process for treatment.


The chlorine silane dissolved with hydrogen chloride gas at the bottom of the discharge hydrogen chloride absorption tower is heated, then is combined with the surplus chlorine silane from the bottom of the spray washing tower, then is sent into the middle part of the hydrogen chloride analysis tower, and the purified hydrogen chloride gas is obtained at the top of the tower through the decompression distillation operation. The tower hydrogen chloride gas flows through the hydrogen chloride buffer tank, and then is sent to the circulating hydrogen chloride buffer tank which is arranged in the trichlorosilane synthesis process; The bottom of the tower removes the hydrogen chloride to obtain the regenerated chlorosilane liquid, most of which is sent back to the hydrogen chloride absorption tower after being cooled, frozen and cooled to be used as an absorbent, and the surplus chlorosilane liquid (namely the chlorosilane separated from the trichlorosilane synthesis gas) is sent to the raw material chlorosilane storage tank of the chlorosilane storage step after being cooled.


Separation and purification process of chlorosilane


The chlorosilane liquid separated by the dry separation step of the synthesis gas is fed into a chlorosilane storage tank of the raw material of the chlorosilane storage step. The chlorosilane liquid separated by the dry separation step of the reduction tail gas is sent to a reduction chlorosilane storage tank of the chlorosilane storage step; The chlorosilane liquid separated by the hydride gas dry separation step is fed into a hydrochlorosilane storage tank of the chlorosilane storage step. The raw material chlorosilane liquid, the reducing chlorosilane liquid and the hydrochlorosilane liquid are respectively pumped out by a pump and sent into different rectification towers of the separation and purification process of chlorosilane.


Trichlorohydrogen silicon hydrogen reduction process


The trichlorosilane refined through the chlorosilane separation and purification process is fed into the trichlorosilane vaporizer of the process, and is heated and vaporized by hot water; The circulating hydrogen gas returned from the dry separation process of reducing tail gas flows through a hydrogen buffer tank, and is also fed into a vaporizer to form a mixed gas with trichlorosilane vapor in a certain proportion.


The mixed gas of the trichlorosilane and the hydrogen from the trichlorosilane vaporizer is sent into a reduction furnace. On the surface of the hot silicon core/silicon rod which is electrified in the reduction furnace, hydrogen reduction reaction occurs to the trichlorosilane, and silicon is generated and deposited, so that the diameter of the silicon core/silicon rod gradually becomes larger until reaching the prescribed size. The hydrogen reduction reaction produces dihydrogen chloride silicon, silicon tetrachloride, hydrogen chloride and hydrogen at the same time, and is sent out to a reduction furnace together with the unreacted trihydrogen chloride silicon and hydrogen, and is cooled by the circulating cooling water of the reduction tail gas cooler, and then is directly sent to the dry separation process of the reduction tail gas.
The hot water is introduced into the jacket of the reduction furnace barrel to remove the heat radiated from the hot silicon core in the furnace to the inner wall of the furnace barrel and maintain the temperature of the inner wall of the furnace barrel. The high-temperature hot water of the jacket of the discharge cylinder is sent to the heat energy recovery working procedure, and after the steam is produced by the waste heat boiler and is cooled, the hot water is recycled to be used by each reduction furnace jacket of the working procedure.
After the silicon core is installed in the reduction furnace, the water jet vacuum pump is used to pump the vacuum before driving, the nitrogen is used to replace the air in the furnace, the hydrogen is used to replace the nitrogen in the furnace (the nitrogen is exhausted), and then the heating operation is carried out. Therefore, the nitrogen is discharged into the ambient air in the driving stage, and a small amount of water for the vacuum pump (which can be discharged as clean water) is needed; In the furnace shutdown and opening stage (about 5-7 days for one time), the mixed gas containing chlorosilane, hydrogen chloride and hydrogen in the reducing furnace is first pressed into the reducing tail gas dry recovery system for recovery by hydrogen gas, then the nitrogen gas is replaced and then exhausted, the polysilicon product is taken out, the waste graphite electrode is removed, and the ultra-pure water in the furnace is washed according to the situation, therefore, the nitrogen gas, the waste graphite and the cleaning waste water are generated in the furnace shutdown stage. The nitrogen gas is harmless gas, therefore, under normal circumstances, the reduction furnace is open and the stopping stage has no harmful gas discharge. The waste graphite is recovered from the original production plant, and the cleaning waste water is sent to the treatment system of acid-alkali wastewater containing chloride for treatment.


Dry separation process for reducing tail gas


The reduction tail gas from the trichlorosilane hydrogen reduction step is separated into chlorosilane liquid, hydrogen and hydrogen chloride gas through the step, and the tail gas is respectively recycled to the device for use.
The principle and process of dry separation of reducing tail gas are very similar to that of dry separation of trichlorosilane. The hydrogen with high purity obtained from the outlet of the temperature-changing pressure-changing adsorber flows through the hydrogen buffer tank, and most of the hydrogen is returned to the hydrogen trichloride silicon hydrogen reduction process to participate in the preparation of polysilicon, and the surplus hydrogen is sent to the silicon tetrachloride hydrogenation process to participate in the silicon tetrachloride hydrogenation; The adsorber regenerates waste gas and sends it to the waste gas treatment process for treatment; The purified hydrogen chloride gas is obtained from the top of the hydrogen chloride analysis tower and sent to a circulating hydrogen chloride buffer tank which is arranged in the trichlorine hydrogen silicon synthesis process; The extra chlorosilane liquid (namely chlorosilane separated from the tail gas of hydrogen trichloride reduction) extracted from the bottom of the hydrogen chloride analysis tower is sent into a reduced chlorosilane storage tank of the chlorosilane storage step.
Silicon tetrachloride hydrogenation process


The refined silicon tetrachloride through the separation and purification process of chlorosilane is fed into the silicon tetrachloride vaporizer of the process, and is heated and vaporized by hot water. The hydrogen from the hydrogen preparation and purification process and the surplus hydrogen from the reduction tail gas dry separation process are mixed in a hydrogen buffer tank, and then the hydrogen is also introduced into a vaporizer to form a certain proportion of mixed gas with silicon tetrachloride vapor.
The mixed gas of silicon tetrachloride and hydrogen from the silicon tetrachloride vaporizer is sent into the hydrogenation furnace. The hydrogenation reaction of silicon tetrachloride takes place near the surface of the hot electrode which is electrified in the hydrogenation furnace, so as to generate silicon trichlorohydride and hydrogen chloride at the same time. The mixed gas containing trichlorosilane, hydrogen chloride, unreacted silicon tetrachloride and hydrogen is sent to the hydrogen dry separation process.
Hot water is introduced into the jacket of the furnace barrel of the hydrogenation furnace to remove the heat radiated from the hot electrode in the furnace to the inner wall of the furnace barrel and maintain the temperature of the inner wall of the furnace barrel. The high-temperature hot water of the jacket of the discharge cylinder is sent to the heat energy recovery working procedure, and after the steam is produced by the waste heat boiler and cooled, the hot water is recycled back to the hydrogenation furnace jacket of the working procedure.


Hydrogenation gas dry separation process


The hydrogen gas from the silicon tetrachloride hydrogenation process is separated into chlorosilane liquid, hydrogen gas and hydrogen chloride gas through the process, and the hydrogen gas is respectively recycled to the device for use.
The principle and process of dry separation of hydrogen gas are very similar to that of dry separation of trichlorosilane. The high-purity hydrogen obtained from the outlet of the temperature-changing pressure-changing adsorber is returned to the silicon tetrachloride hydrogenation process to participate in the silicon tetrachloride hydrogenation after passing through the hydrogen buffer tank; The absorbed regenerated waste gas is sent to the waste gas treatment process for treatment; The purified hydrogen chloride gas is obtained from the top of the hydrogen chloride analysis tower and sent to a circulating hydrogen chloride buffer tank which is arranged in the trichlorine hydrogen silicon synthesis process; The excess chlorosilane liquid (namely chlorosilane separated from the hydride gas) extracted from the bottom of the hydrogen chloride analysis tower is fed into the hydrochlorosilane storage tank of the chlorosilane storage step.
Chlorosilane storage process


The following storage tanks are arranged in the process: 100m1 chlorosilane storage tank, 100m1 industrial grade trichlorosilane storage tank, 100m1 industrial grade tetrachlorosilane storage tank, 100 m1 chlorosilane emergency discharge tank, etc.
The chlorosilane liquid obtained from the dry separation step of the synthesis gas, the dry separation step of the reduction tail gas and the dry separation step of the hydrogenation gas is respectively fed into a raw material, a reduction and a hydrochlorosilane storage tank, and then the chlorosilane liquid is respectively fed as the raw material to different rectification towers of the separation and purification step of the chlorosilane.
The mixed liquid of trichlorosilane and dichlorodihydrosilicon obtained at the top of the first-stage rectifying tower in the separation and purification process of chlorosilane, the trichlorosilane liquid obtained at the bottom of the fourth-stage rectifying tower and the trichlorosilane liquid obtained at the bottom of the sixth-stage rectifying tower and the eighth-stage rectifying tower and the tenth-stage rectifying tower are sent to an industrial-grade trichlorosilane storage tank, and the liquid is mixed in the tank and sold as the industrial-grade trichlorosilane products.
Silicon core preparation process


The technology of zone furnace drawing and cutting is adopted to process and prepare the conductive silicon core which needs to be installed in the furnace during the initial production of the reduction furnace. In the process of preparing silicon core, the silicon core needs to be corroded by hydrofluoric acid and nitric acid, then the silicon core is cleaned by ultrapure water, and then the silicon core is dried. The hydrogen fluoride and the nitrogen oxide gas will escape to the air during the acid corrosion treatment process, so the fan is used for sucking the hydrogen fluoride and the nitrogen oxide air through the wind cover which is covered on the upper part of the acid corrosion treatment tank, and then the gas is sent to the exhaust gas treatment device for treatment, and the exhaust gas is discharged according to the standards.


Product sort operation


The polysilicon rod made in the reducing furnace is removed from the furnace, and is cut off and broken into massive polysilicon. The polysilicon block was corroded by hydrofluoric acid and nitric acid, then cleaned by ultrapure water, and then dried. The hydrogen fluoride and the nitrogen oxide gas will escape to the air during the acid corrosion treatment process, so the fan is used for sucking the hydrogen fluoride and the nitrogen oxide air through the wind cover which is covered on the upper part of the acid corrosion treatment tank, and then the gas is sent to the exhaust gas treatment device for treatment, and the exhaust gas is discharged according to the standards. A bulk polysilicon product that has been detected to meet a specified quality index is delivered for packaging.


Waste gas and residue treatment process


1.Purification of waste gas containing hydrogen chloride


The waste gas discharged in the SiHCl1 purification process, the shutdown of the reducing furnace, the accidental discharge of waste gas, the safe discharge gas of the storage process tank of the chlorosilane and the hydrogen chloride, and the CDI adsorption waste gas are all sent to the waste gas leaching tower by pipelines for washing.
After the exhaust gas is continuously washed by 10%NaOH of the leaching tower, the washing liquid at the bottom of the tower is pumped into the processing procedure of technological waste, and the tail gas is discharged by an exhaust cylinder with a height of 15m.
2.Residue treatment


The residue liquid of the reactor mainly containing silicon tetrachloride and polychlorosilane compounds and the residue liquid of the chlorosilane which is discharged from the rectifying tower and is discharged by the stopping device are sent to the process for treatment.
The liquid to be treated is fed into a residue collecting tank. The liquid is then pressed out by nitrogen gas and sent to the residual liquid leaching tower for washing. 10%NaOH lye was used for treatment. Chlorosilane in waste liquid reacts with NaOH and water and is converted into harmless substances (treatment principle is treated with waste gas containing hydrogen chloride and chlorosilane).
3.acidic waste gas


The acid waste gas generated in the silicon core preparation and product finishing process is pumped to the waste gas processing system through a gas collecting cover. The acid waste gas is washed by 10% lime milk in a spraying tower to remove the fluorine-containing waste gas in the gas, and at the same time, ammonia is added into the washing liquid to reduce most NOx to N2 and H2O. After the gas is dehumidified after washing, the residual NOx in the gas is absorbed by the SDG adsorbent through the solid adsorption method (taking the non-noble metal as the catalyst), and then discharged by the exhaust cylinder with a height of 20m.


Waste silicon powder treatment


The silicon powder discharged from a raw material silicon powder charging dust collector, a cyclone dust collector of a silicon trichlorohydride silicon synthesis workshop and a synthesis reactor is transported into a waste slag funnel through a waste slag transporting tank, enters into an acid washing pipe with a stirrer, dealkali the waste silicon powder (dust) through 11% hydrochloric acid, and dissolves impurities such as aluminum, iron and calcium in the waste silicon. After the washing is finished, the waste residue is filtered by a filter press, sent to a dryer for drying, the dried silicon powder is returned to the trichlorosilane synthesis circulation for use, and the waste liquid is collected into the waste gas residue treatment system waste water and treated together.
The HCl-containing waste gas discharged from the pickling tank and the filtrate tank is sent to an exhaust residue treatment system for treatment.
Process waste treatment process


1.Treatment of class Ⅰ waste liquid


The acid-containing waste liquid treated by the washing tower washing liquid and waste silicon powder is mixed, neutralized and settled in the process, and then filtered by a filter press. The filter residue (mainly SiO2) shall be delivered to the Cement Factory to produce cement (see Annex). The sediment liquid and the filtrate are mainly salt-containing wastewater with high concentration, containing NaCl 200 g/L or more, the part of water does not introduce calcium magnesium ion and sulfate ion in the process operation and treatment, and the water quality meets the production requirements of chlor-alkali, so the salt-containing wastewater pipeline is transported to the caustic soda production line of Sichuan Yongxiang Co., Ltd. as the production raw material for recycling (see Annex). The evaporating condensate is reused to configure alkali liquor.


2.Treatment of class Ⅱ waste liquid


The waste hydrofluoric acid, waste nitric acid and acid washing waste water from the silicon core preparation process and the product finishing process are neutralized and settled by 10% lime emulsion, filtered by a filter press, and the filter residue (mainly CaF2) is sent to a cement factory for producing cement (see Annex). The settling solution and the filtrate are mainly calcium nitrate solution, and after evaporation and concentration, the solution is sold as by-products (see Annex). The evaporating condensate is reused to configure alkali liquor.

test principle


The humidity measuring instrument can be divided into cold mirror type, fully absorption electrolysis type, Al2O3 capacitance type, thin film capacitance type, resistance type, dry wet ball type and mechanical type. Among them, the fully absorption electrolytic micro-water meter and Al2O3 capacitive dew point meter are generally used for the measurement of low humidity range, while the resistance type, dry-wet ball, mechanical humidity meter can only be used for the measurement of relative humidity, the cold mirror type, thin film capacitance type (Vaisala's patent) humidity meter can not only be used for the measurement of low humidity, but also can be used for the measurement of medium and high humidity, that is, relative humidity. The above-mentioned instruments have their own advantages and disadvantages. Among them, the cold mirror dew point meter is the most accurate, the most reliable, the most basic measurement method, is widely used in the standard transmission, but its disadvantage is that the price is relatively expensive, and needs experienced operation and maintenance. 


1.1
Cold mirror dew point meter
1.1.1
Measure principle
When the measured moisture enters into the dew point measuring chamber, the cold mirror surface is swept over; when the temperature of the mirror surface is higher than the dew point temperature of the moisture, the mirror surface is in a dry state; at this time, the light emitted by the light source in the photoelectric exposure device is almost reflected on the mirror surface, the photoelectric sensor senses and outputs the photoelectric signal, and the control circuit compares, amplifies and drives the thermoelectric pump to cool the mirror surface. When the temperature of the mirror surface drops to the dew point temperature of the moisture, the surface begins to dew (frost), the light appears diffuse reflection on the mirror surface, the reflection signal induced by the photoelectric sensor is weakened, the change is compared by the control loop, amplified, the thermoelectric pump is adjusted to make the refrigeration power properly reduced, finally, the temperature of the mirror surface is kept at the dew point temperature of the sample gas. The mirror temperature is induced by a platinum resistance temperature sensor which is close to the lower part of the cold mirror surface and is displayed on the display window.
At present, the world's companies that produce cold mirror dew-point meter, such as GE, Edgetech, Switzerland MBW and so on, all adopt this principle, Britain's MICHELL adopts double-optical path detection system, that is, the reflection light and scattering light are detected at the same time, Finland's Vaisala uses acoustic wave as detection system.
During the measurement process, the water vapor in the measured gas is close to the saturation state with the decrease of temperature. Due to the gravitational effect, the water molecules adsorb on the mirror surface to form a thin water film. This is the first stage of dew formation. When the mirror temperature continues to decrease, the thickness of the water film gradually increases, which is the second stage of the dew formation. In this phase, the force contrast between the gravitational force of water molecules and the surface tension of water film is changed, and the influence of the latter gradually dominates. At this time, any unstable factors on the cooling surface, such as the tiny scar on the mirror surface, will cause the water film to condense into droplets. With the further decrease of the mirror temperature, the dew drops begin to appear. Through the microscope, we can see the isolated growth and irregular distribution of the dew drops, and then the dew layer diffuse on the surface at a very fast speed. At this time, we can think that the liquid-vapor equilibrium begins, namely reaching the dew point.
1.1.2
Structure
1.1.2.1
Mirror
The mirror should be hydrophobic, have good thermal conductivity, wear resistance, corrosion resistance and good optical performance. In the past, gold was used as a mirror, now rhodium is used as the mirror.


1.1.2.2
Mirror cooling


In the past, ethylene ether evaporation, mechanical refrigeration, liquefied gas or dry ice refrigeration, compressed air refrigeration have been used. The most commonly used is thermoelectric refrigeration or thermoelectric combined with mechanical refrigeration (dew point below -60°C). In this paper, thermoelectric refrigeration is emphasized.
Thermoelectric refrigeration, also known as semiconductor refrigeration, is Palput refrigeration (from its English name Peltier). The principle is that when a DC current passes through an NP element composed of two different metals, the heat will be transferred from one metal to another, which is just opposite to the thermocouple temperature measurement. Therefore, when the cold end of Palter is connected to the mirror and the other end is used as the heat dissipation end, the mirror can be cooled. In order to obtain different low temperature, a multi-level superposition method can be adopted. The data given by GE Company of the United States shows that, generally speaking, if the room temperature is 25°C, the temperature difference between the cold and cold end can reach 55°C, the temperature difference between the cold and cold end can reach 75°C, the temperature difference between the cold and cold end can reach 105°C, and the temperature difference between the cold and cold end can reach 120°C when the fifth refrigeration. The cooling capacity of different companies will vary slightly. The higher the temperature at the hot end, the higher the cooling efficiency, and the larger the temperature difference at the hot end. In order to reduce the temperature of the cold end, air cooling, water cooling and mechanical refrigeration are usually used to reduce the temperature of the hot end. But it is not possible to reduce without limits. It is important to note that its refrigeration capacity does not represent the measurement range of the dew point hygrometer. The definition of the measuring range of dew point hygrometer is that the temperature of the mirror surface can be obtained on the mirror surface, and the temperature of the mirror surface can be obtained when the dew or frost layer has a certain thickness. Therefore, under the general dew/frost point, the measuring range of dew point hygrometer is generally 5°C higher than its cooling ability, and under the low frost point, it is generally 10°C~12°C higher. For example, the DP19 dew point meter produced by MBW Company in Switzerland, when the room temperature is 10°C, its lowest measurement range is -60°C, when the room temperature is 20°C, its lowest measurement range is -55°C, when the room temperature is 35°C, its lowest measurement range is -45°C. Because of the high thermal conductivity of hydrogen and helium, the measurement range will be reduced by several degrees. When the pressure of the measured gas increases, the measurement range will also be reduced. For air and nitrogen, under the condition of higher than normal pressure, each additional atmospheric pressure, the measurement range will be reduced about 0.67°C.
1.1.2.3
Temperature measuring device


At present, most of the four-wire platinum resistance is used to measure temperature. The resistance value and temperature of the platinum resistance temperature sensing element are close to the linear relation in a fairly wide temperature range, the precision is high, the stability is good, the output signal is strong, the digital display is convenient.


1.1.2.4
Detection system


At present, except for the cold mirror dew point meter developed recently by Vaisala Company of Finland, which adopts the sound wave principle to measure, the other are all used photoelectric detector to measure and control. The photoelectric detection technology has been used for several decades, and it is mature. But its disadvantage is that it can not distinguish the supercooled water from the frost.


1.1.3
Precautions for use
1.1.3.1
Supercooled water and frost


In the range of 0-20°C, supercooled water is easily formed on the mirror surface. Because the saturated vapor pressure on the ice surface and the water surface is different, if supercooled water is formed on the mirror surface, the measured value is lower than the frost point, and the temperature is different. For example, when the frost point is -10°C, the corresponding supercooled water temperature is -11.23°C. So be very careful at this temperature. If the instrument is equipped with an endoscope, it can be observed and distinguished by the endoscope. At present, most instruments have the function of test, that is, to test their minimum cooling capacity. At this time, we can use the function of test to make the temperature of the mirror be lower than -20°C, ensure the frost on the mirror, and then make a formal measurement.


1.1.3.2
Kelvin effect
The saturated water vapor pressure on the surface is different from that on the plane. When exposed to the metal surface, the equilibrium water vapor pressure, i.e., the saturated water vapor pressure at the curved water surface, is increased due to the effect of surface tension, which is known as the Kelvin effect. Because of the Kelvin effect, the dew point temperature obtained is lower than the dew point temperature of the real measured gas.


1.1.3.2


Raoul effect


It means that the equilibrium water vapor pressure of the system is lower than the saturated water vapor pressure of the pure water when the water-soluble substance exists on the mirror. These water-soluble substances may be intrinsic to the mirror or contained in the measured gas. According to Raoul's law, the decrease of the equilibrium water vapor pressure is proportional to the solution concentration, which is the reason why there will be early condensation before reaching the dew point temperature of the measured gas
The Kelvin effect is just the opposite of the Raoul effect, so it will offset some. However, in the dew point measurement, the Raoul effect is more significant than the Kelvin effect, because the water-soluble substances are inevitably more or less present in the mirror and measured gas, and the impurities in the gas may sometimes occur chemical reaction or photochemical reaction with the water-insoluble substances on the mirror to convert into soluble substances. This situation is more evident in the moisture measurement of industrial process gases. Therefore, it is necessary to remove the solid particles in the gas by adopting proper filter device, and further remove the soluble substances left on the mirror surface by repeated dew condensation and dedew operation, this method is widely used.


In practical work, we often find that the surface of the mirror is not uniform when the surface begins to expose, the layer always appears in a certain area of the mirror, the reason is often caused by scratches on the mirror, because in these defective areas, on the one hand, the residual material is not easy to remove, on the other hand, the defects of the corner play a role of "exposed core", accelerating the process of exposing. Therefore, in the use of the dew point meter, especially when cleaning the mirror, it is necessary to be careful to avoid mechanical damage to the mirror. 


1.1.3.3
Mirror contamination
one is the raoul effect, the other is to change the level of specular background scattering. The raoul effect is mainly caused by water-soluble substances. If the substance in the measured gas (generally soluble salts), the mirror will dew out in advance, which will cause positive deviation of the measurement results. If the pollutants are insoluble in water particles, such as dust, etc., the scattering level of the background will be increased, so that the photoelectric dew-point meter zero drift.


1.1.3.4
Sampling channel


Because the water content in the atmosphere is very high, and the water molecule is polar molecule, it is easy to absorb on the inner wall of the pipeline or through the pipeline. Therefore, the gas path system must be well sealed in the measurement, the thickness of the pipe wall is at least 1mm, so as to prevent the outside environment water intrusion into the leakage. If the temperature of the measuring environment changes greatly, the sealing of the pipeline should be checked again.
If the measured gas is directly discharged into the atmosphere, the problem of water diffusion into the measurement system should be considered. The most commonly used method is to connect a pipe with a proper length in the exhaust port. The length and diameter of the pipe are based on the principle of not affecting the pressure of the measuring chamber. 
The sampling pipeline should be as short as possible, the number of joints should be reduced and the "dead space" should be avoided so as to reduce the interference of the background water.
The sampling pipeline and the measuring cavity wall are clean, the smoothness is good, and the hydrophobic material is selected. Figure 2-2 is the desorption-time curve of various materials when they are subjected to dry gas in the saturated adsorption state. From the experimental results we can get the following order of material selection: stainless steel, PTFE, copper, polyethylene, and, worst, nylon and rubber tubes, should not be used in low frost point measurements. In addition, the outer diameter of the tube is 6 mm or 1/4 inch, although the inner polished stainless steel tube is used in the low frost point measurement.
When measuring the high dew point, we must pay attention to that the dew point is lower than the ambient temperature of 3°C to avoid condensation of water vapor in the pipeline. 
When the dew point hygrometer measures the humidity, the flow range is 0.25L/min~1L/min. In this range, the change of flow velocity does not affect the measurement results.
The sampling can be divided into two kinds, one is the pressure sampling, according to the different sampling methods, it can be divided into the pressure measurement and the atmospheric pressure measurement. See figures 2-3 and 2-4, respectively. The other is measured at atmospheric pressure, that is, the sample is taken by pump. In this case, it will often bring artificial positive pressure and negative pressure because of the different sampling methods. If sampling in the way shown in Figure 2-5, the dew point meter is measured under the condition of pressure, it will bring positive error to the measurement results. If the pump and the flow meter exchange position, the dew point meter is under the condition of negative pressure, it will bring negative error to the measurement. The correct sampling method is shown in figures 2-6.


1.1.4
Application


The measurement range of the dew point hygrometer is wide. At present, the measurement range of a series of dew point hygrometers developed by MBW Company of Switzerland has reached -95°C~70°C, which can meet the majority of measurement requirements.


1.1.5
Pros and cons
Benefits: It is a basic measurement, accurate measurement, and the instrument is stable and drift-free. The instrument with the highest accuracy can reach ±0.1°C.
Disadvantage: High price, high requirements for operators, and need to maintain. Sensitive to pollutants. There is sometimes supercooled water in the -20°C~0°C range, so be especially careful to distinguish supercooled water from frost.　
1.2
A micro water meter for complete absorption electrolysis
1.2.1
Measure principle
By means of continuous sampling, the gas sample flows through an electrolytic cell of a special structure, the moisture of which is absorbed by the phosphorus pentoxide layer as a hygroscopic agent and discharged by electrolysis into hydrogen and oxygen, and the phosphorus pentoxide is regenerated. The reaction process can be expressed as:
P2O5+H2O=2HPO3 
2HPO3=H2+1/2O2+P2O5 
Combined (1), (2), will get:
2H2O=2H2+O2 
When the absorption and electrolysis are balanced, the water entering into the electrolysis cell is absorbed by the phosphorus pentoxide film layer, and is electrolyzed. If the ambient temperature, ambient pressure and gas flow are known, the relationship between the electrolytic current of water and the water content of gas sample can be deduced according to Faraday's law of electrolysis and gas law:
In formula:
Electrolytic current of water, μΑ;
Water content of gas sample, μL/L (i.e. volume ratio)
Gas flow, ml/min
Environmental pressure, Pa;
Absolute temperature of the environment, k;


As can be seen from the above formula, the magnitude of the electrolytic current is proportional to the water content in the gas sample, so the water content in the gas sample can be measured by measuring the electrolytic current of water. Under the condition of standard atmospheric pressure and 20°C, an ideal gas flows through the electrolytic cell at a flow rate of 100ml/min. When the water content of the gas sample is 1μL/L (ppmv), the electrolytic current is calculated from the formula as 13.4μΑ. This kind of instrument usually takes ppmv as unit, and can directly read the ppmv value of the moisture content in the gas sample.
Because of the catalytic effect of platinum electrode, the water electrolysis reaction is a reversible process, so when the measured gas sample is hydrogen, oxygen or contains enough hydrogen and oxygen, the balance moves to the left, the hydrogen and oxygen which have been produced by electrolysis are combined to generate water, and then the secondary electrolysis is carried out, so that the total electrolysis current value is higher, namely, the "hydrogen effect" and the "oxygen effect", or the "composite effect". The experiment shows that the reading of this kind of gas is higher by several to ten ppmv when the instrument is used to measure the water content of this kind of gas, but the deviation concentration reaction is on the background value, so it can be deducted.


1.2.2 
Structure
The instrument is composed of two parts of gas path system and circuit, the gas path system mainly includes an electrolytic cell and a gas path control part.
1.2.2.1
Battery
In the glass tube, two platinum electrodes are wound into a double spiral shape, and phosphorus pentoxide film is uniformly coated between the electrodes as a hygroscopic agent. Under the specified measurement conditions, the inner winding structure can ensure the absorption and electrolysis of all water entering the pool. The glass pool wall is favorable for the uniform phosphorus pentoxide coating. Since platinum has the function of generating hydrogen and oxygen, especially hydrogen-rich gas, to react again to generate water, some companies have adopted rhodium instead of platinum. 
For the dry phosphorus pentoxide coating, when a "absolutely dry" gas sample is introduced and an appropriate DC voltage is applied to the electrode, a small current-background value is generated in the circuit. The value of the background is only related to the structure of the cell, the condition of the coating, the temperature and the type of the sample, but not to the water content of the sample. Because the background value can always be added to the electrolytic current of the moisture contained in the gas sample, the real moisture content of the medium should be deducted from the instrument reading when measuring.
1.2.2.2
Pneumatic control system
The pneumatic system is composed of control valve, electrolytic cell, flow regulating valve, flow meter and dryer. The control of the air flow path is done by the control valve.


1.2.3 
Precautions for use
From the formula, we can know that the measurement results, namely the humidity of the gas μL/L (ppmv) is calculated according to the gas flow and electrolytic current, so the gas flow must be accurately controlled and measured. This kind of instrument generally uses the floater flowmeter, under 20°C, 1atm, uses the air to calibrate. If the condition in use is not a standard condition, for example at a different temperature and pressure, or the measured gas is not air, the measured gas needs to be calibrated again or corrected according to a correction factor.


1.2.4 
Application
The measurement range is from several μL/L(ppmV) to 2000 μL/L(ppmV), and the accuracy is 5% of the reading or 1% of the full range. The invention can be used for a plurality of inert gases, some organic and inorganic gases which do not react with P2O5. Examples include air, nitrogen, hydrogen, oxygen, argon, helium, neon, carbon monoxide, carbon dioxide, sulfur hexafluoride, methane, ethane, propane, butane, natural gas, and certain freon gases. It can not be used for certain corrosive gases and gases which can react with P2O5, such as ethanol, certain acidic gases, unsaturated hydrocarbon gases.


1.2.5 
Pros and cons
Benefits: Absolute measurement, stable, no drift.
Disadvantage: The life of the battery is limited and needs to be regenerated. Both high and low humidity (<1ppmv) shorten their life. Slow response in low humidity. The demand for gas flow rate is high. It cannot be used in some corrosive gases and gases that react with P2O5. There's a background.
1.3
Aluminum oxide capacitance humidity meter
1.3.1
Measuring principle, structure and application range


The instrument has a variety of forms, such as portable battery-operated, data processing with a microprocessor, multi-parameter display, and so on. But its essence is a capacitor, by depositing a thin layer of porous alumina on a conductive substrate and then applying a thin layer of gold to the thin layer of alumina. The conductive substrate and the thin layer of gold form an electrode of the capacitor. The water vapor is absorbed by the porous alumina through the gold thin layer, and the impedance of the capacitor is proportional to the number of water molecules, namely the water vapor pressure. Moisture partial pressure can be obtained by measuring the impedance or capacitance of the capacitor, and dew point value can be obtained by conversion.
The thin layer of aluminum oxide located between the aluminum and gold electrodes is responsive throughout the range of saturated vapor pressure from 10-3Pa (approximately -110°C dew point) to water. Due to its strong affinity for water, coupled with the larger dielectric constant of water, such instruments are highly selective for water, but not responsive to other common gases and organic gases and liquids. 
The accuracy is ±1~±2°C in the middle and high humidity range, and ±2~±3°C in the low humidity range, such as -100°C. The sensor does not react with hydrocarbon gas, CO, CO2 and HCFC-containing gas, but the drift of different gas is different. For certain corrosive gases, such as ammonia, SO3, and chlorine, will damage the sensor and should be avoided as far as possible.


1.3.2
Precautions for use
The usual measurement range of this kind of instrument is -110°C~+20°C. When the dew point is higher, the instrument will produce a larger drift. Attention should also be paid to the temperature coefficient. Because of its response to the partial pressure of water vapor, we should pay attention to the change of the total pressure of gas in the measurement. 
It can avoid dust and oil pollution, and the gas flow rate is larger, which is 3~5(L/min) or even larger.
1.3.3
Pros and cons
Benefits: The invention has wide response range, from 1μL/L (ppmv) to 80%RH, can be installed remotely, can be used in the field, has relatively stable, fast response, small temperature coefficient, has no relation with flow rate change, has high selectivity to water, can be used in a wide range of temperature and pressure, has small daily maintenance amount and small volume.
Disadvantage: The method is an indirect measurement, operating at higher temperatures or some gases causing drift, affected by corrosive gases, which must be periodically calibrated to overcome aging, hysteresis and contamination. Since the response value is non-linear, each sensor needs to be calibrated and cannot be used universally.
1.4
Thin-film capacitive humidity meter
1.4.1
Measuring principle, structure and application range


A polyamine salt or cellulose acetate polymer film deposited on two conductive electrodes is used. The dielectric constant between the two electrodes can be changed when the film absorbs water or loses water. There is also a technique to use thermoset polymers that are resistant to high temperatures, which allows such sensors to be continuously measured at temperatures higher than 100°C. Now I'm using high-molecular films like Visala.
1.The main function is to support other parts of the sensor.
2.One of the electrodes is made of conductive material 
3.Thin film layer. It is the heart of the sensor, the amount of water absorption of the film is related to the relative humidity of the surrounding environment. The thickness of the film is 1-10 (μm).
4.The upper electrode also plays an important role in the performance of the sensor. In order to get a quick response, it is necessary to have a higher water permeability. It is also a conductive material.
5.A contact pad for an upper electrode. Since there are many restrictions on the design of the upper electrode, a separate metal is needed to make good contact.


The measurement range is wide, from -50°C~100°C dew point. It can be used in a wide range of temperature, sometimes without temperature compensation. High temperature resistant thermoset resins allow for continuous measurements of such capacitive humidity sensors at temperatures of 185°C, with the highest temperature used depending on the sensor's packaging material. Another advantage for thermoset resin sensors is that the temperature coefficient is small in the -50°C~100°C temperature range, so it can be easily measured in a wide range.
All relative humidity sensors are temperature sensitive and, if calibrated at one temperature, will cause errors when used at another temperature. One advantage of polymer sensors is that they have less temperature dependence, i.e., smaller temperature coefficients. Therefore, when the use temperature is different from the calibration temperature, the error is small. Electronic temperature compensation is required if used at the limit temperature or if accuracy is high. When the temperature span is less than 50°C, it is easy to compensate the temperature. When the temperature range is wider, it is difficult to compensate the temperature. However, the accuracy of modern polymer sensor can reach ±1%RH in a narrow range, and ±3%RH in a wide range of temperature and humidity. After a period of use, or after contamination, a recalibration is required.


1.4.2
Pros and cons
Benefits: The system has the advantages of fast response, wide temperature and humidity measurement range, good linearity, little hysteresis, good stability and repeatability, low temperature coefficient and low cost.
Disadvantage: Almost nothing.
1.5
Resistance type humidity meter
1.5.1
Measuring principle and structure


The sensitive material takes the polymer solution of quaternary ammonium salt as the matrix, and the functional group is reacted with the resin polymer to produce a thermosetting resin with three dimensional and three dimensional, and has good stability. The change of relative humidity can lead to the change of resistance between the cathode and the anode.


1.5.2
Pros and cons
It has no hysteresis and aging, low temperature coefficient, low cost and low energy consumption. The temperature range is -10°C~80°C, the repeatability is better than 0.5%RH, the accuracy is higher, generally ±2%RH, in a very narrow range can reach ±1%RH. 
Disadvantage: It is an indirect measurement instrument, which needs to be calibrated periodically, and is not suitable for some pollutants. If it is used in a wide range of temperature, it needs temperature compensation. It is more sensitive to pollutants than the capacitive sensor. It is not suitable for low humidity, loss of sensitivity when relative humidity is less than 15%RH, but it still has good performance when relative humidity is close to 100%RH, but condensation sometimes damages the sensor. 
Some pollutants have great influence on resistance sensor, while others have great influence on capacitance sensor. Therefore, when selecting sensor, it mainly depends on the nature of pollutants. 


1.6
Mechanical humidity meter 
1.6.1
Measuring principle and structure 
The length of organic polymer materials such as hair, intestinal membrane, nylon and polyimide will change with the relative humidity. The mechanical humidity meter utilizes this characteristic to make the above material make linear, strip-shaped humidity-sensing element or coat on the elastic material to roll into a loose-wire-shaped humidity-sensing element, and then through the mechanical amplifying device, the change of the geometric amount caused by the change of the humidity is indicated by a pointer or recorded by a recording pen, thereby directly indicating the relative humidity. The invention is suitable for measuring the temperature and humidity of indoor environment such as laboratory, computer room, warehouse and factory building. 


1.6.2
Pros and cons
Benefits: Cheap, not sensitive to most pollutants, no power, and permanent recording  
Disadvantage: drift, if the use of a certain humidity for a long time will lose its sensitivity, can not be used below 0°C, slow response, transport or vibration swing will damage its performance.  
1.7
Dry-wet ball humidity meter 
1.7.1
Principle
The dry-wet ball hygrometer is composed of two thermometers with identical specifications, one is called the dry-ball thermometer, and the temperature bubble is exposed in the measured gas to measure the ambient temperature, and the indication value is expressed by Ta (ta). The other is a wet-ball thermometer, which is wrapped with a specially made gauze cover to keep it wet. When the air around the wet ball is in the unsaturated state, the moisture on the wet ball gauze cover will evaporate continuously, because the moisture evaporates needs to absorb heat, so the temperature of the wet ball will decrease, its indication value is expressed by Tw(tw). The velocity of moisture evaporation of the wet sphere is related to the moisture content of the surrounding gas. When the humidity of the gas is lower, the moisture evaporation is faster, the temperature of the wet sphere is lower, and vice versa. After obtaining the accurate temperature of dry and wet balls, the humidity value is calculated by means of the equation of wet balls.     
Due to its simplicity and low cost, dry-wet ball hygrometers have been the most used type for a considerable period of time in the past.
A humidity meter with good design and maintenance, in the temperature range of 5°C~80°C, if the temperature accuracy is ±0.2°C, the relative humidity accuracy is about ±3%RH. The accuracy of this principle is dependent on the accuracy of the thermometer. Platinum resistance thermometers are often used for some precise measurements. In general, the dry-wet ball hygrometer is a basic measurement method. If the calibrated thermometer is used and the operation is correct, such as the Assmann hygrometer, accurate, reliable and repeatable measurement results can be obtained. So in the past, this hygrometer was often used as a standard. However, many operators, especially in the industrial field, do not have enough energy and time, so the results are not accurate and unreliable. At present, the wet and dry spherical hygrometer is gradually replaced by modern instruments.


1.7.2
Pros and cons
Benefits: When the relative humidity is close to 100%RH, a higher accuracy can be obtained. Although there will be errors if the wet ball thermometer is polluted or used improperly, the maintenance cost is very low because of the simple device. The invention can be used in the situation that the room temperature is higher than 100°C, which is the basic measurement, the stability is good, the stability is simple, the cost is low.
Disadvantage: Some techniques are needed to obtain accurate measurements and calculations are needed to obtain the final results. A large number of gas samples are required, and the gas samples may be humidified by a wet gauze. When the relative humidity of the measured gas is lower than 15%RH, it is very difficult to reduce the temperature of the wet ball. When the temperature of wet ball is lower than 0°C, it is difficult to obtain reliable results. The volume cannot be too small because water is constantly supplied to the wet ball thermometer. Because dust, oil or other pollutants can pollute the gauze, or the water flow is insufficient, the temperature of the wet ball is higher, and the result of relative humidity is higher. In addition, the factors that affect the results are temperature measurement error, wind speed, radiation error and so on. When the temperature difference of dry and wet ball is 0.1°C at 20°C, the relative humidity error is 1%RH.

At present, the mixture gas is more used as the protective gas in industry, which greatly improves the welding quality, and welding speed, and reduces the splash and manpower cost. In order to accurately control the welding quality, it is necessary to analyze the gas concentration of each mixture gas in real time and accurately.
The mixed gas mixing cabinet, also known as gas proportioning device, is a large-flow two-element or multi-element gas mixing device specially designed for gas protection, which is mainly used for the matching of the central gas supply bus and the bus, and the device can mix two or more gases needed to be used according to the requirements of use, and obtain uniform mixed gas. The invention can be widely applied to various mixed gas protection occasions such as railway, ship, chemical industry, mechanical manufacturing, air conditioning and fresh keeping, electric light source, leak detection (alarm), disinfection and sterilization, etc.
Working Principle
The two-element or multi-element gas which needs to be mixed enters a two-stage or multi-stage pressure balancing device through a one-way valve, and the input pressure difference is balanced, thereby ensuring that the pressure of the component gas and the diluted gas before mixing is absolutely the same, and then the flow control valve is adjusted, and the flow rate of various gases can be adjusted according to the desired mixing ratio. In principle, the dynamic gas mixing method is adopted, namely mixing is used, thereby ensuring the uniformity of the mixed gas, having excellent reproducibility and stable proportion.
For the above mixed gases, Chang Ai Company provides solutions for the analysis of various gas concentrations:
0~50%/30% CO2, the rest of argon, CO2 concentration needs to be measured, mainly using the infrared measurement principle（NDIR, None-Dispersive Infra-Red）
0~50% CO2, the rest of nitrogen, CO2 concentration needs to be measured, mainly use the infrared measurement principle（NDIR,None-Dispersive Infra-Red）
0~50% Ar and the rest He gas need to measure the concentration of He gas. The principle of heat conduction is mainly used (TCD,Thermal Conductivity Detection)
0~2% O2, the rest Ar, O2 concentration needs to be measured. The measurement principle of 3D ion flow is mainly used.（3D Limiting Current Type Oxygen Analyzer）
0~10% H2, the rest Ar, H2 concentration needs to be measured. The principle of thermal conductivity measurement is mainly used. (TCD,Thermal Conductivity Detection)
0~20% oxygen, the rest argon, need to measure the concentration of O2, mainly use the ion flow measurement principle（3D Limiting Current Type Oxygen Analyzer）
0~5% oxygen, 0~15% carbon dioxide, the rest argon gas, need to measure the concentration of argon and O2 at the same time, mainly use the ion flow measurement principle（3D Limiting Current Type Oxygen Analyzer）/（NDIR,None-Dispersive Infra-Red）
0-50% argon, the rest helium, no
Related Products:
On line:
1.On line infrared analyzer CI-PC261
2.On line thermal conductivity analyzer CI-PC56
3.On line oxygen analyzer CI-PC962
Portable:
1.Portable Infrared Analyzer CI-PC23
2.Portable thermal conductivity analyzer CI-PC53
3.Portable Oxygen Analyzer GNL-B1F/GNL-2100-3O