This method is applicable to the determination of the dew point of trace water in hydrogen, nitrogen, oxygen, argon, helium, compressed air, phosphine, borane, sulfur hexafluoride and other gases used in the electronic industry process, and the measurement range is 0-90°C. SJ 2799-1987 Determination of trace water molecules in electronic grade gases Visual dew point method SJ2799-1987 standard download decompression password: www.bzxz.net
This method is applicable to the determination of the dew point of trace water in hydrogen, nitrogen, oxygen, argon, helium, compressed air, phosphine, borane, sulfur hexafluoride and other gases used in the electronic industry process, and the measurement range is 0-90°C.

Standard of the Ministry of Electronic Industry of the People's Republic of China Determination of trace water molecules in electronic grade gases Dew point method
SJ2799-87
This standard is applicable to the determination of trace water dew point in electronic industrial process gases such as nitrogen, oxygen, fluorine, nitrogen, compressed air, phosphine, incubation, sulfur hexafluoride, etc., and the measurement range is: >90℃. 1 Definition and principle of the method
1.1 Dew point
Under constant pressure, the gas is gradually cooled and the humidity when the water vapor in the gas reaches saturation is called the dew point. 1.2 Principle of the method
When the measured gas flows through the dew point measurement chamber at a certain flow rate under constant pressure, the metal mirror that can accurately measure the temperature can be lowered. The water vapor in the gas reaches saturation as the temperature of the mirror decreases, and phosphorus begins to appear on the mirror. The measured mirror temperature at this time is the dew point
After measuring the dew point of water in the gas, its water content can be determined. 2 Instruments
2.1 General requirements for instruments
Any instrument designed by different methods can be selected according to the test needs, but it should meet the following basic technical requirements: 2.1.1 The flow rate of the measured gas in and out of the dew point measurement chamber is adjustable. 2.1.2 The temperature drop rate of the mirror surface in the measurement chamber is adjustable and can be cooled to a level sufficient to condense water vapor on the mirror surface. 2.1.3 The dew point can be observed and the dew point temperature can be accurately measured. 2.1.4 The dead volume in the gas system is small and the gas continuity is good. The gas in the dew point measurement cable should be close to the atmospheric pressure. 2.1.5 In the range of -70 to -90℃, the accuracy of the instrument is less than ±1℃. Note: The cooling rate should be as slow as possible (less than i). 2.2 Instrument structure
Generally, the daytime dew point instrument consists of a measuring case, a refrigeration device, a temperature measurement system, a flow control device and a measuring device (see Appendix A), which are described as follows:
2.2.1 Measuring chamber
In order to facilitate the observation of dew point with the naked eye, the measuring chamber is made of stainless steel with a capacity of about 33mm3. The inner diameter of the jet nozzle is 2~2.mm31. The measuring chamber and the mirror body are connected by threads, and the dead volume of the measuring air should be as small as possible. 2.2.2 Refrigeration device
Liquid nitrogen is used as the refrigerant, and a heat-conducting glass made of a metal material with good thermal conductivity, such as copper, is directly inserted into the liquid nitrogen to cool the mirror surface. The mirror body is made of a metal material with high thermal conductivity, such as oxygen-free copper, and the mirror body is partially plated and polished to obtain the mirror surface. Gold should be used to measure highly corrosive gases. The distance between the mirror surface and the gas outlet is 2.5~3mm. If the multi-stage cascade is low enough, semiconductor refrigeration can also be used. 2.2.3 Temperature measurement system
The Ministry of Electronics Industry issued on May 18, 1987
1988-01-01
S2799-87
The temperature of the mirror surface when exposed should be measured as accurately as possible. In order to avoid the influence of temperature differences, the temperature sensing element should be as close to the mirror surface as possible and welded firmly to the mirror body.
2.2.3.1 Temperature sensing element
To measure the dew point temperature, use a precision mercury thermometer, thermocouple, thermistor, or platinum resistance temperature sensing element. Copper-copper thermocouple is currently used.
2.2.3.2 Measuring instrument
Different measuring instruments are used according to different temperature sensing elements. When using thermocouples, a millivoltmeter with a maximum range of 0 to 5m and a graduation value of less than 0.03mv should be used.
When necessary, the temperature measurement system should be calibrated. 2.2.4 Flow regulation and measuring chamber equipment
2.2.4.1 Flow regulation device
The inlet flow of the measuring chamber can be regulated by a sampling valve. 2.2.4.2 Flow measurement device
Different float flowmeters should be used for different gases. The measured flow of the gas sample can be calibrated with a soap film flowmeter. Note: The newly produced KBS-2 dew point test set of the institute is sufficient for full crown testing. 3 Preparation before analysis
3.1 Sampling equipment
3.1.1 Sampling valve: Use a regulating valve with a small dead volume, such as a needle-shaped valve. 3,12 Sampling tube: In principle, use a small-diameter tube as short as possible. Generally, a stainless steel tube, copper tube or thick-walled polytetrafluoroethylene tube with a length not exceeding 2m and an inner diameter not exceeding 4mm is used, and it should be hard-connected as much as possible. Clean the pipes before use, and then blow or dry them. Rubber or latex tubes are not allowed. 3.2 Connection of the test system
Connect the measuring system as shown in Appendix B. 3.3 Test
All joints of the test system should be leak-free, otherwise the measurement results will be too high due to the infiltration of moisture in the air. The test method is as follows
Connect the U-shaped pressure gauge filled with water to the gas outlet of the instrument, adjust the line pressure, so that the pressure difference in the U-shaped tube is 9.8kPa, turn off the gas source, and wait for the water column to drop by no more than 5mm after 5min, indicating that the system is airtight. The gas quality of flammable gas can also be checked by a film sensor.
If the system is found to be leaking, it should be checked and solved in sections. 3.4 Inspection of the temperature measurement system
When using a thermocouple to measure the dew point, the cold end of the thermocouple should be placed in an ice-water mixture. Calibrate the zero point of the millivoltmeter as required.
4 Operation steps
4.1 Open the sampling valve and allow the sample gas to purge the channel and measuring chamber. Generally, the purge should be carried out for about 1 hour before each measurement. For instruments that have been placed and then used again, when the moisture dew point in the measured gas is lower than -60C, it should be purged for 2 seconds before the measurement can be carried out. SJ 2799-87
4.2 Adjust the sample so that the gas flow rate reaches the specified range. 4.3 Put the nitrogen on the thermal conductivity grid and adjust the temperature difference potential of the thermocouple. Adjust the liquid level and control the temperature drop rate of the mirror surface to 2~5℃/min
4.4 Pay attention to observe the mirror surface and record the mV value when the mirror surface is just exposed. 4.5 When stopping the measurement, make sure that the measuring system is sealed to prevent moisture and dust from entering the air. 4.6 Conversion of thermocouple temperature difference electromotive force and dew point value 4.6.1 The calculation formula of thermocouple temperature difference electromotive force dew point value is as follows: Et = atr + bti + et?
Where: Et.--temperature difference electromotive force, mv;
t--dew point value, C;
u--3.9486876x10--
5-4.8374058×10-;
c=-1.961548X10-3,
a, b, c are the correction coefficients of copper-constantan thermocouple. 5 Precautions
5.1 Interference substances
Solid particles or dust, as well as other vapors except water vapor, have a certain influence on the determination of dew point. 5.1.1 Solid impurities and oily dirt
If the solid impurities are not soluble in water, they will not change the dew point value, but will hinder the observation of dew. At this time, the mirror surface can be cleaned with anhydrous ethyl or propylene on absorbent cotton. If necessary, filter the measured gas, and the filter should not adsorb or desorb the water in the gas.
If there is dirt in the measured gas, it should be removed before the gas enters the measurement chamber. 5.1.2 Impurities in the form of vapor
Organic matter with carbon, such as hydrocarbons, will not affect the measurement if the freezing point of hydrocarbons is lower than the dew point of water vapor. On the contrary, hydrocarbons will condense with the water vapor surface first. Therefore, the condensate of hydrocarbons must be separated before the water vapor is condensed. If the measured gas contains methanol, it will condense on the mirror surface with water, and the dew point of methanol and water will be different.
5.2 Cold wall effect
Except for the surface, the temperature of the rest of the instrument and the pipeline should be at least 2°C higher than the dew point of water in the gas. Otherwise, water vapor will condense at the coldest point, changing the water content in the gas sample. 5.3 Cooling rate
When the water content in the gas sample is low, the cooling rate of the mirror should be slow. Because the condensation process of water is relatively slow at this time, the cooling rate is too fast. Before the ice screen grows and reaches stability, no dew is observed, and the temperature is much lower than the dew point. This is the phenomenon of supercooling. Therefore, when approaching the dew point, the cooling rate of the mirror should be as slow as possible. 6 Result processing
6.1 Analysis results
The arithmetic average of the results of three minimum measurements is the new result. 6.2 Conversion of dew point and moisture content
SJ 2799--87
The conversion of dew point to PpM (V/V) or absolute humidity (g/m3) can be found in Appendix C. Report bzxz.net
The report should include the following:
Analysis period, chamber, atmospheric pressure.
Sampling location, number, pressure in the cellar;
Sample name:
Analysis results: Moisture concentration in the sample gas: d.
Any abnormal phenomenon observed during the measurement; Other operations that have been selected and included in this standard; Signature of the analyst.
SJ2799-87
Aiming Recorder A
Surface Dew Point Meter
(Supplementary Parts)
1. Potassium cover 2. Air jet 3. Mirror 4. Fluoroplastic gasket 5. Flange 6. Rubber gasket 7. Screw 8. Thermocouple 9. Flange cover
10.Rubber gasket 11. Outlet
12. Thermocouple wiring
Appendix B
Dew point test device ring
(supplement)
13. Wax
14, card ban
1, analytical gas source 2. Mirror dew point meter 3, Thermocouple 4. Temperature rod 5, Rotor flow meter 6. Compression fitting 5
Contains wet plate
PPm(V/V)
SJ27987
Appendix C
Egg point-PPm - Absolute humidity conversion table
(Supplementary material)
Absolute mud
:—30
Condensation content
PPm(V/V)
Absolute condensation
Contains apparent content
PPm(V/V)
$J2799--87
Continued from the above table
Absolute humidity
0,06734
Contains apparent content
PPm(V/V)
Absolute mud
Contains apparent content
$J2799-87
Absolute humidity|| tt | t||0.0002070
0.0001742
Condensation content
0,06611
0,01699
Absolute degree
0.0001464
0.0001228
0.0001028
0.00008582
0.00007161
9.00005960
|tt||.00002802
000002308
0.00001897
0.00001555
0.00001272
0,000010 39
0.0000074
0.0000046
Additional remarks;
—108
—114
sJ2799-87
missing the above table
Absolute humidity
0.0000033
0.0000016
0.0000012
0.0000008
00000052
0,00000016
This standard was proposed by the Clean Technology Society of the Chinese Institute of Electronics. It was sponsored by the Standardization Institute of the Ministry of Electronics Industry and revised by Yin Enhua, Lang Wenhui, Yu Fenglai of the Semiconductor Institute of the Chinese Academy of Sciences and Yue Changchun Qu Zhang Hefeng of the Standardization Institute of the Ministry of Electronics Industry.
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