CN88211603U - Dynamic Humidity Calibration Device - Google Patents

Abstract

The utility model relates to a calibration device for dynamic humidity, belonging to the field of the testing or calibrating meteorological apparatus, aiming to build a calibration device for low humidity to calibrate the apparatus and the sensor for humidity measurement, comprising an air drying system, an air humidifying system, and a dew point apparatus. The air drying system adopts the arrangement mode of 5A molecular sieve-3A molecular sieve-liquid nitrogen freezing spiral pipe; the air humidifying system uses an activated carbon +HT-1 type catalyst pipe; the thermocouple of the dew point apparatus is welded in a hole under the center of a condensate mirror surface. The calibration device for dynamic humidity is simple and practical, and the calibration range for dynamic humidity is-110 DEG C-20 DEG C bloom point.

Description

The utility model "dynamic humidity calibration device" belongs to the field of testing or calibration of meteorological instruments.

All instruments and sensors that measure relative humidity must be calibrated with other standard humidity methods. Many articles have reviewed humidity standards (for example: (1) KGParker3, Mea3 ure-ment and Control, 12 (2), p.73 (1979); (2) Inamatsu Teruko, Measuring Technology, 5 (3 ), p.27 (1977); (3) Wang Weitong, Analytical Instruments, (3), p.20 (1978); (4) Translated by Hao Guang, Semiconductor Sensitive Devices, (1), p.54, (1986 ). Hasegawa of the American National Bureau of Standards divided the humidity standards into four categories: benchmark, standard, secondary standard and working standard, and outlined the humidity standards such as gravimetric method, double pressure method, double temperature method, double flow method and humidity fixed point method The principle of the method and related instruments developed by the Bureau as secondary standards (S.Hasegawa, ISA Trans., 25 (3), 15 (1986)). Among these methods, the double-flow method (mixed method or split method) The inertia is small and it is suitable for dynamic research, so it is widely used. The dew point method is an absolute humidity measurement method, and the precision dew point meter and the dew point meter can be used as the secondary standard and the working standard respectively.

Yang Guodong and Zeng Yiding (Sensor Technology, (3), p.27 (1986)) introduced several foreign humidity generators with shunt method. This humidity generator mixes (also known as dilution) the dry and wet air streams to obtain a continuous flow of air with a known and adjustable moisture vapor content. Therefore, such devices include dry gas generators and dry gas humidifiers. For example, the M136 humidity calibration device introduced in my country adopts a secondary dilution process, and the water vapor content in the generated constant humidity airflow can be adjusted as needed within 1-3,600,000ppm, and an accurate value is given by a precision dew point meter. The device has a gas drying system capable of obtaining a frost point of -87°C and a constant humidity airflow with a minimum frost point of -73.3°C. The device is highly accurate and has a wide range of variable humidity. However, the structure of the device is complicated, the price is expensive, and the lower limit frost point is still too high, so it is not suitable for the calibration and inspection of lower humidity instruments.

The purpose of the utility model is to establish a low-humidity calibration device for calibrating instruments and sensors for humidity measurement. The humidity dynamic calibration range of this device is -110°C to -20°C frost point (equivalent to 0.001 to 1000ppmH ₂ O).

The utility model is composed of three parts: a gas drying system, a gas humidifying system and a dew point meter.

1. Gas drying system: composed of 5A molecular sieve tube, 3A molecular sieve tube and liquid nitrogen freezing spiral tube. Use 99.99% pure hydrogen in cylinders as the gas source. The drying system is characterized by its arrangement. Different from the commonly used arrangement of 3A molecular sieve-5A molecular sieve-liquid nitrogen freezing spiral tube, the arrangement of 5A molecular sieve-3A molecular sieve-liquid nitrogen freezing spiral tube is adopted. This is because it is noted that the drying efficiency is 5A molecular sieve<3A molecular sieve<liquid nitrogen freezing spiral tube, and the arrangement of the utility model makes the drying of the moisture in the gas gradually tightened, so that the frost point of the dried hydrogen obtained in this way is lower than - 122°C. This dry gas is called "zero point" gas.

2. Gas humidification system: It is composed of activated carbon + catalyst tube, external permeation tube and constant temperature tank for placing the permeation tube. Use cylinders of ordinary hydrogen as the gas source. The utility model adopts HT-1 type catalyst (produced by Dalian Catalyst Factory), which can catalyze the oxygen in ordinary hydrogen into water for utilization. Activated carbon can remove low-level hydrocarbons or oil vapor in ordinary hydrogen. Adjust the water temperature of the constant temperature tank to change the water seepage rate of the permeation tube. The humidity in the mixed airflow can be adjusted by adding an appropriate amount of humidified hydrogen peroxide to the "zero point" airflow (dry airflow) through the needle valve.

3. Dew point meter: used to measure the absolute humidity of the mixed gas. It consists of a ground glass case, a copper temperature sensing rod with a mirror, a copper-constantan thermocouple and a digital voltmeter. Since the accuracy of the dew point meter has a great relationship with the installation position of the thermocouple, the thermocouple is required to be close to the condensation surface. The traditional way is to install the thermocouple in the parallel through hole under the mirror or use a copper plug to obliquely plug the thermocouple under the mirror. These methods are inconvenient to process and not easy to fix. The utility model is to punch a slanted hole under the mirror surface, the bottom of the hole is located at the center of the mirror surface, and the copper-constantan thermocouple is welded in the slanted hole with welding tin. This structure not only facilitates installation but also ensures measurement accuracy.

The utility model includes the connecting pipelines and parts between the drying system, the humidifying system and the dew point meter, all of which are made of glass and stainless steel, and all the connecting parts are sealed and connected by welding or screws to prevent air leakage. The whole device is installed in a constant temperature room to ensure relatively stable working conditions.

Accompanying drawing 1 is the gas flow chart of the utility model. The components inside the dotted line frame are all installed in the instrument case. Together with other components, it constitutes the dynamic humidity calibration device of the present utility model. The names of the components in the figure are: 1. Pure hydrogen cylinder; 2. Pressure reducing valve; 3.5A and 3A molecular sieve tubes; 4. Regulator valve; Exchange tube; 8. Self-made dew point meter; 9. Copper-constantan thermocouple; 10. Ice Dewar bottle; 11. PZ8 digital voltmeter; 12. WTK30-1 needle valve; Sensors, in this picture are alumina humidity sensors; 14. Rotameter; 15. Hydrogen bottle; 16. Activated carbon + HT-1 catalyst tube; 17. Permeation tube; 18. Super constant temperature tank.

Accompanying drawing 2 is a part of the present utility model -- the schematic diagram of the dew point method wet measuring device of label 8-11 part in Fig. 1. In the figure: 21. is the air inlet nozzle; 22. is the glass cover; 23. is the rubber stopper; 24. is the copper temperature-sensing rod with a mirror; 25. is the liquid nitrogen Dewar bottle; 26. is the copper-constantan Thermocouple; 27. is a digital voltmeter; 28. is a U-shaped glass tube; 29. is an ice water Dewar bottle.

The utility model uses hydrogen as a gas source and is easy to detect leaks. Safety is also not an issue due to the sealed connections. Of course, other gases (such as nitrogen, etc.) can also be used as the gas source, but because the liquid nitrogen freezing coil cannot be used, the frost point of the dry air flow is higher, and the lower limit humidity of the calibration is higher.

The utility model adopts one-time dilution of dry and wet air to obtain constant humidity air with different humidity, which can not only obtain low frost point, but also continuously humidify. Structurally, it is simpler than the second dilution method used at present.

Using the utility model, the humidity measuring instrument or the humidity sensor can be calibrated in a wide range of humidity, and its dynamic calibration range is -110°C to -20°C frost point, which is equivalent to a water content of 0.001-1000ppm. Use the dew point meter in the utility model to measure the water content in the drying gas through the high-efficiency color-changing desiccant (containing P ₂ O ₃ ) (see Chinese patent CN86101504), and the result is the same as that of the same type of desiccant (US Aquasorb produced by Mallinckrodt Company) after drying, the gas frost point drops to -96°C and the data listed in _the Soviet Chemical Handbook ( _vol . 10 ^-5 mmHg converted to frost point value -96.6°C) is consistent; it is consistent with other measurement methods (such as the electrolytic moisture meter produced by Shanghai Tangshan Instruments) and the results are consistent. The results of these measurements are listed in Table 1. Table 2 is the typical result of measuring moisture in various gases with the dew point meter in the utility model.

Table 1 Dew point meter accuracy inspection results (dew point, ℃)

Note 1. It is consistent with the Aquasort desiccant produced in the United States, and the gas frost point is lowered to -96°C after drying; it is also consistent with the data in the Soviet Chemical Science Manual,

Note 2. It is the average value of more than four measurement results. The electrolytic moisture meter is produced by Shanghai Tangshan Instrument Factory.

* means that the result is converted from the ppm value to the frost point value.

Table 2 Typical results of dew point meter measuring moisture in various gases

The results in Table 1 and Table 2 show that the accuracy, sensitivity and repeatability of the results measured by the dew point meter in the utility model are all satisfactory.

In order to calibrate the humidity measuring instrument or humidity sensor (for example, to calibrate the aluminum oxide humidity sensor, the utility model device (Figure 1) can be used. It will pass through the drying system (3-7 in Figure 1) and the humidification system (16-18 in Figure 1) The mixed gas flow is divided into two paths, the dew point (moisture content) of the mixed gas in one path is measured with a dew point meter (8 in Figure 1), and the mixed gas flow in the other path passes through the aluminum oxide humidity sensor (Figure 1 In 13), multiple humidity sensors can be connected in series or in parallel to calibrate at the same time. Since the mixed airflow with different water content passes through the humidity sensor, the capacitance value or admittance value of the alumina humidity sensor will change accordingly. The measured balance The electric signal (capacitance value or admittance value, the actual admittance value) of the time-humidity sensor corresponds to the measured value of the dew point meter one by one, so as to achieve the purpose of calibration.

Claims (2)

1, the utility model is the dynamic psychrometric calibrating installation, belongs to the test or the verification field of meteorological apparatus, it by the gas-drying system that comprises molecular sieve and liquid nitrogen frozen spiral pipe, comprise osmos tube etc. and form with the humidification system and the dew point hygrometer of calibration cell.Of the present utility model being characterised in that

(1) the molecule screen casing of gas-drying system and liquid nitrogen frozen spiral pipe arrangement mode are: the spiral pipe of 5A molecule screen casing-3A molecule screen casing-liquid nitrogen frozen.

(2) in the humidification system acticarbon+catalyst tube is arranged, catalyzer adopts HT-1 type catalyzer.

(3) in the dew point hygrometer, copper-constantan thermocouple is welded in the inclined hole under the minute surface, and the inclined hole bottom is positioned at the minute surface center.

2,, it is characterized in that the connection between gas-drying system, humidification system and the dew point hygrometer all adopts welding or screw to be tightly connected by the described dynamic psychrometric calibrating installation of claim 1.

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