The Measuring Principle of Hygrometer in High and Low Temperature Test Chamber
Temperature and humidity is the percentage of the amount of water vapor (vapor pressure) contained in a gas (usually air) and the amount of saturated water vapor (saturated vapor pressure) in the same case as the air, expressed in RH%. Humidity long ago had a close relationship with life, but it was difficult to quantify it. The expression of humidity is humidity, relative humidity, dew point, ratio of moisture to dry gas (weight or volume), and so on.
Humidity measurement method hygrograph humidity measurement from the principle of the division of twenty or thirty. But humidity measurement is always one of the difficult problems in the world measurement field. A seemingly simple quantity value, in depth, involves quite complex physico-chemical theoretical analysis and calculation, beginners may ignore many factors that must be paid attention to in humidity measurement, thus affecting the reasonable use of sensors.
Common humidity measurement methods are: dew point method, wet and dry bulb method and electronic sensor method, dynamic method (double pressure method, double temperature method, shunt method), static method (saturated salt method, sulfuric acid method)
1, Dew point method hygrograph: is to measure the temperature when the wet air reaches saturation, is a direct result of thermodynamics, high accuracy, wide measurement range. Precision dew point instrument for measurement can reach ±0.2°C or even higher accuracy. However, the cold mirror dew-point meter with modern optoelectric principle is expensive and often used with standard humidity generators.
2, Wet and dry bulb hygrometer: this is a wet measurement method invented in the 18th century. It has a long history and is widely used. Wet and dry bulb method is an indirect method, which converts the humidity value from the wet and dry bulb equation, and this equation is conditional: that is, the wind speed near the wet bulb must reach more than 2.5m/s. The common wet and dry bulb thermometer simplifies this condition, so its accuracy is only 5~7%RH, and the wet and dry bulb does not belong to the static method, do not simply think that improving the measurement accuracy of the two thermometers is equal to improving the measurement accuracy of the hygrometer.
3, Electronic humidity sensor method hygrometer: electronic humidity sensor products and humidity measurement belong to the industry that rose in the 1990s in recent years, at home and abroad in the field of humidity sensor research and development has made great progress. Humidity sensors are developing rapidly from simple humidity sensors to integrated, intelligent, multi-parameter detection, creating favorable conditions for the development of a new generation of humidity measurement and control systems, and also raising humidity measurement technology to a new level.
4, Double pressure method, double temperature hygrometer: is based on the thermodynamic P, V, T balance principle, the balance time is longer, shunt method is based on the precise mixing of moisture and dry air. Due to the use of modern measurement and control means, these devices can be quite precise, but because of the complex equipment, expensive, time-consuming operation, mainly used as standard measurement, its measurement accuracy can reach ±2%RH or more.
5, Static method of saturated salt hygrometer: is a common method in humidity measurement, simple and easy. However, the saturated salt method has strict requirements for the balance of liquid and gas two phases, and high requirements for the stability of ambient temperature. It requires a long time to balance, and low humidity points require even longer. Especially when the humidity difference between the indoor and the bottle is large, it needs to be balanced for 6 to 8 hours each time it is opened.
Efficacy of Electronic Expansion Valve in High and Low Temperature Test Chamber
The electronic expansion valve of the high and low temperature test chamber adjusts the water supply rate of the air conditioning evaporator according to the preset program flow, which is called the electronic expansion valve because it belongs to the electronic adjustment mode. It integrates the development trend of refrigeration mechatronics, with the unparalleled characteristics of the expansion valve, and presents the standard for the intelligent system operation of the refrigeration system of the quotation of the high and low temperature test chamber. It is a kind of automatic control environmental protection and energy-saving components with great development prospects, and is the orientation of the development trend of the quotation of the high and low temperature test chamber in the future.
The main purpose of the electronic expansion valve and the hot air conditioning expansion valve is basically the same, and the structure is various, but in the characteristics, the two have great differences. From the perspective of control and maintenance, the electronic expansion valve is composed of three parts: control board, electric actuator and controller. Generally speaking, most of the electronic expansion valve only refers to the electric actuator, that is, the controllable drive equipment and the oil circuit board. In fact, only this part is unable to operate.
The key hardware configuration of the electronic expansion valve control board is designed by single chip microcomputer, such as the control board also needs to operate the DC frequency conversion of the refrigeration compressor and the centrifugal fan, and the method of multi-machine cascade is generally selected. The controller of the electronic expansion valve generally uses thermal resistance or thermal resistance. As a new type of hydraulic control system, electronic expansion valve has been early to improve the definition of throttle organization, which is the key step of the intelligent system of refrigeration system, is the key way and ensure that the refrigeration system is upgraded enough to truly maintain, is a representative of the mechanical and electrical engineering of refrigeration system, has been used in more and more industries. Because of the selection of electronic expansion valves, the awareness of a certain type of system submission to expansion valves existing in the whole process of the refrigeration unit design scheme has been enhanced, and the new pattern of air conditioning expansion valves for system improvement services has played a key role in the development trend of the refrigeration manufacturing industry.
The high and low temperature test chamber can complete the test process according to the pre-set curve, and can accurately control the temperature rate within the range of the heating rate capacity, and can control the heating and cooling rate according to the slope of the set curve.
Temperature control is a heating process, high and low temperature test chamber heating using independent heating, far infrared nickel-chromium alloy high-speed heating wire, P.I.D+S.R system co-channel coordinated temperature control, through microcomputer calculation of output power, to obtain high-precision, high-efficiency electricity benefits. In order to achieve rapid heating and high temperature, the method of increasing the number of heating wires and improving the temperature control performance of software is generally adopted. By using international brand compressors and circulating fans, the chamber has uniform temperature distribution, high efficiency for environment-friendly refrigerant, low energy consumption and saved energy. The use of energy regulation technology in the design of refrigeration system can not only ensure the normal operation of the unit, but also effectively adjust the energy consumption and cooling capacity, so that the refrigeration system is in a good running state.
Technical Characteristics of Refrigeration and Temperature Control System of High and Low Temperature Test Chamber
High and low temperature test chamber is a kind of test equipment widely used in various industries, which is widely used to simulate various environmental conditions and test the durability, reliability and corrosion resistance of products. The technical characteristics of the high and low temperature test chamber are mainly reflected in its refrigeration system and temperature control system.
First of all, the refrigeration system of the high and low temperature test chamber has a high refrigeration capacity and refrigeration speed. During the temperature control process, a refrigeration system is needed to quickly reduce the temperature inside the test chamber. At present, the mainstream refrigeration system mainly has two kinds of compression refrigeration system and refrigerant loop circulation system. Among them, the compression refrigeration system has a high refrigeration capacity and refrigeration speed, which can quickly reduce the temperature inside the test chamber to the set temperature, but also to ensure the stability of the temperature.
Secondly, the temperature control system of the high and low temperature test chamber has high accuracy and stability. The temperature control system is the core part of the whole test chamber, which realizes the accurate control and stability maintenance of the internal temperature of the test chamber through the adjustment and control of the refrigeration system and the heating system. The current mainstream temperature control system mainly includes PID control system and intelligent control system. Among them, the PID control system has the characteristics of high precision and high stability, which can realize the accurate control of the temperature inside the test chamber, and is suitable for the test environment with high requirements for temperature control accuracy. The intelligent control system has the characteristics of more intelligent, and can realize the automatic control and adjustment of the internal temperature of the test chamber through self-learning algorithm and big data analysis technology, which is suitable for the occasions with relatively broad test environment requirements.
In summary, the technical characteristics of the high and low temperature test chamber are mainly reflected in its refrigeration system and temperature control system. The compression refrigeration system and PID control system have the characteristics of high cooling capacity, high cooling speed, high temperature control accuracy and high stability, which are suitable for the test environment requiring high temperature control accuracy and stability. In the future, with the development of artificial intelligence and Internet of Things technology, the control system of high and low temperature test chamber will continue to develop and improve in the direction of intelligence, automation and remote control, so as to better meet market demand.
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