How does the constant temperature and humidity box work?
- Clicks:427 Release time:2009/9/26
I. Introduction:
    The constant temperature and humidity chamber refers to a test chamber capable of simultaneously applying temperature and humidity stress. With the development of industrial products in China, in recent years, China has introduced a large number of test systems from abroad, which played an important role in the development and finalization of industrial products in China. However, due to its complexity, the test chambers appeared in operation. Many problems have arisen, and problems have not been solved in time, which greatly extended the test period and affected the development of products. The reason for these phenomena is that they do not understand the working principle of the comprehensive test. To this end, we have made some brief explanations on the basic working principle of the test box, and how to analyze and judge the failure of the test equipment of the comprehensive test chamber.
Second, the principle :
The constant temperature and humidity chamber is composed of a refrigeration system, a heating system, a control system, a temperature system air circulation system, and a sensor system. The above systems belong to two major aspects of electrical and mechanical refrigeration. The following is a preliminary description of the working principle and working process of several major systems.
2.1 Refrigeration system : The refrigeration system is one of the key parts of the comprehensive test chamber. In general, the cooling mode of the test chamber is mechanical refrigeration and auxiliary liquid nitrogen refrigeration. The mechanical refrigeration uses vapor compression refrigeration. They are mainly composed of compressor, condenser, throttling mechanism and evaporator. To achieve -55 ° C, single-stage refrigeration is difficult to meet the requirements, so the test box cooling method generally uses cascade cooling. The refrigeration system of the constant temperature and humidity chamber produced by our company (Shanghai Shangqun Electronic Technology Co., Ltd.) consists of two parts, called high temperature part and low temperature part, each part is a relatively independent refrigeration system. The evaporation of the refrigerant in the high temperature portion absorbs heat from the refrigerant in the low temperature portion and vaporizes; the evaporation of the low temperature portion of the refrigerant absorbs heat from the object to be cooled (air in the test chamber) to obtain the cold amount. Between the high temperature portion and the low temperature portion is an evaporative condenser which is both a condenser for the high temperature portion and a condenser for the low temperature portion. The high temperature part of the STH series test chamber uses medium temperature refrigerant, and the low temperature part of the refrigerant uses low temperature refrigerant, and the temperature inside the box can reach -70-150 °C.
2.2 Heating system: The heating system of the test box is relatively simple compared to the refrigeration system. It mainly consists of high-power electric resistance wire. Because the heating rate required by the test box is large, the heating system of the test box has relatively large power, and the bottom plate of the test box is also provided with a heater.
2.3 Control system : The control system is the core of the comprehensive test chamber, which determines the important parameters such as the heating rate and accuracy of the test chamber. Most of the controllers in the test box now use PID control, and a small number of control modes using PID and fuzzy control are combined. Since the control system is basically in the category of software, and this part is in use, there is generally no problem.
2.4 Temperature system : The temperature system is divided into two subsystems: humidification and dehumidification.
The humidification method of the test box generally adopts the steam humidification method, that is, the low pressure steam is directly injected into the test space to humidify. This humidification method has the ability to humidify, has a high speed, and is sensitive to humidification, and is particularly easy to achieve forced humidification when cooling.
  There are two ways to dehumidify the test chamber: mechanical refrigeration dehumidification and dry dehumidification. The principle of dehumidification of mechanical refrigeration dehumidification is to cool the air below the dew point temperature, so that the water vapor larger than the saturated moisture content is condensed and precipitated, thus reducing the humidity. Dehumidification of the dryer uses the air pump to pump out the air in the test chamber, and injects the dry air. At the same time, the humid air is sent to the recyclable dry to be dried, and then dried and sent to the test chamber, so that the cycle is dehumidified repeatedly. . Most of the comprehensive test chambers now use the former dehumidification method, and the latter dehumidification method can make the dew point temperature reach 0 °C. It is suitable for occasions with special requirements, but it is more expensive.
2.5 Sensor System: The sensors in the test chamber are mainly temperature and humidity sensors. Platinum groups and thermocouples are used in temperature sensors. There are two methods for measuring humidity: dry-wet bulb thermometer method and solid-state electronic sensor direct measurement method. Due to the low measurement accuracy of the dry and wet ball method, the current test chamber is gradually replacing the wet and dry balls with solid-state sensors for humidity measurement.
2.6 Air circulation system: The air circulation system generally consists of a centrifugal fan and a motor that drives it. It provides a circulation of air inside the test chamber.
In summary, only by deep understanding of the working principle and working process of the test box can the problems of the test box during operation be quickly solved. I hope this article can be beneficial to the personnel who are engaged in the operation and maintenance of environmental equipment management. Jointly promote the development of environmental engineering in China.
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