Brief introduction of working principle of constant temperature and humidity box
I. Introduction:
Constant temperature and humidity chamber refers to a test chamber that can simultaneously apply temperature and humidity stress. With the development of China's industrial products, in recent years, China has introduced a large number of test systems from abroad, which has played an important role in the development and finalization of China's industrial products. Many problems have occurred, and the problems cannot be solved in time, which greatly prolongs the test cycle and affects the product development work. The reason for these phenomena is that they do not understand the working principle of the comprehensive test. To this end, we made some brief explanations of the basic working principle of the test chamber, and introduced how to analyze and judge the failure of the test equipment of the comprehensive test chamber.
Second, the principle:
The constant temperature and humidity box is composed of a refrigeration system, a heating system, a control system, a temperature system, an air circulation system, and a sensor system. The above systems are divided into two major aspects of electrical and mechanical refrigeration. The following describes 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 integrated test chamber. In general, the refrigeration methods of the test chamber are mechanical refrigeration and auxiliary liquid nitrogen refrigeration. The mechanical refrigeration uses vapor compression refrigeration. They are mainly composed of a compressor, a condenser, a throttle mechanism and an evaporator. Due to the low temperature of our test To achieve -55 ℃, single-stage cooling is difficult to meet the requirements, so the cooling method of the test chamber generally uses cascade cooling. The refrigeration system of the constant temperature and humidity box 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 part absorbs the heat from the refrigerant in the low temperature part and vaporizes; the evaporation of the refrigerant in the low temperature part absorbs heat from the object to be cooled (air in the test chamber) to obtain the cooling capacity. The high temperature part and the low temperature part are connected by an evaporative condenser, which is both the condenser of the high temperature part and the condenser of the low temperature part. The high temperature part of the STH series test box uses medium temperature refrigerant, and the low temperature part of the refrigerant uses low temperature refrigerant. The temperature in the box can reach -70-150 ℃.
2.2 Heating system: The heating system of the test chamber is relatively simple compared to the refrigeration system. It is mainly composed of high-power resistance wire. Due to the large heating rate required by the test box, the power of the heating system of the test box is relatively large, and a heater is also provided on the bottom plate of the test box.
2.3 Control system: The control system is the core of the comprehensive test box, which determines the important indicators such as the heating rate and accuracy of the test box. At present, most of the controllers of the test chamber adopt PID control, and a few adopt PID and fuzzy control. Since the control system basically belongs to the category of software, and this part is generally used, there will be no problems.
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 for humidification. This humidification method has a high humidification capacity, fast speed, and sensitive humidification control, and it is easy to realize forced humidification especially when the temperature is lowered.
There are two ways to dehumidify the test box: mechanical refrigeration dehumidification and dry dehumidification. The dehumidification principle of mechanical refrigeration dehumidification is to cool the air below the dew point temperature, so that water vapor larger than the saturated moisture content is condensed and precipitated, which reduces the humidity. Dryer dehumidification is to use the air pump to draw out the air in the test box, and inject the dry air, and at the same time send the humid air into the recyclable drying to dry, and then send it into the test box after drying, so repeat the cycle to dehumidify . At present, most comprehensive test chambers adopt the former dehumidification method, and the latter dehumidification method can make the dew point temperature reach below 0 ℃. Suitable for occasions with special requirements, but the cost is more expensive.
2.5 Sensor system: The sensors in the test chamber are mainly temperature and humidity sensors. Platinum sensors and thermocouples are mostly used in temperature sensors. There are two methods for measuring humidity: the dry and wet bulb thermometer method and the solid-state electronic sensor direct measurement method. Because the measurement accuracy of the wet and dry bulb method is not high, the current test box is gradually replacing the wet and dry bulb with a solid-state sensor to measure the humidity.
2.6 Air circulation system: The air circulation system generally consists of a centrifugal fan and a motor that drives its operation. It provides circulation of air in the test chamber.
In summary, only by thoroughly understanding the working principle and working process of the test chamber can the problems arising during the operation of the test chamber be resolved quickly. Hope this article can be helpful to the personnel engaged in environmental equipment management, operation and maintenance. Jointly promote the development of China's environmental engineering.
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