The constant temperature and humidity test chamber is composed of a refrigeration system, a heating system, a control system, a temperature system, an air circulation system, and a sensor system.
Refrigeration system: It 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 compressors, condensers, throttling mechanisms and evaporators. The temperature and low temperature must reach -55 ℃, single-stage refrigeration is difficult to meet the requirements, so the cooling method of the test chamber generally uses cascade refrigeration. The refrigeration system of the constant temperature and humidity test chamber environmental test box produced by our company is composed of two parts, called high temperature part and low temperature part, each part is a relatively independent refrigeration system.
High temperature system: The evaporation of the refrigerant 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 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 TMJ 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 ℃.
Control system: It 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 of the constant temperature oscillator basically belongs to the category of software, and this part is generally used, there will be no problems.
Heating system: Relative to the cooling system, it is relatively simple. 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.
Humidification and dehumidification system: The temperature system of the constant temperature and humidity test chamber 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.
Sensor part: The sensors of the constant temperature and humidity test box 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. Great progress has been made in the field of humidity sensor research at home and abroad. Humidity sensors are rapidly developing from simple moisture-sensitive components to integrated, intelligent, and 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. Functional components of constant temperature and humidity test chamber http: //
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