The high and low temperature damp heat box refers to a test box that can simultaneously apply temperature and humidity stress. With the needs of 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.
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.
1. Control system
The control system is the core of the high and low temperature test chamber, which determines the temperature rise rate, accuracy and other important indicators of the test chamber. At present, most of the controllers of the test chamber adopt PID control, and a few adopt PID and fuzzy control. PID controllers are generally used without problems.
2. Heating system
The heating system of the high and low temperature damp heat 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.
3. Refrigeration system
The refrigeration system is one of the key parts of the high and low temperature damp heat test chamber. In general, the refrigeration methods of high and low temperature test chambers are mechanical refrigeration and auxiliary liquid nitrogen refrigeration. Mechanical refrigeration uses vapor compression refrigeration. They are mainly composed of compressor, condenser, throttle mechanism and evaporator. Due to the temperature of the test The low temperature must reach -55 ℃, and it is difficult for single-stage refrigeration to meet the requirements. Therefore, the refrigeration method of the high and low temperature test chamber generally adopts cascade refrigeration. 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 test box uses medium-temperature refrigerant HP80, and the low-temperature part uses low-temperature refrigerant R23 (environmental protection type). The temperature in the box can reach -70 ℃. The high and low temperature test chamber only starts R404A (energy saving and consumption reduction) when dehumidifying, and starts R404A and R23 when the temperature is reduced.
Fourth, the sensor system
The sensors in the high and low temperature 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. Due to the low measurement accuracy of the wet and dry bulb method, the high and low temperature damp heat test chamber produced by Wuhan Shangshi Test Equipment Co., Ltd. is gradually replacing the wet and dry bulb with a solid-state sensor to measure the humidity.
5. Humidity system
The humidity system is divided into two subsystems: humidification and dehumidification.
1. The humidification method 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.
2. There are two dehumidification methods: mechanical refrigeration dehumidification and dry dehumidification.
a. 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. Most of the test boxes on the market use this dehumidification method.
b. The desiccant dryer uses an air pump to draw out the air in the test box and inject the dry air. At the same time, the wet air is sent to the recyclable drying for drying. After drying, it is sent to the test box again. 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. It is recommended that customers require manufacturers to equip suitable dehumidification methods according to company budgets and actual test needs.
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 box.
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