The constant temperature and humidity test chamber supports its work by six systems, including refrigeration system, heating system, and control system. The constant temperature and humidity test chamber test equipment has the functions of simulating high temperature and low temperature, temperature and humidity in the natural environment and other climate functions. Therefore, the normal operation of the six major systems is indispensable. The following is a detailed technical explanation of the six systems of constant temperature and humidity chamber we analyzed, please refer to customers for reference.
1. Control system of constant temperature and humidity chamber
The control system is the core of the comprehensive test chamber, which determines the heating rate, accuracy and other important indicators of the test chamber.
At present, most of the controllers of constant temperature and humidity chamber use PID control, and a few use the combination of PID and fuzzy control. Because the control system basically belongs to the category of software, and this part generally does not have problems during use.
2. Humidity system of constant temperature and humidity chamber
The temperature system is divided into two subsystems, humidification and dehumidification.
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 high humidification ability, high speed, and sensitive humidification control, and is easy to achieve forced humidification especially when cooling down.
There are two dehumidification methods: 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 the water vapor greater than the saturated moisture content is condensed and precipitated, thus reducing the humidity. Dehumidification of the dryer is to use the air pump to extract the air in the test chamber and inject the dry air. At the same time, the humid air is sent to a recyclable dryer for drying, and after drying, it is sent to the test chamber, and the dehumidification is repeated in this cycle.
At present, most comprehensive test chambers use the former dehumidification method and the latter dehumidification method, which can make the dew point temperature below 0 °C. It is suitable for occasions with special requirements, but the cost is more expensive.
3. Refrigeration system of constant temperature and humidity chamber
The refrigeration system is one of the key parts of the comprehensive test chamber. Generally speaking, the refrigeration methods are mechanical refrigeration and auxiliary liquid nitrogen refrigeration. The mechanical refrigeration adopts vapor compression refrigeration, which is mainly composed of a compressor, a condenser, a throttling mechanism and an evaporator.
If the low temperature of our test is to reach -55°C, it is difficult to meet the requirements of single-machine refrigeration. Therefore, the refrigeration method of constant temperature and humidity chamber generally adopts cascade refrigeration.
The refrigeration system of the constant temperature and humidity chamber consists of two parts, called the high temperature part and the low temperature part, and each part is a relatively independent refrigeration system. The evaporation of the refrigerant in the high temperature part absorbs the heat of the refrigerant from the low temperature part and evaporates; the evaporation of the refrigerant in the low temperature part absorbs heat from the object to be cooled (the 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.
4. Heating system of constant temperature and humidity chamber
The heating system of the test chamber is relatively simple compared to the cooling system. It is mainly composed of high-power resistance wires. Due to the large heating rate required by the test chamber, the heating system power of the test chamber is relatively large, and the bottom plate of the test chamber is also equipped with a heater.
5. Sensor system of constant temperature and humidity chamber
The sensors are mainly temperature and humidity sensors. The most commonly used temperature sensors are platinum resistance and thermocouples.
There are two kinds of humidity measurement methods: dry and wet bulb thermometer method and solid-state electronic sensor direct measurement method. Due to the low measurement accuracy of the wet and dry bulb method, the current constant temperature and humidity chamber is gradually replacing the wet and dry bulb with solid-state sensors to measure humidity.
6. Air supply circulation system of constant temperature and humidity chamber
The air circulation system generally consists of a centrifugal fan and a motor that drives its operation. It provides the circulation of air in the test chamber.