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Working principle of constant temperature and humidity test chamber

The temperature and humidity test chamber is composed of a refrigeration system, a heating system, a control system, a humidity system, a supply air circulation system, and a sensor system. The above systems belong to two major aspects of electrical and mechanical refrigeration. The working principle and working process of several main systems are described below.

1. Refrigeration system: The refrigeration system is one of the key parts of the constant temperature and humidity machine. Generally speaking, the refrigeration methods are mechanical refrigeration and auxiliary liquid nitrogen refrigeration. Mechanical refrigeration uses vapor compression refrigeration. They are mainly composed of a compressor, a condenser, a throttling mechanism and an evaporator. If the temperature of our test is to reach -55 ° C, single-stage refrigeration is difficult to meet the requirements, so the refrigeration method of the constant temperature and humidity machine generally uses cascade refrigeration. The refrigeration system of a constant temperature and humidity machine is composed 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 machine) to obtain the cooling capacity. The high-temperature part and the low-temperature part are connected by an evaporative condenser, which is both a condenser of the high-temperature part and a condenser of the low-temperature part.

2. Heating system: Compared with the refrigeration system, the heating system is relatively simple. It is mainly composed of high-power resistance wires. Due to the large heating rate required for the test, the power of the heating system is relatively large, and a heater is also provided on the bottom plate of the testing machine.

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 testing machine. Most of the tester's controllers use PID control, and a small number of them use a combination of PID and fuzzy control. Because the control system basically belongs to the category of software, and in the process of using this part, generally no problems occur.

4. Humidity system: The temperature system is divided into two subsystems: humidification and dehumidification.

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