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Working principle of Qingdao constant temperature and humidity machine

Qingdao constant temperature and humidity machineThe working principle



Constant temperature and humidity machine by the refrigeration system, heating system, control system, humidity system, air supply system, and sensor system, the above system is divided into electrical and mechanical refrigeration two major aspects. The working principle and working process of several major systems are described below.


1. Refrigeration system: Refrigeration system is one of the key parts of constant temperature and humidity machine. Generally speaking, refrigeration methods are mechanical refrigeration and auxiliary liquid nitrogen refrigeration, mechanical refrigeration using steam compression refrigeration, they are mainly composed of compressors, condensers, throttling mechanism and evaporator. If we test the temperature at low temperatures to reach 55 ℃, single-stage refrigeration is difficult to meet the requirements, so constant temperature and humidity machine refrigeration methods generally use laminated refrigeration. The refrigeration system of constant temperature and humidity machine consists of two parts, which are called high temperature part and low temperature part respectively, each part is a relatively independent refrigeration system. The evaporation of refrigerants in the high temperature part is vaporized by the heat of the refrigerant from the low temperature part, while the evaporation of the cryogenic part of the refrigerant absorbs heat from the cooled object (the air in the test machine) to obtain the cold quantity. Between the high temperature part and the low temperature part is connected with a evaporation condenser, which is not only the condenser of the high temperature part, but also the condenser of the low temperature part.


2. Heating system: Heating system relative to the refrigeration system, is relatively simple. It mainly has high-power resistance wire composition, because the test requirements of the heating rate is large, so the heating system power is relatively large, and in the test machine bottom plate also has a heater.


3. Control system: The control system is the core of the comprehensive test box, which determines the heating rate of the test machine, accuracy and other important indicators. Most of the controller of the test machine adopts PID control, and there are also a few parts that use the control mode of PID and fuzzy control phase combination. Because the control system basically belongs to the scope of the software, and this part in the use of the process, generally do not appear problems.


4. Humidity system: The temperature system is divided into two subsystems of humidification and dehumidification. Humidification method generally uses steam Humidification method, the low pressure steam directly injected into the test space humidification. This humidification method humidification capacity, fast, humidification control sensitive, especially in cooling easy to achieve forced humidification.


There are two kinds of dehumidification methods: mechanical refrigeration dehumidification and drying 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 condenses and precipitate, thus reducing the humidity. Dryer dehumidification is the use of air pump will be the gas in the test box extraction, and the dry air injection, while the wet air into recyclable drying for drying, after drying and into the test box, so repeated circulation for dehumidification. Now most of the comprehensive test box using the former Dehumidification method method, the latter one of the dehumidification methods, can make the dew point temperature reached 0 ℃ a bit. Suitable for occasions with special requirements, but the cost is more expensive.


5. Sensor System: Sensors are mainly temperature and humidity sensors. Temperature sensors are used in platinum groups and thermocouples. There are two methods of measuring humidity: the wet and dry ball thermometer method and the solid-state electronic sensor direct measurement method. Because the measurement accuracy of dry and wet ball method is not high, the current constant temperature and humidity box is gradually taking the solid state sensor instead of dry and wet ball to measure the humidity.


6. Air Supply Circulation System: the airborne circulation system generally has a centrifugal fan and the motor that drives its operation. It provides a cycle of air in the test machine.