The constant temperature and humidity test chamber is composed of control system, heating system and temperature system. These systems are respectively related to electrical and mechanical refrigeration. The following is a preliminary introduction to the principles and working processes of these systems.
The control system is the core of the comprehensive test chamber, which determines the important parameters such as the heating rate and accuracy of the test chamber. Most of the controllers in the test box now use PID control, and a small number of control modes using PID and fuzzy control are combined. Because the control system is basically in the category of software, and this part generally does not have problems during use.
Heating system: The heating system of the constant temperature and humidity test chamber is relatively simple compared to the refrigeration system. It mainly consists of high-power resistance wire. Because the heating rate required by the test box is large, the heating system power of the test box is relatively large. And there is also a heater on the bottom of the test box.
Temperature system: divided into two subsystems of humidification and dehumidification.
(1) Humidification: 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 to humidify. This humidification method has good humidification ability, high speed and sensitive humidification control (especially, it is easy to achieve forced humidification when cooling).
(2) Dehumidification: There are two dehumidification methods in the test chamber: mechanical refrigeration dehumidification and dry dehumidification.
The principle of dehumidification of mechanical refrigeration dehumidification is to cool the air below the dew point temperature, so that the water vapor larger than the saturated moisture content is condensed and precipitated, thus reducing the humidity; the dehumidification of the dryer is to use the air pump to extract the air in the test chamber, and the dry air is taken out. At the same time of injecting, the humid air is sent to the recyclable dry for drying, and then sent to the test chamber after drying (so repeated cycles for dehumidification). Now most of the comprehensive test chambers adopt the former dehumidification method, the latter The dehumidification method can make the dew point temperature reach 0 °C, which is suitable for occasions with special requirements (but the cost is more expensive).
The control system is the core of the comprehensive test chamber, which determines the important parameters such as the heating rate and accuracy of the test chamber. Most of the controllers in the test box now use PID control, and a small number of control modes using PID and fuzzy control are combined. Because the control system is basically in the category of software, and this part generally does not have problems during use.
Heating system: The heating system of the constant temperature and humidity test chamber is relatively simple compared to the refrigeration system. It mainly consists of high-power resistance wire. Because the heating rate required by the test box is large, the heating system power of the test box is relatively large. And there is also a heater on the bottom of the test box.
Temperature system: divided into two subsystems of humidification and dehumidification.
(1) Humidification: 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 to humidify. This humidification method has good humidification ability, high speed and sensitive humidification control (especially, it is easy to achieve forced humidification when cooling).
(2) Dehumidification: There are two dehumidification methods in the test chamber: mechanical refrigeration dehumidification and dry dehumidification.
The principle of dehumidification of mechanical refrigeration dehumidification is to cool the air below the dew point temperature, so that the water vapor larger than the saturated moisture content is condensed and precipitated, thus reducing the humidity; the dehumidification of the dryer is to use the air pump to extract the air in the test chamber, and the dry air is taken out. At the same time of injecting, the humid air is sent to the recyclable dry for drying, and then sent to the test chamber after drying (so repeated cycles for dehumidification). Now most of the comprehensive test chambers adopt the former dehumidification method, the latter The dehumidification method can make the dew point temperature reach 0 °C, which is suitable for occasions with special requirements (but the cost is more expensive).
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