The working principle of constant temperature humidity chamber

The working principle of constant temperature humidity chamber

Constant temperature humidity chamber is a commonly used testing machine products, mainly for electronic parts, industrial materials, finished products in the development, production and inspection of each link of the test to provide constant humidity and heat, complex high and low temperature alternating test environment and test conditions.

Working principle of constant temperature and humidity box

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

  1. Refrigeration system: Refrigeration system is one of the key parts of constant temperature and humidity box.Generally speaking, refrigeration methods are mechanical refrigeration and auxiliary liquid nitrogen refrigeration. Mechanical refrigeration adopts steam compression refrigeration, which is mainly composed of compressor, condenser, throttling mechanism and evaporator.If the low temperature of our test should reach -55℃, single-stage refrigeration is difficult to meet the requirements, so the refrigeration method of constant temperature and humidity machine is generally used in the overlapping refrigeration.The refrigeration system of the constant temperature and humidity box is composed of two parts, respectively called the high temperature part and the low temperature part, 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 vaporizes;The evaporation of the low-temperature part of the refrigerant absorbs heat from the cooled object (the air in the testing machine) to obtain the cold amount.An evaporative condenser is used between the high temperature part and the low temperature part. It is both the condenser of the high temperature part and the condenser of the low temperature part.
  2. Heating system: Heating system is relatively simple compared with refrigeration system.It is mainly composed of high-power resistance wire, due to the test requirements of the heating rate is large, so the heating system power is relatively large, and in the bottom plate of the testing machine is also equipped with a heater.
  3. Control system: the control system is the core of the comprehensive test chamber, which determines the temperature rising rate, precision and other important indicators of the testing machine.Now the controller of the testing machine mostly uses PID control, there are a few use PID and fuzzy control combination of control mode.Because the control system basically belongs to the category of software, and this part in the use of the process, generally will not appear a problem.
  4. Humidity system: the temperature system is divided into two subsystems: humidification and dehumidification.

Humidification method generally adopts steam humidification method, that is, low pressure steam is directly injected into the test space humidification.This humidification method has the advantages of high humidification speed and sensitive humidification control. It is easy to realize 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 saturation moisture content is condensed out, so as to reduce the humidity.Dehumidifier is to use the air pump to extract the air in the test box, and the dry air is injected, at the same time, the wet air is sent into the recycled dry for drying, and after drying, it is sent into the test box, so repeated circulation for dehumidification.Now most of the comprehensive test chamber using the former dehumidification method, the latter dehumidification method, can make the dew point temperature up to 0℃.Suitable for occasions with special requirements, but the cost is more expensive.

5 sensor system: sensors are mainly temperature and humidity sensors.Platinum group and thermocouple are the most commonly used temperature sensors.There are two kinds of humidity measurement methods: dry and wet bulb thermometer and solid state electronic sensor direct measurement method.Because the measurement accuracy of dry and wet bulb method is not high, now the constant temperature and humidity box is gradually replacing the dry and wet bulb with solid-state sensor to measure humidity.

  1. Air supply and circulation system: the air circulation system is generally composed of centrifugal fans and motors that drive its operation.It provides air circulation within the testing machine.