How to measure humidity in an environmental Test Chamber?

Environmental Test Chamber refers to equipment that can simulate environmental factors, mainly referring to temperature, humidity, light, rain, sand and other equipment. Among them, the equipment that needs to control humidity is a constant temperature and humidity Test Chamber. The humidity in the environmental Test Chamber can be controlled independently within a certain range. For example, the humidity of the constant temperature and humidity Test Chamber can be controlled at about 20%~98%RH. How is the humidity of the environmental Test Chamber measured?

First of all, let's understand the definition of humidity. Humidity refers to the amount of water vapor in the air, and it is also a physical standard to measure the degree of humidity. The humidity we refer to in life is relative humidity, generally expressed in %RH (relative humidity). The professional term is the percentage of the water vapor pressure in the gas to the saturated water vapor pressure of the gas. It is mainly used to indicate the degree of saturation of water vapor.

In the process of measuring humidity, people have continuously invented and adopted a variety of methods, mainly telescopic humidity measurement, evaporative humidity measurement (wet and dry bulb humidity measurement), dew point humidity measurement, electronic humidity measurement, etc. Among them, humidity measurement is more accurate and free from environmental interference. Most precision equipment uses both psychrometer and electronic humidity measurements.

The humidity measurement of the environmental Test Chamber is also based on these humidity measurement methods, mainly using the wet and dry bulb test method and the electronic humidity sensor test method. Among them, the accuracy of the electronic humidity measurement method is higher, but the probability of being interfered by impurities and oils in the air is higher, which will interfere with the humidity test. Because the sensor of the electronic humidity measurement method needs to be tested in a pure environment, and the items or water sources in the test box will inevitably contain impurities, so in addition to being able to accurately control the humidity in the initial test, in the long run, the electronic humidity measurement method accuracy. Lowering the humidity measurement results in larger deviations.

Compared with the electronic humidity sensor, the dry and wet bulb test method is more practical, less susceptible to environmental influences, and will not cause aging. Although the accuracy is not as good as electronic humidity measurement, it can also meet the requirements of use. Maintenance of the wet bulb hygrometry method is very simple. In actual use, you only need to add water to the wet bulb regularly and replace the wet bulb gauze. Therefore, it is not difficult to understand why the mainstream temperature and humidity Test Chambers still use the wet and dry bulb method to measure humidity instead of electronic humidity sensors.