Discussion on humidity measurement method of small constant temperature and humidity box
Common humidity measurement methods include: dry wet ball method, dynamic method, static method and electronic sensor method.
1. Wet and dry bulb method
The dry wet bulb method is a direct method, which uses the dry wet bulb equation to convert the humidity value, and this equation is conditional: that is, the wind speed around the wet bulb must reach more than 2.5m/s. The common dry and wet bulb thermometer simplifies this condition, so its accuracy is only 5~7%rh, and the dry and wet bulb does not belong to the static method. Don't frugally think that just advancing the measurement accuracy of two thermometers is advancing the measurement accuracy of the hygrometer.
2. Dynamic method:
According to the thermodynamic P, V, t balance principle, the balance time is long, and the split flow method is based on the accurate mixing of moisture and dry air. Due to the use of modern measurement and control methods, these equipment can be made quite precise, but because the equipment is complex, expensive, time-consuming and labor-consuming, it is mainly used for scale measurement, and its measurement accuracy can reach more than ± 2% RH.
3. Static method
Saturated salt method is a common method in humidity measurement, which is simple and easy. However, the saturated salt method has strict requirements for the balance of liquid and gas phases, and the constant temperature and humidity test chamber has high requirements for the stability of the ambient temperature. It requires a long time to balance when used, and the low humidity point requires longer. Especially when the difference between the indoor humidity and the humidity in the bottle is large, it needs to be balanced for 6~8 hours each time.
4. Electronic humidity sensor method
Electronic humidity sensor products and humidity measurement belong to the occupations developed in the 1990s. In recent years, great progress has been made in the research and development of humidity sensors at home and abroad. The sensor of the walk-in constant temperature and humidity test chamber is developing rapidly from the frugal humidity sensor to the direction of integration, intelligence and multi parameter detection, which creates favorable conditions for the development of a new generation of humidity measurement and control system and advances the humidity measurement skills to a new level.