Common humidity measurement methods for constant temperature and humidity testing machines

Common humidity measurement methods are: dynamic method (double pressure method, dual temperature method, split flow method), static method (saturated salt method, sulfuric acid method), dew point method, dry and wet bulb method and electronic sensor method.
① The dual pressure method and dual temperature method are based on the thermodynamics P, V, T balance principle, and the balance time is longer, and the split method is based on the precise mixing of moisture and dry air. Due to the modern measurement and control methods, these equipment can be made quite precise, but because the equipment is complex, expensive, and time-consuming and labor-intensive, it is mainly used for standard measurement, and its measurement accuracy can reach ±2%RH.
②The saturated salt method in the static method is the most common method in humidity measurement and is simple and easy to implement. However, the saturated salt method has strict requirements for the balance of liquid and gas phases, and higher requirements for the stability of the ambient temperature. It requires a long time to balance, 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 it is turned on.
③The dew point method measures the temperature when the humid air reaches saturation, which is a direct result of thermodynamics, with high accuracy and wide measurement range. The accuracy of the precision dew point meter for measurement can reach ±0.2℃ or even higher. However, the cold mirror dew point meter using modern photo-electric principle is expensive, and it is often used in conjunction with a standard humidity generator.
④ Wet and dry bulb method, which is a method of measuring humidity invented in the 18th century. It has a long history and is most commonly used. The wet and dry bulb method is an indirect method. It uses the wet and dry bulb equation to calculate the humidity value, and this equation is conditional: that is, the wind speed near the wet bulb must reach 2.5m/s or more. Ordinary dry and wet bulb thermometers simplify this condition, so its accuracy is only 5~7% RH, and the dry and wet bulb is not a static method. Don’t simply think that as long as the measurement accuracy of two thermometers is increased, the humidity is increased. The measurement accuracy of the meter.
⑤Electronic humidity sensor method
Electronic humidity sensor products and humidity measurement belong to the industry that emerged in the 1990s. In recent years, domestic and foreign humidity sensor research and development have made great progress. Humidity sensors are developing rapidly from simple humidity sensors to integrated, intelligent, and multi-parameter detection, creating favorable conditions for the development of a new generation of humidity measurement and control systems, and also improving humidity measurement technology to a new level



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