Common humidity measurement introduction

The common humidity measurement introduces the principle of humidity measurement is divided into two or thirty different. However, humidity measurement has always been one of the famous problems in the world metrology field. A seemingly simple magnitude, immersed in it, involves rather complex physico-chemical theoretical analysis and calculations. The beginner may ignore many of the factors that must be taken into account in the humidity measurement and thus affect the reasonable use of the sensor.
Common methods of humidity measurement include: dynamic method (double pressure method, dual temperature method, diverting method), static method (saturated salt method, sulfuric acid method), dew point method, wet and dry ball method and electronic sensor method.
1 The double pressure method and the double temperature method are based on the principle of thermodynamics P, V and T balance. The equilibrium time is long. The diversion method is based on the accurate mixing of absolute moisture and absolute dry air. Due to modern measurement and control methods, these equipments can be made very precise. However, due to the complicated and expensive equipment, the operation is time-consuming and labor-consuming. It is mainly used as a standard measurement, and its measurement accuracy can reach ±2% RH or more.
2 The saturated salt method in the static method is the most common method of humidity measurement and is simple and easy to implement. However, the saturated salt method has strict requirements on the balance between liquid and gas phases, and has a high requirement for the stability of the ambient temperature. Used to wait for a long time to balance, low humidity requirements longer. Especially when the humidity in the room and the difference in humidity inside the bottle are large, it takes 6 to 8 hours for each opening.
3 The dew point method measures the temperature when the humid air reaches saturation, and is a direct result of thermodynamics. It has high accuracy and wide measurement range. Precision dew point metering accuracy can reach ±0.2°C or even higher. However, the cold mirror type dew point meter using the modern light-electricity principle is expensive, and is often used together with a standard humidity generator.
4 Wet and dry ball method, this is the method of measuring humidity that was invented in the 18th century. Has a long history and is most commonly used. The wet and dry ball method is an indirect method that uses the wet-and-dry ball equation to calculate the humidity value. The equation is conditional: that is, the wind speed must be 2.5 m/s or more in the vicinity of the wet bulb. The commonly used wet and dry bulb thermometer simplifies this condition, so its accuracy is only 5 to 7% RH. Dry and wet bulbs do not belong to the static method. Do not simply think that increasing the measurement accuracy of two thermometers is equivalent to increasing the humidity. Accuracy of measurement.
5 Electronic Humidity Sensors Electronic Humidity Sensors and Humidity Measurements belong to the rising industries of the 1990s. In recent years, considerable progress has been made in the field of humidity sensor research and development at home and abroad. Humidity sensors are rapidly developing from simple moisture sensors to integrated, intelligent, multi-parameter detection, which has created favorable conditions for the development of a new generation of humidity measurement and control systems, and has also brought humidity measurement technology to a new level.

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