Temperature and humidity meter common measurement methods

From the principle of humidity measurement of temperature and humidity meter division of twenty or thirty. But the humidity measurement has always been one of the world famous problem in the metrology area. A seemingly simple values, underneath it, physical - involves quite complicated Chemical theoretical analysis and calculation, ChuSheZhe may be ignored in humidity measurement must pay attention to many factors, thus influence on the reasonable use of the sensor. Dynamic method (common humidity measurements are: Dual pressure method, dual temperature method, the shunt method) , a static method ( Saturated salt method, sulfuric acid method) , dew point method, wet and dry bulb and electronic sensor method. (1) dual pressure method, dual temperature method, is based on the thermodynamics of P, V, T balance principle, balance time is longer, shunt method is based on the absolute humidity and precise mixture of absolute dry air. The adoption of modern measurement and control means, these devices can be quite precise, but due to the equipment complex, expensive, operation time consuming work, mainly for the use of standard measurement, the measurement precision can reach & plusmn; More than 2% RH. (2) saturated salt method, the static method is the most common method of humidity measurement, simple and feasible. But the saturated salt law of liquid and gas two-phase equilibrium is strict, higher requirements on the stability of the environment temperature. Requirements to use for a long time to balance, low humidity point for longer. Especially in the indoor humidity and humidity difference is bigger, the bottle open all need to balance 6 ~ 8 hours at a time. (3) dew point method, wet air reaches saturation temperature is measured, is a direct result of the thermodynamics, high accuracy, wide measurement range. Measurement with a precision dew-point meter accuracy can reach & plusmn; 0. 2 ℃ or higher. But with modern - light Electrical principle of the cold mirror dew-point meter is expensive, and often standard humidity generator systems. (4) dry wet ball method, which is invented by wet method in the 18th century. With a long history, the most commonly used. Dry wet ball method is an indirect method, which use wet and dry bulb equation conversion humidity value, and this equation is conditional, namely wind speed near the wet bulb must reach 2. More than 5 m/s. Common use of dry wet bulb this condition is simplified, so its accuracy is only 5 ~ 7% RH, wet and dry bulb does not belong to the static method, don't simply think that as long as to improving the measuring accuracy of two thermometer is to improve the measurement precision hygrometer. (5) electronic humidity sensor method, electronic humidity sensor products belong to the rise of industry in the 90 s and humidity measurement, in recent years, both at home and abroad have made great progress in the field of research and development of humidity sensor. Moisture sensor is from simple moisture sensor to integration, intelligent, the direction of the rapid development of multi-parameter detection, for the development of a new generation of humidity measurement and control system has created favorable conditions, and to increase the humidity measurement technology to a new level.