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A hygrometer and humidity is defined in the metering law that humidity is defined as "; the amount of images state."; Humidity daily life within the meaning of relative humidity, represented by RH%. In sum, the gas (usually air) contained in the water vapor (water vapor pressure) and its percentage of air saturated water vapor (saturation vapor pressure) under the same circumstances. Humidity and life long before there is a close relationship, but with a number to indicate more difficult. For representation humidity have absolute humidity, relative humidity, dew point ratio, wet and dry gas (weight or volume) and so on. Second, humidity measurement and humidity measurement hygrometer from the principle of division two, thirty species. But humidity measurement has always been the field of metrology world famous one of the problems. A seemingly simple value, bottom up, involving very complex physics - Theoretical analysis and computational chemistry, kicking the tires may be overlooked by many factors must be noted in the humidity measurements, thus affecting the rational use of the sensor. Common humidity measurement methods are: dynamic method (dual pressure method, dual-temperature method, split method), a static method (saturated salt method, sulfuric acid), Dew Point, wet and dry bulb method and electronic sensor method. ① double pressure method, dual-temperature method is based on the thermodynamics longer P, V, T balance principle, equilibrium time, split method is based on the exact mix of absolute humidity and absolutely dry air. Thanks to modern measurement and control instruments, these devices can be done quite sophisticated, because equipment complex, expensive, time consuming and functioning, primarily as a standard measurement purposes, the measurement accuracy up to ± 2% RH or more. ② static method of saturated salt method, is the humidity measurement is the most common method, simple. But saturated saline solution method, gas two-phase equilibrium requires very strict, high stability requirements of the ambient temperature. With them a long time to balance requirements, low humidity require a longer point. In particular, the difference between the indoor humidity and the humidity of the bottle is large, a balance needs to turn on every 6 to 8 hours. ③ method is to measure the dew point temperature of moist air reaches saturation, it is a direct result of thermodynamics, high accuracy, wide measuring range. Precise dew point measurement accuracy by up to ± 0.2 ℃ or even higher. But with modern light - electricity principle of chilled mirror hygrometer is expensive, often supporting the use of standard humidity generator. ④ dry and wet bulb method, which is the measured wet method was invented in the 18th century. Long history, the most commonly used. Wet and dry bulb method is an indirect method, which uses the equation in terms of the wet and dry bulb humidity, and this equation is conditional: the wind speed near the wet-bulb necessary to achieve 2.5m / s or more. Common use of wet and dry bulb thermometer simplifies this condition, so its accuracy is only 5 ~ 7% RH, wet bulb does not belong to the static method, we do not simply believe that as long as the two thermometers improve measurement accuracy is equivalent to increase the humidity meter measurement accuracy. ⑤ electronic humidity sensor method electronic humidity sensors and humidity measurement industry belongs to rise in the 1990s, in recent years, at home and abroad in the humidity sensor research and development has made considerable progress. Humidity sensor is moving from simple humidity sensor to the integrated, intelligent, multi-parameter detection of the direction of rapid development, for the development of a new generation of humidity measurement and control system has created favorable conditions, but also the humidity measurement technology to a new level. Copyright? 2009 Xiamen Egret based Electronic Co. www.lujidz.com Min ICP No. 09034441 -2