Design Of High Accuracy Heated Twin Humidity Sensor

Humidity is a type of fundamental information of weather forecasting and atmospheric monitoring. In order to avoid the influence of snow and rain,a humidity sensor is commonly installed in a radiation shield . However, the water drop evaporation on the surface of the radiation shield can increase the humidity of the air around the sensor during the process of rainfall and after rainfall, which cause humidity measurement data higher than the actual air humidity. In addition,a sensor exposed at a high humidity environment in the long term will damage the sensor. In order to eliminate the effect of wet error,a heated twin humidity sensor system is proposed, which can reduce the wet error by heating the rain cap alternately .A rain cap is proposed for this double heated humidity sensor system. A computational fluid dynamic (CFD) method is implemented to obtain the characteristic parameters of the rain cap. To keep continuous measurement, a alternate heating method is used to heat the rain caps. Low noise and high linearity measurement of the temperature and humidity was achieved by using a 24-bit analog-digital converter and a capacitance-to-digital converter. An Optidew Vision chilled mirror dew point hygrometer worked as a reference,while a genetic algorithm was constructed to correct the temperature drift. All collected data will be sent to the host computer interface display.The relative humidity accuracy can reach ± 1%RH by using a genetic algorithm to fitting the sensor. The water wet error can be reduced from 10%RH to ± 1%RH in 6 minutes. Compared to the traditional humidity sensor,the heated twin humidity sensor not only has the characteristics of high-accuracy and rapid response, but also can realize the continuous measurement of relative humidity. It may be helpful to provide a relatively accurate air temperature measurement result.