Humidity sensor for radiosonde and its measuring circuit

Humidity sensors are easy to condense and have humidity fluctuation, moreover, their board distributed capacitances affect measurement results under a high altitude environment. Therefore, this paper proposes a sandwich plate capacitive humidity sensor integrated with a snake like platinum resistance heater and its prepared method. Then, it studies the measuring circuit for the sensor. The humidity sensor with heater was designed using Micro-electric-mechanic System(MEMS) technology, the temperature distribution of sensor surface was analyzed and the function relationship between environment temperature, heating power and heating temperature were obtained by using finite element analysis. To suppress the temperature and zero drifts effectively and reduce the influence of parasitic capacitance on measurement, a humidity measurement circuit based on the capacitor charging and comparative law was designed. The ground experimental results on the sensor show that the humidity sensitivity is about 2.3%RH·pF-1, hysteresis is about 0.7%F·S, and the repeatability is about 1.9%. Moreover, it gives the measurement uncertainty about 4%, time constance about 0.5 s. In conclusion, the humidity sensor and measurement circuit have good temperature stability, and is suitable for working at a low temperature correctly. ©, 2014, Chinese Academy of Sciences. All right reserved.