电容式湿度传感器在汽–水系统中的静态响应特性分析

电介质的介电理论表明,同一压力和温度下的饱和水和饱和蒸汽,介电常数相差较大。基于此理论,该文利用电容法进行湿度标定实验研究,及对电容式湿度测量仪的静态特性进行分析。实验中采用向空气中喷雾化水滴的方式来模拟湿蒸汽,应用所设计的多电极同轴圆筒形电容传感器测量蒸汽湿度。测量电路以电容为测量参数,以电压为输出信号,通过输出与电容值成正比的电压值的大小来反应电容量的大小。实验结果表明,传感器电容值不随空气流量的增加而变化,其稳定性较好;在实验范围内该传感器的灵敏度不是一个定值,最大灵敏度为0.045nF/1%;湿度越小该传感器的可重复性越好,随着湿度的增加,其可重复性概率逐渐减小,其可重复性指标值为3.68%;随着汽流湿度的逐渐增加,传感器电容逐渐增大,湿度在小于12%的范围内,其线性度较差,而湿度范围在3%~8%时,其线性度较好。

Analysis of Static Response Performance of Capacitance Sensors for Measuring Humidity of Wet Steam in Air and Water Systems

From the dielectric theory,it could be known that the static dielectric constant of the water is very different from the steam on the same pressure and temperature.Based on this fact,steam humidity was measured via capacitance in an experiment.For the static dielectric constant of the steam and air is similar,the method that using nozzle to spray water into air was employed to simulate the flowing wet steam.A novel coaxial cylindrical capacitance sensor was designed to measure the steam wetness,and one measuring circuit was suggest,which used the voltage as the export signal.The experiment results shows that export of the measuring circuit is a constant with the changing of air flow rates,the stability of the capacitance sensor is well;the sensitivity of the sensor is not a constant,the max value of sensitivity is 0.045nF/%;the repeatability is decreasing with the steam humidity increasing,the max repeatability is 3.68%;the capacitance is increasing with the steam humidity increasing,the relationship between wetness and capacitance variety is nonlinear if the humidity is less than 12%,and relationship between wetness and capacitance is linear if humidity is between 3%-8%.