谐振腔测量蒸汽湿度不确定性分析改进

分析了现有的采用微波谐振腔测湿理论计算水蒸汽介电常数公式的不确定性,并在微扰理论的基础上,根据谐振时电磁场储能相等的原理,推导了工程应用计算公式。为了补偿在实测时由于温度的变化导致的计算公式中谐振腔基准频率偏移,根据在体膨胀系数定义和线膨胀系数定义下计算结果应一致的规则,建立了热膨胀模型。对三种测湿计算公式产生的误差进行了分析比较,给出了理论计算的不确定度比较曲线。结果表明,采用本文提出的计算公式,经补偿可以提高测量精度三倍甚至以上。

Error analysis and improvement of microwave resonant cavity method in steam turbine exhaust wetness measurement

The uncertainty of existing formulas used to theoretical calculate the dielectric constant of wet steam is analyzed,then based on perturbation method and the electric field energy equals to the magnetic field energy when resonance,a wetness formula used in engineering is deduced.In order to compensate the excursion of resonant frequency generated by the change of temperature,and on the principle that the calculate result should be exactly equal whatever using the definition of coefficient of volume expansion or linear expansion,a model of cavity heat expanding is introduced.three wetness formulas' errors are analyzed and compared,then the theoretical uncertainty comparison curves are generated.Results show that according to theoretical calculate data,using the formula this paper introduced can increase the measurement precision in three times after compensate.