【作者】 赵伟国；

【导师】 宋执环； 梁国伟；

【作者基本信息】 浙江大学 ， 控制科学与工程， 2009， 博士

【摘要】 随着工业过程自动化水平的不断提高,人们对流量测量的要求越来越高。流量测量作为一项复杂的技术,需要根据被测流体的种类,流动状况以及测量的场合等条件来研究相应的测量方法。热式流量测量方法是一种基于热传递原理的直接式质量流量测量方法,以压损低、量程范围大、精度高等优点而得到广泛的应用,但在介质变化、大管径、不均匀流场等情况还有待进一步完善。本文以热式流量测量方法为基础,深入研究了气体质量流量的测量技术。在单传感器气体质量流量测量方面,针对现有温度补偿电路的缺点,提出了基于温补型热膜探头和温控型铂电阻的热式气体流量测量方法。针对单传感器气体测量中因管径增大而导致测量精度下降的问题,提出了多传感器信息融合的热式气体流量测量方法,并研制了基于ARM处理器的多传感器气体流量样机。在不规则管径的流场测量中,管内流速分布不均匀,从而影响流量测量的精度,针对这一问题,提出了基于GA和LS-SVM的热式气体质量流量测量方法。本文的主要工作和创新点如下:1)针对热式流量传感器的温度补偿元件非线性,以及传感器的输出电压与测量元件的电阻有关,从而导致测量精度较差的问题,提出了温补型的单传感器气体流量测量方法。该方法采用一种将测量电阻和温度补偿电阻集成于同一基片上的热膜探头作为传感元件,通过在不同温度和电流下进行了温度特性的实验研究,确定了热膜探头的工作电流。然后分析了测量电阻和温度补偿电阻在测量电路中的关系,设计了一种新型气体流量测量电路。最后通过实验数据建立了测量模型。实验结果表明该流量测量方法对提高气体流量测量的精度和一致性是有效的。2)针对热式流量传感器在流量测量中需要外部增加温度补偿电路,传感器补偿过程操作繁琐、耗时,而且补偿效果较差的问题,提出了一种温控型的单传感器气体流量测量方法。采用单一铂电阻PT20作为测量元件,在无额外补偿电路的情况下,通过设计铂电阻的温度控制算法,使铂电阻工作在两个不同的设定温度,从而由铂电阻的输出电压计算出气体的流量,消去了气体温度对测量的影响,实现了气体流量的测量以及温度补偿。实验表明该方法提高了测量精度。3)针对单传感器气体测量中测量精度不高的问题,提出了基于多传感器信息融合的热式气体流量测量方法。采用对数线性法将4个铂膜电阻PT20分布于测量管道内的不同位置,用于测量气体的流量。按照流体流速分布的特点,提出了基于流速相对距离的数据剔除方法。然后对4个传感器的测量结果采用方差最小的加权融合算法,计算出气体的质量流量。温度融合算法采用分析校正方法,对流量进行温度修正。4)工业管道的不规则引起了管内流速分布的紊乱,而流速分布是影响流量测量的主要因素。针对上述问题,提出了基于LS-SVM的热式气体质量流量测量方法。采用4个热式流量传感器,分别获取管道中不同位置的气体流量。通过流量标定实验,获得不同质量流量下测量管道内4个传感器的电压数据。然后应用GA和LS-SVM算法建立了流量测量模型,实现了不对称流场分布的流量测量。实验结果表明该方法是有效的。5)在多传感器融合的热式气体质量流量测量方法的基础上,设计了基于ARM处理器的多传感器气体质量流量仪样机。整个样机的设计考虑了仪表的扩展性和可靠性。更多还原

【Abstract】 With the development of automation in industrial process, the demand for flow measurement increase.As a complicated technology,it need to study the measurement according to the fluid’s variety, flow state and application.Thermal mass flow measurement is based on heat transfer principle. Although the measurement has some advantages such as low press loss, large dynamic range and high preicison in practical application, it still has some limits. Study should be done to it closer in various conditions, large pipeline and disoder flow field.Study on the thermal gas mass flow measurement was proposed in the dissertation. When single sensor was used, the measurements based on temperature compensation and temperature control were introduced in order to overcome the shortages of the conventional temperature compensation. With the increment of the pipeline ,the multi-sensor fusion measurement and instrument were designed to solve the single gas flow measurement. In the disorder flow field resulted from the irregular pipeline, the measurement based on GA and LS-SVM was presented to improve the the precison.The main work and contributions are as follows:1) As the compensation resistor is non-linear and the output voltage of the sensor is related with the sensing resistor,the measurement is not accurate. The single sensor measurement based on temperature compensation was proposed. The sensing element was a probe made up of sensing resistor and compensation resistor. Firstly, the operation current of the probe was determined by study of the temperature characteristics at different surrounding temperatures and various currents. Then, the relationship between the sensing resistor and the compensation resistor on the probe was analyzed. The new sensor circuit with the function of temperature compensation was developed to decrease the influence of the surrounding temperature. Finally, the measurement model of the flow measurment was established according to the data from the experiments. The research results showed that the measurement have good consistency and high accuracy.2) As the conventional constant temperature compensation employs an additional circuit, the compensation process is complex and cann’t improve the result greatly.The single sensor measurement which used temperature control was proposed.The sensing element was platinum resistor PT20. Without the other compensation circuit, the constant temperature algorithm was designed to control the resistor at two different temperatures, and the gas flowrate was obtained from the output voltage of the sensor. The research results showed that the measurement can improve the accuracy.3) A multi-sensor measurement was introduced in order to solve the problem of the single sensor flow measurement. The four platinum resistors PT20 were distributed in pipeline according to the Log-linear method. The data elimination method was adopted based on the fluid flow distribution. The least weighted data fusion algorithm was designed and the mass flow was obtained. The temperature fusion corrected the mass flow using the math correcting method.4) As the disorder flow field resulted from the irregular pipeline influenced the flow measurement, the method based on LS-SVM was proposed for the gas mass flow measurement. Four thermal flow sensors were distributed in the pipeline in order to acquire the flowrate of different characteristic point. Through the calibration test, the voltages of the sensors were obtained at different mass flowrate. From these data, the gas mass flow model was established based on GA and LS-SVM. In the measurement process, the mass flow was computed using the model. The experimental reseach showed the mesurement was valid.5) Based on the multi-sensor mass flow measurement, the gas flow instrument using ARM was developed. The expansibility and reliability of instrument were considerated.更多还原