介电法结合称重法检测纸板微水分的实验研究

采用介电法可对绝缘纸板的微水分进行在线实时检测,称重法则可直观地了解纸板试样的水含量.两种方法结合可使介电法检测微水分实用化,利用实验系统,通过对绝缘纸板试样的介电参数及质量在干燥过程中的同步检测,可得出绝缘纸板试样的水质量分数及与其介电参数的关系.     

绝缘纸板干燥过程微水分检测机理与试验

绝缘纸板中的微水分对电力变压器的使用寿命有严重影响,因此,实时精确监测绝缘纸板微水分含量对于电力变压器的生产具有重要意义.由于绝缘纸板微水分含量的变化必然引起材料介电性能的变化,对介电性能进行检测即可有效检测微水分含量的变化.文中采用边缘场电容传感器技术研究绝缘纸板介电性能的变化过程.分析了频率对电容传感器检测信号的影响因素.通过对绝缘纸板的介电极化和介电损耗的研究,提出了频率对电信号影响的理论模型.根据试验数据和介电谱曲线,建立了无油绝缘纸板内的水分质量分数与复介电常数关系的数学模型.     

一种变压器绕组绝缘纸板微水分测量传感器

介绍一种测量微水分的电容式传感器,它利用同一平面上两平行电极形成的边缘电场感应被测纸板水分变化,体积小,灵敏度高,安装方便.由它构成的微水分测量系统,可以用于大型变压器绕组现场干燥过程中的绝缘纸板微水分检测.     

变压器绝缘纸板微水分在线检测研究

采用介电法与称重法对绝缘纸板在线干燥过程进行研究。对传感器测试信号与被测纸板水分质量分数之间的关系进行统计处理，建立相应的指数规律计算公式。并对层压纸板的水分扩散过程进行分析并进行相应的验证试验，结果表明在微水分含量的情况下，可用层压纸板局部区域的水分测量结果近似表示整体的水分质量分数。     

变压器绝缘纸板微水分在线监控系统

介绍一种绝缘纸板微水分检测系统，它可用于大型电力变压器器身整体干燥过程中绝缘纸板中水的质量分数的在线实时监控，专门设计的电容式传感器可以感应干燥罐中器身的微水分变化，其输出信号经放大、变换后，由单片机处理数据并显示。描述了系统的硬件结构和软件设计，并讨论了软硬件的抗干扰措施。     

电容式大测深绝缘纸板微水份测量传感器

介绍一种测量深度较大的电容式微水份传感器，它利用同一平面上两平行浮动电极形成的边缘电场感应被测纸板较深处的水份变化，在低频正弦驱动源的作用下，从由传感器和绝缘纸板构成的等效阻容耦合电路的输出电压中得到与绝缘纸板微水份有关的幅值和相差角，利用特定的函数关系得出绝缘纸板含水质量分数。在结构设计上充分考虑了厚绝缘纸板微水份测量的特点，使该传感器满足了灵敏度高、测量深度大、性能稳定和安装方便的设计要求：由它构成的微水份测量系统，可以用于现场干燥过程中的变压器绝缘纸板微水份检测。     

Dielectrometry of orthotropic textile materials

The model of an attachable electrocapacitance screened transducer was considered. The direct and inverse problems were solved and the inspection zones of a transducer and also its optimal construction parameters that provide a high sensitivity to anisotropy in the dielectric properties of orthotropic materials were determined. The effective dielectric permittivity of a flax fiber was studied at different humidities depending on the frequency of an electromagnetic field oriented along or across the fiber. A dielectrometric method for evaluating the quality of a flax fiber was developed.     

非破坏性水分测量仪的设计

非破坏性水分快速、准确的测量是粮食工业中需要解决的关键技术。为了实现粮食检测过程中的统一化和标准化,用于现场的非破坏性水分快速测量仪的设计是十分必要的。文中在研究电容传感器结构的基础上,分析了非破坏性水分测量的原理,提出一种基于电容传感器的谷物水分测量的设计方法,给出适合该种传感器的检测电路和水分测量仪系统组成。实践表明,此设计方法具有较高的准确性和应用推广价值。     

Determination of Soil Moisture Profile from Surface Reflection Coefficient Measurements

The in situ of volumetric soil moisture content (SMC) as a function of depth may be determined using surface reflection coefficient measurements at multiple discrete electromagnetic frequencies. The feasibility of this technique is demonstrated through computer simulation by deriving empirical relationships between the number of frequencies, the frequency range, and the number of soil layers for which the SMC is estimated. The SMC profile was obtained to a depth of 1.5 m by inverting, through function minimization, a simulation of the reflection coefficient from layered dielectric materials. The number of soil layers in which SMC could be resolved was found to be twice the number of frequencies used. The required bandwidth increased with the number of soil layers from 20 MHz for 6 layers to 140 MHz for 16 layers. Within some assumptions about the nature of the radio wave propagation, the theoretical accuracy of the estimate depended only on the quantization errorintroduced by having to consider discrete layers of uniform soil with finite widths. The method will enable sensitive measurements of SMC profiles at lower cost and lower complexity than methods which use analysis of steps or pulses, such as time-domain reflectometry (TDR), and should be well suited for routine use by horticulturists and soil researchers.     

数字式谷物水分测试仪

给出了以AT89C52单片机为核心的谷物水分测试仪的硬件组成，并详细介绍了信号处理和测量方法。通过对传感器的标定并进行相应的回归处理，可得到介质损失角和谷物水分的函数关系，并将此函数关系存入单片机的存储器中。这样检测系统只要测量出谷物的介质损失角，单片机通过查表和计算即可获知谷物的水分含量。实验表明：该仪器重复性好，测量精度高。