Detection of strength limiting defects in cellular glasses by dielectric measurements

Cellular (foamed) glasses are a prime candidate for certain structural applications, such as support of the silvered glass concentrator mirrors in solar thermal energy systems. An economical nondestructive measurement of strength-limiting defects in these materials would permit development of designs in which the material is subjected to a higher working stress level and maintains the same probability of failure. This would result in weight and cost savings for any application. A method of measuring the capacitance of well-defined regions of a specimen was investigated. Large voids were found to produce significant localized changes in the capacitance of the specimen. The feasibility of locating the large, strength limiting defects in this porous material has been demonstrated for one type of cellular glass. Means of producing an image from this type of data and an implementation scheme for on-line production measurements are discussed.     

Vapor Pressure of Water at Its Triple Point

The vapor pressure of water at its triple point was measured with exceptionally high accuracy by realizing it with a special apparatus and measuring the pressure with the NBS precision mercury manometer. The vapor pressure apparatus had a system for circulating the liquid water. Actual triple point conditions were established with a thin sheet of freshly distilled liquid flowing down over an exposed mantle of ice frozen on a vertical well. This technique reduced non-volatile contaminants and the vapor was repeatedly pumped to remove accumulated volatile contaminants. A diaphragm pressure transducer was used to separate the water vapor from the helium used to transmit the pressure to the manometer. The value found for the vapor pressure of water at its triple point was 611.657 Pa with an uncertainty of ± 0.010 Pa from random errors, computed at 99 percent confidence limits. The systematic errors are estimated to be insignificant relative to the random errors.     

±800kV穗东换流站换流变套管的电容介损试验

介绍了对于换流变的电容型套管的电容介损的测试过程和测试方法,分析了现场测试异常的数据,提出了解决方法。     

Impedance model of electrolyte-insulator-semiconductor structure with porous silicon semiconductor

We present a generic impedance model for the porous silicon|electrolyte structure that is valid for a range of interfacial layers and bias in these structures. The model is validated using three widely different porous structures: short irregular silicon columns and pores, long cylindrical silicon columns and pores; and branched interconnected silicon microchannels and voids in a mesh structure. The model incorporates appropriate RC or constant phase elements for the different parts of the porous structure, namely, the top of the silicon columns (channels)|electrolyte, the column (channel) walls|electrolyte in the pores/channels, and the electrolyte|semiconductor interface at the base of the pores/channels. This physical model underscores the effects of column/channel depletion and accumulation, either due to applied bias or change of surface charge, to the impedance spectra of the device. The model helps to explain why the porosity needs to be optimized for specific applications and helps as a measurement tool for optimization.     

浅谈电力电容器电容的控制

通过阐述与电容器生产制造有关的环境、原材料、生产设备、操作和设计等几个方面的影响因素,提出了具体对电容器电容控制的方法,同时通过统计浸油后/浸油前电容增长率来作为电容器电容控制的一个重要参数,对电容器生产过程中出现的电容偏差进行调整。     

电容层析成像三维成像算法研究与软件设计

为了研究循环流化床中气体 -固体的分布规律 ,基于电容层析成像得到的二维断面浓度分布 ,利用一种线性差值算法 ,构建固体颗粒的三维浓度分布。三维图像的显示采用 C 语言和 Open GL系统完成 ,并将该算法用于循环流化床中 ,结果清楚地显示了气泡的发展变化过程。     

Multiple-mode structural vibration control using negative capacitive shunt damping

This paper deals with a novel shunt circuit, which is capable of suppressing multimode vibration amplitudes by using a pair of piezoceramic patches. In order to describe the characteristic behaviors of a piezoelectric damper connected with a series and a parallel resistor-negative capacitor branch circuit, the stiffness ratio and loss factor with respect to the non-dimensional frequency are considered. The mechanism of the shunt damper is also described by considering a shunt voltage constrained by shunt impedance. To obtain a guideline model of the piezo/beam system with a negative capacitive shunting, the governing equations of motion are derived through the Hamilton’ s principle and a piezo sensor equation as well as a shunt-damping matrix is developed. The theoretical analysis shows that the piezo/beam system combined with a series and a parallel resistor-negative capacitor branch circuit developed in this study can significantly reduce the multiple-mode vibration amplitudes over the whole structural frequency range.     

基于相关检测的电容传感器的研究

介绍了一种高精度的电容传感器，应用相关检测技术，利用集成乘法器AD835来检测电容传感装置电容量的微小变化。这种方法比传统的电容检测传感器精度提高数百倍，而且系统不受外界缓变量的影响。该系统已在纤维检测方面得到很好的应用。     

一种工业用高频抗杂散小电容测量电路

介绍了一种工业用高频抗杂散小电容测量电路。该电路基于电荷转换原理,并采用差分结构产生输出信号。它有直至几兆赫兹的可编程测量频率。廉价且易于单片集成。通过采用特殊的开关安排,可以消除包括开关元件在内的杂散电容的影响,使得测量电路具有好的稳定性和线性衣０．３ｐＦ的分辨率。     

电容型设备及避雷器的绝缘在线检测

针对电容型设备及避雷器的绝缘在线检测的有关问题,进行了论述,说明了在线检测的必要性。