一种用于电流环校准的瞬态电流倍增器设计

为解决脉冲电流测量系统中所用电流环满量程校准的需求,该文基于感应电流叠加原理设计实现一种瞬态电流倍增器,利用镜像交叠扣合的两块PCB形成螺旋缠绕闭合回路,使得通过套接在其内部的电流环中的感应电流得到增加.试验结果表明:利用重复性较好的小幅度过阻尼振荡电流作为输入信号,经倍增后所获感应电流波形特征能够保持高度一致,峰值最...     

提高测试系统柔性的一种方法

一般测试系统的现场测试单元按固化的程序工作，灵活性较差。     

一种基于FPGA的串行通讯设计

随着微电子技术的快速发展 ,FPGA,CPLD等芯片在仪器、仪表中得到广泛应用 ,而串口通讯是测控技术的一个重要环节 .本文介绍一种通用的串行通讯的设计方案 ,结合 FPGA特点 ,克服了单片微机的许多缺点 ,提高了系统硬件的稳定性和时效性 .1　 FPGA简介现场可编程门阵列 FPGA( field programmablegate array)是美国 XILINX公司于 1 984年首先开发的一种通用型用户可编程器件 ,既具有门阵器件的高集成度和通用性 ,又有可编程逻辑器件用户可编程的灵活性 .FPGA由可编程逻辑单元阵列、布线资源和可编程的 I/ O单元阵列构成 ,一个 FPG…     

VISUAL FOXPRO环境下一种串行通信软件的开发

基于对象语言PASCAL提供的端口数组,本文介绍了一种在VISUAL FOXPRO环境下用手工编码实现访问串行数据的方法。它成功的实现了计算机数据库和外部设备的串行通讯。     

机载光电跟瞄平台伺服系统中电流环的设计与仿真

主要叙述了机载光电跟瞄平台伺服系统中电流环的组成并对电流调节器这一关键环节的设计进行了重点分析,在MATLAB的环境下对建好的电流环模型进行了仿真.     

单相光伏并网逆变器的两种定频滞环电流控制算法研究

传统的滞环电流控制算法具有实现简单、动态响应快、对负载参数变化不敏感、电流跟踪误差小等优点,但也存在开关频率随电流变化率变化而波动,造成网侧滤波电感设计困难、功率模块应力及开关损耗增大的不足.通过分析滞环电流控制算法的原理和开关频率波动的原因,提出了基于积分法的定频滞环电流控制算法和基于最小二乘法的定频滞环电流控制算法,无需额外模拟电路的优点,提高系统控制精度,并可以实现数字化.MATLAB仿真结果表明,这两种算法在实现滞环电流控制的同时保持定频,降低并网电流畸变率,无论电网稳定还是电网波动,都能较好地实现同步并网.     

一种交流微电流源的设计

在工程上有时候需要较小的恒定电流,而运算放大器的某些特性可以很好的满足工程上的需求。以下介绍一种交流微电流源的设计原理及其实验方法,并对其的恒流效果进行验证。本设计主要通过EWB5.0进行模拟仿真。     

一种厂用低压变压器过流继电保护方式的改进

本文通过对一起因厂用低压变压器低压侧母排相问短路而烧坏400V开关的事例分析，探索了低压变压器继电保护基础上的改进技术，发现了在实际运行中出现的问题，并进行了相应的技术改进。     

nA级泄漏电流测量仪的一种校准方法

本文简要介绍了泄漏电流测量仪nA级微小泄漏电流示值的一种校准方法,并通过实例分析了该方法主要误差影响因素及相关注意事项。     

电动汽车共模电流抑制方法的研究

针对电动汽车中沿电缆和底盘传导的共模电流是电动汽车产生电磁干扰的重要原因,分析了共模电流传导回路的阻抗特性,分析结果表明,在研究频率范围内(1～30MHz),共模回路存在串联谐振和并联谐振,分别导致共模电流出现极大值和极小值.为了抑制共模电流,基于互感原理开发了一种有源共模电感,与传统电感相比,有源电感具有较大的电感量和较好的高频特性,有源电感在电缆的适当位置可以产生最佳的共模电流抑制效果.     

ZnO nanowire growth by electric current heating method: A study on the effect of substrate temperature

In this study, we report the growth of ZnO nanowire on quartz glass substrates with Au-catalyst assistance by electric current heating of ZnO ceramic bar. The effect of substrate temperature on the properties of ZnO nanostructures has been investigated systematically. Structural analysis indicates that the grown ZnO crystals belong to hexagonal phase with preferential growth along (0 0 2) orientation. Scanning electron microscopic studies reveal the aligned ZnO nanowires were grown at 800 °C. The typical length and diameter of nanowires are in the uniform ranges of 4–20 μm and 20–100 nm, respectively, showing their high aspect ratio of about 1000. We have made an attempt to discuss about the change in ZnO nanostructures with different substrate temperatures and the possible mechanism for the growth of nanowires. Optical reflectance studies show the infrared reflectivity was controlled through the substrate temperature.     

Design of bipolar current source with amplitude up to 200 mA

One of the major requirements on the performance of a current source used for existing sensors is its amplitude stability. A method for designing a bipolar current source with amplitude up to 200 mA is developed. Its operating frequency is 10 kHz. The application of automatic control principles to the design of such a source makes the required amplitude stability possible. The circuit and its test data, including the maximum output amplitude, internal impedance, output regulation, and adjustment characteristic for an actual source, are given. This current source has successfully been used to excite the sensor of a continuous casting slag detector     

面向GPU的循环合并

针对现有的将C或Fortran程序映射到通用图形处理单元(GPU)的自动转换工具主要关注将单个循环生成一个独立的GPU内核,从而阻碍了对循环间数据重用的利用的问题,提出一种新的面向GPU的循环合并的代码变换方法,该方法通过循环分块(strip mining)和冗余计算等手段达到消除迭代间数据依赖的目的,并可充分利用GPU片上的共享内存进行线程间数据交换,从而将此类程序高效地映射到GPU上.通过典型程序在GPU上的实验表明,该新方法由于能够减少对全局内存的访问,带来了最多高达1.96倍的加速比.     

Non-uniform surface current distribution on parallel wire loop antennas using curved patches in the method of moments

The normalised magnitudes of the axial and circumferential surface current components (relative to the local wire axis) on parallel wire loop antennas were investigated, for different operating frequencies and spacing distances. The modelling method employed a two-dimensional electric surface patch integral equation formulation solved by independent piecewise-linear basis function methods in the circumferential and axial directions on the wire surface. The loops are each fed by simple axially directed delta-function excitation sources. The aim was to obtain a deeper understanding of non-uniform current distributions and the way they influence losses; the loss predictions using the presented technique for multiple parallel loop antennas are compared with those from other well-established methods (but only capable of modelling simple configurations) and are shown to be in good agreement. The effects of varying the parameters of the configuration are investigated and discussed.     

提高ZnO变阻器电性能的研究

ZnO变阻器电气性能的提高对避雷器的运行可靠性起着主要作用.本文首先采用两种新型球磨工艺制备了细化的ZnO陶瓷变阻器的添加剂.并且通过改进粘结剂和无机/有机复合侧面绝缘层配方,使ZnO变阻器的残压比、2ms方波通流、4/10μs大电流冲击等电性能有了大幅度的改善.     

A practical method for singular integral equations of the second kind

A convenient and efficient numerical method is presented for the treatment of Cauchy type singular integral equations of the second kind. The solution is achieved by splitting the Cauchy singular term into two parts, allowing one of the parts to be determined in a closed-form while the other part is evaluated by standard Gauss-Jacobi mechanical quadrature. Since the Cauchy singularity is removed after this manipulation, the quadrature abscissas and weights may be readily available and the placement of the collocation points is flexible in the present method. The method is exact when the unknown function can be expressed as the product of a fundamental function and a polynomial of degree less than the number of the integration points. The proposed algorithm can also be extended to the case where the singularities are complex and is found equally effective. The proposed algorithm is easy to implement and provides a shortcut for programming the numerical solution to the singular integral equation of the second kind.     

A study on phase-noise reduction method in phase-locked loop systems

Experimental studies are carried out on phase noise and the correlation coefficient between the phase and average current noises of the voltage-controlled oscillator in phased-locked loop (PLL) systems. The precise phase stabilization technique is discussed, and new methods to reduce the phase noise are described in PLL systems, using the correlation.     

Effect of electric current on the creep deformation of lead

Using the impression test, the effect of electric current on the creep deformation of Pb was studied in the temperature range of 343-403 K and under the punching stress of 11.1-30.5 MPa. During the impression test of constant load, a direct electric current in a range of 0-5 A passed through the punch into the Pb-sample. A steady state creep with sudden jumps in the impression curves was observed. A power-law relation was used to describe the dependence of the steady state impression velocity on the punching stress. The average stress exponent increased from 3.2 to 4.0 with increasing electric current and the apparent activation energy was 36.0 kJ/mol for small punching stresses. For large punching stresses, the average stress exponent decreased with increasing electric current and the apparent activation energy decreased from 63.5 kJ/mol to 49.7 kJ/mol with increasing electric current from 0 to 5 A.