Comment and discussion on digital processing of PD pulses

Some of the more salient aspects of the digital processing technology of PD signals are examined. Most of the efforts in this field are concentrated on the application of digital analyzers for pulse height analysis, pattern recognition and identification of the physical phenomena. It is demonstrated that errors in the signal processing unit can lead to dominant mistakes in the interpretation of the test results     

A note on Pareto statistics of partial microdischarge spots

Pareto statistics of microdischarges have been examined within two different representations. The first one is the commonly used height (amplitude) representation while the second is the newly proposed representation based on areas of plane spots created by microdischarges on dielectric surfaces.     

超声测距数字信号采集系统

介绍了一个完整的超声测距数字信号采集系统,该系统包括通用超声波发射电路,超声波接收电路和ＰＣ机数据采集系统。     

基于PCI总线的CCD数字相机采集系统设计

针对高速图像信号采集系统中数据传输量大的特点,提出了一种基于PCI总线的CCD数字相机采集系统的设计方法,给出了系统整体设计方案。采集系统以Camera Link和PCI总线为接口,结合FIFO、PCI9054和FPGA来实现计算机对CCD相机的设置和图像数据的采集。Camera link接口实现低压差分信号至TTL信号的转化和相机与图像采集卡之间的串行通信,PCI9054实现本地端与PCI端的桥接使用户接口设计简单,FIFO实现对高速采集后的海量数据进行缓存,FPGA实现整个系统的时序控制。这很好的解决了计算机与数字相机进行高速、大数据量传输的难题。     

波导大功率负载长度对微放电的影响

波导大功率负载作为微波系统重要的终端器件,在航天系统上有非常广泛的应用.基于航天工程应用,对波导负载内部不同位置的微放电阈值进行分析,通过仿真软件截取负载不同位置的电场强度,从而进一步分析计算各个位置上的微放电阈值.结果表明,对于不同的波导负载吸收长度,内部电场强度并非线性变化,因此设计波导负载时应留有足够的吸收长度,...     

激光测距的高速采集与处理电路的设计

针对激光测距接收电路提出了将激光回波数字化处理的方法。基于激光测距中激光信号脉冲窄、上升沿陡、实时性要求高的特点,提出了采用ADC FPGA DSP的高速数据采集与实时处理的设计方案,详细介绍了电路的具体设计方法。分别对2MHz正弦波和重复频率5kHz脉宽为80ns的窄脉冲进行了采集实验,结果表明电路满足设计要求。     

基于FPGA及数字倍频技术实现数据同步采集的研究

应用GPS授时技术提出一种电力系统交流电气信号同步采集的设计方案.设计采用自顶向下的设计方法,选用了可编程逻辑控制器件FPGA芯片作为硬件开发平台完成GPS系统对时、数字倍频、A/D转换同步采样控制和数据存储的集成.实现了电力系统内部不同变电站之间以及变电站内部不同单元之间数据同步采集及存储等功能.此外给出了使用综合开发平台Quartus II设计软件进行的仿真与分析.数据同步采集在电力系统集成保护中具有实际应用价值.     

用于电能质量检测的数据采集卡研制

结合电能质量五项指标,开发了用于电能质量检测的数据采集卡.该卡采用了DSP数字信号处理器和PCI总线技术,能实时采集数据.并采用了两片六通道高速A/D转换器和运用了锁相同步技术,对三相电压和电流信号能进行定时采样和等间隔采样,这样得到的数据对于下一步电能质量指标进行分析更为合理.本文最后还简要介绍了DSP的C语言开发和PCI插卡的驱动程序编写技术.     

基于LabVIEW和数据采集卡的数字序列输出研究

首先介绍了数字序列输出的设计思想和用到的主要函数,在基本理论支撑的基础上,结合虚拟仪器技术,提出了一种以美国NI公司推出的虚拟仪器开发软件LabVIEW为开发环境,利用数据采集卡的数字硬件资源来进行数字序列输出的实现方法,有效地解决了多数字序列输出时的同步问题.所述方法在实际应用中取得了良好的效果.     

Electron avalanches. II. Fractal morphology of partial microdischarge spots on dielectric barriers

For pt.I see ibid., vol.10, no.4, p. 689-699 (2003). Microdischarge spots appearing on surfaces of dielectric barriers in sandwiched electrode systems have been studied. The study has been focused on streamer microdischarges which are a subject of continual interest not only in plasma physics (dielectric barrier discharges) but also in HV technology (partial discharges). The microdischarge spots have been visualized using photographic films that have played the role of dielectric barriers in experiments. The digitized pictures of microdischarge spots have been subjected to multifractal analysis. An inner structure of spots has been revealed and ascribed to streamer heads. The monofractal nature of the overall sets of microdischarge spots as well as the monofractality of the borders of the dark spot centers has been indicated. The inner structure of the dark centers has been classified as a non-fractal planar object. The study represents a first attempt to analyze microdischarge spots on dielectric barriers using general multifractal formalism.     

Compensation for unknown acquisition delay caused by digital receiver without external synchronization in NMR and MRI

The unknown acquisition delay problem caused by a digital receiver without external synchronization in NMR and MRI applications is discussed in detail. An effective procedure is suggested for overcoming the problem. The main features of the proposed method include minimal hardware modifications and highly efficient algorithms. It is important to note that this method does not rely on any special architecture for the digital receiver. To test the method, a digital receiver was implemented using a commercially available single-chip IC. Finally, the method was verified on a 0.3-T home-built MRI system. The experimental results show that the proposed method may be a useful tool for correcting the unknown acquisition delay arising from commercially available digital receivers without external synchronization in NMR and MRI.     

GLED的简易制程

要制作高级的GLED必须实施相关的专利技术,并与现有的制程诀窍相结合,这对于想试产GLED的普通厂家来说无疑是件困难的事.介绍如何应用现有的管形荧光灯设备和材料实施GLED的简易生产.     

Simplified analysis of feedback amplifiers

A very simple and general method for the analysis of feedback amplifiers with large-loop gain is presented in this paper. The general properties of feedback amplifiers, such as gain and input and output resistances, are obtained using an open-loop circuit where the loading effect of the feedback network is easily taken into account. Emphasis is placed on quick, intuitive, and reliable calculations, useful for both the analysis and design of feedback amplifiers.     

Measurement of 10-fs laser pulses

We report full characterization of the intensity and phase of ~10-fs optical pulses using second-harmonic-generation frequency-resolved-optical-gating (SHG FROG). We summarize the subtleties in such measurements, compare these measurements with predicted pulse shapes, and describe the implications of these measurements for the creation of even shorter pulses. We also discuss the problem of validating these measurements. Previous measurements of such short pulses using techniques such as autocorrelation have been difficult to validate because at best incomplete information is obtained and internal self-consistency checks are lacking. FROG measurements of these pulses, in contrast, can be validated, for several reasons. First, the complete pulse-shape information provided by FROG allows significantly better comparison of experimental data with theoretical models than do measurements of the autocorrelation trace of a pulse. Second, there exist internal self-consistency checks in FROG that are not present in other pulse-measurement techniques. Indeed, we show how to correct a FROG trace with systematic error using one of these checks     

Phase-controlled amplification of few-cycle laser pulses

Intense ultrashort waveforms of light that can be produced with an exactly predetermined electromagnetic field are essential in a number of applications of extreme nonlinear optics, most prominently in laser-driven sources of high-energy attosecond radiation. Field reproducibility in each laser shot requires stabilization of the carrier-envelope phase. The authors analyze different schemes of phase-stable pulse amplification and identify constraints limiting the precision with which the phase can be maintained. Next, they describe a phase-stabilized laser system based on a 20-fs multipass Ti:sapphire amplifier supplemented with a fiber compression stage for producing pulses in the few-cycle regime. It is shown that the amplifier introduces only a slow millihertz phase drift and, therefore, can be seeded by a standard phase-stabilized oscillator. This residual phase drift is assigned primarily to the beam pointing instability and can be precompensated in the phase-control loop of the seed oscillator using a feedback signal from a phase detector placed in the amplifier output. The phase stability of the resultant 5-fs 400-/spl mu/J pulses at a 1-kHz repetition rate is subsequently independently verified by higher order harmonic generation, in which different carrier-envelope phase settings are shown, both theoretically and experimentally, to produce distinctly different spectral shapes of the XUV radiation. From a series of such spectral patterns, the authors succeed in calibrating the value of the carrier envelope phase (with a /spl plusmn//spl pi/ ambiguity), which in turn allows them to fully characterize the temporal structure of the electric field of the laser pulses. The estimated precision of the phase control on the XUV target is better than /spl pi//5, which reduces the timing jitter between the driving laser pulse and the XUV bursts to /spl sim/ 250 as and opens the way to generate stable isolated attosecond pulses.     

Generation of attosecond X-ray laser pulses

We propose to generate as-X-ray laser pulses by beating of two or more X-ray laser lines with a frequency separation in the range of 10/sup 15/ Hz. We focus on nickel-like X-ray lasers, some of which have a few almost equidistant laser gain lines with an appropriate difference frequency. It is shown that in the case of three or more lines, these can be phase-locked by means of a Langmuir wave generated in the gain medium at a suitable electron density.     

Simplified predetermination of line current harmonics

In predetermining line current harmonics of controlled AC/DC converters, the effects of commutation and DC ripple must be taken into account frequently, as for example in the case of medium-size DC drive applications. Based on a suitable normalization, the dominant parameters determining the current harmonics are the line and DC side reactances, respectively, and the DC voltage. This forms the basis for a systematic comparison of the accuracy of analytical formulas, describing the commutation or the DC ripple effect only. By the aid of these results, the validity ranges of different approximation formulas can be estimated and the most important question answered concerning the proof of the conventional assumption of a “sufficiently” smoothed DC current. In order to predetermine line current harmonics as easily as possible, the most effective formula can be obtained out of corresponding decision areas. Thereby, the allowable error is restricted to 2% of the fundamental, confirmed by comparing results of digital simulation studies     

一种新的简化负荷模型结构

好的负荷模型需要反映负荷的本质特征,并能够精确地仿真实测曲线.从系统辨识的角度来看,负荷模型是变电站大量电能消耗元件的一个等值模型,同时负荷模型具有参数不唯一的特点,这就使得简化负荷模型的辨识成为可能,负荷模型的简化辨识也会为工程实际应用带来方便.采用了ZIP负荷模型加感应电动机的综合负荷模型,针对我国配电网的特点,从参数灵敏度的角度出发,提出了将灵敏度小的感应电动机参数部分固定,仅辨识灵敏度较大参数的方法,并用残差分析指标对简化后的负荷模型的准确性加以验证,证明了简化模型参数的可行性,并为进一步研究辨识参数简化后的模型的统计学规律奠定了基础.     

静电放电的简化放电模型

分析了静电电磁兼容问题中的一个重要部分：放电电流及其产生的瞬态电磁场;针对在研究抗静电干扰措施时,复杂的放电模型参数难以获得的问题,提出了一种简化的放电模型,给出的放电电流波形的要求;利用电磁瞬态程序EMTP对该简化模型进行近似计算,并对通过该模型计算出的放电电流进行时域、频域分析。     

简化型Z源并网逆变器

针对传统Z源逆变器电路体积庞大、启动冲击大、输入电流断续造成直流电压利用率低,提出了一种简化型Z源逆变器拓扑.该拓扑在基本保持传统Z源逆变器升压能力的前提下,减少阻抗网络中高压电容的数量,用二极管为直通状态下的阻抗网络电感电流提供续流电路,减小了电路的体积及设计成本,同时该拓扑不存在启动冲击问题,保证了输入电流的连续.将该拓扑应用于三相并网系统,基于dq坐标系电流解耦及阻抗网络电容电压恒定的原则设计了控制系统.对其稳态输出、并网功率突变、输入电压扰动等情况进行了仿真分析,验证了拓扑的可行性及性能.