基于密集频谱校正的电流信号高准确度分离技术

为实现具有密集频谱的频谱校正分离,通过研究基于复调制移频和低通滤波器的传统Zoom-FFT方法和频谱校正方法,提出一种电流信号高准确度分离方法。该方法采用基于复解析带通滤波器和复调制移频的频谱细化方法和比值校正法对电流信号进行频谱细化校正,实现电流信号的高准确度分离。研究结果表明,该文采用的频谱细化校正方法运算量小,计算速度快、准确度高,能够实现电流信号的高准确度分离。     

永磁同步电机矢量控制系统的研究

本文主要介绍了交流永磁同步电机在现阶段的优势。然后从其控制策略入手,从实际应用的角度出发,对永磁同步电机矢量控制的一种实用系统,从硬件和软件两方面介绍了控制系统的实现。本系统以TI公司的TMS320F2812数字信号处理器为控制核心,核心DsP通过识别给定信号,以及利用反馈的转数和电流信号,进行运算,输出矢量控制信号。信号经过驱动器,最终控制由IGBT构成的三相逆变桥实现一个电流和转速双闭环的永磁同步电机的调速。     

检测供电电源电路的设计与实现

利用MAxIM司生产的精密高端电流检测放大器MAx47I实现以地为参考的电流/电压的转换,用高线性度模拟光电耦合器HCNR201信号隔离,实现本系统对外部供电电源的功耗测量.详细介绍了MAX471的工作原理及其在电流检测中的应用,并给出了用HCNR201和运算放大器实现检测电压的隔离传输电路.     

基于“S”注入法的小电流接地系统单相接地故障定位方案研究

由于线路自身特点,小电流接地系统故障率高,且查找困难。针对故障点的定位问题,采用“S注入法”进行了单相接地故障仿真。建立了基于母线侧电压互感器二次侧注入信号电流,在故障点前后检测特定频率信号电流来实现故障定位的模型,通过实验仿真,验证了定位方案的可行性。     

互易法校准压电型声发射传感器的研究与实现

声发射传感器的校准是实现声发射定量技术的前提,依据电声换能器互易原理,在计算互易常数的基础 上,建立了适用于压电型声发射传感器表面波和纵波互易的校准系统。通过设置特定的激励信号波形,依据接收 电压信号与激励电流信号之间的时间延迟,准确获取电流信号与电压信号对应的特征值,实现了声发射传感器的表面波和纵波互易校准。由于传感器的尺寸效应,传感器在高频时的表面波速度灵敏度低于纵波灵敏度,不确定度评定结果表明,声发射传感器速度灵敏度的互易法校准不确定度为1. 2 dB。     

基于TMS320F28335的数据采集系统设计与实现

设计了一个基于TMS320F28335数字信号处理器的数据采集系统,能够实现对一个三相电机驱动器的电流信息采集和处理工作。本设计给出了基本的电流信号调理电路,并给出了DSP的软件设计流程和数据采集波形。经过试验验证,证明本设计能够正确采集三相电流大小,达到了设计目的和要求。     

薄板TIG焊熔池谐振法熔透自适应控制

在直流电流上附加正弦波焊接电流,诱发熔池金属振荡,通过电弧电压检测熔池谐振信号,此谐振信号与熔池尺寸有良好对应关系。实验研究了影响熔池谐振信号产生的电弧因素,通过建立以直流变动电流电源、步进电弧、微计算机数据采集和反馈控制为主体的焊接熔透控制系统,实现了薄板对接焊缝熔宽的实时控制,获得良好焊缝成形。在有意识地改变外部影响因素条件下,取得了满意的自适应控制效果。     

浅谈煤矿井下煤炭输送智能控制系统

对于煤矿皮带输送系统的具体情况，针对运输中出现的打滑、过载、无负载、联轴断裂等情况，研究开发了井下皮带输送智能控制系统。该系统给出了软硬件实现方案，重点对上级和下级皮带机的负载电流信号进行分别测量，可编程序控制器将采集到的负载电流信号进行比较和运算处理。系统投运后能自动根据负载的大小来实时控制托运电机加、减速度，从而实现智能化控制，可节约电能，并为企业节约维修金。     

反馈式磁阻传感器小电流检测系统的研究

介绍了采用闭环反馈控制方法的小电流测量原理。采用对低磁场有高灵敏度的磁阻传感器HMC1021作为信号采集模块,以低功耗和高性能的DSP芯片TMS320F2812为主控制芯片,从而实现对微弱信号的精确测量和快速处理。     

基于自抗扰控制的直流微电网双向Buck-Boost变换器控制策略研究

为了降低直流微电网母线电压的波动,提出基于自抗扰控制的双向Buck-Boost变换器控制策略。运用直流母线电压外环、直流变换器电感电流内环的控制方法实现直流微电网与储能系统之间的能量双向流动。进一步提出基于扩张状态观测器观测输出总扰动,包括负载电流和母线电压的变化,在负载扰动电流影响系统的直流母线电压最终输出前,主动从外环被控对象的输入信号电感电流或输出信号母线电压中提取扰动信息,然后尽快用控制信号将其消除,从而大大降低其对被控量的影响,以有效抑制暂态直流母线的电压波动和冲击,在母线电压产生波动时能够快速恢复到正常的工作状态。仿真验证表明:储能系统可以通过控制策略实现能量的双向传递,并且当母线产生功率波动和电流冲击时,储能系统可以使直流母线电压稳定,提高了系统的可靠性。     

Harmonic analysis of sideband signals generated in plasmas

When a small ac voltage with two frequencies was biased to a probe in low pressure inductively coupled plasma, sideband current signals were observed. It was found that two frequencies of the small bias voltage are mutually modulated in the plasma, and this modulation results in the sideband current signals. Experiments for measurement of the sidebands were carried out at various pressures, correlations between the sidebands and the plasma state were investigated. The sidebands were not observed when the plasma was not generated; therefore these signals were produced by the nonlinearity of the sheath. The electron temperature could be obtained from the sideband signals, and it was in good agreement with that from a single Langmuir Probe.     

小波变换在钢球表面裂纹电涡流检测中的应用

电涡流检测是五大常规无损检测方法之一，检测方便、快捷，适合用于钢球表面裂纹的在线检测。然而电涡流检测信号微弱，识别困难，必须采用比较有效的信号处理方法对信号进行处理。本文用小波变换处理钢球表面裂纹电涡流检测信号，可以有效的降噪与消除干扰，加强信号特征，达到对钢球表面裂纹的定性检测从而对钢球进行质量评估。     

基于涡流检测信号的金属曲面距离测量方法研究

为提高曲面试件的涡流测距精度,提出一种基于涡流信号差值的测距修正方法.该方法通过研究不锈钢平板试件与曲面试件涡流信号的不同,拟合计算出曲面涡流信号和平面涡流信号之间差值与曲面试件曲率的定量关系.利用这一函数关系,对不同曲率试件的测量结果进行补偿,可修正由于试件存在曲面造成的测量误差.通过实验进行可行性验证,对平板试件与...     

Time-Frequency Analysis of Pulsed Eddy Current Signals

Detection and measurement of the material loss due to corrosion in aircraft fuselage lap splices are of great importance to life management of ageing aircraft. Pulsed eddy current (PEC) techniques have shown the potential to fully characterise these structures. However, variations in the probe lift-off, the interlayer gaps and material thinning produce similar PEC signals, making signal interpretation very difficult. This paper describes time-frequency analysis algorithms applied to pulsed-eddy current signals from lap-joint specimens containing simulated flaws. The effect of probe lift-off, interlayer gap, and material thinning on PEC signals is examined in three-dimensional space (amplitude-time-frequency). This study shows that the time-frequency analysis of PEC signals provides specific visual patterns that can be related to the interlayer gap, lift-off, and material loss.     

Eddy Current Signal Deconvolution Technique for the Improvement of Steam Generator Tubing Burst Pressure Predictions

Eddy current techniques are extremely sensitive to the presence of axial cracks in nuclear power plant steam generator tube walls, but they are equally sensitive to the presence of dents, fretting, support structures, corrosion products, and other artifacts. Eddy current signal interpretation is further complicated by cracking geometries more complex than a single axial crack. Although there has been limited success in classifying and sizing defects through artificial neural networks, the ability to predict tubing integrity has, so far, eluded modelers. In large part, this lack of success stems from an inability to distinguish crack signals from those arising from artifacts. We present here a new signal processing technique that deconvolves raw eddy current voltage signals into separate signal contributions from different sources, which allows signals associated with a dominant crack to be identified. The signal deconvolution technique, combined with artificial neural network modeling, significantly improves the prediction of tube burst pressure from bobbin-coil eddy current measurements of steam generator tubing.     

Novel pseudo RMS current converter for sinusoidal signals using a CMOS precision current rectifier

A very simple pseudo RMS-to-DC current converter for sinusoidal signals is described. The most salient feature of the circuit is that it uses a CMOS precision current rectifier consisting of only two transistors and thus operates throughout in the current domain. The full-wave rectifier was built using CD4007 devices and tested. It was observed that the transfer curve is sharp even at low nanoampere input levels. The converter is expected to work up to 100 kHz.<>     

Comparison of conventional,through-wall and remote field eddy current techniques

A through-wall eddy current system produces similar signals for defects of equal size, independent of the location of the defects in the sample being tested. The remote field eddy current technique is also reported to generate similar signals for equal defects, independent of the location of the defects in the wall of the tube which is being inspected. A theoretical study of an ideal conventional through-wall eddy current system is presented, and the results are compared with the results of a remote field eddy current system. It is shown that while the remote field system does not always obey the one-dimensional skin effect equation, it detects external material loss with nearly equal sensitivity to internal material loss. Experimental results are presented which show that the complex plane displays of similar ID and OD defects are similar in shape, size and orientation.     

Characterizing the performance of eddy current probes using photoinductive field-mapping

We present a new method for characterizing the performance of eddy current probes by mapping their electromagnetic fields. The technique is based on the photoinductive effect, the change in the impedance of an eddy current probe induced by laser heating of the material under the probe. The instrument we developed maps a probe's electric field distribution by scanning an infrared laser beam over a thin film of gold lying underneath the probe. Measurements of both photoinductive signals and flaw signals for a series of similar probes demonstrate that the impedance change caused by an electrical-discharge-machined (EDM) notch or a fatigue crack is proportional to the strength of the photoinductive signal. Thus, photoinductive measurements can supplant the use of artifact standards to calibrate eddy current probes. Furthermore, the shape and symmetry of the probe's field pattern can reveal defects in probe construction. By combining photoinductive measurements of a probe's field strength with a theoretical model, we are able to quantitatively predict the probe's performance under hypothetical conditions. To model commercial eddy current probes with ferrite cores, we developed a procedure to treat them as effective air-core probes. We obtained good agreement between the flaw signals calculated using this effective-coil approach and actual fatiguecrack signals measured with commercial probes. We also calculated probabilities of detection for target flaws in titanium alloys for a series of commercial probes. The results reveal how probe sensitivity can affect the reliability of an eddy current inspection.This article is dedicated to Professor Bertram A. Auld on the occasion of his 70th birthday and his retirement from Stanford University.     

A new current sensor based on the measurement of the apparentcoercive field strength

A current sensor that uses the change of the apparent coercive field strength caused by the current to be measured is introduced. The apparent coercive field strength is derived from the magnetizing current by detecting the zero crossing points of the average magnetic flux of a core pair. The current is periodically measured at a frequency which is the same as that of the magnetizing current of the sensor. The current sensor shows a standard deviation of the nonlinearity of less than 0.002%, and can measure transient current signals with an 80-kHz sampling rate