Noise analysis of digital ultrasonic nondestructive evaluation system

Being one of the five most commonly used nondestructive testing (NDT) routines, ultrasonic testing (UT) is under fast development in recent years, with more attention being focused on quantitative testing and nondestructive evaluation (NDE). In the evaluation of pressure vessels and piping, UT is utilized not only in manufacturing quality controlling, but also in-service monitoring and residual life prediction, such as the inspection of welded joints, monitoring of crack propagation, evaluation of materials property deterioration.In ultrasonic NDE and quantitative NDT, one of the main factors disturbing the reliability and accuracy of test is noise encountered during inspection. At present, a digitized instrument is increasingly preferred in practice. Considering every step, from wave emitting to digitalization of analog signal, the following noises usually emerge—the electronic circuit noise of instrument; structure noise caused by grain boundaries of material under testing; ringing noise due to oscillation of probe; digital noise of finite-word digital system; pulse noise by virtue of fluctuation of inspection circumstance. Among these, the most serious is the structure noise encountered in the testing of coarse-grained austenite stainless steel, which affects the defect signal, making the least detectable defect size increase. In the present paper the characteristics, detriment and elimination algorithms of electrical noise, pulse noise, ringing noise and structure noise in a digital ultrasonic NDE system are discussed. A physical model of the digital ultrasonic NDE system is established, and noises are classified into different categories from the viewpoint of the model. The characteristics of electrical noise are analyzed; an algorithm of extremum filtering constructed to eliminate the pulse noise; high-pass filter and wavelet packet are employed to process ringing noise; the features of structure noise are studied and it is de-noised by wavelet transform (WT) and wavelet packet transform (WPT). The results obtained from real-world signal show that the electrical noise can be taken approximately as white noise with a Gaussian distribution. The algorithm of extremum filtering can filter the pulse noise without any effect on other information in the signal. Wavelet packet algorithm is more suitable for the elimination of long-term ringing noise than high-pass filter under the condition of less loss of defect echo. Processing the signals of coarse-grained austenite stainless steel samples with defects by use of WT and WPT concludes that as structure noise can be divided into certain frequency bands, generally different from those of defect echoes by WT and WPT, the defect can be pointed out, and the signal-to-noise ratio enhanced substantially after the threshold processing of frequency components of signals followed reconstruction.     

Research on data diagnosis method of acoustic array sensor device based on spectrogram

Acoustic array sensor device for partial discharge detection is widely used in power equipment inspection with the advantages of non-contact and precise positioning compared with partial discharge detection methods such as ultrasonic method and pulse current method. However, due to the sensitivity of the acoustic array sensor and the influence of the equipment operation site interference, the acoustic array sensor device for partial discharge type diagnosis by phase resolved partial discharge(PR...     

改进的电缆中间接头局放信号去噪方法

针对电力电缆中间接头局部放电信息检测系统实际采集到的局部放电信号含有噪声的问题,提出了一种将快速傅里叶变换与改进小波包变换相结合的处理方法,对于周期性窄带干扰,选取快速傅里叶变换来处理;对于白噪声,通过一种改进的阈值函数的小波包算法进行处理。实际应用结果表明,该方法去噪效果明显,不仅有效去除了局部放电脉冲信号中的噪声,可较好地保留了原始信号的有用信息。     

SOC estimation of lithium battery based on adaptive untracked Kalman filter

电池荷电状态（SOC）的准确估计是电池管理系统的关键问题,对电池的可靠性和安全性至关重要。由于多数情况下建立的电池模型精度不够高、电池系统的噪声统计是未知的或不准确的,这都会对锂离子电池系统的SOC估计会产生较大影响。本文采用二阶RC等效模型,可减小电池模型带来的误差;同时结合SageHusa滤波算法与无迹卡尔曼滤波（UKF）算法提出了一种新的SOC估计方法,基于噪声统计估计器的自适应无迹卡尔曼（AUKF）滤波算法,它可以对系统噪声进行实时修正以提高SOC的估算精度。并通过比较AUKF和UKF来验证SOC估计方法的准确性和有效性。实验结果表明,AUKF具有更高的SOC估计精度和自适应能力,在脉冲放电工况和动态工况下的估计精度均能保持在4.68%以内,可以有效地估计电池的SOC值。     

High heat flux point source sensitivity and localization analysis for an ultrasonic sensor array

State estimation procedures using the extended Kalman filter are investigated for a transient heat transfer problem in which a high heat flux point source is applied on one side of a thin plate and ultrasonic pulse time of flight is measured between spatially separated transducers on the opposite side of the plate. This work is an integral part of an effort to develop a system capable of locating the boundary layer transition region on a hypersonic vehicle aeroshell. Results from thermal conduction experiments involving one-way ultrasonic pulse time of flight measurements are presented. Uncertainties in the experiments and sensitivity to heating source location are discussed. One key finding is that sensitivity to heating source location is greater in the direction normal to the ultrasonic pulse propagation path. Scaled sensitivities to boundary conditions and thermal conductivity are presented and analyzed for all possible source locations using a square sensor grid. While sensitivity to the primary heat flux was determined to be the highest, sensitivity to the other parameters is either on the same order of magnitude or one order of magnitude less. Two different measurement models are compared for heating source localization: (1) directly using the one-way ultrasonic pulse time of flight as the measurement vector and (2) indirectly obtaining distance from the one-way ultrasonic pulse time of flight and then using these obtained distances as the measurement vector in the extended Kalman filter. Heating source localization results and convergence behavior are compared for the two measurement models. Two areas of sensitivity analyses are presented: (1) heat source location relative to sensor array position, and (2) sensor noise. The direct measurement model produced the best results when considering accuracy of converged solution, ability to converge to the correct solution given different initial guesses, and smoothness of convergence behavior.     

Optimal hydrogenerator governor tuning with a genetic algorithm

The authors investigate the application of a genetic algorithm for optimizing the gains of a proportional-plus-integral controller for a hydrogenerator plant. The genetic algorithm was applied to optimal tuning of a governor for a hydrogenerator plant. Analog and digital simulation methods are compared for use in conjunction with the genetic algorithm optimization process. It is shown that analog plant simulation provides advantages in speed over digital plant simulation. This speed advantage makes application of the genetic algorithm in an actual plant environment feasible. The genetic algorithm is shown to possess the ability to reject plant noise and other system anomalies in its search for optimizing solutions     

采煤机变频器的软件设计与实验研究

为提高采煤机利用电能的效率,针对SPWM脉宽调制的变频器直流电压利用率低、输出电流的谐波含量高的问题,以数字信号处理器TMS320F2812为核心,CPLD为辅助控制电路,DSP完成算法设计,CPLD实现逻辑控制与键盘显示,最大发挥各自的性能.采用软件法实现空间矢量脉宽的调制.实验结果表明：该方法比硬件法谐波含量相对减少,电机电流的谐波小,实现了频率调节范围为1～50 Hz,低的电机高频噪声,高的电压利用率.     

柴油机排气噪声有源消声系统的设计与实现

为解决柴油机排气低频噪声问题,基于噪声有源消声技术理论,选用与排气噪声相关的转速信号作为数字信号处理控制器的参考信号,以自适应陷波滤波算法为基础,采用次级通路离线自适应建模方式,设计了单通道有源噪声前馈控制系统,并在Matlab平台上进行仿真分析,最终选取迭代步长μ为0.003.在某柴油机排气管路上进行了排气噪声有源消...     

含水合物松散沉积物声速剖面成像技术研究

本文基于射线理论的超声层析成像技术,采用自适应消噪技术除去天然气水合物（NGH）实验模型固有噪声,运用直射线追踪法和基于联合迭代重建算法（Simultaneous Iterative Reconstruction Techniques, SIRT）的迭代重建法实现超声层析成像的正演和反演,针对水合物实验获取的波形,得到NGH在松散沉积物中形成时的地层声速剖面结构图像。结果表明,使用超声层析成像技术获取的含NGH沉积物的二维声速剖面结构能够准确反应不同时刻沉积物中NGH饱和度及分布情况,并且纵横波速度剖面结构的变化趋势大体相同。同时本文也结合常用的NGH声速预测模型,针对实验数据,对声速与NGH饱和度之间的关系进行了讨论。     

基于CIGRE HVDC标准模型的脉冲触发装置的改进

换流器脉冲触发控制系统是直流控制系统的重要组成部分,提升高压直流输电系统脉冲触发装置的控制精度和阀故障恢复速度,对保证交直流电网安全稳定具有重要意义。因此,提出了一种改进的脉冲触发控制装置,即基于CIGRE HVDC标准模型,在其脉冲触发控制装置中引入输入选择器和前置滤波器,滤除输入脉冲触发装置信号中的谐波和噪声,以提高触发脉冲的控制精度。在系统发生阀故障时,对比改进前后两种模型的触发脉冲波形。结果表明,改进后的脉冲触发装置仍能保持脉冲等间隔触发,有利于系统从故障中快速恢复,降低了换相失败的发生几率。     

Fuzzy logic based DSP controlled servo position control for ultrasonic motor

In this paper, position control of an ultrasonic motor was implemented on the basis of fuzzy reasoning. A digitally controllable two phase serial resonant inverter was developed to drive the ultrasonic motor by using a TMS320F243 digital signal processor. The driving frequency was used as a control input in the position control loop. The position characteristics obtained from the proposed drive and control system were demonstrated and evaluated by experiments. The experimental results verify that the developed position control scheme is highly effective, reliable and applicable for the ultrasonic motor.     

A comparison of extended Kalman filter,particle filter,and least squares localization methods for a high heat flux concentrated source

State estimation procedures using the extended Kalman filter, particle filter, and least squares are investigated for a transient heat transfer problem in which a high heat flux concentrated source is applied on one side of a thin plate and ultrasonic pulse time of flight is measured between spatially separated transducers on the opposite side of the plate. This work is an integral part of an effort to develop a system capable of locating the boundary layer transition region on a hypersonic vehicle aeroshell. Results from thermal conduction experiments involving one-way ultrasonic pulse time of flight measurements are presented. Comparisons of heating source localization measurement models are conducted where ultrasonic pulse time of flight readings provide the measurement update to the extended Kalman filter, particle filter, and least squares. Two different measurement models are compared: (1) directly using the one-way ultrasonic pulse time of flight as the measurement vector and (2) indirectly obtaining distance from the one-way ultrasonic pulse time of flight and then using these obtained distances as the measurement vector. For the direct model, the Jacobian required by the extended Kalman filter and least squares is obtained numerically using finite differences and a finite element forward conduction solution. For the indirect model, the derivatives with respect to the state variables are obtained in closed form. Heating source localization results and convergence behavior are compared for the three inverse methods and the two measurement models. The extended Kalman filter, least squares, and particle filter methods using the one-way ultrasonic pulse time of flight measurement model (direct model) produced similar results when considering accuracy of converged solution, ability to converge to the correct solution, and smoothness of convergence behavior. The results provide quantified justification for moving forward with development of an extended Kalman filter-based localization solution.     

基于时频分析法的开关柜避雷器泄漏电流检测

  目的  在电力系统中,开关柜避雷器承担着抑制瞬态过电压和泄放脉冲大电流的重要作用,对于维持其正常稳定运行具有重大意义。  方法  为了有效抑制噪声对泄漏电流信号检测的干扰,提出了一种基于自相关系数与卡方检验优化的时频分析方法。首先通过电流传感器和分流器两种测量结果进行分析,然后利用基于自相关系数与卡方检验优化的小波变换消除信号中的噪声干扰,实现最优分解尺寸的确定,从而更好地适应小信噪比场合。  结果  通过软件平台分析得出在分流器的测量基础上利用优化后的小波算法去噪的抗干扰能力更强,波形质量更好。最后研制了一款泄漏电流在线检测装置,对提出的泄漏电流检测模型加以验证。  结论  实验结果表明该装置能够较好地实现避雷器泄漏电流的实时检测。     

圆阵模式空间的文化粒子群极大似然测向算法

在冲击噪声背景下给出了一种估计相干和非相干信源的均匀圆阵测向方法,即基于模式空间的低阶极大似然算法(MODE-FLOM-ML)。该算法对均匀圆形阵列的输出信号进行模式激励,使其成为模式空间内的虚拟阵列;在此基础上构造模式空间的分数低阶矩阵,成功地估计出信源的来波方向。为了快速求解所提的基于模式空间的测向算法,利用文化算法和粒子群算法的优点,设计了一种可快速进行多维搜索的文化粒子群算法。Monte-Carlo仿真试验证明了所提的CP-MODE-FLOM-ML方法在检测性能上优于基于模式空间的ROC-MUSIC和FLOM-MUSIC。     

AVL燃烧分析仪去除燃烧噪声的研究

不改变测压装置结构，在1135柴油机上进行了缸压曲线、燃烧放热率曲线误差修正研究。使用AVL燃烧分析仪进行试验，摸索出不同的去除噪声的方法的变化规律。在综合效果较好的条件下，对数字滤波、均值滤波进行对比试验。试验证明：用AVL燃烧分析仪的Concerto软什可以采用线性滤波（数字滤波）和非线性滤波（均值滤波）的方法，对燃烧曲线的误差修正采用均值滤波进行误尊处理，其效果比数字滤波更好，用其来计算其他参数，结果更准确。     

摩托车用二冲程汽油机智能点火器的研制

本文提出一种由PIC单片机控制的摩托车用智能点火系统，系统介绍了它的基本原理、系统构成、工作特点和实验研究。该系统可以根据磁电机的脉冲信号输出点火角可调的点火脉冲，实现了点火提前角的数字式控制，其结构简单，可以满足发动机对点火系统的要求。     

混合Box-Jenkins模型交替辨识及在电厂脱硝系统中的应用

混合的Box-Jenkins模型能够较好地表征含噪声干扰系统的特性,针对该模型提出了基于粒子群优化算法的过程模型与噪声模型交替估计辨识方法,避免了常规方法直接对过程模型和噪声模型共同辨识容易陷入局部最优的缺陷。仿真试验表明:交替估计算法可以达到对混合Box-Jenkins模型的精确辨识,其误差约为常规辨识的1/10。为验证方法的实用性,以某电厂机组烟气脱硝系统为对象,建立混合Box-Jenkins模型,利用粒子群算法进行交替辨识,所得过程模型与实际输出基本一致,取得了较好的参数辨识效果,该方法可应用到工业过程中这类系统的参数辨识。     

发电机励磁系统参数辨识扰动信号与辨识精度分析

为提高发电机励磁系统参数辨识精度,以MEC3300T型励磁系统为例,提出分别采用伪随机信号和阶跃信号作为扰动信号,利用混沌遗传算法对励磁系统的参数进行辨识,分析了不同的采样频率下不同扰动信号与参数辨识精度的关系及在相同的采样频率下不同信噪比的扰动信号对参数辨识精度的影响。结果表明,采用PRBS信号作为扰动信号时,辨识结果的相对误差随着采样频率的改变有一定的波动,而STEP信号为扰动信号时辨识结果的相对误差相对稳定;同一采样频率下,采样PRBS与STEP信号辨识结果的相对误差均随信噪比的增加呈指数增长。     

New noise rejection techniques on pulse-by-pulse basis for on-linepartial discharge measurement of turbine generators

On-line partial discharge tests for turbine generators are useful for recognizing abnormal or deteriorated stator winding insulation without a machine outage. One problem related to such a test is additional installation of sensors. We propose that wires of a resistance temperature detector (RTD) embedded in a stator slot are applied as a partial discharge sensor in the form of an RF coupler. The other problem is electrical noise that is a pulse similar to partial discharge in frequency characteristic and has higher amplitude than partial discharge. The sensors in two steam turbine generators showed enough sensitivity and broad frequency bandwidth to facilitate the elimination of noise from the partial discharge measurement. Two new techniques of noise rejection on a pulse-by-pulse basis are investigated with the multiple sensors. One is founded on the correlation between pulse height in two frequency bands. The other is based on the correlation between pulse height from the two partial discharge sensors. It was found that each noise rejection technique was successful in a trial testing     

一种旋转机械振动信号降噪的新方法研究

提出了采用开-闭和闭-开组合数学形态滤波器处理旋转机械振动信号的新方法。研究了数学形态滤波器对含有不同类型、不同强度噪声的振动信号的处理方法。仿真计算及实验结果表明数学形态滤波器对振动信号有很好的滤波效果,特别是对于不明原因的脉冲干扰处理,比其它数字滤波器有明显的优势。