混沌态杜芬振子与弱正弦信号参量估计

建立了一个对微弱正弦信号参量变化极其敏感的动力学系统.首先对多参量简化杜芬方程进行了改进,采用梅尔尼科夫过程函数讨论了方程的解和微分流形的演化情况;分析了非高斯色噪声对杜芬振子混沌运动行为的影响;进而提出了一种新的非高斯色噪声背景下正弦信号参量估计方法.理论分析和仿真实验都表明,此杜芬振子混沌状态下对任何零均值噪声具有免疫力,对正弦信号参量变化极为敏感.     

Uncertainties in quantization-noise estimates for analog-to-digitalconverters

Estimates of quantization noise, obtained by stimulating an ideal analog-to-digital converter with a sine wave contained in the input range, are affected by an appreciable uncertainty, which may affect SNR and ENB specifications, especially in the case of low resolution devices. The uncertainty can be eliminated, when possible, by the use of an input sine wave bringing the converter into saturation. The different effects of additive noise on the noise estimates obtained by the various test procedures are also discussed, showing, in particular, that quantization noise may be overestimated by histogram testing with a nonsaturating input sine wave. Therefore, any noise specification should clearly make reference to the test signal parameters and to the instrumentation characteristics     

光纤水听器调制激光光源的一种实现方法

在干涉型光纤水听器的信号检测技术中,采用相位载波零差检测方式,直接调制激光光源,具有明显的优越性。提出了一种实现方法,通过产生高频正弦波,对激光光源(多量子阱分布反馈激光器),进行直接驱动调制。光源调制输出波形精确多样(正弦波、三角波(包括锯齿波)和方波),输出频率大范围(0～20MHz),连续可调。实验表明达到了水听器对光源的要求。此调制技术也可在光纤通信等其它领域得以应用。     

基于声学法测温的声波飞渡时间研究

声波飞渡时间的准确测量是声学法测温中影响温度场测温准确性的主要因素。采用互相关分析法计算单一频率声波信号及宽带频率声波信号的声波飞渡时间,仿真结果表明宽带频率信号由于具有较强的抗噪能力在计算声波飞渡时间时不受声波信号周期、信号延时时间等因素的限制,可用于工程实践。同时采用频率为40kHz的正弦波超声波探测器在均匀温场条件下对超声波信号的衰减程度进行试验研究,试验结果表明40kHz的正弦波超声信号在不经过放大处理条件下,其可测温场的距离仅为160mm。     

ADC Testing With Verification

An important method for analog-to-digital-converter (ADC) testing is sine wave fitting. In this method, the device is excited with a sine wave, and another sine wave is fitted to the samples at the output of the ADC. The acquisition device can be analyzed by looking at the differences between the fitted signal and the samples. The fit is done using the least-squares (LS) method. If the samples of the error (the difference between the fitted signal and the samples) were random and independent of each other and of the signal, the LS fit would have very good properties. However, when the error is dominated by quantization error, particularly when a low bit number is used or the level of the measured noise is low, these conditions are not fulfilled. The estimation will be biased, and therefore, it must be corrected. The independence of the error samples is more or less true if the sine wave is noisy or dither is used. In these cases, the correction is not necessary. Therefore, it is reasonable to analyze the effect of the potentially unnecessary correction to noisy data, and it is desirable to determine the magnitude of the noise from the measurements. In this paper, these two questions are investigated. The variance of the corrected estimator is investigated, and a new noise estimation method is developed and analyzed.      

基于ARM微处理器的气动变载荷摩擦磨损试验机测控系统

针对不同固体材料在不同条件下的摩擦磨损实验要求,设计了一种基于ARM微处理器的气动变载荷摩擦磨损试验机测控系统。采用气动加载方式,加载形式包括正弦波、方波、锯齿波、三角波、随机波等。气动加载采用Fuzzy-PID闭环控制,提高了动态加载性能。可通过测量实验中的摩擦力、摩擦系数、磨损量、温度、振动等参数来研究变载荷对材料摩擦磨损性能的影响。最后对A3钢材料的摩擦磨损性能进行试验,证明该试验机性能稳定,测控系统准确可靠。     

微电阻率成像测井仪发射电路设计

针对微电阻率成像测井仪的特点,设计了一种基于PWM方式的正弦信号发射源。该系统以PIC单片机为主控芯片,并利用其产生的PWM信号,经半桥功率放大,低通滤波,最后由变压器输出正弦波,为微电阻率成像测井提供信号激励源。实验结果表明,正弦波幅度满足采集电路要求,信噪比满足数据处理电路要求。发射电路已成功运用于实际仪器中,取得了良好的应用效果。     

The use of DFT windows in signal-to-noise ratio and harmonicdistortion computations

The discrete Fourier transform (DFT) can be used to compute the signal-to-noise ratio (SNR) and harmonic distortion of a waveform recorder. When the data record contains a non-integer number of cycles of the sine wave, energy leaks from the sine wave and its harmonics to adjacent frequencies. A.L. Benetazzo et al. (1992) describe a windowed DFT method for computing the RMS value of a sine wave from the magnitude of the main lobe of its DFT and recommend the use of minimum energy windows. We present criteria for choosing the DFT window. A constraint for the window coefficients is derived to insure that quantization error does not influence the estimate of the amplitude of a sine wave from the main lobe of its DFT     

非均匀采样条件下残周期正弦波形的最小二乘拟合算法

对一种用三参数正弦波拟合算法实现的四参数最小二乘正弦波拟合算法进行了实验研究。主要针对在极低频率正弦信号测量控制过程中问题比较突出的,以不足一个信号周期且非均匀采样的部分信号波形估计其4个参数的工程问题。提出了一种以局部周期正弦波形实现的四参数拟合方法,其优点是无需先验初值估计。仿真及实验均证明了该方法的有效性和可行性,从而为波形参数测量与控制提供了一种实现方式。     

正弦波形参数拟合方法述评

回顾了四参数正弦波曲线拟合方法及相关问题的研究进展,包括拟合算法的研究,拟合算法的比较研究,拟合算法的评价研究,以及不同条件下拟合算法的研究进展.针对拟合算法的误差界研究进展以及如何降低拟合误差的滤波技术进展情况也进行了专门介绍.另外介绍了相应的单参数、双参数、三参数正弦波拟合研究进展状况以及多频正弦参数估计技术进展状况.     

A new adaptive control of dual-motor driving servo system with backlash nonlinearity

In order to weaken the influence of backlash nonlinearity on a dual-motor driving servo system, we first establish the state-space model of the system. We then propose a new adaptive controller combining a projection algorithm with backstepping control for the first time, to the best of our knowledge, and analyze its stability. In the simulation analysis, we respectively choose a triangular wave, sawtooth wave, and random signal as the input signal. Simulation results validate a higher tracking accuracy and stronger adaptability of the proposed control law than that of mere backstepping control. In the experimental tests, we respectively choose a step signal and sine signal and simultaneously apply a white noise signal to the system output after 3 s in each test. The test results validate a stronger adaptability and robustness than that of mere backstepping control.     

The implementation of a digital sine wave oscillator using theTMS320C25: distortion reduction and applications

The implementation of a digital sine wave oscillator using the TMS320C25 digital signal processor (DSP) is described. The system is implemented with the Dalanco Spry model 25 DSP board, and a software system is designed whereby an IBM PC host computer provides control of the waveform generator functions and parameters. Waveforms are generated using the lookup-table (LUT) method. The methods of direct LUT and linear interpolation of missing samples are implemented and compared with a method that uses a trigonometric identity to reduce the harmonic distortion of the sine wave by effectively increasing the table length of the direct LUT method. The results of an experiment performed in the digital domain are presented without consideration of the problem of analog reconstruction. The oscillator can produce a sine wave without the nonuniform sampling distortion associated with fractional addressing, over the range of 7.2 Hz to 58.8 kHz, with a resolution of 7.2 Hz using 384 data words. The trigonometric identity method uses less data memory than other methods for the same distortion levels. Waveforms for the sum of two sine waves, a frequency swept sine wave, amplitude modulation (AM), and frequency modulation (FM) signals are shown as applications of the waveform generator     

Precision Differential Sampling Measurements of Low-Frequency Synthesized Sine Waves With an AC Programmable Josephson Voltage Standard

We have developed a precision technique to measure sine-wave sources with the use of a quantum-accurate ac programmable Josephson voltage standard. This paper describes a differential method that uses an integrating sampling voltmeter to precisely determine the amplitude and phase of high-purity and low-frequency (a few hundred hertz or less) sine-wave voltages. We have performed a variety of measurements to evaluate this differential technique. After averaging, the uncertainty obtained in the determination of the amplitude of a 1.2 V sine wave at 50 Hz is 0.3 $muhbox{V/V}$ (type A). Finally, we propose a dual-waveform approach for measuring two precision sine waves with the use of a single Josephson system. Currently, the National Institute of Standards and Technology (NIST) is developing a new calibration system for electrical power measurements based on this technique.      

一种四参数正弦参量估计算法的改进及实验分析

结合频率估计和三参数正弦波拟合实现的四参数最小二乘拟合算法,具有算法简洁、无须预估参数、无须迭代、绝对收敛、运算速度高等特点。但在实际应用中效果很不稳定,对较低位数A/D的情况,经常准确度很低或给出错误结果。针对这一问题,进行了实验分析,给出了改进措施,明确了算法使用的边界限制条件,从而为该方法的推广应用奠定了基础。数据实验结果验证了改进措施和边界条件的有效性与可行性。该改进算法可用于正弦波形4个参数的测量与估计。     

High pwder Nd-YAG laser welding of SiC particle reinforced aluminium alloy 2124

Abstract

The effects of different Nd-YAG laser output waveforms on the weldability of a SiC particle reinforced aluminium alloy 2124 have been studied. The results show that although the square waveform can produce the greatest depth-of-penetration among the three different waveforms studied, i.e. continuous wave, sine wave and square wave, a high level of porosity was observed in the weld. Alternatively, porosity free welds with a reasonable depth-of-penetration can be obtained by using a sine waveform operated at high peak powers. However, the results also show that it would be difficult to stop theformation of aluminium carbides entirely in the fusion zone simply by varying the laser output parameters and the waveform. In order to stop the, formation of carbides, a new laser joining technique has been developed. This involved brush plating of nickel on the joining surfaces before laser welding. The results of the corrosion tests of the weld zone show that welding with a nickel coating would result in a much lower corrosion current than that without nickel coating.     

直接拉伸循环荷载作用下混凝土滞回特性实验研究及定量分析

由于直接拉伸试验较为困难,可靠的数据十分少有。采用液压闭环伺服材料试验机MTS322试验装置(MTS)对混凝土进行了高应力轴拉往复试验,试验采用正弦波进行加载。对混凝土应力和应变的相位差引起的滞回现象进行研究。加载时应变波和应力波的相位差与卸载时不同,加载与卸载的相位差导致了一个不对称的滞后回路。随着加载频率的增加,混凝土的耗散角减小,约为其切线模量的“X”形夹角的一半。     

Synthesising gene clock with toggle switch and oscillator

The usefulness of a genetic clock lies in its role to stimulate a sequence of logic reactions for sequential biological circuits. A clock signal is a periodic square wave, its amplitude alternates at a steady frequency between fixed minimal and maximal levels. Transition between the minimum and the maximum is instantaneous for an ideal square wave; however, the function is unrealisable in physical bio‐systems. This research develops a new genetic clock generator based on a genetic oscillator, in which, a sine wave generator is adopted as a signal oscillator. It is shown that combination of a genetic oscillator with a toggle switch is able to generate clock signals forming an efficient way to generate a near square wave. In silico study confirms the proposed idea.Inspec keywords: genetics, oscillators, biological techniques, square‐wave generators, switchesOther keywords: toggle switch, genetic clock, logic reaction sequence, sequential biological circuits, clock signal, periodic square wave, physical biosystem, genetic clock generator, sine wave generator, signal oscillator, genetic oscillator     

Digital spectra of nonuniformly sampled signals. II. Digitallook-up tunable sinusoidal oscillators

For Part I see ibid., vol.37, no.2, June 1988. The author presents theories and applications of a digital spectrum analysis technique for a class of nonuniformly sampled signals. The structure of the harmonic components present in a digitally synthesized sine wave is analyzed using a table look-up method. The digital table look-up method offers several desirable features, such as high-frequency stability and precision control of both the frequency and the phase of the generated sine wave. However, undesirable spurious harmonic components are generated when one tries to tune to different frequencies by manipulating the memory-addressing mechanism rather than loading a new waveform sample into the waveform memory, which is generally time-consuming and sometimes infeasible. The frequencies, amplitudes, and phrases of all the spurious harmonic components are derived in closed form     

基于假人冲击响应评估抗冲地砖防护性能试验研究

由于水下爆炸在极短时间内产生的巨大冲击加速度会致舰船人员严重损伤、而新型抗冲击地砖通过橡胶材料可吸收冲击能量、降低舰员脚底部载荷,用双波冲击机模拟3种典型冲击强度,用国际标准假人作为试验载体,记录冲击过程中假人主要部位的冲击响应,并对试验结果进行分析、评估。结果表明,舰员抗冲击地砖具有较好的抗冲击防护作用,可衰减60%以上冲击载荷,能有效降低舰员冲击损伤程度。     

A comparative evaluation of some practical algorithms used in theeffective bits test of waveform recorders

A comparative evaluation of programs used in the effective bit test is described. Several methods of determining the best-fit sine wave were tested using computer-generated data contaminated to varying degrees with white noise. These data were supplemented with actual records of sine waves obtained using fast digitizers with 6- to 12-bit resolution and recorded lengths of 512-2000 words. The programs were evaluated for relative accuracy, absolute accuracy, and efficiency, both in terms of how often each method converged and also of how much computer time each method took to converge. It has been found that in some cases the accuracy varies with record length and preliminary investigations of this effect are reported