Optimization of Parameters of a Gamma-Absorption Densimeter under Increased Detector Loadings

Mathematical relations for choosing the optimum parameters of a gamma-absorption densimeter under increased detector loadings are proposed. The criterion is the minimum density measurement error.     

Choice of the Nominal Transformation Function for a Gamma-Absorption Densimeter under Increased Detector Loadings

The nominal transformation function proposed for a gamma-absorption densimeter under increased detector loadings makes it possible to reduce the systematic error (approximation error) by 4–5 times as compared with the exponential function used in practice. Mathematical relations and techniques of calculating the coefficients of the function which enable us to describe the function using three points of the approximation segment (range) and a set of experimental data by means of the least-squares method are given. It is shown theoretically that in choosing the detector regime it is necessary to restrict our attention to increased loadings with the portion of counting errors not greater than 1/3.     

Potential Accuracy of Estimation of the Information Parameter of a Homodyne Laser Doppler Vibrometer Signal

This paper describes the analysis of the potential accuracy of estimation of the signal modulation index of a homodyne laser Doppler vibrometer with frequency modulation and known and unknown non-information parameters of the signal. The Rao — Cramer inequality is used to obtain expressions for calculating the lower bound of variance of the modulation index estimate and study its relationship with a signal/noise mixture. Recommendations on the choice of conditions for measuring the amplitude of vibro-displacement by the homodyne Doppler laser vibrometer are given.     

Selection of the separation between source and tested object for a gamma-absorption densimeter in the divergent-beam configuration

Formulas estimating the effect of gamma-beam divergence on the systematic and statistical components of errors in density measurements have been obtained. An engineering method for selection of the separation between the source and tested object for a gamma-absorption densimeter operating in the configuration of divergent beam with amplitude compensation for scattered radiation has been developed. We have estimated the efficiency of the densimeter using an isotopic gammasource with the error in density measurements prescribed on the stage of design.     

非高斯随机振动试验并行控制策略研究

针对非高斯随机振动试验控制中功率谱均衡与峭度均衡相互干涉,影响控制精度的问题,提出非高斯随机振动试验并行控制策略。在提出整个系统控制流程的基础上,分别给出功率谱均衡控制算法和峭度均衡控制算法。对蕴含峭度信息的随机信号产生机理展开研究,先给出信号产生的流程图,然后推导出符合控制系统要求的随机信号设计参数。利用功率谱设计滤波器,通过卷积运算调制出用于系统控制的驱动信号。仿真与试验结果表明,采用非高斯随机振动试验并行控制策略进行系统控制,其输出响应谱与参考谱的误差完全满足工程中常用的±3 dB控制要求,峭度控制也达到很高的精度,满足工程试验要求,从而验证该控制策略的有效性。     

A Densimeter for Precision Measurements of Densities of Liquids with an Increased Elasticity of Intrinsic Saturated Vapors

A vacuum two-capillary densimeter intended for precision measurements of densities of liquids with an increased elasticity of intrinsic saturated vapors is described. The densimeter design makes it possible to fill it in the operation mode without the occurrence of bulk or wall pockets with intrinsic saturated vapors. The temperature and concentration dependences of densities of Na–K–Cs alloys measured with this densimeter have demonstrated a high reliability of the device and accuracy of the obtained results. The measurement error is within 0.1%.     

Performance limitations of networked control systems with quantization and packet dropouts

This paper investigates the problem of optimal tracking performance of networked control systems (NCSs) with quantization and packet-dropouts. The system under consideration is linear time-invariant (LTI), multi-input multi-output (MIMO), where an H₂ norm of error signal between the reference input and the system output is used as the tracking performance index. The impacts of packet-dropouts in the communication channel and the quantized input and output are studied. The goal is to obtain the minimal error in tracking a random signal, by searching through all possible stabilizing two-parameter controllers. It is shown that, the minimum value of tracking error is closely related to the reference input signal direction, the non-minimum phase zeros and unstable poles of the given plant, including the locations and directions. We also demonstrated the quantization error and the packet-dropouts may degrade the tracking performance. A typical example is given to evaluate the theoretical results.     

Adaptive output feedback tracking of nonlinear systems with uncertain nonsymmetric dead-zone input

In this paper, the problem of adaptive practical tracking is investigated by output feedback for a class of uncertain nonlinear systems subject to nonsymmetric dead-zone input nonlinearity with parameters of dead-zone being unknown. Instead of constructing the inverse of dead-zone nonlinearity, an adaptive robust control scheme is developed by designing an output compensator including two dynamic gains based respectively on identification and non-identification mechanism. With the aid of dynamic high-gain scaling approach and Backstepping method, stability analysis of the closed-loop system is proceeded using non-separation principle, which shows that the proposed controller guarantees that all closed-loop signal is bounded while the output of system tracks a broad class of bounded reference trajectories by arbitrarily small error prescribed previously. Finally, two examples are given to illustrate our controller effective.     

Measurement of distorted exponential signal components using maximum likelihood estimation

Exponential signal is a suitable stimulus for dynamic ADC testing because of the simplicity of the generating RC circuit. A potential distortion source of the ideal exponential shape is the dielectric absorption of the capacitor, whose effect can be represented by additional superimposed exponential components with longer time constant and smaller peak value. Measurement of the distortion of the exponential signal by using a reference waveform recorder with known nonlinearity is the initial step in the calibration of an ADC testing stand with exponential stimulus, along with the assessment of its uncertainty. Lack of the orthogonality of stimulus signal components makes classical analysis methods difficult to apply.This paper presents a method for measurement of multiexponential signal components as an example of the more general task of signal decomposition where signal components are non-orthogonal. The proper optimization procedure based on the ML method will be presented, which usually reaches the global minimum of the cost function. Effectiveness will be shown by simulation, and by application to measurement of a multiexponential signal acquired by a reference waveform recorder with known error parameters.     

考虑控制电信号中间量的机床运动控制误差数据驱动建模方法

现有数据驱动的机床运动控制误差建模方法通常使用端到端的模型,即通过机器学习算法直接构建参考轨迹信息(速度、加速度等)与伺服误差之间的模型,以降低建模复杂度。然而,该方法忽视了控制电信号对运动控制系统非线性扰动的反映,而导致建立的模型精度受限。为解决此问题,提出了一种使用控制电信号作为中间量的数据驱动运动控制误差建模方法。该方法采集参考轨迹信息(速度、加速度、急动度等)、控制电信号、跟踪误差以及构造的换向特征,构建并训练基于参考轨迹信息的控制电信号预测网络,以及基于电信号和参考轨迹信息的运动控制误差预测网络,利用控制电信号这一中间量有效反应系统所受非线性扰动的特点,实现了高精度的运动控制误差数据驱动建模。在实际验证测试时,将参考轨迹信息输入电信号预测网络,而后将得到的预测控制电信号和参考轨迹信息输入跟踪误差预测网络,即可实现运动控制误差的预测。通过实验对所提出的建模方法进行了验证,所提出方法相对于传统的端到端建模方法,运动控制误差的预测精度在X轴和Y轴分别提升16.33%和20.42%,误差补偿后运动控制轮廓精度相较于未补偿提升85.59%,验证了所提出方法的可行性。     

基于LabVIEW的自动锯床位置控制系统的设计

设计了一套位置控制系统,该位置控制系统由步进电机、光电编码器、数据采集卡及LabVIEW软件平台构成。通过在LabVIEW软件中编写控制程序,将计算机给定的位置信号与采集卡采集到的实际位置信号进行比较,然后通过PID运算,将位置偏差信号转换成控制步进电机转向和转速的信号,带动同步带和指针移动,实现位置控制。多次试验证明,系统运行稳定可靠,其位置控制稳态精度≤＆#177;2 mm。该系统特别对于非NI公司的数据采集系统具有借鉴作用。     

Analysis of aged CD-R: From optical HF signal defects to digital errors

This article focuses on the CD-R defects that cause digital errors when decoding the HF signal delivered by the optical pickup of a player. We often remark that the error rate is not correlated with any of the parameters currently used to qualify the HF signal. We develop a more precise analysis of the HF signal than those of the analysers, in order to explain how errors happen in this case. The information is obtained mainly from the complete histogram of the positions of the transitions. We also check particular signal segments such as the beginnings of data frames. Using these analysis tools, we highlight different kinds of defects on aged CD-R. One of them consists in micrometre-sized dark spots, which are localized on the dye layer. More generally, the defects due to ageing cannot be characterised only by the standard parameters given by analysers.     

基于DDS算法的12导联心电信号发生器设计

心电信号发生器是研发智能心电仪器的关键设备,心率连续可变是心电信号发生器研究的难点。提出了一种用DDS(direct digital frequently synthesis)算法合成心率连续可变的多导联心电信号的方法,并在基于ARM的嵌入式实时操作系统uC/OS-II上用软件实现了该方法。首先证明了用软件实现DDS算法产生心电信号的可行性;针对心电信号的频率特点给出了算法的基本参数;并根据DDS算法思想给出了一种查找表(LUT)长度调整的方法;最后分析了本方法误差的主要来源,通过理论推导得出系统误差为26×10-6。实验结果证明本方法行之有效,具有理论和实际意义。     

Model reference adaptive control of a time-varying parabolic system

Related to the error dynamics of an adaptive system, averaging theorems are developed for coupled differential equations which consist of ordinary differential equations and a parabolic partial differential equation. The results are then applied to the convergence analysis of the parameter estimate errors in the model reference adaptive control of a nonautonomous parabolic partial differential equation with lowly time-varying parameters.     

基于变分贝叶斯平行因子分解的缺失信号的恢复

现有的工程信号处理方法都是基于完整的数据采集,并没有考虑缺失信号的处理。而在工程实际中,由于人为因素和自然界不可抗拒的因素,有时会造成传感器失效,从而造成信号采集的缺失。为了消除信号缺失对工程信号处理的消极影响,提出了一种基于变分贝叶斯平行因子分解的信号恢复方法。首先利用平行因子分析理论将采集的振动信号构造成三维张量,同时结合贝叶斯方法,引入潜在变量和超参数,建立贝叶斯平行因子概率图模型;其次采用变分贝叶斯算法推导出因子矩阵和超参数的后验分布,从而进一步推断出缺失元素的分布预测;最后通过分析该模型的下界,初始化参数的选择,使该算法更好的解决信号缺失问题。利用均方根误差和相对平方根误差对该算法的性能进行评估,仿真和实验结果表明,随着缺失比例的增大,变分贝叶斯平行因子分解算法相较于传统的低秩张量补全算法,误差更小,能够更加有效的恢复缺失的信号,有效地解决了工程信号处理中因传感器失效而引起的信号缺失的问题。     

A high-resolution digital time-interval measurement instrument

A new method for time-interval measurements is described and the results of measurements on a prototype are given. This method uses a virtually periodic exponential signal as the reference clock and consists of measuring both the phase deviation and the number of cycles of this clock signal between the beginning and the end of the unknown time-interval. The use of two auxiliary sinusoidal signals in order to measure the phase of the corresponding periodic exponential signal is discussed, also considering the main causes of error. The functional block diagram of the prototype is described in detail and the measurement results show that a resolution improvement of two orders of magnitude with respect to the period of the clock signal can easily be obtained.     

Effect of the Multiplicative Instrumental Error on X-Ray Measuring Instrument Characteristics

Mathematical relations between the multiplicative instrumental component of the measurement error in a tested parameter and the level of uctuations of characteristics of an electronic channel are obtained for certain forms of amplitude distributions and conditions of selecting pulses from a detector. It is shown theoretically that the instrumental error plays an important role in choosing the main and optimum parameters of the measurement tools, in particular, under increased detector loadings. Practical methods of taking into account and reducing significantly the instrumental error for particular situations are given with reference to the use of SBM-20 counters in gamma-absorption densimeters.     

Seismic Signal Processing for Estimating the Path of a Moving Vehicle

The application of signal energy parameters to estimate the motion of objects with continuous influence on soil in systems of passive seismic location is considered. Statistics for measured values of signal powers with account for energy properties of the medium are proposed. The influence of displacement of the object on the ratio of signal powers on different sensors is analyzed. The results of testing the algorithm for estimating the parameters of the path of rectilinear motion of a car are given.     

嵌入式时栅角位移传感器短周期误差分析与补偿

为提高嵌入式时栅角位移传感器测量精度,从传感信号形成机理出发,对短周期误差成因进行了详细分析。通过对绕组等效分析和激励信号分析,确定了短周期误差的主要特性为一次和二次误差,一次误差来源为零点残余误差和直流分量误差,二次误差来源为激励信号正交误差。针对短周期误差补偿,提出了基于超限学习机的误差补偿方法,通过对测量值与真实值样本的训练得到模型最优参数,根据模型参数建立短周期误差模型,利用所得误差模型实现对短周期误差的补偿。实验结果表明,短周期误差分析结果与传感器实际误差特性一致,采用该补偿方法传感器短周期误差大幅度降低,降低了约96%。对比和重复性实验表明,该方法与谐波补偿法相比精度提高了约1倍,误差补偿效果更优,同时方法具有良好的测量稳定性,对提高嵌入式时栅角位移传感器的测量精度具有重要的理论和现实意义。     

Improvement of the measurement uncertainty of a high accuracy single sinker densimeter via setup modifications based on a state point uncertainty analysis

The single sinker densimeter with magnetic suspension coupling is one of the state of the art methods for the accurate measurement of fluid densities. The uncertainties of experimental pressure, density and temperature data, measured with a single sinker densimeter, were thoroughly evaluated following the uncertainty propagation law. The main uncertainty sources of each magnitude were determined. Based on this statistical study, several modifications were performed to reduce the uncertainty associated to each magnitude. Firstly two new PTR-25 probes were added. Secondly a new pressure transducer for the low pressure range was added. Finally the sinker of the densimeter was replaced by a bigger one to improve the balance reading. After these modifications the uncertainty of each magnitude was evaluated and validated with a Monte Carlo simulation. Results yielded a significant reduction of 44% in temperature uncertainty, more than 92% on pressure below 2 MPa, and more than 22% on density.