Influence Of Measurement Noise Research Articles

Target range evaluation using video sensor and analysis of the influence of measurement noise and errors

This paper presents mathematical model of determining target range by analyzing video frame during the tracking. The contribution of effective parameters to accuracy are analyzed and values of standard deviation are determined. .

Structural Damage Detection using Best Approximated Dead Load Redistribution

Presented in this article is a novel damage detection method based on best approximation of dead load stress redistribution due to damage. It is a simple, economical, fast, and passive method that requires no artificial means of loading. The measurement is made of strain readings due to dead load at different stages of the structure during its life cycle. The approach is by finding a ‘null plane’, which is a unique identity of each structural member, such that the measurement is closest to its orthogonal projection on this null plane. The detection procedure resembles the process of finding the shortest distance from a point to a plane in elementary geometry. Both theoretical proof with a flexibility formulation and practical procedure with a stiffness formulation are given. The feasibility of the proposed method, together with the false positive test, are studied in a numerical example of a synthetic frame structure. Measurement noise influence is also conducted using perturbed strain measurement.

Damage detection of mono-coupled periodic structures based on sensitivity analysis of modal parameters

A sensitivity-based method for localization and assessment of damage in mono-coupled periodic structures is presented in this paper, in which slopes and curvatures of mode shapes are used to localize damage, and natural frequencies are then utilized to quantify the damage. The expressions of sensitivity coefficients of mode shapes, slopes, and curvatures of a mono-coupled periodic system are first derived in terms of receptances of periodic element. A mono-coupled periodic spring-mass system with 10 degrees of freedom is used to carry out a sensitivity study to compare the sensitivities of natural frequencies, mode shapes, slopes, and curvatures to damage. The results show that the sensitivities of these modal parameters in a mono-coupled periodic structure do not depend on the structural parameters, and therefore there is no need for a prior analytical model of the structure. The study also demonstrates that among these modal parameters, curvatures of modal shapes are most sensitive but slopes of mode shapes seem to be more indicative of damage location. A 20-element mono-coupled periodic spring-mass system is adopted to demonstrate the capacity of the proposed method to localize and quantify damages in the mono-coupled periodic system. Finally, a 3-storey near mono-coupled periodic experimental building is used to verify the actual application of the proposed method in consideration of the influence of measurement noise and non-perfect periodicity of actual engineering structures. Numerical and experimental results illustrate that only using a few lower modes with or without noise pollution can accurately detect damages in a mono-coupled periodic or a near mono-coupled periodic structure, either single or multiple damage locations and slight or severe damages.

Load profile estimation in electric transmission networks using independent component analysis

It is important to estimate electric loads profiles in the deregulated environment where competing entities need to assess the load demands based on partial knowledge of the system. Independent component analysis (ICA) is a statistical technique used to separate linear mixtures of statistical independent source signals by maximization of negentropy. In this paper, we apply ICA to estimate load profiles using only a small set of active line flow measurements without prior knowledge of the electric network model parameters or topology. A filtering based preprocessing technique is used to ensure statistical independence of load components. The influence of measurement noise and nonlinearity of the power flow model are also investigated. The proposed approach is demonstrated for a five-bus system as well as the IEEE 30-bus system.

Examples of Analysis of Stochastic Processes Based on Time Series Data

Time series data from stochastic processes described by the Langevin equation are analyzed. Analysis is based on estimation of the deterministic and random terms of the Langevin equation from data. The terms are presented as fields and inspected visually. Forming a model of the process, the terms are also used to reconstruct the deterministic and stochastic process trajectories. The deterministic term is approximated by an analytical ansatz. The equations obtained by the approximation are used to generate deterministic process trajectories and to study their linear stability. Influence of measurement noise on the estimates is also discussed.

OS09W0054 Impact force identification of CFRP laminated plates using PZT sensors

The information of applied external forces is very important and useful in the assessment of integrity of structures. An identification method of impact force is presented in this paper. First, the relation between force histories and strain responses is formulated based on the finite element method (FEM). By applying this formulation, an error vector that indicates the force location is defined with strain responses measured at multiple points in a structure. The inverse problem can be solved with the conventional least-square method, but in an actual system, the identified force history has a large oscillation because of the influence of measurement noise and FEM modeling error. To overcome this difficulty, second, the present paper proposes a reliable force identification method that imposes the penalty on the derivative of the force history. The present method has been applied to carbon fiber reinforced plastic (CFRP) laminated plates with a SMART Layer embedded lead zirconate titanate (PZT) piezoelectric sensors. The experimental results for two kinds of plates are reported in this paper. According to the results of force location and history identification, the validity of the present method is verified, and the influence of the modeling error involved in the finite element model is discussed.

Optimal Estimation of Dynamic Loads for Multiple-Input System Using Wiener Filtering Technique. 1st Report. Basic Study and Experiment Verification.

An optimal method is developed to estimate the dynamic loads for systems subjected to multiple inputs. The method focuses on minimizing the ensemble mean square error of the estimation. First, the inverse system analysis technique is employed to establish the error estimation equation. Then, by applying the noncausal Wiener filtering theory, the optimal estimator of dynamic loads is derived out. Both numerical simulation and experimental results demonstrate that the method is of a good ability in suppressing the influence of measurement noises than conventional methods, which based on solving inverse matrix of transfer function, and is rather effective and practicable for dynamic load estimation.

Tracking filters and models for seeker applications

Two-state tracking filters are considered for seeker applications. Estimation of the line-of-sight (LOS) rate is the main purpose and equations of motion for the LOS are discussed and simplified for design. An observer approach is applied, the filter transfer functions are given and the gain is designed by pole placement. Also a measurement time delay is taken into account. The filter properties are investigated for deterministic LOS rotations, which is a case of practical interest, corresponding to target maneuvers. The influence of measurement noise is also considered.

A new method and device for motion accuracy measurement of NC machine tools. Part 1: principle and equipment

This paper describes in two parts a new method and device for measuring motion accuracy of numerical control (NC) machine tools. In the first part, the measurement principle and the characteristics of the prototype device are proposed. The device consists of a double-bar linkage with two rotary encoders. The working range of the device is disc-shaped with a radius of almost the double the link length, except a small area around the centre of the disc and an outer area both around the change points of the linkage at the centre and the circumference of the disc. Because the method has high resolution for any measuring point within the working range, it can be applied to measure most items of motion accuracy of NC machine tools. The method is particularly suitable to measure the trajectory accuracy of circular motions. The device has a compact structure and its installation on a machine tool to be measured is simple and quick. The experimental results show that the prototype device has very good response to small displacement and good repeatability with high precision to the measurement of circular motion trajectories. The influence of measurement noise is hardly observed in the experimental results.

Estimation of the local thermal conductivity field of a plane heterogeneous medium with infrared image processing and the volume-averaging method

The estimation of local thermophysical properties can be of paramount importance in the study of heterogeneous media. The volume-averaging method is used to implement an estimation method of a local thermal conductivity field of a two-dimensional heterogeneous medium. The method is tested with experimental transient temperature fields, obtained with a calibrated sample with an infrared camera. A large number of images was processed in the transient state. The same intrinsic stationary field is estimated from each image. By means of repeated estimations, this method reduces the measurement noise influence.

Calibration of a hexapod machine tool using a redundant leg

Parallel configurations are recently being applied to the machine tool with the hopes of greater rigidity, stability, and accuracy than conventional multi-axis structures allow. However, the many calibration methods presently available for serial machine tools are not applicable to hexapod type structures. A calibration method is presented that uses a ball–bar or other simple length measuring device to act as an ‘extra leg,’ allowing calibration of the hexapod's true kinematic parameters. This method utilizes a total least squares minimization, does not require any special hexapod configuration or difficult six degree of freedom pose measurements, and is effective with as few as one additional length sensor. Selection of calibration pose sets is briefly discussed, as well as the influence of measurement noise on calibration accuracy. Simulations show the potential for this algorithm to significantly reduce errors to the point where machining errors are within 5–10 times the measurement errors.

Estimation of Local Thermophysical Properties of a One-Dimensional Periodic Heterogeneous Medium by Infrared Image Processing and Volume Averaging Method

Abstract The estimation of local thermophysical properties can be of paramount importance in the study of heterogeneous media. The volume averaging method, here reduced to a one-dimensional line averaging, is used to implement an estimation method of local thermal resistivity field, for a stratified medium. The method is tested with experimental transient temperature fields obtained with a calibrated stratified sample by an infrared camera. A large number of images are processed at the transient state. The same intrinsic stationary field is estimated from each image. By repeated estimations, this method reduces the measurement noise influence. [S0022-1481(00)01701-1]

Optimal Estimation of Dynamic Loads for Multiple-Input System

An optimal method is developed to estimate the dynamic loads for systems subjected to multiple inputs. The method focuses on minimizing the ensemble mean square error of the estimation. First, the inverse system analysis technique is employed to establish the error estimation equation. Then, by applying the noncausal Wiener filtering theory, the optimal estimator of dynamic loads is derived out. Numerical simulation work demonstrates that the method is of a good ability in suppressing the influence of measurement noises on estimation accuracy. Meanwhile, the simulating calculation of load estimation by a conventional method is also performed and the comparison of both results shows that the method proposed in this paper is rather effective and practicable for dynamic load estimation.

Hardware and software systems for the determination of charged particle parameters in low pressure plasmas using impedance-tuned langmuir probes

Abstract A computer-controlled, impedance-tuned Langmuir probe data acquisition system and processing software package have been designed for the diagnostic study of low pressure plasmas. The combination of impedance-tuning and a wide range of applied potentials (± 100 V) provides a versatile system, applicable to a variety of analytical plasmas without significant modification. The automated probe system can be used to produce complete and undistorted current-voltage (i-V) curves with extremely low noise over the wide potential range. Based on these hardware and software systems, it is possible to determine all of the important charged particle parameters in a plasma; electron number density ( n e ), ion number density ( n i ), electron temperature ( T e ), electron energy distribution function (EEDF), and average electron energy (〈e〉). The complete data acquisition system and evaluation software are described in detail. A LabView (National Instruments Corporation, Austin, TX) application program has been developed for the Apple Macintosh line of microcomputers to control all of the operational aspects of the Langmuir probe experiments. The description here is mainly focused on the design aspects of the acquisition system with the targets of extremely low noise and reduction of the influence of measurement noise in the calculation procedures. This is particularly important in the case of electron energy distribution functions where multiple derivatives are calculated from the obtained i-V curves. A separate C-language data processing program has been developed and is included here to allow the reader to evaluate data obtained with the described hardware, or any i-V data imported in tab separated variable format. Both of the software systems are included on a Macintosh formatted disk for their use in other laboratories desiring these capabilities.

Orthogonal modal reconstruction of a wave front from phase difference measurements

The problem of retrieving the expansion coefficients of a wave front from phase difference measurements in a square domain has been studied using the orthogonality properties of the Gram polynomials. An expression for the coefficients to be obtained independently as weighted sums over the experimental data is given and the influence of measurement noise in the estimate will be analysed, obtaining very good agreement with previous results of zonal and modal estimation with phase difference measurements.

A study on higher-order disturbance observer and robust stability

In earlier papers, it has been reported that a fast and precise servo system, which has low sensitivity to parameter variation and disturbance, can be realized with simple structure by using a high-order disturbance observer. However, no clear and simple design method satisfying specifications for robust stability, the influence of measurement noise, and relative stability (damping characteristics) for large parameter variation has been proposed. In this paper, we clarify the class of robust servo systems realized by adjusting the order of the disturbance observer and the control parameters. We apply this strategy to the design of a second delay system, such as a position servo system, and realize a high-performance robust servo system using a high-order disturbance observer. © 1999 Scripta Technica, Electr Eng Jpn, 128(1): 37–44, 1999

Sub-surface feature location and identification using inverse TLM techniques

This paper describes several techniques involving transmission line matrix modelling which can be used to locate and characterize inhomogeneous features within a circuit package where the thermal response to heating of the underside is inspected at the top surface. These are used to confirm a semi-empirical thermal non-destructive testing approach to the determination of the lateral dimensions of a feature. The time to maximum contrast is an important parameter which can be used to estimate the depth of the same feature. This paper then describes our approach to the determination of feature thermal parameters and the influence of measurement noise on overall accuracy of the estimate.

Hardware and software systems for the determination of charged particle parameters in low pressure plasmas using impedance-tuned Langmuir probes

A computer-controlled, impedance-tuned Langmuir probe data acquisition system and processing software package have been designed for the diagnostic study of low pressure plasmas. The combination of impedance-tuning and a wide range of applied potentials (± 100 V) provides a versatile system, applicable to a variety of analytical plasmas without significant modification. The automated probe system can be used to produce complete and undistorted current-voltage (i-V) curves with extremely low noise over the wide potential range. Based on these hardware and software systems, it is possible to determine all of the important charged particle parameters in a plasma; electron number density ( n e ), ion number density ( n i ), electron temperature ( T e ), electron energy distribution function (EEDF), and average electron energy (〈ε〉). The complete data acquisition system and evaluation software are described in detail. A LabView (National Instruments Corporation, Austin, TX) application program has been developed for the Apple Macintosh line of microcomputers to control all of the operational aspects of the Langmuir probe experiments. The description here is mainly focused on the design aspects of the acquisition system with the targets of extremely low noise and reduction of the influence of measurement noise in the calculation procedures. This is particularly important in the case of electron energy distribution functions where multiple derivatives are calculated from the obtained i-V curves. A separate C-language data processing program has been developed and is included here to allow the reader to evaluate data obtained with the described hardware, or any i-V data imported in tab separated variable format. Both of the software systems are included on a Macintosh formatted disk for their use in other laboratories desiring these capabilities.

Robustness metrics for measuring the influence of additive noise on the performance of statistical classifiers

This paper presents a novel quality measure called robustness. The robustness measure quantifies the influence of measurement noise in the attribute values on the credibility of the classification of a case. It is assumed that the type of distribution of the noise-generating process is known. It is not simple to measure the robustness in the general situation where the noise-free distribution of the attributes is unknown. Therefore, two approximations are suggested and compared with the robustness measure based on the noise-free distribution of the attributes. The usefulness of the suggested robustness measure is explored in a simulation experiment.

Parameters of the O( 1S) excitation process deduced from photometer measurements of pulsating aurora

Intensity time-series of the 427.8 nm N 2 + (1NG) (0,1) band and 557.7 nm O( 1S- 1D) line emissions were obtained with 0.05 s time resolution during intervals of pulsating aurora. Using an impulse response function analysis technique in conjunction with synthetic intensity time-series constructed using measured data, we estimate the influence of measurement noise and a non-linear component of the covariance between the 557.7 nm and 427.8 nm intensity time-series on the inferred parameters of an O( 1S) indirect excitation model. Non-linear effects had no additional influence beyond that of measurement noise on estimates of an indirect process. After accounting for the influence of measurement noise, indirect excitation accounts for between 30% and 100% of O( 1S) production, with an average for our measurements of 58%. The average effective lifetime of the species responsible for the indirect excitation process is 0.13 s. The average percentage contribution from the indirect process is 14% lower, and the effective lifetime slightly longer, than values obtained when noise is not accounted for. Non-linearities between the auroral emissions limit the determination of the O( 1S) effective lifetime by this technique. We obtain an O( 1S) effective lifetime distribution with a mean of 0.71 s and a sharp cut-off at the radiative lifetime of ∼0.80 s. O( 1S) state effective lifetimes decrease as average incident electron energies, determined from the relative O( 1S- 1D) and N 2 + (1NG) intensities, increase. Collisional deactivation of the O( 1S) state can account for only of the order of 55% of the energy dependence of the O( 1S- 1D) and N 2 + (1NG) intensity ratio.