Large Measurement Errors Research Articles

A high-accuracy and low-complexity phasor estimation method for PMU calibration

Due to the increasing development of renewables in power systems, the requirements for phasor measurement units (PMUs) become higher. A PMU calibrator is an important tool to test and calibrate PMUs to ensure their measurement performance. This device can provide accurate reference values for error analysis of PMUs. In this paper, a phasor algorithm with low computational complexity and high accuracy is proposed for the PMU calibrator. This method reduces the processor requirements and development cost of the calibrator, thereby facilitating its popularization. At first, an enhanced discrete Fourier transform (DFT) method is put forward: 1) the frequency response of the windowed DFT method is analyzed to reveal its large measurement errors under dynamic conditions; 2) the parameter requirements of the DFT window that is regarded as a lowpass filter are analyzed, and thus a lowpass filter with better filtering performance is designed as the window coefficients to improve the estimation accuracy. Then, based on the enhanced DFT algorithm, a calibrator algorithm framework consisting of two-stage filters and signal recognition module is established. This algorithm can consider the anti-interference ability and dynamic measurement accuracy at a low reporting rate. Simulation and experimental test results show that the proposed calibrator algorithm provides high-accuracy measurements of the static and dynamic signals with low computational complexity.

Closed-Form Solution and Experimental Verification for the Axisymmetric Deformation Problem of Blistering Circular Thin Polymer Films under Uniformly Distributed Gas Pressure.

The existing studies indicate that the measurement formulas used in blister test techniques, which are used to measure the mechanical properties of thin-film/substrate systems, are usually given based on an approximation—that is, the applied direction of the uniformly distributed transverse load is always vertical, while the applied direction of the uniformly distributed gas pressure is always perpendicular to the surface of the thin film. This approximation will lead to a large measurement error. In this study, we obtained the analytical solution to the problem of axisymmetric deformation of blistering circular thin polymer films under the action of uniformly distributed gas pressure via the power series method. An example is given to illustrate the error caused by the approximation mentioned above, and the validity of the solution presented here is verified. The result shows that the chance of error caused by the approximation increases with the increase in the applied load, and it far exceeds the allowable error of measurement when the applied load is relatively large. In addition, the related experiments of the blistering circular thin polymer film under uniformly distributed gas pressure are carried out, and the experimental results are compared with the theoretical results. The comparison results show that the analytical solution given in this paper is correct. The solution presented here is of great significance to improve the measurement accuracy of the blister test technique.

Lead-Wire-Resistance Compensation Technique Using a Single Zener Diode for Two-Wire Resistance Temperature Detectors (RTDs)

In remote measurement systems, the lead wire resistance of the resistance sensor will produce a large measurement error. In order to ensure the accuracy of remote measurement, a novel lead-wire-resistance compensation technique is proposed, which is suitable for a two-wire resistance temperature detector. By connecting a zener diode in parallel with the resistance temperature detector (RTD) and an interface circuit specially designed for it, the lead-wire-resistance value can be accurately measured by virtue of the constant voltage characteristic of the zener diode when reverse breakdown occurs, and compensation can thereby be made when calculating the resistance of RTD. Through simulation verification and practical circuit testing, when the sensor resistance is in 848–2120 Ω scope and the lead wire resistance is less than 50 Ω, the proposed technology can ensure the measuring error of the sensor resistance within ±1 Ω and the temperature measurement error within ±0.3 °C for RTDs performing 1000 Ω at 0 °C. Therefore, this method is able to accurately compensate the measurement error caused by the lead wire resistance in two-wire RTDsand is suitable for most applications.

Data-driven experimental modal analysis by Dynamic Mode Decomposition

This paper discusses the application of Dynamic Mode Decomposition (DMD) to the extraction of modal properties of linear mechanical systems, i.e., experimental modal analysis (EMA). First, theoretical background of the DMD is briefly reviewed and its relevance to the Ibrahim time-domain method is discussed. Second, DMD is applied to a single DOF system and multi-DOF discrete system to discuss the applicability and interpretation of the DMD as a method of EMA. Furthermore, the effects of measurement errors on the results of DMD are discussed. It is shown that with relatively small measurement errors, DMD can capture modal parameters accurately. However, with relatively large measurement errors, DMD fails to capture modal parameters. Finally, DMD is applied to experimentally-obtained displacement field of a cantilevered beam, and its modal parameters are extracted. It is shown that the modal parameters extracted by DMD are as accurate as the ones obtained by the existing modal parameter extraction method.

PUF PAS를 이용한 대기 중 PCBs 농도 산정

This study was conducted to evaluate the use of low volume air sampler (LVAS) and polyurethane foam disk passive air samplers (PUF PAS) for better measurement of atmospheric polychlorinared biphenyls (PCBs) concentrations. Air samples were collected by a low volume air sampler (LVAS) and PUF PAS, a total of two pairs were continuously collected at the same time for 4 weeks. A good correlation was shown [MonoCB∼DiCB : R²=0.8289(p=0.012), TriCB∼HexaCB : R²=0.8388(p<0.0001)] between atmospheric PCBs concentration measured by the LVAS and PUF PAS. The sampling rate of all PCBs isomers showed higher than which were measured by other researchers in different cities. However, trace POPs such as PCBs may involve relatively large analytical errors in measurement, and as a result the air sampling rate of the respective PCB isomer is also likely to involve errors. The method of using a regression straight line between the concentrations obtained by the LVAS and those from the PUF PAS was judged better than the method using the sampling rate, since the former compensated for the experimental errors in the process of evaluation of atmospheric PCBs concentrations using the PUF PAS.

A new overreading model for wet gas vortex metering based on vorticity transport mechanism

Abstract Vortex flowmeters are widely used in wet gas metering, however, the output gas flowrate is over-predicted, leading to large measurement error. To improve the wet gas measurement accuracy by vortex flowmeters, the meter overreading was modelled based on the particle-laden vorticity dynamic equation and vorticity transport mechanism. The scaling parameters were revealed and different droplet entrainment conditions were considered. For the experiments, an annular mist flow loop with film metering device was developed to study the vortex metering characteristics. Then, a new overreading equation was developed by using the scaling group of droplet mass loading and macroscopic Stokes number. Finally, performances of the existing overreading correlations were evaluated and analyzed in detail. The results indicate that the proposed equation provides a uniform prediction for the meter overreading, the relative deviations are within ±1.0% error band, and the predicted accuracy is greatly improved compared with other overreading correlations.

Ratiometric thermal sensing based on dual emission of YBO3:Ce3+, Tb3+

Abstract A new temperature measurement strategy based on the luminescence of Ce3+ and Tb3+ doped YBO3 was proposed. Dual emissions of Ce3+ and Tb3+ have different thermal dependencies, which can be used to overcome those limitations such as low signal discriminability and large measurement error. A series of Ce3+ and/or Tb3+ doped YBO3 samples were synthesized by hydrothermal method, and the influences of temperature on the photoluminescence (PL) intensity of Ce3+ 5d-4f transition and Tb3+ 4f-4f transition were discussed in detail. Compared with the single emission of YBO3:1.0%Ce3+, fluorescence intensity ratio (FIR) variation of Ce3+ blue emission and Tb3+ green emission in YBO3:1.0%Ce3+, 1.0%Tb3+ has been studied as a function of temperature in the range of 288–328 K. The absolute sensitivity of YBO3:1.0%Ce3+, 1.0%Tb3+ was 1.18 %K−1, higher than that of YBO3: 1.0%Ce3+ (0.70 %K−1). The results suggest that YBO3:Ce3+, Tb3+ is a good candidate as optical thermometry in the physiological range.

Research on outer diameter measurement method of ring forging based on standard deviation resampling

The utilization rate of forging materials and the forging process parameters are affected by the shape and size of forgings. The measurement of the shape and size of forgings plays a key role in forging quality and efficiency of industrial production. At present, the laser measurement method is commonly used in forging measurement. The relatively large errors in the laser measurement are mainly caused by the dust at the measurement site, the angular deviation of the object and laser scanner, and the system error of the laser scanner. Therefore, a measurement method of outer diameter of ring forgings based on standard deviation algorithm is presented in this paper. Firstly, after resampling by the standard deviation algorithm, the more accurate data are obtained. Secondly, the good arc feature of the point cloud data is obtained by means of mean filter. Finally, the outer diameter of ring forgings is obtained by using ellipse fitting based on least squares principle. The feasibility of this method is verified by measuring two ring forgings with different outer diameters in the experiment.

Photo-Based Range-of-Motion Measurement: Reliability and Concurrent Validity in Children With Cerebral Palsy.

To investigate intrarater and interrater reliability, agreement, and concurrent validity of a smartphone photography-based application compared with a universal goniometer in children with cerebral palsy. Range of motion of hip abduction, popliteal angle, and ankle dorsiflexion was measured with a universal goniometer and a photography-based application in children with cerebral palsy, Gross Motor Function Classification System levels I to V.A 2-way random-effects intraclass correlation coefficients and Bland-Altman plots, standard error of measurement, and smallest detectable change were used for analyses. The application had good to excellent reliability and concurrent validity compared with a universal goniometer, while the large measurement error of both methods suggests that changes of 10° to 23° are needed to be certain that changes over time are not results of measurement error. A photography-based goniometer can be a reliable and valid tool when measuring range of motion in children with cerebral palsy.

Patient-reported quality indicators to evaluate physiotherapy care for hip and/or knee osteoarthritis- development and evaluation of the QUIPA tool

BackgroundThere is no physiotherapy-specific quality indicator tool available to evaluate physiotherapy care for people with hip and/or knee osteoarthritis (OA). This study aimed to develop a patient-reported quality indicator tool (QUIPA) for physiotherapy management of hip and knee OA and to assess its reliability and validity.MethodsTo develop the QUIPA tool, quality indicators were initially developed based on clinical guideline recommendations most relevant to physiotherapy practice and those of an existing generic OA quality indicator tool. Draft items were then further refined using patient focus groups. Test-retest reliability, construct validity (hypothesis testing) and criterion validity were then evaluated. Sixty-five people with hip and/or knee OA attended a single physiotherapy consultation and completed the QUIPA tool one, twelve- and thirteen-weeks after. Physiotherapists (n = 9) completed the tool post-consultation. Patient test-retest reliability was assessed between weeks twelve and thirteen. Construct validity was assessed with three predefined hypotheses and criterion validity was based on agreement between physiotherapists and participants at week one.ResultsA draft list of 23 clinical guideline recommendations most relevant to physiotherapy was developed. Following feedback from three patient focus groups, the final QUIPA tool contained 18 items (three subscales) expressed in lay language. The test-retest reliability estimates (Cohen’s Kappa) for single items ranged from 0.30–0.83 with observed agreement of 64–94%. The intraclass correlation coefficient (ICC) and 95% confidence interval (CI) for the Assessment and Management Planning subscale was 0.70 (0.54, 0.81), Core Recommended Treatments subscale was 0.84 (0.75, 0.90), Adjunctive Treatments subscale was 0.70 (0.39, 0.87) and for the total QUIPA score was 0.80 (0.69, 0.88). All predefined hypotheses regarding construct validity were confirmed. However, agreement between physiotherapists and participants for single items showed large measurement error (Cohen’s Kappa estimates ranged from − 0.04-0.59) with the ICC (95% CI) for the total score being 0.11 (− 0.14, 0.34).ConclusionsThe QUIPA tool showed acceptable test-retest reliability for subscales and total score but inadequate reliability for individual items. Construct validity was confirmed but criterion validity for individual items, subscales and the total score was inadequate. Further research is needed to refine the QUIPA tool to improve its clinimetric properties before implementation.

Image Distortion in Biplanar Slot Scanning: Patient-specific Factors.

Error within imaging measurements can be due to processing, magnification, measurement performance, or patient-specific factors. Previous length measurement studies based on radiographs have shown good intraclass correlation coefficients (ICCs) on single images; but have not assessed interimage distortion. In our study, "image distortion in biplanar slot scanning: technology-specific factors" we determined that there is minimal image distortion due to the image acquisition when using biplanar slot scanning. In this study, we aim to determine the role of patient-specific factors in image distortion, specifically evaluating interimage distortion. Digital radiographs and biplanar slot scanner images were reviewed in 43 magnetically controlled growing rod (MCGR) patients. Fifty-five postoperative anteroposterior digital radiographs, 184 follow-up biplanar slot-scanner scanner posteroanterior and 76 biplanar slot-scanner scanner laterals were measured by 2 residents and 1 attending. The manufacturer reported average actuator diameter of 9.02 mm was used as our reference width. Overall, within image interobserver ICC were moderate to excellent (0.635 to 0.983), but the interimage ICCs were poor (0.332). Digital radiographs consistently overestimated the MCGR actuator width (mean=9.655) and biplanar slot-scanner scanner images underestimated it (mean=8.935). The measurement range was large with biplanar slot-scanner scanner posteroanterior (up to 15%) and lateral (22%) measurements and with digital radiographs (39%). Patients with abnormal muscle tone had higher degrees of measurement variability. We found that neither biplanar slot scanning nor digital radiography was precise or accurate. Digital radiographs consistently overestimated MCGR actuator width and biplanar slot scanning underestimated it. The poor ICC's within and between image subtypes and large standard error of measurement reflected a magnitude of distortion that needs to be accounted for when using length measurements clinically. Unlike the clinically insignificant error that we noted in our previous study "image distortion in biplanar slot scanning: technology-specific factors" (0.5% to 1.5% of the measurement), the error noted in this study (0.2% to 38.5% of the measurement) has the potential to be clinically significant. Patients who have abnormal muscle tone had larger measurement errors, likely stemming from motion during the slot scanning process. Level III.

Magnetic field distribution of magnetic encoder with TMR sensor using finite element analysis

Selecting a cost effective magnetic encoder is an important step in electrical machines motor drive system design. Resolvers and high-resolution encoders provide excellent measurement accuracy. However, market competition has forced designers to look into less expensive solutions that have relatively large measurement errors. This paper studies the effect of TMR sensor measurement errors on magnetic field performance. The magnetic flux distribution of the encoder, and the distance effect between magnet and TMR sensor were simulated using finite element method. The simulation results of different types of materials for bearings of the encoder are compared. The magnetic field distribution performance degradation due to different types of materials for encoder is identified. The results show an acceptable magnetic flux distribution on ceramic material with the bearings of the encoder. The material of the disc magnet were determined to achieve high performance characteristics. In addition, the flux density become decreases and increases when TMR sensor is located at far-off or near distances from a field source, magnet. Therefore, there is optimal flux density need for investigating new allocation between magnetic sensors and magnet. The distance of magnet with TMR sensor also the main factor and 2 mm is identified as the best position and ceramic is good for bearing to reduce magnetic interference.

Measurement of the distance to the central stars of Nebulae by using Expansion methods with Alladin Sky Atlas

The usual methods of distance determination in Astronomy parallax and Spectroscopic with Expansion Methods are seldom applicable to Nebulae. In this work determination of the distances to individual Nebulae are calculated and discussed. The distances of Nebulae to the Earth are calculated. The accuracy of the distance is tested by using Aladin sky Atlas, and comparing Nebulae properties were derived from these distance made with statistical distance determination. The results showed that angular Expansions may occur in a part of the nebulae that is moving at a velocity different than the observed velocity. Also the results of the comparison of our spectroscopic distances with the trigonometric distances is that the spectroscopic distances are 55% larger. Since using trigonometric parallaxes with large relative measurement errors can introduce systematic errors, we carried out a Monte Carlo simulation of the biases introduced by selection effects and measurement errors. It turns out that a difference between both distance scales of the observed size is expected for the present day data if the underlying distance scales are identical.

Measuring and using information gained by observing diffraction data.

The information gained by making a measurement, termed the Kullback-Leibler divergence, assesses how much more precisely the true quantity is known after the measurement was made (the posterior probability distribution) than before (the prior probability distribution). It provides an upper bound for the contribution that an observation can make to the total likelihood score in likelihood-based crystallographic algorithms. This makes information gain a natural criterion for deciding which data can legitimately be omitted from likelihood calculations. Many existing methods use an approximation for the effects of measurement error that breaks down for very weak and poorly measured data. For such methods a different (higher) information threshold is appropriate compared with methods that account well for even large measurement errors. Concerns are raised about a current trend to deposit data that have been corrected for anisotropy, sharpened and pruned without including the original unaltered measurements. If not checked, this trend will have serious consequences for the reuse of deposited data by those who hope to repeat calculations using improved new methods.

Electrochemical area of graphene-supported metal nanoparticles from an atomistic approach

In electrochemical catalysis, parameters such as current, resistance, or capacitance must be referred to the electrochemically exposed area, otherwise they lack physical sense. For this reason it is necessary to know this exposed area as accurately as possible. Although there are several experimental methods to estimate the electrochemically exposed area, these are usually not suitable for different metals and present large errors in measurements, for example when two or more metals are mixed. Moreover, the technical difficulties of carrying out this type of measure mean that it is often necessary to resort to approximations with great error, such as the spherical approach, with the aim of having an approximate value of the area. In this work, Molecular Dynamics simulations were performed to study the morphology of graphene-supported nanoparticles. A method for the calculation of the electrochemically active surface area is proposed and tested for Pt, Au, and Pt/Au nanoalloys. These results are compared with existent experimental data and a model is proposed for the calculation of the electrochemically active area for supported nanoparticles of different sizes.

Limited mass-independent individual variation in resting metabolic rate in a wild population of snow voles (Chionomys nivalis).

Resting metabolic rate (RMR) is a potentially important axis of physiological adaptation to the thermal environment. However, our understanding of the causes and consequences of individual variation in RMR in the wild is hampered by a lack of data, as well as analytical challenges. RMR measurements in the wild are generally characterized by large measurement errors and a strong dependency on mass. The latter is problematic when assessing the ability of RMR to evolve independently of mass. Mixed models provide a powerful and flexible tool to tackle these challenges, but they have rarely been used to estimate repeatability of mass-independent RMR from field data. We used respirometry to obtain repeated measurements of RMR in a long-term study population of snow voles (Chionomys nivalis) inhabiting an environment subject to large circadian and seasonal fluctuations in temperature. Using both uni- and bivariate mixed models, we quantify individual repeatability in RMR and decompose repeatability into mass-dependent and mass-independent components, while accounting for measurement error. RMR varies among individuals, that is, is repeatable (R=.46) and strongly co-varies with BM. Indeed, much of the repeatability of RMR is attributable to individual variation in BM, and the repeatability of mass-independent RMR is reduced by 41% to R=.27. These empirical results suggest that the evolutionary potential of RMR independent of mass may be severely constrained. This study illustrates how to leverage bivariate mixed models to model field data for metabolic traits, correct for measurement error and decompose the relative importance of mass-dependent and mass-independent physiological variation.

Research on the Effects of Calibrated Position on Digital Image Correlation Measurement of Dual Camera in Engineering Application

To explore the influence of calibration position on digital image correlation measurement of dual cameras in engineering application, an experimental method of displacement stepping for digital image correlation measurement of dual cameras under different calibration locations is designed. Through precise displacement stepping of samples, the results of digital image correlation measurement and dial gauge measurement are compared. The influence of different calibration locations on the measurement results of digital image correlation method with dual cameras is analyzed. The results show that when the calibration position and collection conditions are unified, there will be no large displacement measurement error, and the discreteness of repeated measurement results is relatively small. The calibration position has more influence on the measurement of ordinary glass in the measuring optical path than that of quartz glass. The relative error caused by calibration position is relatively large for small displacement measurement and relatively small for large displacement measurement

Research on In Situ Stress Measurements in Reinforced Concrete Beams Based on the Core‐Drilling Method

To increase the accuracy of the core‐drilling method in measuring the in situ stresses within concrete beams, this paper developed a special core‐drilling machine system, studied the surface stress release rule of concrete beams through finite element simulations, and then carried out verification tests. The effects of the borehole diameter, drilling depth, strain sensor size, and borehole position on the measurement accuracy were studied. The results showed that borehole diameters of 100 mm, 75 mm, and 50 mm can achieve stress release and that the smaller the borehole diameter was, the easier it was to release the stress. When using the smallest borehole, the stress concentration range around the borehole was narrow, and there was little damage to the original structure. The strain gauge size influenced the actual measurement results. An excessively large strain gauge will be disturbed by drilling because of the limited size of the borehole. An excessively small strain gauge will be easily influenced by the inhomogeneity and randomness of the concrete materials, resulting in large measurement error. The difference between the measured concrete stress and the theoretical value was less than 10%, and the average error was only 6.03%, indicating the feasibility of the proposed method.

Multidimensional Information Fusion in Active Sonar via the Generalized Labeled Multi-Bernoulli Filter

Under the conditions of low detection probabilities, high clutter rates, low data-sampling rates, large measurement errors, and unknown prior information of the target position, multi-object tracking is difficult. This paper proposes a multidimensional information fusion method in active sonar via the generalized labeled multi-Bernoulli (GLMB) filter. After modeling the position measurement, radial velocity measurement and amplitude measurement of the target and clutter, new target births are adaptively generated by the measurement-driven model, predictions are made by the target motion model and updates are performed via multidimensional measurements with the generalized likelihood in the GLMB filter, which enables the measurement information of different dimensions to be elegantly applied to information fusion and significantly improves the filter performance. The contribution of specific dimension measurement to fusion can be evaluated by the Kullback-Leibler (KL) divergence. In the efficient implementation, we propose flat Gibbs sampling to realize multiple hypothesis optimization. Moreover, the filtering recursion is derived from Gaussian mixtures. Simulations are presented to verify the proposed method.

Using sensors to measure technology adoption in the social sciences

Empirical social sciences rely heavily on surveys to measure human behavior. Previous studies show that such data are prone to random errors and systematic biases caused by social desirability, recall challenges, and the Hawthorne effect. Moreover, collecting high frequency survey data is often impossible, which is important for outcomes that fluctuate. Innovation in sensor technology might address these challenges. In this study, we use sensors to describe solar light adoption in Kenya and analyze the extent to which survey data are limited by systematic and random error. Sensor data reveal that households used lights for about 4 h per day. Frequent surveyor visits for a random sub-sample increased light use in the short term, but had no long-term effects. Despite large measurement errors in survey data, self-reported use does not differ from sensor measurements on average and differences are not correlated with household characteristics. However, mean-reverting measurement error stands out: households that used the light a lot tend to underreport, while households that used it little tend to overreport use. Last, general usage questions provide more accurate information than asking about each hour of the day. Sensor data can serve as a benchmark to test survey questions and seem especially useful for small-sample analyses.