Systematic Measurement Errors Research Articles

Compensation for the Systematic Error of Spectral Measurements of the Background Concentration of Methane in the Earth's Atmosphere

Compensation for the Systematic Error of Spectral Measurements of the Background Concentration of Methane in the Earth's Atmosphere

Die Anwendung des telezentrischen Strahlenganges in der Augenoptik zur Bestimmung des Hornhautscheitelabstandes

Purpose. Nowadays, a video centering system is often used to determine centering data. Nevertheless, these are often additionally checked manually afterwards. An important pa- rameter is the vertex distance (VD). This is often determined using a measuring ruler with a millimeter scale. Also during refraction a classical millimeter scale on the trial frame is used to determine the VD. Due to the difference between the location of the measuring scale used and the location of the real VD, there is a systematic measurement error. Material and Methods. At the Berlin University of Applied Sciences (BHT), a measurement tool was developed on the basis of an object-side telecentric beam path, which enables the determination of the real VD independent of distance. The validation of this measurement tool was performed in two different series of measurement. In the first series of tests, the measurements were performed on test subjects using a measuring tool, a video centering system (“visuReal” from Hoya) and a measuring ruler, and the results were compared. In the second series, VD measurements were taken using the measuring tool and millimeter scale on defined test sections for objectification purposes. Results. In the first series of measurements, the VD values obtained using the millimeter scale were lower than those de- termined with the other instruments (statistically significant at the 5% level with Friedman test). The difference between the VD values of the measuring tool and the video centering system, on the other hand, was small on average and not statistically significant. In the series of measurements on de- fined test sections, the measuring tool showed a significantly better approximation to the actual length of the defined test distance than the measuring ruler. Conclusion. The series of measurements show that the de- termination of the VD by the measuring tool and the video centering system are very similar on average and that the measured values of the measuring tool are closer to the orig- inal value than the measured values of the measuring ruler. Thus, the determination of the VD by means of a simple scale should be dispensed with in the future. Keywords telecentric beam path, vertex distance, vertex distance meas- urement, trial frame, refraction

At-line porosity sensing for non-destructive disintegration testing in immediate release tablets

Fully automated at-line terahertz time-domain spectroscopy in transmission mode is used to measure tablet porosity for thousands of immediate release tablets. The measurements are rapid and non-destructive. Both laboratory prepared tablets and commercial samples are studied. Multiple measurements on individual tablets quantify the random errors in the terahertz results. These show that the measurements of refractive index are precise, with the standard deviation on a single tablet being about 0.002, with variation between measurements being due to small errors in thickness measurement and from the resolution of the instrument. Six batches of 1000 tablets each were directly compressed using a rotary press. The tabletting turret speed (10 and 30 rpm) and compaction pressure (50, 100 and 200 MPa) were varied between the batches. As expected, the tablets compacted at the highest pressure have far lower porosity than those compacted at the lowest pressure. The turret rotation speed also has a significant effect on porosity. This variation in process parameters resulted in batches of tablets with an average porosity between 5.5 and 26.5%. Within each batch, there is a distribution of porosity values, the standard deviation of which is in the range 1.1 to 1.9%. Destructive measurements of disintegration time were performed in order to develop a predictive model correlating disintegration time and tablet porosity. Testing of the model suggested it was reasonable though there may be some small systematic errors in disintegration time measurement. The terahertz measurements further showed that there are changes in tablet properties after storage for nine months in ambient conditions.

Transmission line parameters estimation in the presence of realistic PMU measurement error models

Proposals have been presented in literature to estimate line parameters and monitor their changes. Synchrophasor measurements from phasor measurement units (PMUs) have appeared as a possible breakthrough for accurate estimation. However, few methods consider a realistic measurement chain including PMUs and instrument transformers and their systematic and random error contributions. This paper proposes an improved method to simultaneously estimate line parameters and systematic measurement errors on multiple network lines. The algorithm is designed to deal with realistic PMU measurement errors and, in particular, with phase-angle errors caused by common time-base errors on multiple PMU channels. The impact of PMU measurement errors is investigated to achieve a comprehensive view of the performance under realistic conditions. The results obtained on an IEEE test network prove the advantages of the proposed method with respect to other recent methods and its robustness in the presence of mismatches in the error model.

Methodology to calculating the temperature around an evaporating droplet using a set of thermocouples

A new approach is proposed to calculating the gas/vapor temperature field in the immediate vicinity of a droplet using a set of thermocouples. The schemes used in the experiments are based on convective and combined droplet heating. The air temperature during droplet heating was varied in the range of 100–500 °C, and the droplet radii from 1 mm to 1.7 mm. The paper describes data processing algorithms and methods for calculating the gas/vapor temperature field around a droplet using three to five series of measurements and shows the advantages of this approach over non-contact optical techniques. We also determine the applicability range of the proposed method for temperature field calculation and the limits of systematic and random measurement error variation. The instantaneous droplet radius and the initial air temperature around it are shown to be the main factors influencing the gas/vapor temperature distributions around an evaporating droplet. The experimental data are compared to earlier research findings. The results indicate that reliable gas/vapor temperature fields around evaporating liquid droplets can be obtained even with inexpensive equipment.

Meniscus-Corrected Method for Broadband Liquid Permittivity Measurements with an Uncalibrated Vector Network Analyzer

We present a novel broadband permittivity characterization method for liquids measured in a semi-open vertically oriented test cell with an uncalibrated vector network analyzer. For this goal, we utilize three scattering matrices measured at different levels of liquid in the cell. With mathematical operations, we remove the effects of systematic measurement errors caused by both the vector network analyzer and a meniscus shaping the top of the liquid samples in such a type of test cell. To the best authors’ knowledge, this is the first of such a calibration-independent method dealing with meniscus. We verify its validity by comparing our results with the data available in the literature and with the outcomes of our previously published calibration-dependent meniscus removal method (MR) for propan-2-ol (IPA), a 50% aqueous solution of IPA and distilled water. The new method yields results comparable with the MR method, at least for IPA and the IPA solution, revealing, however some problems when testing high-loss water samples. Nevertheless, it allows one to cut down on expenditures in the system calibration engaging skilled labor and expensive standards.

Revealing systematic errors in hole drilling measurements through a calibration bench: the case of zero-depth data

An accurate estimation of the measurement error in the hole drilling method is needed to choose an appropriate level of regularization and to perform a sensitivity analysis on the stress results. The latest release of ASTM E837 standard for the hole drilling method includes a procedure aimed at estimatingthe standard deviation of the random error component on strain measurements, proposed by Schajer. Nevertheless, strain measurements are also affected to some extent by systematic errors which are not included in the estimation and need to be compensated. For example, an error in the rosette gage factor orin the identification of the zero-depth datum systematically affects all strain measurements in a strongly correlated fashion. This paper describes a calibration bench, designed to superimpose a reference bending stress distribution on a given specimen while simultaneously performing a hole drilling measurement.Since the reference solution is known a priori and shares the measurement instrumentation, the hole geometry and the stepping process with the actual residual stress distribution, the bench provides the user with a direct validation of the obtained accuracy. In addition, strategies aimed at compensating systematicerrors can be tested on the reference solution and then applied on the residual stress evaluation. The imperfect hole geometry and drilling alignment are proven to cause a significant underestimation of stresses near the surface, as they lead to an incorrect identification of the zero-depth datum. It is shown that this effect can be corrected through the proposed calibration bench.

A 3-DoF motion error measurement system based on film interferometry

To accomplish the simultaneous measurement of motion errors for a topography measurement system, a 3-DoF (Degree of Freedom) motion error measurement system based on film interferometry is proposed. An optical flat was the moving unit, whereas a prism group consisting of two equilateral prisms and a right-angle prism formed the stationary sensing head. There was an air wedge between the prism group and the optical flat. A horizontally incident laser beam was used to generate an interferogram, the phase shift of which was directly related to the standoff variation, yaw, and roll. The interferogram was captured by a camera and combined with an in-house-developed image processing algorithm, and the above three motion errors could be simultaneously obtained. The experimental results demonstrated that the linear and angular measurement accuracies of the system were ±0.08 µm and ±0.55″, and the repeatability represented by the standard deviation was within 40 nm and 0.4″.

Modeling and Compensation of Inertial Sensor Errors in Measurement Systems

In the field of surveying and mapping, inertial sensor deterministic errors are poorly understood, and error calibration and compensation are not carried out. Thus, in this study, the effects of three types of deterministic errors (i.e., bias, scale factor error, and installation error) in a conventional inertial measurement unit (IMU) error model on a navigation system are theoretically deduced and verified by simulation. Subsequently, navigation experiments are carried out to investigate the effects of the three deterministic errors on the navigation system. The experimental results show that the gyro bias has the strongest influence on the navigation and positioning accuracy of the system. Consequently, we designed a two-position continuous calibration scheme to calibrate the IMU. The calibration scheme can simultaneously calibrate the bias error of the gyroscope and the accelerometer. When calibrating the bias error of the 0.005°/h order of magnitude, the maximum relative error is 13.16%, and the rest of the calibration relative errors are less than 10%, which verifies the effectiveness of the calibration path designed in this paper. The system is compensated by using the IMU bias calibration results, and the navigation experiment results show that the position accuracy and heading accuracy are improved by 72.68% and 79.65%, respectively, through the calibration and compensation of IMU bias error. Therefore, the position and heading accuracy of the system will be greatly improved by calibrating and compensating the bias error through the two-position calibration path before the IMU is used.

Machine Learning Based Position Prediction of a Target Tracked by Multi-Aperture Positioning System

This paper proposes a machine learning-based position prediction approach to determine the position of a light-emitting diode (LED) target using a new measuring system called the multi-aperture positioning system (MAPS). The measurement system is based on a photogrammetric approach using an aperture mask and a single camera sensor. To achieve high accuracy in position calculation, several complex algorithms with high computational complexity are used. The accuracy of the system is equal to or better than that of existing photogrammetric devices. We investigate whether a neural network (NN) can replace the algorithms currently used in the system software to increase the measurement frequency with similar accuracy. Simulated images are used to train the NN, while real images are used to measure performance. Previously, various algorithms were used to calculate the position of the target from the captured images. Our approach is to train an NN, using thousands of labeled images, to predict the position of the target from these images. We investigate whether systematic measurement errors can be avoided; not all factors affecting the measurement precision are yet known, can always be accurately determined, or change over time. When NNs are used, all information contained in the images is learned by the model, considering all influences present at the time of training. Results show that the trained NN can achieve similar performance to the previously used Gaussian algorithm in less time since no filters or other pre-processing of images are required. This factor directly affects the measurement frequency of the MAPS. The light spot center was detected with sub-pixel accuracy without systematic errors in contrast to some of the previously used algorithms. The simulation of the sensor images needs to be improved to investigate the full potential of the NN.

High-precision tomography of ion qubits based on registration of fluorescent photons

We develop a new method for high-precision tomography of ion qubit registers under conditions of limited distinguishability of logical states. It is not always possible to achieve low error rates during the readout of the quantum states of ion qubits due to the finite lifetime of excited levels, photon scattering, detector dark counts, low numerical aperture, etc. However, the model of fuzzy quantum measurements makes it possible to ensure precise tomography of quantum states. To do this, we developed a fuzzy measurement model based on counting the number of fluorescent photons. A statistically adequate algorithm for the reconstruction of quantum states of ion qubit registers based on fuzzy measurement operators is proposed. The algorithm uses the complete information available in the experiment and makes it possible to account for systematic measurement errors associated with the limited distinguishability of the logical states of ion qubits. We show that the developed model, although computationally more complex, contains significantly more information about the state of the qubit and provides a higher accuracy of state reconstruction compared to the model based on the threshold algorithm.

THEORETICAL RESEARCHES OF THE EMBEDDED FIBER-OPTIC SYSTEM OF TESTING DEFORMATION AND TEMPERATURE OF POLYMER COMPOSITES

This article describes the results of theoretical researches of the system of optical testing of polymer composites by the method of two optical fibers with different sensitivity to deformation and temperature, using integrated arrays of fiber Bragg gratings. The features of the primary data processing from the optical testing system embedded into the composite are considered by the methods of weighted arithmetic mean and approximation by the Gaussian function. The basic relations for calculating the error in determining the temperature and strain with the help of fiber-optic embedded testing systems are obtained. A numerical model of the interrogator has been constructed, which makes it possible to estimate the systematic error of deformation and temperature measurements, including taking into account the noise of a real interrogator. It is shown that, taking into account a number of assumptions for the problem of simultaneous embedded testing of composites with fiber Bragg gratings, it is advisable to apply he method of primary processing of testing data using the approximation of the real spectra of fiber Bragg gratings by the Gaussian function, while in order to increase the reliability of testing, it is necessary to take into account the temperature correction characteristic of a particular interrogating device.

Rating and ranking preparedness characteristics important for veterinary workplace clinical training: a novel application of pairwise comparisons and the Elo algorithm.

Quantitatively eliciting perspectives about a large number of similar entities (such as a list of competences) is a challenge for researchers in health professions education (HPE). Traditional survey methods may include using Likert items. However, a Likert item approach that generates absolute ratings of the entities may suffer from the "ceiling effect," as ratings cluster at one end of the scale. This impacts on researchers' ability to detect differences in ratings between the entities themselves and between respondent groups. This paper describes the use of pairwise comparison (this or that?) questions and a novel application of the Elo algorithm to generate relative ratings and rankings of a large number of entities, on a unidimensional scale. A study assessing the relative importance of 91 student "preparedness characteristics" for veterinary workplace clinical training (WCT) is presented as an example of this method in action. The Elo algorithm uses pairwise comparison responses to generate an importance rating for each preparedness characteristic on a scale from zero to one. This is continuous data with measurement variability which, by definition, spans an entire spectrum and is not susceptible to the ceiling effect. The output should allow for the detection of differences in perspectives between groups of survey respondents (such as students and workplace supervisors) which Likert ratings may be insensitive to. Additional advantages of the pairwise comparisons are their low susceptibility to systematic bias and measurement error, they can be quicker and arguably more engaging to complete than Likert items, and they should carry a low cognitive load for respondents. Methods for evaluating the validity and reliability of this survey design are also described. This paper presents a method that holds great potential for a diverse range of applications in HPE research. In the pursuit quantifying perspectives on survey items which are measured on a relative basis and a unidimensional scale (e.g., importance, priority, probability), this method is likely to be a valuable option.

Estimating speed-through-water by Dynamic Factor Models fusing metocean and propeller data

In vessel performance analysis, reliable information about speed-through-water (STW) is key for realistic modeling of the single ship’s fuel efficiency. It is paramount that STW measurements are reliable such that they can be adopted as input in fuel consumption forecast models. This paper presents a study where three variations of a Dynamic Factor Model are used to estimate the STW. A simulation study is presented to demonstrate the estimation and smoothing techniques for the Dynamic Factor Model. The model variations are then applied to real vessel data, including STW and propeller measurements, in combination with metocean data (sea currents). The present study suggests that the developed model can minimize the systematic STW measurement error even under highly non-stationary conditions.

Optical Saturation Produces Spurious Evidence for Photoinduced Superconductivity in K_{3}C_{60}.

We discuss a systematic error in time-resolved optical conductivity measurements that becomes important at high pump intensities. We show that common optical nonlinearities can distort the photoconductivity depth profile, and by extension distort the photoconductivity spectrum. We show evidence that this distortion is present in existing measurements on K_{3}C_{60}, and describe how it may create the appearance of photoinduced superconductivity where none exists. Similar errors may emerge in other pump-probe spectroscopy measurements, and we discuss how to correct for them.

Intra- and inter-session reliability and repeatability of an infrared thermography device designed for materials to measure skin temperature of the triceps surae muscle tissue of athletes.

Infrared thermography devices have been commonly applied to measure superficial temperature in structural composites and walls. These tools were cheaper than other thermographic devices used to measure superficial human muscle tissue temperature. In addition, infrared thermography has been previously used to assess skin temperature related to muscle tissue conditions in the triceps surae of athletes. Nevertheless, the reliability and repeatability of an infrared thermography device designed for materials, such as the Manual Infrared Camera PCE-TC 30, have yet to be determined to measure skin temperature of the triceps surae muscle tissue of athletes. The purpose was to determine the procedure's intra- and inter-session reliability and repeatability to determine skin temperature within the Manual Infrared Camera PCE-TC 30 thermography device in the triceps surae muscle tissue of athletes, which was initially designed to measure the superficial temperature of materials. A total of 34 triceps surae muscles were bilaterally assessed from 17 healthy athletes using the Manual Infrared Camera PCE-TC 30 thermography device to determine intra- (at the same day separated by 1 h) and inter-session (at alternate days separated by 48 h) reliability and repeatability of the skin temperature of the soleus, medial and lateral gastrocnemius muscles. The triceps surae complex weas measured by a region of interest of 1 cm2 through five infrared thermography images for each muscle. Statistical analyses comprised intraclass correlation coefficient (ICC), standard error of measurement (SEM), minimum detectable change (MCD), systematic error of measurement, correlation (r), and Bland-Altman plots completed with linear regression models (R 2). Intra- and inter-session measurements of the proposed infrared thermography procedure showed excellent reliability (ICC(1,2) = 0.968-0.977), measurement errors (SEM = 0.186-0.232 °C; MDC = 0.515-0.643 °C), correlations (r = 0.885-0.953), and did not present significant systematic error of measurements (P > 0.05). Adequate agreement between each pair of measurement moments was presented by the Bland-Altman plots according to the limits of agreement and non-significant linear regression models (R 2 = 0.000-0.019; P > 0.05). The proposed procedure to determine skin temperature within the Manual Infrared Camera PCE-TC 30 thermography device presented excellent intra- and inter-session reliability and repeatability in athletes' triceps surae muscle tissue. Future studies should consider the SEM and MDC of this procedure to measure the skin temperature of soleus, medial, and lateral gastrocnemius muscles to promote triceps surae muscle prevention and recovery in athletes.

Comparison between passive knee kinematics during surgery and active knee kinematics during walking: A preliminary study.

Recovery of function is among a patient's main expectations when undergoing total knee arthroplasty (TKA). However, normal gait knee function is not always completely restored, which can affect patient satisfaction and quality of life. Computer-assisted surgery (CAS) allows surgeons to evaluate passive knee kinematics intra-operatively. Understanding associations between knee kinematics measured during surgery and during daily activities, such as walking, could help define criteria for success based on knee function and not only on the correct alignment of the implant or the leg. This preliminary study compared passive knee kinematics measured during surgery with active kinematics measured during walking. Eight patients underwent a treadmill gait analysis using the KneeKG™ system both before surgery and three months afterwards. Knee kinematics were measured during CAS both before and after TKA implantation. The anatomical axes of the KneeKG™ and CAS systems were homogenised using a two-level, multi-body kinematics optimisation with a kinematic chain based on the calibration measured during CAS. A Bland-Altman analysis was performed before and after TKA for adduction-abduction angle, internal-external rotation, and anterior-posterior displacement over the whole gait cycle, at the single stance phase and at the swing phase. Homogenising the anatomical axes between CAS and treadmill gait led to limited median bias and limits of agreement (post-surgery -0.6 ± 3.6 deg, -2.7 ± 3.6 deg, and -0.2 ± 2.4 mm for adduction-abduction, internal-external rotation and anterior-posterior displacement, respectively). At the individual level, correlations between the two systems were mostly weak (R2 < 0.3) over the whole gait cycle, indicating low kinematic consistency between the two measurements. However, correlations were better at the phase level, especially the swing phase. The multiple sources of differences did not enable us to conclude whether they came from anatomical and biomechanical differences or from measurement system errors.

Systematic Errors of Electric Field Measurements in Ferroelectrics by Unit Cell Averaged Momentum Transfers in STEM.

When using the unit cell average of first moment data from four-dimensional scanning transmission electron microscopy (4D-STEM) to characterize ferroelectric materials, a variety of sources of systematic errors needs to be taken into account. In particular, these are the magnitude of the acceleration voltage, STEM probe semi-convergence angle, sample thickness, and sample tilt out of zone axis. Simulations show that a systematic error of calculated electric fields using the unit cell averaged momentum transfer originates from violation of point symmetry within the unit cells. Thus, values can easily exceed those of potential polarization-induced electric fields in ferroelectrics. Importantly, this systematic error produces deflection gradients between different domains seemingly representing measured fields. However, it could be shown that for PbZr0.2Ti0.8O3, many adjacent domains exhibit a relative crystallographic mistilt and in-plane rotation. The experimental results show that the method gives qualitative domain contrast. Comparison of the calculated electric field with the systematic error showed that the domain contrast of the unit cell averaged electric fields is mainly caused by dynamical scattering effects and the electric field plays only a minor role, if present at all.

Bottom-Up Generated Height Gauges for Silicon-Based Nanometrology.

Steady progress in integrated circuit design has forced basic metrology to adopt silicon lattice parameter as a secondary realization of the SI meter that lacks convenient physical gauges for precise surface measurements at a nanoscale. To employ this fundamental shift in nanoscience and nanotechnology, we propose a set of self-organized silicon surface morphologies as a gauge for height measurements within the whole nanoscale (0.3-100 nm) range. Using 2 nm sharp atomic force microscopy (AFM) probes, we have measured the roughness of wide (up to 230 μm in diameter) singular terraces and the height of monatomic steps on the step-bunched and amphitheater-like Si(111) surfaces. For both types of self-organized surface morphology, the root-mean-square terrace roughness exceeds 70 pm but has a little effect on step height measurements having 10 pm accuracy for AFM technique in air. We implement a step-free 230-μm-wide singular terrace as a reference mirror in an optical interferometer to reduce the systematic error of height measurements from >5 nm to about 0.12 nm, which allows visualizing 136-pm-high monatomic steps on the Si(001) surface. Then, using a "pit-patterned" extremely wide terrace with dense but counted monatomic steps in a pit wall, we have optically measured mean Si(111) interplanar spacing (313.8 ± 0.4 pm) that agrees well with the most precise metrological data (313.56 pm). This opens up avenues for the creation of silicon-based height gauges using bottom-up approaches and advances optical interferometry among techniques for metrology-grade nanoscale height measurements.

Improving the accuracy of EDXRF results in gold alloy analysis by matrix effect correction

Energy-Dispersive X-Ray Fluorescence (EDXRF) is a faster non-destructive analysis and demands less sample preparation than the fire assay technique. This research sought to minimise the matrix effect (inter-element) by studying the role of matrix-specific materials and thus improving the accuracy of EDXRF in gold alloy analysis. The combination of empirical calibration with standardless Fundamental Parameter (FP) was expected to fine-tune the analysis of precious metals, such as gold (Au), silver (Ag), and copper (Cu). The acquired R2 of 0.9999 for all metals signalled an alignment between the certified value and EDXRF measurement. The technique was validated with CRMs to determine corrective K-factors to realign systematic measurement errors due to alloy mixture. The relative error (rel%) for all measurements was <0.1 rel%. The relative standard deviation (%rsd) was reduced to <0.11%rsd for pure Au, 0.16%rsd for Au-Ag and Au-Cu mixture, and <0.20%rsd for Au-Ag-Cu mixture with K-factor correction. A similarity to the fire assay might reduce bias. The null hypothesis of equal mean values of fire assay and XRF data was confirmed by the student's t-test. This outcome showed that the XRF provided acceptable precision and verified the null hypothesis on the equivalence between mean results.