Convenient Calibration Method Research Articles

Unsupervised Domain Adaptation for Gesture Identification Against Electrode Shift

Surface electromyogram (sEMG)-based hand gesture recognition, which interprets commands given by humans through sEMG signals, performs well in many studies. However, its recognition accuracy drops dramatically due to electrode shift since the distributions of motion classes are changed. Although calibrating the system with newly collected samples after electrode shift maintains the accuracy, collecting labeled samples is inconvenient and time-consuming since the procedure is rigid. However, the calibration may not work properly without label, especially when the change is significant. This study proposes a user friendly and convenient calibration method for hand gesture recognition by an unsupervised domain adaptation method, which only obtains the unlabeled samples of preselected benchmark classes from users in calibration. The change of benchmark classes is captured by unlabeled samples by a clustering method. The other classes are estimated based on the benchmark classes by regression models. As a result, the information of all classes is used to calibrate the system. Linear discriminant analysis is used to demonstrate our model. A dataset with ten subjects is collected to verify the performance empirically. Experimental results confirm that our method utilizes the unlabeled benchmark class samples in calibration and achieves 75.55% average accuracy. Our method is more robust to electrode shift and improves around 8.5% accuracy consistently on all subjects compared with the methods without calibration or label information in calibration. Although the accuracy of our method is slightly less than the ones using label calibration samples, our calibration data collection is more convenient and less complicated.

Moisture–Conductivity Calibration for Electrical Imaging of Horticultural Substrate

Electrical imaging studies of laboratory- and small-scale plant root zones are gaining increasing attention. However, for essential moisture–conductivity calibrations on numerous substrate columns with variability in dry density, the use of one conventional strategy is relatively laborious or complicated. Thus, in this work, a relatively convenient calibration method is presented, and the objective is to identify its feasibility and potential to assess the effects of factors (e.g., volumetric water content (VWC), and dry density) on conductivity and establish necessary moisture–conductivity curves for porous materials (e.g., soils and substrates). In the method, with a specially designed fixture, variable VWCs, dry densities and related complex conductivities of the samples can be easily acquired through static compaction. The results show that the in-phase conductivity (or magnitude of conductivity) increases with the increasing VWC or dry density, primarily owing to the increase in the dominant pore water connectivity. Moreover, the effect of dry density on conductivity is relatively smaller than that of VWC. Thus, for the substrates at dry densities with certain variability, good power law relations (R2 ≥ 0.99) between in-phase conductivity (or magnitude of conductivity) and VWC at different frequencies can be established. Overall, the proposed approach is practical, promising, and relatively time- and labor-saving.

Traceability of network time service to UTC(NIM): online calibration

Network time service provided by Network Time Protocol (NTP) servers is widely used to synchronize the clocks of computers and other networked equipment. With the rapid development of smart devices and their applications, more NTP servers as time sources need to be calibrated to a legal time reference. This work proposes using a low-cost and convenient calibration method to investigate the time service capability of ten NTP servers located at different cities in China. The uncertainties (k = 2) of the time offsets between Coordinated Universal Time (National Institute of Metrology) and network time from NTP servers for a single measurement are generally less than 150 ms, and the uncertainties (k = 2) of the mean time offsets for 24 h are less than 85 ms. Calibration results were found at the same level when applying the two time references, which were maintained a time offset less than 10 ns and located more than 1000 km apart.

A Calibration and 3-D Measurement Method for an Active Vision System With Symmetric Yawing Cameras

In this study, we propose a 3-D measurement method for an active stereo vision system with two symmetric yawing cameras. First, we establish a measurement model with five constant systematic parameters and five variables. Second, we present a design for a relatively simple and convenient calibration method to determine the constant systematic parameters for the active vision system. In our proposed method, the initial yaw angles of two cameras are calibrated with a minimum of three equal interval points in a common field of view (FOV). The initial pitch angles are calibrated with at least one point in this common FOV. The initial yaw angles are used in the following calibration processes of the baseline length and the optical offset. The baseline length is calibrated with respect to two such points with known horizontal distance. An offset used to compensate for the difference between the actual optical centers of the two cameras along their optical axes is also computed with at least one feature point with the cameras yawed at different angles. Third, an associated measurement method for objects in the common FOV is presented. The proposed method computes 3-D positions of feature points in the common FOV using these five constant systematic parameters and five variables. This active stereo vision system design does not require repeated calibration for varying yaw of the two cameras to conduct measurements once the five constant systematic parameters have been calibrated offline. We conduct comparative experiments, and the results verify the effectiveness of the proposed method.

Improved Method for Acoustic Identification of Free Conductive Particle Defects in GIL

The presence of free conductive particles in gas-insulated transmission lines (GIL) is the most significant threat to their insulation. The non-invasive identification of free conductive particle defects in GILs is extremely challenging. Existing identification methods which use the acoustic amplitude-flight time (AAFT) pattern are not often adopted on site due to their faulty theory, non-robust extraction algorithm, and generally inaccurate calibration. In this study, the theory established by L. E. Lundgaard is expanded by deriving estimation equations related to the particle's moving state. A new method for extracting the state information from the raw data of acoustic signals is established and the robustness of the acoustic identification method is enhanced. A convenient calibration method is also developed by building a standard collision signal generator. The proposed methods are validated in a scale GIL model and a real GIL model. The results of this study may represent a workable reference for GIL condition monitoring.

A flexible calibration method for the intrinsic and mechanical parameters of panoramic line-scan cameras

Panoramic line-scan cameras provide high definition images with a quasi uniform distribution of the sensing elements. Unfortunately, calibration of such devices with classic techniques is not possible making their use, in computer vision field, not straightforward. We propose a flexible and convenient calibration method for the computation of intrinsic and mechanism parameters of such systems by using images of a simple calibration pattern. Unlike existing approaches, the proposed method considers a full geometrical model and does not make any unattainable assumption such as concentricity of images, a priori knowledges about camera poses or coincidence of the rotation axis with the optical center. Using few images taken with free poses, the calibration is performed in two steps. First, the intrinsic parameters are computed using sets of 2D/3D point correspondences that are generated automatically by exploiting the structure of the calibration rig. Then, thanks to the parameterization of the projection of a 3D straight line, the mechanical parameters are computed using points at infinity. For each step, closed form solutions and iterative refinement techniques are presented. The proposed approach is validated with both synthetic and real data collected by our prototype.

Preliminary research on focal plane calibration method in LAMOST based on flexible planar target

In the large sky area multiobject optical fiber spectroscopy telescope project, to capture the spectrum of a particular object, the optical fiber positioner must position the optical fiber end face to a specified location on the focal plane. The accuracy of the optical fiber positioner is guaranteed by feedback from photogrammetry. Photogrammetry accuracy is based on accurate calibration. However, given the complexities in the optical fiber focal plane and the optical fiber positioner, the accurate standard point is considerably difficult to obtain, which results in insufficient calibration accuracy. To solve this problem, a convenient calibration method based on the combination of small, planar targets is proposed. In this method, each optical fiber positioner positions the optical fiber to several designed locations, which are relatively accurate. These points form a high-precision, two-dimensional point array that can be used as the planar target. In this manner, each optical fiber positioner can be regarded as a small, high-precision planar target. All small, high-precision planar targets are assembled to form the flexible planar target, which is used for calibration. The experimental result indicates that this method is highly accurate and can be applied in focal plane calibration.

Calibration of excitation function measurement based on corona cage test results.

Corona cage approaches are crucial for research on the corona characteristics of conductors. Calibration is an indispensable task for determining excitation functions, which are used to predict corona performance of long transmission lines through extrapolation from measurements of short lines in corona cages. In this paper, the amplification factor G is calculated through a frequently adopted method, propagation analysis of high-frequency corona current along a short line. Another convenient calibration method, based on distributed parameter equivalent circuits, is established. The results for G obtained through propagation analysis and equivalent circuits are compared. To verify the rationality of calculation parameters in propagation analysis and equivalent circuits, a calibration experiment based on the excitation caused by a simulated monopulse current was performed. The results of the proposed calibration method and the calibration experiment are in good agreement.

Convenient Calibration Procedure for Structured Light Projection System

We present a convenient calibration method for structured light projection system. The proposed clibration approach can realize 3D shape measurement without projector calibration, without system calibration, without precise linear z stage to be used, the relative position between camera and projector can be arbitrary, and the only involved device is a plane board. Experiment results validated that the accuracy of the proposed approach.

Rapid GC-MS Analysis of Pesticide Residues Using Analyte Protectants

A multi-residue method was developed to determine pesticides in foods using analyte protectants to compensate for matrix effects. Promising analyte protectants and combinations of these analyte protectants were evaluated for masking active sites in gas chromatography systems. The optimal combination of analyte protectants was determined to be the mixture of polyethylene glycol and olive oil. Calibration curves for analyte protectants in both neat solvents and matrix-matched standards were compared and similar response enhancement was observed. This result suggests a convenient calibration method using a combination of analyte protectants in neat solvent instead of the conventional matrix-matched standards calibration method.

O.071 Magnetic field interactions in adjustable hydrocephalus shunts

Panoramic line-scan cameras provide high definition images with a quasi uniform distribution of the sensing elements. Unfortunately, calibration of such devices with classic techniques is not possible making their use, in computer vision field, not straightforward. We propose a flexible and convenient calibration method for the computation of intrinsic and mechanism parameters of such systems by using images of a simple calibration pattern. Unlike existing approaches, the proposed method considers a full geometrical model and does not make any unattainable assumption such as concentricity of images, a priori knowledges about camera poses or coincidence of the rotation axis with the optical center. Using few images taken with free poses, the calibration is performed in two steps. First, the intrinsic parameters are computed using sets of 2D/3D point correspondences that are generated automatically by exploiting the structure of the calibration rig. Then, thanks to the parameterization of the projection of a 3D straight line, the mechanical parameters are computed using points at infinity. For each step, closed form solutions and iterative refinement techniques are presented. The proposed approach is validated with both synthetic and real data collected by our prototype.

An Enhanced Calibration Scheme for the EDM Hole-Drilling Strain Gage Method for the Measurement of Residual Stress in Ferrous Materials

Recent studies revealed that EDM hole-drilling strain gage method is applicable for the measurement of residual stress in materials with higher hardness and toughness. However, the metallurgical transformation layer formed on the wall of the hole induces an additional stress and therefore generates a measurement error. Usually this error can be calibrated by estimating and reducing the hole-drilling induced extra stress, σIS. However, the value of σ IS is highly sensitive to the EDM parameters. Accordingly, the current study aimed at lowering σ IS by optimizing the working parameters of pulse current, pulse-on duration and pulse-off duration with experiments. An inverse power law relationship was constructed to predict the magnitude of the hole-drilling induced stress where was referred. A convenient calibration method was proposed where calibration factor can be easily determined. The calibrated results revealed good accuracy where deviation is no more than 10 MPa. The accuracy of the proposed calibration scheme was confirmed in study.

PH Measurements in Monoethylene Glycol (MEG) + Water Solutions

A convenient calibration method for pH measurements in monoethylene glycol (MEG) + water solvents is described. The calibration has to be performed once for each electrode type. pH measurements were performed in CO2(g, ∼1 bar)-saturated solutions of 60 and 90 wt % MEG at 4−80 °C with varying NaHCO3 and KHCO3 contents. Reproducible data were obtained using several different electrodes. Theoretical aspects are reviewed.

Calibration of the spring constant of AFM cantilever

Several methods have been developed in recent years to calibrate the spring constant of atomic force microscopy (AFM) cantilever. In the present work, an effective and practical improvement is made on these methods to provide a more convenient calibration method. Simplifying the originally tedious procedures by just examining the cantilever's dimensions in scanning electron microscopy (SEM) and the resonance frequency of the cantilever from Q curves in AFM system, the spring constants of different cantilevers are calculated by the methods of Cleveland and Sader. The results are close to the nominal values provided by the manufacturers, which indicates that simplifying the procedures is valid and reliable. Moreover, it shows that spring constants acquiring by Cleveland method is more close to their nominal values than Sader's method does.