Practical Calibration Research Articles

Continuous-wave coherent Raman spectroscopy for improving the accuracy of Raman shifts.

Raman spectroscopy is an appealing technique that probes molecular vibrations in a wide variety of materials with virtually no sample preparation. However, accurate and reliable Raman measurements are still a challenge and require more robust and practical calibration methods. We demonstrate the implementation of a simple low-cost continuous-wave (cw) stimulated Raman spectroscopy scheme for accurate and high-resolution spectroscopy. We perform shot noise-limited cw stimulated Raman scattering as well as cw coherent anti-Stokes Raman scattering on polystyrene samples. Our method enables accurate determination of Raman shifts with an uncertainty below 0.1 cm-1. The setup is used for the characterization of reference materials required for the calibration of Raman spectrometers. Compared with existing standards, we provide an order of magnitude improvement of the uncertainty of Raman energy shifts in a polystyrene reference material.

Method of multichannel calibration for unmanned aerial vehicle surveillance radar

Amplitude and phase errors among the different channels including antenna and receiver of the unmanned aerial vehicle surveillance digital array radar will deteriorate the beam pattern and cause the invalid digital beam formation, and then severely affect the performance of radar. Based on in-the-field calibration method, this study presents a practical calibration method that combines the external and internal calibration together. Experiments are designed for an X-band linear antenna array with 16 unit cells, whose period is about half wavelength, and the measured results show that the proposed algorithm is an attractive way to calibrate the digital array radar efficiently.

Damage identification for frame structures using vision-based measurement

Extracting physical parameters for damage identification problems from full-field measurements is a promising research because of the recent spread of vision-based measurement techniques in the experimental mechanics. This paper presents a vision-based measurement framework using the camera system for damage identification. The framework is composed of four procedures: camera calibration, image processing, system identification and sensitivity analysis. In contrast to traditional finite-point measurements, the camera system allows considerably greater non-contact measurement flexibility. Such flexibility has two important benefits: first, less number of modes is required for modal-based damage identification problems; and second, more physical parameters could be extracted, taking advantage of the plentiful experimental data. A laboratory test comparing the camera system to traditional accelerometer measurement is conducted to confirm the above advantages. Further statistic analysis shows that the major drawback of this technique is that the camera system presents high levels of noise in small vibration responses at higher frequencies. Suitable strategies to circumvent this disadvantage are developed. Moreover, a technique for practical camera calibration without the requirement that the objective plane should be strictly perpendicular to the camera axis is also demonstrated and verified by the proposed laboratory test.

EFFECTS OF VARIATION IN MEASUREMENT CHAIN ON TEMPERATURE MEASUREMENT CALIBRATION WITH RESISTANT TEMPERATURE SENSORS

Temperature is one of the most important key parameter to consider in measurement and mechanical engineering, because every measurement has to be conducted with reference to standard temperature conditions (20 °C, ISO 1). Strictly speaking, almost every measurement depends on the accuracy of the temperature measurement, which requires proper calibration. Therefore, standards list detailed criteria to fulfil temperature calibration with high precision. In fact, any calibration is only valid, if the whole measurement chain is taken into account. This would make recalibration necessary with each variation of the components in the measuring set-up (varying cable length, different measurement channel etc.), which is time-consuming or even impossible in practice. For that reason, this paper presents a practicable calibration strategy, which specifies each component individually and later combines the calibration results according to the composition of the measurement chain. This provides a fast and useful way to achieve the required accuracy of temperature measurement. The examined, exemplary measurement chain consists of an industrial platinum resistance thermometer (IPRT), cables with different lengths, an electrical amplifier and a reference temperature calibrator.

A novel design for magneto-optical microscopy and its calibration

Magneto-optical microscopy for superconducting films is always involved with extreme environments, such as high vacuum and cryogenic temperature. In these applications, devices of high spatial resolution and compact focusing are often required. Besides, the calibration process is also of importance for quantitative measurement of magnetic fields. In this paper, we present a comprehensive module design for magneto-optical microscopy based on a combination of an infinity optical system and dynamic sealing technique. This technique gets rid of the limit of distance between the sample and the microscope, and also guarantees no influences of windows on image resolution. In addition, for the problem of uneven illumination, a practical calibration method is presented and verified through experimental results. As a result, the novel module and its calibration method make the technology of magneto-optical microscopy have wide applications.

Array‐based target localisation in ATSC DTV passive radar

This work investigates the use of passive radar array-based localisation, with a focus on experimental demonstration and practical array calibration aspects. Passive radar target localisation often employs multilateration, where a set of hyperbolic equations from range differences or elliptic equations from bistatic ranges are solved to determine the three-dimensional (3D) target position. An alternative uses array-based direction finding to provide an accurate measurement of target bearing, and intersects the bearing vector with a bistatic range ellipsoid to obtain a 3D target position. Continuous-wave digitally modulated signals like digital television (DTV) provides stable power spectra and long integration times, and these support fine range and Doppler resolutions to isolate multiple targets without the association difficulties of multilateration. The Bartlett method can then be used on individual targets, giving bearing estimates of much higher accuracy than the array beamwidth. This was shown experimentally with an electrically small array yielding small angular errors in both azimuth and elevation. Using a DTV-based passive radar, a target at 20 km receiver range was located with an accuracy of ∼250 m in a 3D position. Furthermore, a procedure for in-situ array calibration using opportunistic air targets is reported.

Determining the effect of relative size of sensor on calibration accuracy of TEM cells

The time-domain calibration coefficient of a D-Dot sensor should be identical across various transverse electromagnetic (TEM) cells to comply with the IEEE Std 1309. However, in our previous calibration experiments, poor consistency was observed. The size of D-Dot sensors relative to TEM cells is considered the main reason for this poor consistency. Therefore, this study aims at determining the calibration coefficient of a D-Dot sensor. We calculate the theoretical coefficient as a reference. Practical calibration experiments involve the processing of TEM cells with three different sizes. To observe the response more clearly, corresponding models are constructed and numerical simulations are performed. The numerical simulations and experimental calibration are in good agreement. To determine the calibration accuracy, we quantify the accuracy using the relative error of the calibration coefficient. By comparing the coefficients obtained, it can be concluded that the perturbation error is about 15% when the relative size is over 1/3. Further, the relative size should be less than 1/5 to obtain a relative error below 10%.

Dental Perspective on Biomedical Waste and Management – A Knowledge, Attitude, and Practice Survey: A Cross-sectional Study

Title: “DENTAL PERSPECTIVE ON BIOMEDICAL WASTE AND MANAGEMENT, A KNOWLEDGE, ATTITUDE AND PRACTICE SURVEY: A CROSS- SECTIONAL STUDY”. Abstract: Background: The Biomedical waste is known as the second dangerous waste in the world that needs to be properly managed. Since the implementation of the biomedical Waste Management Rules 1998, every concerned health personnel is expected to have proper knowledge, practice and capacity to guide others for waste collection and management, and proper handling techniques. Objective: This study was planned to evaluate the practical calibration and awareness of Dental surgeons in disposal of hazardous biomedical waste generated during Dental treatment into color coded disposing bags at a Dental clinics. Methods: A cross-sectional, a pretested, semi structured questionnaire based survey containing 53 questions to assess the knowledge, attitude and practice on biomedical waste management among Dental surgeons. Results were expressed as a number and percentage of respondents for each question and Chi-square test was performed for inferential statistical analysis with p value <0.05 indicating level of significance. Results: Results show that a large percentage of the Dentist were not aware of the process of biomedical waste management (89%) whereas about half of the subjects were moderate to slightly aware about the recycling/reusing of Dental materials. Conclusion: The study revealed that knowledge, attitude and practice regarding biomedical waste management among were low. Periodical sensitization and training program should be conducted for health care providers.

A practical method to calibrate and optimise automatic exposure control devices for computed radiography (CR) and digital radiography (DR) imaging systems using the signal-to-noise ratio (SNR) metric

We have established in recent virtual clinical trials that signal-to-noise ratio (SNR) is the most appropriate metric for calibrating AEC devices used with digital imaging systems for chest, abdomen, pelvis and spine radiography. However, the practical calibration of such devices is not straightforward. The purpose of this study was to expand on previous work by developing a practical method for AEC calibration using the validated SNR metric that may be used by medical physicists in the field for phosphor plate radiography (CR) and direct digital radiography (DR - wireless and integrated) imaging systems. This methodology used a uniform tissue equivalent phantom (Poly-methyl methacrylate (PMMA)) so comparison was made with an installation vendor’s method of using copper plates. System transfer properties (STP) of each system were derived to linearise all images required for analyses. All STP correction was done in real time. The relationship between detector air kerma (DAK) and STP corrected SNR was then derived at four tube voltages (60, 80, 100 and 120 kVp) and using this relationship, together with the target value of the calibration metric (SNRtarget), it was possible to calculate the DAK required at each tube voltage to derive a calibration curve for each system; CR systems exhibited a linear increase with kVp, DR systems exhibited a ‘U’ shape. The curve derived using the vendor’s method was not considered optimised because it did not hold SNR constant. This work has demonstrated that a relatively simple method to calibrate AEC devices, using an easily accessible tissue equivalent phantom, can be used in the field in real time by medical physicists working with installation engineers. AEC calibration curves that produce clinically adequate image quality with acceptable patient dose have been installed in our radiology department for CR and DR systems using the methodology described in this paper.

Applicability of a practical calibration for the small-type OSL dosimeter for measuring doses from direct X-rays and penetrating X-rays affected by scattered radiation

Applicability of a practical calibration for the small-type OSL dosimeter for measuring doses from direct X-rays and penetrating X-rays affected by scattered radiation

Four points: one-pass geometrical camera calibration algorithm

Conventional geometrical camera calibration algorithms are usually based on running some iterative algorithms on test images obtained carefully from reference objects with precisely known pattern. Providing these test images and running the iterative algorithms are often time-consuming and sometimes costly. In addition, they are usually very sensitive to image distortions. To overcome these problems, an efficient and practical camera calibration method using a single rectangular reference object is proposed. The reference object can be as simple as an A4-size paper placed on a table. Using the coordinate of four corner points of reference image, generate eight equations. This paper first describes an analytical method to solve the equations and then provides a step-by-step algorithm. The proposed algorithm is evaluated using simulated images generated with both Autodesk 3ds Max software and Microsoft Camera Calibration data set. The results show that the accuracy of the proposed method is very close to the best ones available, while its sensitivity to distortion and computational load is the least. In addition, the required reference object is the simplest one.

Environment-Adaptive Calibration System for Outdoor Low-Cost Electrochemical Gas Sensors

To date, air pollution has caused over seven million deaths worldwide. Real-time monitoring is an efficient solution to prevent and mitigate air pollution. However, air quality monitoring networks are not currently dense enough to cover a large area because of the cost. With the development of low-cost electrochemical gas sensors, the current air quality monitoring network could be extended to a large area with a relatively high-resolution ratio. Nevertheless, the electrochemical gas sensors are not accurate enough compared to standard sensors if they are not carefully calibrated. Therefore, we proposed an environment-adaptive calibration (EAC) system dedicated to the implementation of a collaborative calibration technique for outdoor low-cost electrochemical gas sensors. The EAC system uses a new practical calibration algorithm operating on the Raptor IoT cloud platform that was developed as part of the H2020 Captor project. The system can identify the linear characteristics of gas sensors according to weather conditions, which is valuable prior knowledge for the calibration and the unique character of the EAC system. The outstanding performance of the EAC system is verified by the evaluation of a long-term measurement campaign, in which various metrics are considered, e.g., the goodness-of-fit, target diagram, and daily residuals.

An improved kinematic model for serial robot calibration based on local POE formula using position measurement

Purpose This paper aims to propose a calibration model for kinematic parameters identification of serial robot to improve its positioning accuracy, which only requires position measurement of the end-effector. Design/methodology/approach The proposed model is established based on local frame representation of the product of exponentials (local POE) formula, which integrates all kinematic errors into the twist coordinates errors; then they are identified with the tool frame’ position deviations simultaneously by an iterative least squares algorithm. Findings To verify the effectiveness of the proposed method, extensive simulations and calibration experiments have been conducted on a 4DOF SCARA robot and a 5DOF drilling machine, respectively. The results indicate that the proposed model outperforms the existing model in convergence, accuracy, robustness and efficiency; fewer measurements are needed to gain an acceptable identification result. Practical implications This calibration method has been applied to a variable-radius circumferential drilling machine. The machine’s positioning accuracy can be significantly improved from 11.153 initially to 0.301 mm, which is well in the tolerance (±0.5 mm) for fastener hole drilling in aircraft assembly. Originality/value An accurate and efficient kinematic calibration model has been proposed, which satisfies the completeness, continuity and minimality requirements. Due to generality, this model can be widely used for serial robot kinematic calibration with any combination of revolute and prismatic joints.

Consistent kinematics and dynamics calibration of lightweight redundant industrial manipulators

Absolute accuracy is one of industrial manipulator’s key performance characteristics, which is critical for emerging robotics applications such as laser cutting, riveting, and carbon fiber placement as well as for many machining operations. On the other hand, arrival of new uses such as collaborative robots needs the estimation of interaction efforts with the operator or with the environment (hand-guiding, collision detection, and free backlash assembly). This paper presents an approach to organize an integrated kinematic and dynamic calibration procedure to improve quality of models appropriate for trajectory planning and motion control. Along with bringing theoretical insights and novel arguments, we give hands-on recommendations on selection of parameters priors, initial guesses on calibration poses and trajectories, setting active constraints, algorithms tuning, and experimental data filtering which is necessary to perform consistent robot calibration in practice. We illustrate the study with experimental data and description of actual calibration performed on the KUKA Light-Weight Robot using vision-based metrology and dedicated software. In contrast to authors preceding works, this paper includes a more complete entire procedure description, analysis of dynamic calibration sensitivity with respect to kinematic parameters estimates and a chapter on how calibration results can be used for model-based trajectories planning using virtual holonomic constraints approach.

Easily implemented approach for the calibration of alignment and retardation errors in a channeled spectropolarimeter.

Calibration of the channeled spectropolarimeter is significant for the quantitative application of this instrument. In current calibration methods for a channeled spectropolarimeter, an absolute angle between the coordinate system of an auxiliary polarizer and the global coordinate system of the instrument is usually indispensable. The effectiveness of calibration depends on the precision of the absolute angle, while it is usually difficult to achieve in a practical calibration process. This paper presents an easily implemented method to simultaneously calibrate the alignment and retardation errors of high-order retarders for a channeled spectropolarimeter. In the presented method, the requirement of an absolute angle between the coordinate system of an auxiliary polarizer and the global coordinate system of the instrument is replaced by only rotating a relative angle in the coordinate system of the auxiliary polarizer itself. First, we theoretically derive the modified reconstruction model considering the alignment errors of high-order retarders. By analyzing and summarizing the modified reconstruction model, the calibration and compensation models of the alignment and retardation errors are further proposed. Then, two linearly polarized beams with a relative angle of 45° between them are utilized to determine the alignment and retardation errors. Based on these results, the alignment and retardation errors can be compensated by a software correction algorithm without any precise mechanical adjustments. The effectiveness and feasibility of the presented method are verified by numerical simulations and experiments. The advantage of easy implementation makes this calibration method more suitable to apply in the laboratory and to be on track for correcting the channeled spectropolarimeter.

A new microscopic telecentric stereo vision system - Calibration, rectification, and three-dimensional reconstruction

In stereo vision based three-dimensional (3D) measurements, calibration and stereo matching are the most challenging tasks for accurate 3D reconstruction. In this paper, a new microscopic telecentric stereo vision system is proposed to retrieve 3D data of micro-level objects by direct triangulation from two accurately calibrated telecentric cameras. The complex projector calibration procedure commonly seen in traditional structured-light based systems can be avoided. Besides, an improved and practical calibration framework of telecentric cameras is presented. Compared with existing calibration methods which retrieve the distortion parameters without reasonable initial guesses, our proposed approach derives reliable initial guesses for all the camera parameters to avoid the local minima problem based on the estimation algorithms before iterations. To realize precise sub-pixel stereo matching, we propose an effective searching algorithm based on the epipolar rectification of the absolute phase maps obtained from fringe projection profilometry. Experimental results indicate that a measurable volume of 10 mm (L) × 7 mm (W) × 7 mm (H) is achieved with the standard deviation of 1.485 μm.

Validation and Calibration of Freeway Reliability Methodology in the Highway Capacity Manual: Method and Case Studies

Traffic congestion costs drivers an average of $1,200 a year in wasted fuel and time, with most travelers becoming less tolerant of unexpected delays. Substantial efforts have been made to account for the impact of non-recurring sources of congestion on travel time reliability. The 6th edition of the Highway Capacity Manual (HCM) provides a structured guidance on a step-by-step analysis to estimate reliability performance measures on freeway facilities. However, practical implementation of these methods poses its own challenges. Performing these analyses requires assimilation of data scattered in different platforms, and this assimilation is complicated further by the fact that data and data platforms differ from state to state. This paper focuses on practical calibration and validation methods of the core and reliability analyses described in the HCM. The main objective is to provide HCM users with guidance on collecting data for freeway reliability analysis as well as validating the reliability performance measures predictions of the HCM methodology. A real-world case study on three routes on Interstate 40 in the Raleigh-Durham area in North Carolina is used to describe the steps required for conducting this analysis. The travel time index (TTI) distribution, reported by the HCM models, was found to match those from probe-based travel time data closely up to the 80th percentile values. However, because of a mismatch between the actual and HCM estimated incident allocation patterns both spatially and temporally, and the fact that traffic demands in the HCM methods are by default insensitive to the occurrence of major incidents, the HCM approach tended to generate larger travel time values in the upper regions of the travel time distribution.

Online Calibration of the Geographic-Frame-Equivalent Gyro Bias in Dual-Axis RINS

Dual-axis rotational inertial navigation system (RINS) has been widely used in long-term marine navigation for recent years. With all constant biases averaged out, those gyro biases related to geomagnetic or gravitational field, which cannot be averaged out, become the main error source. In this paper, the geographic-frame-equivalent (G-F-E) gyro bias is defined by integrating the gyro biases caused by all kinds of external fields. A practicable online calibration method is proposed by deducing the error propagation rules. The calibration equation is established by observing position errors at three points, and the optimal solution of the G-F-E gyro bias is obtained using the least square method. Static and sailing experimental results show that the G-F-E gyro bias can be calibrated during the 6-h initial alignment. The proposed calibration method can further improve the position accuracy of a dual-axis RINS by 30% compared with the previous method when the G-F-E gyro bias changes.

Development of a Practical Calibration Procedure for a Clinical SPECT/MRI System Using a Single INSERT Prototype Detector and Multimini Slit-Slat Collimator

In the context of the INSERT project, we have been developing a clinical single photon emission computed tomography (SPECT) insert for a magnetic resonance imaging (MRI) system, in order to perform simultaneous SPECT/MRI of the human brain. This system will consist of 20 CsI:Tl scintillation detectors, 5-cm wide and 10-cm long, with a 72-channel silicon photomultiplier (SiPM) readout per detector, and a multimini slit-slat (MSS) collimator set up in a stationary partial ring. Additionally the system has a custom-built transmit/receive MR coil to ensure compatibility with the SPECT system. Due to the novel design of the system/collimator, existing geometric calibration methods are not suitable. Therefore we propose a novel and practical calibration procedure that consists of a set of specific independent measurements to determine the geometric parameters of the collimator. This procedure was developed utilizing a prototype system that consists of a reduced-size single detector with a 36-channel SiPM-based readout and a single MSS collimator module. Validation was performed by reconstructing different imaging phantoms, using a rotating stage to simulate a tomographic acquisition. Regarding uniformity, the coefficient of variation (COV) for the cylinder phantom reconstructed with correct calibration parameters is 6.7%, whereas the COV using incorrect parameters is 9.4%. The quality of the phantom reconstructions provide evidence of the applicability of the proposed method to the calibration of the prototype system. This procedure can be easily adapted for the final INSERT system.

Optimization of high resolution COSMO model performance over Switzerland and Northern Italy

In our previous work, a practicable objective three-parameter multivariate calibration method build on a quadratic meta-model was introduced leading to the optimization of COSMO model. The process had been applied initially for a regional climate model (RCM) providing a considerable alternative to the, more standard, expert tuning techniques. Based on the successful implementation of this method, the calibration of the model on the operational level is undertaken in the present work. A larger number of parameters are selected in order to optimize the model performance for a high horizontal resolution (~2 km) over the domain of Switzerland and Northern Italy as well an extensive period of one year. The influence of the variables is associated to daily forecasts such as daily minimum and maximum 2 m temperature as well as 24 h accumulated precipitation. The increased computational demands and the substantial complexities regarding the application of a meta-model for a large parameter number are successfully tackled. The forecast skill of the 2-m temperature was improved by lowering the temperature bias by 0.2 °C. Contradictory, a small decrease in forecast skill for precipitation and dew point was observed. There is practically no change in forecasted wind speed when using the optimum set of parameters as none of the parameters tested is directly affecting model's ability to forecast wind. Currently, the results indicate a relatively low benefit with respect to the computational cost of the method as it remains expensive for a regular usage of the calibration procedure.