Measurement Error Analysis of Seawater Refractive Index: A Measurement Sensor Based on a Position-Sensitive Detector.

The seawater refractive index is an essential parameter in ocean observation, making its high-precision measurement necessary. This can be effectively achieved using a position-sensitive detector-based measurement system. However, in the actual measurement process, the impact of the jitter signal measurement error on the results cannot be ignored. In this study, we theoretically analysed the causes of long jitter signals during seawater refractive index measurements and quantified the influencing factors. Through this analysis, it can be seen that the angle between the two windows in the seawater refractive index measurement area caused a large error in the results, which could be effectively reduced by controlling the angle to within 2.06°. At the same time, the factors affecting the position-sensitive detector's measurement accuracy were analysed, with changes to the background light, the photosensitive surface's size, and the working environment's temperature leading to its reduction. To address the above factors, we first added a 0.9 nm bandwidth, narrow-band filter in front of the detector's photosensitive surface during system construction to filter out any light other than that from the signal light source. To ensure the seawater refractive index's measuring range, a position-sensitive detector with a photosensitive surface size of 4 mm × 4 mm was selected; whereas, to reduce the working environment's temperature variation, we partitioned the measurement system. To validate the testing error range of the optimised test system, standard seawater samples were measured under the same conditions, showing a reduction in the measurement system's jitter signal from 0.0022 mm to 0.0011 mm, before and after optimisation, respectively, as well as a reduction in the refractive index's deviation. The experimental results show that the refractive index of seawater was effectively reduced by adjusting the measurement system's optical path and structure.

Stress Distribution within the Peri-Implant Bone for Different Implant Materials Obtained by Digital Image Correlation.

Stress distribution and its magnitude during loading heavily influence the osseointegration of dental implants. Currently, no high-resolution, three-dimensional method of directly measuring these biomechanical processes in the peri-implant bone is available. The aim of this study was to measure the influence of different implant materials on stress distribution in the peri-implant bone. Using the three-dimensional ARAMIS camera system, surface strain in the peri-implant bone area was compared under simulated masticatory forces of 300 N in axial and non-axial directions for titanium implants and zirconia implants. The investigated titanium implants led to a more homogeneous stress distribution than the investigated zirconia implants. Non-axial forces led to greater surface strain on the peri-implant bone than axial forces. Thus, the implant material, implant system, and direction of force could have a significant influence on biomechanical processes and osseointegration within the peri-implant bone.

Thermoelastic wave generation and its longitudinal wave propagation measurement by a microscopic optical interferometer.

Laser ultrasonics is a noncontact measurement method that uses a laser-induced elastic wave source in combination with an optical surface displacement-tracking system. This study compared the performances of two optical interferometers with different characteristics when applied to measurement of pulsed thermoelastic waves. The surface displacement-tracking system was designed to measure the center of the microscopic view. A pulsed laser beam irradiated a black ink layer to generate the thermoelastic waves. The out-of-plane displacement on the axially opposite side was then measured using either a Michelson interferometer or a Sagnac interferometer. The objective lens of the system was of a type commonly used in biological observations. The Michelson interferometer estimated a maximum displacement of 0.43 nm and a maximum sound pressure of 24.7 kPa. The signal-to-noise ratios from 16 averages were 14.9 dB (Michelson interferometer) and 19.2 dB (Sagnac interferometer). Furthermore, this paper compares the performance of the numerically estimated Sagnac interferometer outputs calculated from the measured Michelson interferometer outputs with the experimentally obtained Sagnac interferometer outputs. The numerically estimated Sagnac interferometer's output was shown to be identical to the experimentally acquired output. The Michelson interferometer requires a higher average operating frequency (i.e., it needs a longer data acquisition time), although this interferometer does offer superior displacement output linearity. This property enables calculation of the sound pressure from the displacement amplitude. These findings indicated that combination of the measurement points of the Sagnac interferometer with those of the sparsely distributed Michelson interferometer reduced the measurement time when compared with a single use of the Michelson interferometer while also maintaining the data acquisition quality.

Advances in Aeroengine Cooling Hole Measurement: A Comprehensive Review.

Film cooling technology is of great significance to enhance the performance of aero-engines and extend service life. With the increasing requirements for film cooling efficiency, researchers and engineers have carried out a lot of work on the precision and digital measurement of cooling holes. Based on the above, this paper outlines the importance and principles of film cooling technology and reviews the evolution of cooling holes. Also, this paper details the traditional measurement methods of the cooling hole used in current engineering scenarios with their limitations and categorizes digital measurement methods into five main types, including probing measurement technology, optical measurement technology, infrared imaging technology, computer tomography (CT) scanning technology, and composite measurement technology. The five types of methods and integrated automated measurement platforms are also analyzed. Finally, through a generalize and analysis of cooling hole measurement methods, this paper points out technical challenges and future trends, providing a reference and guidance for forward researches.

High-Sensitivity Seawater Refraction Index Optical Measurement Sensor Based on a Position-Sensitive Detector.

The refractive index of seawater is one of the essential parameters in ocean observation, so it is necessary to achieve high-precision seawater refractive index measurements. In this paper, we propose a method for measuring the refractive index of seawater, based on a position-sensitive detector (PSD). A theoretical model was established to depict the correlation between laser spot displacement and refractive index change, utilizing a combination of a position-sensitive detector and laser beam deflection principles. Based on this optical measurement method, a seawater refractive index measurement system was established. To effectively enhance the sensitivity of refractive index detection, a focusing lens was incorporated into the optical path of the measuring system, and simulations were conducted to investigate the impact of focal length on refractive index sensitivity. The calibration experiment of the measuring system was performed based on the relationship between the refractive index of seawater and underwater pressure (depth). By measuring laser spot displacement at different depths, changes in displacement, with respect to both refractive index and depth, were determined. The experimental results demonstrate that the system exhibits a sensitivity of 9.93×10-9 RIU (refractive index unit), and the refractive index deviation due to stability is calculated as ±7.54×10-9 RIU. Therefore, the feasibility of this highly sensitive measurement of seawater refractive index is verified. Since the sensitivity of the refractive index measurement of this measurement system is higher than the refractive index change caused by the wake of underwater vehicles, it can also be used in various applications for underwater vehicle wake measurement, as well as seawater refractive index measurement, such as the motion state monitoring of underwater navigation targets such as AUVs and ROVs.

Measurement Method for Contact Wire Wear Based on Stereovision.

The contact wire wear is an important parameter to ensure the safety operation of electric railways. The contact wire may break if the wear is serious, which leads to transportation interruptions. This study proposes an optical measurement method of contact wire wear, using stereovision technology. The matching method of stereovision based on line-scan cameras is proposed. A lookup-table method is developed to exactly determine the image resolution caused by the contact wire being in different spatial positions. The wear width of the contact wire is extracted from catenaries' images, and the residual thickness of the contact wire is calculated. The method was verified by field tests. The round-robin tests of the residual thickness at the same location present excellent measurement repetitiveness. The maximum difference value between dynamic test results and ground measurement results is 0.13 mm. This research represents a potential way to implement condition-based maintenance for contact wire wear in the future in order to improve the maintenance efficiency and ensure the safety of catenary infrastructure.

Investigation of the accuracy of dynamic condylar position: A model study.

OBJECTIVES: To evaluate dynamic condylar positions by integrating mandibular movement recording data and cone-beam computed tomography (CBCT) and to investigate its accuracy via dynamic model experiments. METHODS: A polyvinyl chloride skull model was utilized. A robot arm was used to operate the mandible to perform mouth opening, closing, protrusion, and lateral movements. A recording device, worn on the skull, was used to record the dynamic process and an optical position tracking (OPT) system was used to simultaneously trace the movements. A self-developed software module was used to evaluate the dynamic condylar position by integrating the dynamic tracing data and a virtual skull model derived from CBCT images. Errors were defined as differences between the dynamic coordinates of six landmarks around the condylar area derived from the software module (test) and OPT system (gold standard). RESULTS: The condylar position errors were 0.76 ± 0.31, 0.55 ± 0.15, and 0.68 ± 0.23 mm for mouth opening, bilateral, and protrusion movements, respectively. Furthermore, the errors for small, moderate, and large mouth opening movements were 0.62 ± 0.19, 0.69 ± 0.29, and 0.94 ± 0.31 mm, respectively. The errors for all movements, except for large mouth opening, were significantly less than 1 mm (P < 0.05). The error was not different from 1 mm in the large mouth opening movement (P > 0.05). CONCLUSIONS: Our developed method of achieving dynamic condylar position by integrating mandibular movement recording data and CBCT images is clinically reliable. CLINICAL SIGNIFICANCE: This study proved the reliability of evaluating dynamic condylar position using a commercial dynamic recording instrument and CBCT images.

Investigation of Slagging Condition in a Zhundong Coal-Fired Boiler via In Situ Optical Measurement of Gaseous Sodium.

In this study, a portable spectral analysis instrument based on spontaneous emission spectroscopy (SES) was developed for the in situ, non-intrusive, and quantitative measurement of gaseous Na inside ZD coal-fired boilers, which is mainly applied for predicting slagging in furnaces. This technology is needed urgently because the problem of fouling and slagging caused by high alkali metals in ZD coal restricts the rational utilization of this coal. The relative extended uncertainty for the measurement of gaseous Na concentration is Urel = 10%, k = 2, which indicates that measurement data are reliable under working conditions. It was found that there is a clear linear relationship between the concentration of gaseous Na and fouling in high-alkali coal boilers. Therefore, a fast and efficient method for predicting the slagging and fouling of high-alkali coal boilers can be established by using this in situ online real-time optical measurement.

Flexible Measurement of High-Slope Micro-Nano Structures with Tilted Wave Digital Holographic Microscopy.

Digital holographic microscopy is an important measurement method for micro-nano structures. However, when the structured features are of high-slopes, the interference fringes can become too dense to be recognized. Due to the Nyquist's sampling limit, reliable wavefront restoration and phase unwrapping are not feasible. To address this problem, the interference fringes are proposed to be sparsified by tilting the reference wavefronts. A data fusion strategy including region extraction and tilt correction is developed for reconstructing the full-area surface topographies. Experimental results of high-slope elements demonstrate the validity and reliability of the proposed method.

A High-Precision Multi-Beam Optical Measurement Method for Cylindrical Surface Profile.

To automatically measure the surface profile of a cylindrical workpiece, a high-precision multi-beam optical method is proposed in this paper. First, some successive images for the cylindrical workpiece's surface are acquired by a multi-beam angle sensor under different light directions. Then, the light directions are estimated based on the feature regions in the images to calculate surface normal vectors. Finally, according to the relationship of the surface normal vector and the vertical section of the workpiece's surface, a depth map is reconstructed to achieve the curvature surface, which can be employed to measure the curvature radius of the cylindrical workpiece's surface. Experimental results indicate that the proposed measurement method can achieve good measurement precision with a mean error of the curvature radius of a workpiece's surface of 0.89% at a reasonable speed of 10.226 s, which is superior to some existing methods.

A New Vision Measurement Technique with Large Field of View and High Resolution.

The three-dimensional (3D) displacement resolution of conventional visual measurement systems can only reach tens of microns in cases involving long measuring distances (2.5 m) and large fields of view (1.5 m × 1.5 m). Therefore, a stereo vision measurement technology based on confocal scanning is proposed herein. This technology combines macroscopic visual measurement technology with confocal microscopic measurement technology to achieve a long measuring distance, a large field of view, and micron-level measuring resolution. First, we analyzed the factors affecting the 3D resolution of the visual system and developed a 3D resolution model of the visual system. Subsequently, we fabricated a prototype based on the resolution model and the proposed stereo vision measurement technology. The 3D displacement resolution measurement results in the full field of view show that the displacement resolutions of the developed equipment in the x-, y-, and z-directions can reach 2.5, 2.5, and 6 µm, respectively.

Monitoring of Particulate Fouling Potential of Feed Water with Spectroscopic Measurements.

The modified fouling index (MFI) is a crucial characteristic for assessing the fouling potential of reverse osmosis (RO) feed water. Although the MFI is widely used, the estimation time required for filtration and data evaluation is still relatively long. In this study, the relationship between the MFI and instantaneous spectroscopic extinction measurements was investigated. Since both measurements show a linear correlation with particle concentration, it was assumed that a change in the MFI can be detected by monitoring the optical density of the feed water. To prove this assumption, a test bench for a simultaneous measurement of the MFI and optical extinction was designed. Silica monospheres with sizes of 120 nm and 400 nm and mixtures of both fractions were added to purified tap water as model foulants. MFI filtration tests were performed with a standard 0.45 µm PES membrane, and a 0.1 µm PP membrane. Extinction measurements were carried out with a newly designed flow cell inside a UV-VIS spectrometer to get online information on the particle properties of the feed water, such as the particle concentration and mean particle size. The measurement results show that the extinction ratio of different light wavelengths, which should remain constant for a particulate system, independent of the number of particles, only persisted at higher particle concentrations. Nevertheless, a good correlation between extinction and MFI for different particle concentrations with restrictions towards the ratio of particle and pore size of the test membrane was found. These findings can be used for new sensory process monitoring systems, if the deficiencies can be overcome.

Distributed Optical Measurement System for Plate Fin Heat Exchanger.

The acquirement of the flow information in plate-fin heat exchanger (PFHE) is limited by its metal structure and complex flow condition. This work develops a new distributed optical measurement system to obtain flow information and boiling intensity. The system utilizes numerous optical fibers installed at the surface of the PFHE to detect optical signals. The attenuation and fluctuation of the signals reflect the variation of the gas-liquid interfaces and can be further used to estimate the boiling intensity. Practical experiments of flow boiling in PFHE with different heating fluxes have been carried out. The results verify that the measurement system can obtain the flow condition. Meanwhile, according to the results, the boiling development in PFHE can be divided into four stages with the increase in the heating flux, including the unboiling stage, initiation stage, boiling developing stage, and fully developed stage.

Integrated Optical Deformation Measurement with TIR Prism Rods.

In this paper, a novel optical measurement principle for deformation, especially torsion, is presented. A laser beam is guided via total internal reflection (TIR) in a prism rod. Every single reflection causes an increasing change in the beam path, which can be measured by its effect on the outcoupling position of the laser. With a diameter of the prism rod of 10 mm and a length of 120 mm, the system achieves torsion sensitivities between 350 µm/° and more than 7000 µm/°, depending on the actual torsion angle φ. A decency level of sensitivity is defined for comparison, which is exceeded by a factor of ~55 at φ=0. The presented principle of TIR prism rods can be adapted to measure different load cases. Using two laser beams, bending and torsion can be distinguished and combined load cases analyzed. The resulting system can be integrated into machine elements, such as screws, to perform condition monitoring on mechanically loaded components.

The Effect of Non-Measured Points on the Accuracy of the Surface Topography Assessment of Elements 3D Printed Using Selected Additive Technologies.

The paper presents the results of research aimed at evaluating the surface topography including the analysis of the number of unmeasured points of the samples 3D printed using four additive technologies (i.e., PolyJet Matrix, fused deposition modeling, selective laser sintering, and selective laser melting). The samples were made in three variants of location on the printing platform of 3D printers. Measurements of the samples' surface topography were carried out using a Talysurf CCI Lite optical profilometer and a Talysurf PGI 1230 contact profilometer. The percentage of non-measured points for each sample and the parameters of the surface topography were determined. Then, the non-measured points were complemented and the topography parameters for the corrected surface were recalculated. In addition, to perform comparative measurements, each surface was measured using a contact profilometer Talysurf PGI 1230. Preliminary results of the research showed that the measurement of the surface topography of the samples made using selective laser sintering technology with the Taysurf CCI optical measuring system is very unreliable, as the number of non-measured points for the analyzed samples was higher than 98%. The highest accuracy of optical measurement was obtained for PJM technology and three variants of location on the printing platform of the 3D printer.

Establishing the lower bacterial concentration threshold for different optical counting techniques.

This work compares several physical and optical techniques used in fundamental research and industrial applications to detect bacteria in water. Optical techniques such as, UV-absorbance spectroscopy, laser particle counting, turbidimetry and Z-Sizer light scattering, and a direct observational physical technique, the plate count method, were compared when measuring the concentration of E.coli in tenfold dilution from a stock solution. Estimates of the detection threshold limit of E.coli for the different optical counting techniques and the relationship between colony-forming units (CFU) and tenfold dilutions was established. Optical methods have generated interest due to the rapid response of just minutes, non-destructive approach and minimal sample preparation but their use is still limited to concentrations of up to 4 Log E.coli/mL. In contrast, the plate count method is still a reliable technique for water quality analysis despite its long response time of 24 h.

Optical Measurement of Molar Absorption Coefficient of HbA1c: Comparison of Theoretical and Experimental Results.

Diabetes can cause dangerous complications if not diagnosed in a timely manner. The World Health Organization accepts glycated hemoglobin (HbA1c) as a measure of diagnosing diabetes as it provides significantly more information on the glycemic behavior from a single blood sample than the fasting blood sugar reading. The molar absorption coefficient of HbA1c is needed to quantify the amount of HbA1c present in a blood sample. In this study, we measured the molar absorption coefficient of HbA1c in the range of 450 nm to 700 nm using optical methods experimentally. We observed that the characteristic peaks of the molar absorption coefficient of HbA1c (at 545 nm and 579 nm for level 1, at 544 nm and 577 nm for level 2) are in close agreement with those reported in previous studies. The molar absorption coefficient values were also found to be close to those of earlier reports. The average molar absorption coefficient values of HbA1c were found to be 804,403.5 M−1cm−1 at 545 nm and 703,704.5 M−1cm−1 at 579 nm for level 1 as well as 503,352.4 M−1cm−1 at 544 nm and 476,344.6 M−1cm−1 at 577 nm for level 2. Our experiments focused on calculating the molar absorption coefficients of HbA1c in the visible wavelength region, and the proposed experimental method has an advantage of being able to easily obtain the molar absorption coefficient at any wavelength in the visible wavelength region. The results of this study are expected to help future investigations on noninvasive methods of estimating HbA1c levels.

Development of a Three-Dimensional Optical Verification Technology without Environmental Pollution for Metal Components with Different Surface Properties.

Nowadays, the optical measuring approach is widely used in the precision machining industry due to high measurement efficiency. In the industry, measuring devices play a crucial role in the field of quality assurance. In practical engineering, the green measurement approach indeed plays an important role in the industry currently. In this study, a state-of-the-art green technique for three-dimensional (3D) optical measurements without environmental pollution is demonstrated, which is an environmentally friendly optical measurement method. This method can perform precise optical measurement without matte coatings. This work dealt with the possibility of measuring four metal components that were not sprayed with anything. The differences in the optical measurement results between with and without matte coatings were investigated and analyzed. It was found that the research result has practical value in the precision machining industry because average size errors of the four measurement objects with different surface properties can be controlled at about 3 µm, 0.1 µm, 0.5 µm, and 9 µm. A technical database with industrial value was established for optical measurements of metal components with different surface properties without matte coatings, which can serve as an alternative to the conventional 3D optical measurement.

New Conceptional Study of a Portable Highly Sensitive Photometric Raman Sensor.

Quality control and reaction monitoring are necessary to ensure the consistency of any kind of mixing or reaction process. In this context, a novel portable high-sensitivity sensor prototype based on the Raman effect is presented in this study. The elongated probe head is designed for (but not limited to) monitoring high temperature batch processes for quality assurance. Thanks to the highly sensitive special detectors, concentration differences of up to 50 mmol/L can currently be detected, which facilitates compliance with high product quality standards. In addition, seamless reaction tracking is possible. Small individual adjustments through simple, intuitive mechanical components provide a high degree of flexibility in reaction selection by the end user. Specially developed software automates the evaluation process and gives the user visual signals about the current status and progress of the batch as well as an emergency stop if temperature limits could damage individual components. By using all the individual components developed, the problem of the limited integration times of previous spectrometric measuring instruments could be reduced. The prototype was validated using concentration measurements of various substances that occur as standard in batch processes. In addition, this article provides an outlook on the fact that Raman measurements can also be carried out successfully and reliably in explosive environments in the future with the prototype presented.

Hot Spot Detection of Photovoltaic Module Based on Distributed Fiber Bragg Grating Sensor.

The hot spot effect is an important factor that affects the power generation performance and service life in the power generation process. To solve the problems of low detection efficiency, low accuracy, and difficulty of distributed hot spot detection, a hot spot detection method using a photovoltaic module based on the distributed fiber Bragg grating (FBG) sensor is proposed. The FBG sensor array was pasted on the surface of the photovoltaic panel, and the drift of the FBG reflected wavelength was demodulated by the tunable laser method, wavelength division multiplexing technology, and peak seeking algorithm. The experimental results show that the proposed method can detect the temperature of the photovoltaic panel in real time and can identify and locate the hot spot effect of the photovoltaic cell. Under the condition of no wind or light wind, the wave number and variation rule of photovoltaic module temperature value, environmental temperature value, and solar radiation power value were basically consistent. When the solar radiation power fluctuated, the fluctuation of hot spot cell temperature was greater than that of the normal photovoltaic cell. As the solar radiation power decreased to a certain value, the temperatures of all photovoltaic cells tended to be similar.