Maximum Measurement Error Research Articles

Imaging model and vision measurement method considering refraction effect of flat glass windows in tunnel construction

Vision measurement has become an indispensable technology in tunnel construction. However, the harsh construction environment necessitates the provision of a certain thickness of flat glass windows to protect the vision system. This, in turn, leads to an obvious refraction effect, rendering the pinhole model and traditional vision measurement methods inadequate. As such, this paper offers a comprehensive solution to this problem. Firstly, the imaging model under the refraction of flat glass is shown based on the virtual camera and virtual space point, respectively. Secondly, a three-parameter calibration method for flat glass was proposed, which could determine the refractive index, unit normal vector, and light path normal distance. A practical dynamic interval constraint was introduced to address the failure of the epipolar constraint in refraction image pairs. Lastly, a new binocular disparity method is presented to avoid the impact of refraction distortion on the solution accuracy of three-dimensional coordinates. Effectiveness experiments are conducted, showing a refractive index relative error within ±1%, a miniaturized and efficient dynamic interval constraint, a maximum reconstruction error of 0.120 mm, and a maximum measurement error of only 0.093 mm. A series of stability experiments are also performed under different target attitudes, glass attitudes, working distances, and pollution conditions. The results demonstrate the robustness of the proposed solution. Although the scheme is developed for the vision system in harsh tunnel construction environments, it can serve as a reference for any vision measurement applications under glass protection windows.

Calibration Method for Airborne Infrared Optical Systems in a Non-Thermal Equilibrium State.

Airborne infrared optical systems equipped with multiple cooled infrared cameras are commonly utilized for quantitative radiometry and thermometry measurements. Radiometric calibration is crucial for ensuring the accuracy and quantitative application of remote sensing camera data. Conventional radiometric calibration methods that consider internal stray radiation are usually based on the assumption that the entire system is in thermal equilibrium. However, this assumption leads to significant errors when applying the radiometric calibration results in actual mission scenarios. To address this issue, we analyzed the changes in optical temperature within the system and developed a simplified model to account for the internal stray radiation in the non-thermal equilibrium state. Building upon this model, we proposed an enhanced radiometric calibration method, which was applied to the absolute radiometric calibration procedure of the system. The radiometric calibration experiment, conducted on the medium-wave channel of the system within a temperature test chamber, demonstrated that the proposed method can achieve a calibration accuracy exceeding 3.78% within an ambient temperature range of -30 °C to 15 °C. Additionally, the maximum temperature measurement error was found to be less than ±1.01 °C.

Study on Bearing Capacity of Honeycomb Sandwich Structure Embedded Parts

In the composite structure of spacecraft, the honeycomb sandwich structure is the basic bearing component used to bear and transmit loads. To explore the influencing factors on the bearing capacity of honeycomb sandwich structures, this study combines local tests and speckle measurement systems to conduct tensile tests on 10 test specimens with different parameters. Firstly, a comprehensive assessment was conducted on the accuracy of the loading and measurement system, the rationality of the testing method, and the mechanical properties of the test piece. It was found that the maximum measurement error of the speckle measurement system did not exceed 0.01 mm, and the differences between the yield load and failure load measured using different inner diameters of the compression ring were 0.15% and 3.84%, respectively. This indicates that the measurement system is accurate and that the influence of the inner diameter of the compression ring can be ignored. Moreover, it was found that considering the accuracy retention ability of the structure under load, the allowable load of the embedded parts is about 90% of the yield load. Finally, the data of specimens with different parameters were compared and it was found that the strength of the honeycomb sandwich structure is directly proportional to the thickness of the skin, the density of the honeycomb core cells, and the size of the embedded parts.

High-precision temperature-compensated fiber Bragg grating axial strain sensing system based on a dual-loop optoelectronic oscillator with the enhanced Vernier effect.

A temperature-compensated fiber Bragg grating (FBG) axial strain sensor based on a two-dual-loop optoelectronic oscillator (OEO) with the enhanced Vernier effect is proposed and experimentally demonstrated. The sensing head consists of two cascaded FBGs, one of which acts as a sensing FBG to measure both the axial strain and temperature and the other as a reference FBG to detect temperature. Acting as the optical carrier, the reflected optical signal of the sensing head is divided into two paths with opposite dispersion coefficients and slightly different lengths to achieve an enhanced Vernier effect. After being divided by a wavelength division multiplexer, the optical signal launches into two electrical paths with different electrical bandpass filters (EBPFs) for frequency division multiplexing. The EBPF I selects the microwave signal generated by the sensing FBG, while the EBPF II selects the microwave signal generated by the reference FBG. Therefore, the axial strain and temperature can be recovered by recording the microwave frequency within EBPF I, and the temperature can be interrogated by tracking the microwave frequency within EBPF II. The axial strain applied on the sensing FBG can be distinguished by solving the cross-sensitivity matrix. The results show that the sensitivity of the dual-loop OEO is much greater than that of the single-loop OEO. The maximum measurement error for the axial strain is 0.112µε, and the maximum temperature compensation error is as low as 0.024°C in the dual-loop OEO, which is far less than that in the single-loop OEO. The enhanced Vernier effect not only improves the sensitivity, but also reduces the temperature compensation error.

In-situ calibration method for thermocouples in accelerating rate calorimeter based on multiple fixed-points and Joule heat

To solve the problem of temperature drift of thermocouples in accelerating rate calorimeter caused by long-term operation, an in-situ calibration method based on multiple fixed-points and Joule heat is proposed in this article. Firstly, the heat transfer model of the calorimeter is established, and the validity of the method is verified by numerical simulation. Secondly, a multiple fixed-points graphite calibrator and a cylindrical electronic resistance element are designed. Finally, the in-situ calibration is carried out. The calibration results show that the maximum permissible measurement error of the sample thermocouple after calibration is better than 0.220 °C and that the bias of consistency in-situ calibration method is smaller than 0.110 °C. In addition, a di‑tert‑butyl peroxide in toluene solution with a mass percent of 20% is selected as the experimental sample. The sample experiment results show that the kinetic and thermodynamic parameters are closer to the reference values after thermocouples calibration.

A temperature sensor based on Er3+/Yb3+ co-doped tellurite fiber for real-time thermal monitoring of transformers

In this paper, a temperature sensor based on fluorescence intensity ratio (FIR) technique is prepared by the dual curing method. The pumping threshold is only 0.1 mW for the application of real-time thermal monitoring on small transformers. This not only greatly reduces the thermal effects accumulated by laser irradiation but also contributes to the integration and portability of the light source. Based on the FIR, the temperature information could be demodulated through tracking the fluorescence spectral changes. The basic temperature sensing characteristics of this sensor were evaluated, which showed that the maximum stability deviation and reproducibility error were within ±1.1 K and ±0.8 K, respectively. Notably, it has a maximum measurement error of only 0.61 K when applied to the temperature monitoring of transformers. And a fast time response of 2.1 s was exhibited in the cyclic exhalation experiment. This proposed sensor is suitable for mass production due to its resistance to electromagnetic interference, low pumping power, fast time response, excellent stability and reproducibility.

Development of an accurate optical sensor for the in situ real-time determination of the chemical oxygen demand of seawater.

Chemical oxygen demand (COD) is an important indicator for monitoring the quality of seawater. The COD of seawater reflects the levels of organic pollutants in the water. Methods that are commonly used to measure the COD of seawater have high accuracy, good repeatability, and low costs. However, using them for the in situ real-time monitoring of the COD of seawater is unfavorable because they require complex procedures and a long measurement time and may cause pollution to the environment. This paper reports on an optical sensor that accurately determines the COD of seawater in situ. The COD determination is based on the absorption of ultraviolet and visible lights with different wavelengths by organic matter in the water. Single-point LEDs emitting lights with different wavelengths (254, 265, 280, and 546nm) were used as sources of excitation lights, and photodiodes were used as receiving devices. The optical system, circuit system, and mechanical structure of the sensor were efficiently integrated. The inversion of the COD of seawater was obtained after turbidity correction using the multiple linear regression algorithm. The maximum measurement error, detection limit, and repeatability of the sensor were 5%, 0.05 mg/l, and 0.62%, respectively. Moreover, the R2 values for correlations between COD values and absorbance values measured at three wavelengths (254, 265, and 280nm) were above 0.99. Overall, the sensor is suitable for the in situ real-time monitoring of the COD of seawater. It requires a short measurement time and generates no pollution.

INFORMATION-MEASURING SYSTEM FOR CONTROL OF APPLES BY SIZE IN THEIR SORTING

The article provides information about the information-measuring system of the layout of the complex for sorting apples, which allows you to determine the maximum diameter of an apple when it moves along a roller conveyor. The control algorithm is based on the use of automated thresholding using the method of moments, as well as the Advanced Morphology operation. Studies have shown that the maximum diameter measurement error does not exceed 2 mm, and the influence of radial distortion is reduced to 0.17 % as a result of calibration.

Turning Lakes Into River Gauges Using the LakeFlow Algorithm

AbstractRivers and lakes are intrinsically connected waterbodies yet they are rarely used to hydrologically constrain one another with remote sensing. Here we begin to bridge the gap between river and lake hydrology with the introduction of the LakeFlow algorithm. LakeFlow uses river‐lake mass conservation and observations from the Surface Water and Ocean Topography (SWOT) satellite to provide river discharge estimates of lake and reservoir inflows and outflows. We test LakeFlow performance at three lakes using a synthetic SWOT data set assuming the maximum measurement errors defined by the mission science requirements, and we include modeled lateral inflow and lake evaporation data to further constrain the mass balance. We find that LakeFlow produces promising discharge estimates (median Nash‐Sutcliffe efficiency = 0.88, relative bias = 14%). LakeFlow can inform water resources management by providing global lake inflow and outflow estimates, highlighting a path for recognizing rivers and lakes as an interconnected system.

Development of an ultrasonic linear encoder

PurposeIn this investigation, a linear encoder system based on the ultrasonic transducer has been proposed. Ultrasonic transducers are usually designed for distance measurements, such as the time of flight method and sonar system. These applications are defined as discrete-length measurement technologies. The purpose of this study is to develop a continuous displacement measurement system using ultrasonic transducers.Design/methodology/approachA modified signal processing based on heterodyne signaling is implemented in this system. In the proposed signal processing, there is an automatic gain control module, a phase-shifting module, a phase detection module, an interpolation module and especially a frequency multiplication module, which can enhance the resolution and reduce the interpolation error simultaneously.FindingsThe proposed system can generate the encoding signals and is compatible with most motion control systems. For the experimental result, the maximum measurement error and standard deviation are about −0.027 and 0.048 mm, respectively. It shows that the proposed encoder system has the potential for displacement measurement tasks.Originality/valueThis study reveals an ultrasonic linear encoder that is capable of generating an incremental encoding signal, accompanied by a corresponding signal processing methodology. In contrast to the conventional heterodyne signal processing approach, the proposed multiplication method effectively reduces the interpolation error that arises because of multiple reflections.

A Study on a Novel Inverted Ultra-Short Baseline Positioning System and Phase Difference Estimation

Autonomous underwater vehicles (AUVs) are important tools for exploring and studying the ocean. To improve the stealthiness of AUV positioning, a new type of inverted ultra-short baseline (i-USBL) positioning system is proposed in this paper. The system uses a surface GPS buoy as a positioning base station to transmit positioning signals to the AUV, which receives the signals through the i-USBL and calculates its own coordinates. In this way, the power consumption of the AUV will be lower, improving its endurance. In addition, azimuth observation is one of the key observation quantities in ultra-short baseline positioning systems. Therefore, this paper derives two phase difference estimation algorithms for azimuth measurement, which are the Least Mean Square (LMS) algorithm and the Discrete Fourier Transform (DFT) algorithm. Simulation results show that when the signal-to-noise ratio (SNR) is less than or equal to 0 dB, the DFT algorithm has higher accuracy; when SNR is greater than or equal to 10 dB, LMS has slightly higher accuracy than DFT; however, DFT is more stable than LMS at all SNRs. When SNR is 20 dB, the maximum azimuth measurement error of LMS and DFT is 0.3301° and 0.2204°, respectively, which can meet the positioning accuracy requirements. The average running times of LMS and DFT are 0.085 s and 0.011 s, respectively, and LMS has a faster running speed. In summary, the LMS algorithm can be used for azimuth observation when the SNR is good, and DFT can be applied when the SNR is poor.

Accurate and Rapid Measurement of Soil Dry Depth Using Ultrasonic Reflection Waves

Soil dry depth is a key parameter that determines soil fertility and nutrient availability, ultimately affecting crop yield and quality. However, accurately measuring the dry depth of soil has been a challenge. In this work, we propose using reflective ultrasonic waves to measure dry depth in soil. Four soil types, including clay, sandy loam, silty loam, and sandy were prepared and the feasibility of the method was demonstrated through theoretical analysis. An experimental measurement system was established to verify the consistency between ultrasonic measurements and manually measured values. Two statistics were used in Ordinary Least Squares (OLS) regression to evaluate the model fit: R-square (R2) and Root mean square error (RMSE). The results indicate that the proposed method provides a higher accuracy in estimating the dry depth of sandy loam and silty loam (R2 values of 0.9899 and 0.992 for sandy loam, RMSE values of 1.57% and 1.5% for silty loam) than those of the clay and sandy samples (R2 values of 0.9896 and 0.9874 for clay, RMSE values of 1.66% and 1.77% for sandy). The maximum measurement errors for all the soil type predictions are below 6%; the overall accuracy was acceptable. Our findings suggest that ultrasonic measurement is an efficient and cost-effective approach for measuring soil dry depth, which could enable the precise control of irrigation water usage and the conservation of valuable water resources.

Error Analysis of a Coordinate Measuring Machine with a 6-DOF Industrial Robot Holding the Probe

A complex surface measurement is important for quality control and manufacturing processes. Articulated arm coordinate measuring machines (AACMMs) are widely used in measuring the complex surface. However, the AACMMs that are currently used always require manual operation, which reduces efficiency and introduces operator errors. This study presents a measuring device with a 6−DOF industrial robot holding a contact probe, which realizes the automation measurement of a complex surface and eliminates operator errors compared with the traditional measurement process of an AACMM. In order to explore the source of the measuring errors of the device, the influence of three measurement parameters (approaching velocity, contact angle, and measurement position) on the measurement error of the device is analyzed in this paper. A calibration ball measurement experiment is conducted for each parameter. The results show that the optimal approaching velocity of the measuring device is around 2 mm/s, the probe should be as perpendicular as possible to the surface being measured during the measurement, and the maximum measurement error at different positions is 0.1979 mm, with a maximum repeatability error of 0.0219 mm. This study will help improve the automation measuring errors of the AACMM by utilizing an industrial robot to hold the probe, pushing for a wider application of the AACMM.

A Novel Fiber-Optic Ice Sensor to Identify Ice Types Based on Total Reflection.

To address the issues of not accurately identifying ice types and thickness in current fiber-optic ice sensors, in this paper, we design a novel fiber-optic ice sensor based on the reflected light intensity modulation method and total reflection principle. The performance of the fiber-optic ice sensor was simulated by ray tracing. The low-temperature icing tests validated the performance of the fiber-optic ice sensor. It is shown that the ice sensor can detect different ice types and the thickness from 0.5 to 5 mm at temperatures of -5 °C, -20 °C, and -40 °C. The maximum measurement error is 0.283 mm. The proposed ice sensor provides promising applications in aircraft and wind turbine icing detection.

Steady-state error estimation and calibration of a shielded total temperature probe for turbomachinery

Accurate measurement of the total gas temperature plays a vital role in the performance research of turbomachinery. The total temperature thermocouple (TC) used in the measurement often needs to be specially designed and calibrated. In the past, the calibration was usually completed by a complex and highly costly experiment. The present work developed a new shielded total temperature probe (NTTP) for relatively low-temperature gas measurement. Meantime, this new design's characteristics and different error sources are analyzed based on the Conjugate Heat Transfer (CHT) simulation method. The CHT results show that the thermal conduction error is kept at a small value in the range of Mach number from 0.2 to 0.6; The velocity error contributes more than 90% of the total error. Four standard temperature probes are selected for the comparison. The maximum measurement error is 1.13 K, which is 331.62%, 119.4%, 61.6% and 59.5% lower than the standard type-A, B, C and D, respectively. Moreover, the detailed flow field and the influence of TC junction position on measurement accuracy are discussed. With the increases of the junction away from the supporting, the total measurement error of the NTTP increases first and then decreases. To vindicate the applicability of the proposed design, the measurement error of the NTTP is verified by a new experimental method with the relatively static fluid as the gas flow source. The testing results show that when the inflow's Mach number is 0.52, the measurement error of the NTTP is about 40% lower than that of the type-C total temperature probe.

Design of Full Stokes Vector Polarimetry Based on Metasurfaces for Wide-Angle Incident Light

Polarization measurement plays an important role in optical detection, communication, and imaging systems. Compact polarimetry with a wide angle of incident light will break the restrictions of the limited incident angle and improve its practicality. In this paper, a full Stokes vector polarimetry with a wide incident angle of ±20°, based on a two-dimensional metasurface, is proposed. According to the simulation results, the maximum measurement error of the Stokes vector at 20° oblique incidence is 0.09. The light transmittance of the proposed structure is higher than 83%. Moreover, the tilt angle of the incident light can be determined with a calculation error lower than 0.5°, according to the focusing position of the transmitted light on the focal plane. The operating wavelength of the proposed polarimetry is set to 530 nm of green light, which makes it a potential application in visible light communication and underwater optical systems.

Three-Dimensional Displacement Measurement of Micro-Milling Tool Based on Fiber Array Encoding

The vibration of the micro-milling tool presents a significant chaotic vibration phenomenon, which has a great influence on the tool life and part machining precision, and is one of the basic problems restricting the improvement of machining efficiency and machining accuracy in micro-milling. To overcome the difficulty of the traditional vibration measurement method with the online measurement of micro-milling tool multi-dimensional vibration, a three-dimensional (3D) measurement method of the micro-milling tool is proposed based on multi-fiber array coding, which converts the tool space motion into a decoding process of the optical coding array employing the tool modulating the multi-fiber array encoding. A 6 × 6 optical fiber array was designed, and a 3D motion platform for micro-milling tools was built to verify the characteristics of the optical fiber measurement system. The measurement results show that the measuring accuracy of the system reached 1 µm, and the maximum linear error in x-, y-, and z-direction are 1.5%, 2.58%, and 2.43%, respectively; the tool space motion position measurement results show that the maximum measurement error of the measuring system was 3.4%. The designed system has unique coding characteristics for the tool position in the space of 100 µm3. It provides a new idea and realization means for the online vibration measurement of micro-milling tools.

A Cautionary Note on Using Smart Plugs for Research Data Acquisition

The availability of low-cost smart plugs that measure and control loads has encouraged their use as a research tool to disaggregate end-user loads. While there has been extensive research on the cybersecurity implications, and demand response capabilities, of smart plugs, there has been little investigation of their primary function: Measuring loads. In this study, we analyze the accuracy of power and energy measurements reported by 5 smart plugs from different manufacturers, with a specific focus on the accuracy of the meters when load levels change rapidly, as is often the case with power electronic loads. The study included Belkin, TP-Link, Etekcity, Emporia, and Sonoff smart plugs, with loads switching at frequencies of 0.01Hz to 2Hz, in addition to the steady-state loads often used for testing these devices. Data indicate significant errors in both energy and power measurement when used to monitor highly variable loads. While maximum energy measurement error for the Belkin product never exceeded 1.7%, maximum energy measurement errors were 54–100% for the other 4 brands. Power measurement accuracy was highly dependent on load variability, with all units exhibiting substantial errors when loads varied, even at rates as low as 0.01-0.05 Hz. All units also exhibited reporting delays of 3–6 seconds, with some delays as high as 20 seconds. The large, load-dependent, errors, call into question the use of these devices for research data acquisition, particularly for monitoring highly variable power electronic loads.

A wireless demodulation system based on a multi-parameter resonant sensor.

This paper proposes a wireless passive measurement system that supports real-time signal acquisition, multi-parameter crosstalk demodulation, and real-time storage and calculation. The system consists of a multi-parameter integrated sensor, an RF signal acquisition and demodulation circuit, and a multi-functional host computer software. The sensor signal acquisition circuit uses a wide frequency detection range (25 MHz-2.7GHz) to meet the resonant frequency range of most sensors. Since the multi-parameter integrated sensors are affected by multiple factors, such as temperature and pressure, there will be interference between them, so the algorithm for multi-parameter decoupling is designed, and the software for sensor calibration and real-time demodulation is developed to improve the usability and flexibility of the measurement system. In the experiment, temperature and pressure dual-reference integrated surface acoustic wave sensors in the condition of 25-550 °C and 0-700kPa are used for testing and verification. After experimental testing, the swept source of the signal acquisition circuit can meet the output accuracy in a wide frequency range, and the detection result of the sensor dynamic response is consistent with that of the network analyzer, with a maximum test error of 0.96%. Furthermore, the maximum temperature measurement error is 1.51%, and the maximum pressure measurement error is 5.136%. These results indicate that the proposed system has good detection accuracy and demodulation performance, and it can be used for multi-parameter wireless real-time detection and demodulation.

A New Online Monitoring Method for Water-in-Oil Droplet Based Microfluidic Devices

The online water-in-oil (w/o) droplet monitoring is essential for the uniformity of the droplet based microfluidic devices. In this work, a contactless impedance detection (CID) method for online w/o droplet monitoring in microfluidic devices is proposed. In the proposed method, a new CID sensor, which can work at low working frequency and overcome the unfavorable influence of coupling capacitance, is developed to obtain the impedance information of the w/o droplet. Based on the obtained impedance information, measurement models are established to realize online measurement of drop length and dispersed phase holdup. Then the coefficients of variation (CVs) of the two measured parameters are calculated to evaluate the uniformity of the droplets for online monitoring. Online monitoring experiments of w/o droplet were carried out in a microfluidic device with a 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}\,\,\times $ </tex-math></inline-formula> 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> microchannel. The experimental results verify the effectiveness of the proposed droplet monitoring method. The developed CID sensor can realize impedance measurement at a working frequency lower than 50kHz. The drop length and dispersed phase holdup are useful parameters for online monitoring of droplets. With the established measurement models, the maximum relative error of droplet length measurement is less than 10% in the droplet length range of 1.5mm-3.5mm. And the maximum error of dispersed phase holdup measurement is less than 5% in the dispersed phase holdup range of 0.20-0.67.