Measurement Accuracy Of Sensors Research Articles

Monocular vision-based low-frequency vibration calibration method with correction of the guideway bending in a long-stroke shaker.

Calibration is required to maximize the sensitivity and measurement accuracy of vibration sensors. In this study, a low-frequency vibration calibration method is proposed that is based on the concept of monocular vision. In this method, we employ a high-accuracy edge extraction method to extract the edges of sequential images so as to obtain the high calibration accuracy. However, the proposed method must rely on a long-stroke shaker to provide vibration excitation to the sensor, and the bending in the guideway caused by the mechanical processing reduces the calibration accuracy, especially at very low frequencies. The proposed setting compensates for the bending using an additional monocular vision technique to significantly improve the calibration accuracy. To validate the calibration accuracy of the proposed method, a comparison was conducted between results obtained via the laser interferometry, the Earth's gravitation method, and the proposed method when applied to calibrate the sensitivity of a tri-axial acceleration sensor at frequencies between 0.04 and 8 Hz. The results of the comparison showed the proposed method calibrated the sensor sensitivity with high accuracy and was able to accurately account for the bending when the frequency was lower than 0.3 Hz. In contrast, the calibration accuracy of the laser interferometry decreased because of the bending.

Design of Inclinometer Based On STM32

This paper introduces an angle sensor based on STM32 microprocessor. Firstly, it introduces the power circuit module. Then it analyzes the angle acquisition principle and signal output type of MPU9250, then analyzes the CAN transceiver module, and finally introduces the software architecture. The sensor has a CAN output interface that can be directly applied to the CAN network architecture. The experimental results show that the sensor measurement accuracy reaches ±0.1°, which can meet the needs of industrial angular position measurement.

A study of the possibility of using 3D modelling and 3D printing for electrical capacitance tomography sensor

Nowadays, the optimization of energy consumption and resources is one of the most urgent topics in worldwide industry. The energy consumption monitoring and control in various multiphase flow industrial applications, where a proper flow characteristic and an optimal phase mixture control is crucial, is hard to perform due to the physical and chemical complexity of the processes. The Electrical Capacitance Tomography (ECT) is one of the relatively cheap non-invasive measurement methods that can help in the monitoring and control of optimal energy and resources dozing in industrial processes. ECT diagnostics systems use unique sensors that can non-intrusively detect spatial capacitance changes caused by spatial changes in the electrical permittivity of industrial process components. One of the latest ECT extensions is a three-dimensional measurement strategy that uses a multilayer structure of the capacitance sensor. In this paper, the authors propose a novel approach to the 3D ECT sensors fabrication process that uses 3D computer modelling and 3D printing to easily get any sensor shape, electrode layout, scale and shielding strategy. This study compares the measurement abilities of a 3D ECT sensor fabricated using a traditional hand-made technique with the 3D printed device. The results have proven the potential of the new 3D print-based sensor regarding its significant fabrication time reduction as well as the improvement of the overall 3D ECT sensor measurement accuracy and stability.

Soil Moisture Sensor Test with Mississippi Delta Soils

Abstract. One of the methods for irrigation scheduling is to use sensors to measure the soil moisture level in the plant root zone and apply water if there is a water shortage for the plants. The measurement accuracy and reliability of the soil moisture sensors are critical for sensor-based irrigation management. This study evaluated the measurement accuracy and repeatability of the EC-5 and 5TM soil volumetric water content (SVWC) sensors, the MPS-2 and 200SS soil water potential (SWP) sensors, and the 200TS soil temperature sensor. Six 183 cm × 183 cm × 71 cm wooden compartments were built inside a greenhouse, and each compartment was filled with one type of soil from the Mississippi Delta. A total of 66 sensors with 18 data loggers were installed in the soil compartments to measure SVWC, SWP, and soil temperature. Soil samples were periodically collected from the compartments to determine SVWC using the gravimetric method. SVWC measured by the sensors was compared with that determined by the gravimetric method. The SVWC readings from the sensors had a linear regression relationship with the gravimetric SVWC (r2 = 0.82). This relationship was used to calibrate the sensor readings. The SVWC and SWP sensors could detect the general trend of soil moisture changes. However, their measurements varied significantly among the sensors. To obtain accurate absolute soil moisture measurements, the sensors require individual and soil-specific calibration. The 5TM, MPS-2, and 200TS sensors performed well in soil temperature measurement tests. Individual temperature readings from these sensors were very close to the mean of all sensor readings. Keywords: Irrigation, Sensors, Soil types, Soil water content, Soil water potential.

Temperature Sensitivity Study of Eddy Current and Digital Gauge Probes for Oxide Measurement

ABSTRACTNovel fuels are part of the nationwide effort to reduce the enrichment of Uranium for energy production. Fuel performance is determined by irradiating tfuel plates. The plate checker used in this experiment at Idaho National Lab (INL) performs nondestructive testing on fuel rod and plate geometries with two different types of sensors: eddy current and digital thickness gauges. The sensors measure oxide growth and sample thickness on research fuels, respectively. Sensor measurement accuracy is crucial because even microns of error is significant when determining the viability of an experimental fuel. One parameter known to affect the eddy current and digital gauge sensors is temperature. Since both sensor accuracies depend on the ambient temperature of the system, the plate checker has been characterized for these sensitivities. Additionally, the manufacturer of the digital gauge probes has noted a rather large coefficient of thermal expansion for their linear scale. In this work, the effect of temperature on the eddy current and digital gauge probes is evaluated, and thickness measurements are provided as empirical functions of temperature. Additionally, an experimental coefficient of thermal expansion for the probe material has been reported and compared with the manufacturer’s specifications.

Assessment of the measurement accuracy of inertial sensors during different tasks of daily living

The low cost and ease of use of inertial measurement units (IMUs) make them an attractive option for motion analysis tasks that cannot be easily measured in a laboratory. To date, only a limited amount of research has been conducted comparing commercial IMU systems to optoelectronic systems, the gold standard, for everyday tasks like stair climbing and inclined walking. In this paper, the 3D joint angles of the lower limbs are determined using both an IMU system and an optoelectronic system for twelve participants during stair ascent and descent, and inclined, declined and level walking. Three different datasets based on different hardware and anatomical models were collected for the same movement in an effort to determine the cause and quantify the errors involved with the analysis. Firstly, to calculate software errors, two different anatomical models were compared for one hardware system. Secondly, to calculate hardware errors, results were compared between two different measurement systems using the same anatomical model. Finally, the overall error between both systems with their native anatomical models was calculated. Statistical analysis was performed using statistical parametric mapping. When both systems were evaluated based on the same anatomical model, the number of trials with significant differences decreased markedly. Thus, the differences in joint angle measurement can mainly be attributed to the variability in the anatomical models used for calculations and not to the IMU hardware.

Investigation of the Dynamic Behavior of a Super High-rise Structure using RTK-GNSS Technique

Super high-rise structures have a significant deformation under ambient excitations such as earthquake and wind, which may lead to structural instability and even damage. To capture the dynamic characteristics of a super high-rise structure under construction (i.e., Tianjin 117 tower), Real Time Kinematic - Global Navigation Satellite Systems (RTK-GNSS) sensors are employed to derive the horizontal displacement of the structure. Considering the defects in measurement accuracy of RTK-GNSS sensors, a Type 1 Chebyshev high-pass digital filter is firstly employed and thus the output results are smoothed. Subsequently, based on the smoothed signals, the natural frequencies and the corresponding damping ratios are extracted via FFT (Fast Fourier Transform) and RDT-LDM (random decrement technique combined with logarithmic decrement method). It is found that the results from the field measurement coincide with the numerical simulation. Finally, the structural parameters are successfully obtained and illustrated graphically.

Study on the method of precision adjustment of star sensor

Star sensors are indispensable spatial measurement sensors for high-resolution earth observation and astronomical observations, and the demand for high measurement accuracy of satellite sensors continues to increase; thus, the star sensor optical machine adjustment error cannot be ignored. The commonly used installation error correction method cannot solely meet the precision analysis requirements. In this paper, the relationship between the optical machine installation and the star sensor measurement error is analyzed, and several common adjustment error correction methods are compared. An adjustment method for optical machines is proposed to meet the requirements of very high precision star sensors. The assembly precision requirements of the investigated very high precision star sensor are analyzed considering the whole machine, and then the optical components are controlled through optical precision adjustments to satisfy the precision requirements. Finally, through the complete machine calibration, the star sensor precision adjustment for an optical machine structure is verified. This method meets the requirements of very high precision sensors and is suitable for the precision adjustment of optical machine structures, which is of practical significance to improve the precision of star sensors.

Investigation of the Temperature Compensation of FBGs Encapsulated With Different Methods and Subjected to Different Temperature Change Rates

The temperature compensation effect strongly influences the measurement accuracy of FBG sensors. The most widely used compensation methods can be classified into three types depending on the FBG encapsulation method: 1) dual-grating differential measurement for fully pasted FBGs, 2) dual-grating differential measurement for prestretched FBGs with both ends fixed, and 3) the addition of a temperature-reference FBG. In current reports, temperature compensation is performed based on the assumption that the wavelength shifts of the two FBGs are the same (or proportional to each other) and are synchronous with the temperature variation. However, because of uncertainties in workmanship and the thermal flow differences between different encapsulated FBGs, the validity of this assumption is doubtful. In this paper, the compensation characteristics of each method at different heating rates are investigated through a series of experiments and theoretical analyses. A detailed comparative analysis shows that Method 2 can be considered the optimal temperature compensation scheme in terms of both compensation accuracy and stability, whereas Method 1 is slightly inferior to Method 2. In addition, Method 3 is roughly equivalent to Method 1 and slightly inferior to Method 2 when the heating rate is <;0.8 °C/min; however, when the heating rate is ≥1 °C/min, Method 3 is considerably inferior to both Method 1 and Method 2. The results indicate that the compensation effect is determined by both the FBG encapsulation method and the temperature change rate, thus revealing the deficiency of the current compensation assumption.

Pitot sensor air flow measurement accuracy: Causal modelling and failure risk analysis

Industrial sensors efficiency is commonly determined by the ability to provide accurate indications during a mission. In addition, several techniques and methods are incorporated to increase sensors measurement accuracy. These examinations are classified into experimental and theoretical classes. Experimental examinations focus on determining the flow coefficient variation, which results from the installation effect and flow characteristics. Theoretical proposals deal principally with formulation of the instrument reliability function. These formulations integrate different parameters which affect the sensor measurement accuracy during a given mission. This paper discusses the failure risk and effect analysis for the Pitot sensors system measurement accuracy during a given mission. In addition, a set of factors is used to determine the causal diagram and to model the corresponding hazard function. These factors are subject to statistical analysis in the second part of this paper. The current study is also driven by a practical need to well manage aeronautical problems linked to Pitot sensors system malfunctioning during a flight.

Progression of the vibratory analysis technique by improving the piezoelectric sensor measurement accuracy

AbstractThe piezoelectric sensor is the best choice for large industrial installations for instantaneous monitoring and premature fault diagnosis of electromechanical systems. In this work, we made a study on the piezoelectric detection and the piezoelectric sensor then a model of the physical behavior of this sensor extracted. The developed model of measurement accuracy as a function of the relative vibration movement is validated by experimental tests and simulation. The good choice of the damping rate allowed to improve the parameters of the sensor on the one hand and to advance the technique of vibratory analysis on the other hand.

Void fraction measurement in cryogenic flows. Part II: Void fraction capacitive sensor performances in chilldown experiments

This manuscript describes the work performed on void fraction measurements a cryogenic flow by means of a customized capacitive sensor. In a preceding activity, described in Part I, the instrument was developed and validated at room conditions. In the current study, the probe is exploited to detect the gaseous content during liquid nitrogen chilldown experiments. The sensor performances are evaluated both numerically and experimentally. The numerical simulations lead to the development of a new calibration formula improving the sensor measurement accuracy down to ±6.0%FS, within 99% confident interval. The experimental campaign mainly reveals a dependency of the sensor performance on the pressure and temperature variations during the cooldown of the test section. The so-called “thermal effect” therefore modeled and two compensation equations are derived. The void fraction results accordingly corrected, match the single-phase flows reference conditions within ±2% discrepancy. Background light visualizations are also performed allowing the optical verification of the flow regimes. For a specific flow condition, a correlation between the recorded light intensity and the capacitive measurements is obtained. By means of the high-speed movies, the capacitive sensor response time is also evaluated to be 100 Hz.

Nonlinear Analytical Redundancy Method for Sensor Fault Diagnosis in an Automotive Application

Sensors have been widely implemented in vehicle systems for control, driving, and vehicle condition monitoring purposes. In a typical automotive vehicle, there are 60-100 sensors on board and is projected to reach 200 sensors per car. Those sensors provide rich information to ensure safe vehicle operation. However, like any dynamic systems, sensors are vulnerable to degrade or fail over time, which leads to the need of real-time sensor fault diagnosis. Analytical redundancy has been the key model-based approach for sensor fault diagnosis. However, existing analytical redundancy approaches are limited to linear systems, or some special cases of nonlinear systems. In this paper, the analytical redundancy approach is extended to nonlinear systems in general to ensure the accuracy of sensor measurements. Parity relations based on nonlinear observation matrix are formulated to characterize system dynamics and sensor measurements. Robust optimization is designed to identify the coefficient of parity relations that can tolerate certain level of measurement noise and model uncertainties. At last, sensor fault diagnosis in an air intake system is employed to demonstrate the effectiveness of the proposed method.

The pointing and vibration isolation integrated control method for optical payload

A pointing and vibration isolation integrated control method for optical payload in the satellite system with a Pointing and Vibration Control Platform (PVCP) is developed and verified. Firstly, the dynamic model of the satellite system is formulated. This satellite system contains a payload, a PVCP and a satellite body. Three pointing control methods are proposed depending on different measurement information. By comparing the three methods, one reasonable control method is chosen for the pointing controller. This method could reduce the disturbance from the satellite body motion to the pointing control accuracy as well as the control error caused by the measurement accuracy of sensors. Then, the whole satellite attitude control loop is developed considering a rapid maneuver and rapid orientation mission. Finally, a series of verification experiments of the dynamic model of PVCP are carried out, and then the rotation accuracy, the stroke of PVCP, and the whole satellite attitude control loop are verified by numerical simulations. The results show that the pointing accuracy and attitude angular velocity of payload are improved using the integrated control method.

Comparison of nasal and forehead oximetry accuracy and pressure injury in critically ill patients

BackgroundIn critically ill patients, clinicians can have difficulty obtaining accurate oximetry measurements. ObjectiveTo compare the accuracy of nasal alar and forehead sensor measurements and incidence of pressure injury. Methods43 patients had forehead and nasal alar sensors applied. Arterial samples were obtained at 0, 24, and 120 hours. Oxygen saturations measured by co-oximetry were compared to sensor values. Skin was assessed every 8 hours. ResultsOxygen saturations ranged from 69.8%-97.8%, with 18% of measures < 90%. Measurements were within 3% of co-oximetry values for 54% of nasal alar compared to 35% of forehead measurements. Measurement failures occurred in 6% for nasal alar and 22% for forehead. Three patients developed a pressure injury with the nasal alar sensor and 13 patients developed a pressure injury with the forehead sensor (χ2 = 7.68; p = .006). ConclusionsIn this group of patients with decreased perfusion, nasal alar sensors provided a potential alternative for continuous monitoring of oxygen saturation.

Determining Forest Duff Water Content Using a Low-Cost Standing Wave Ratio Sensor.

Forest duff (fermentation and humus) water content is an important parameter for fire risk prediction and water resource management. However, accurate determination of forest duff water content is difficult due to its loose structure. This study evaluates the feasibility of a standing wave ratio (SWR) sensor to accurately determine the forest duff water content. The performance of this sensor was tested on fermentation and humus with eight different compaction levels. Meanwhile, a commercialized time domain reflectometry (TDR) was employed for comparison. Calibration results showed that there were strong linear relationships between the volumetric water content (θV) and the SWR sensor readings (VSWR) at different compaction classes for both fermentation and humus samples. The sensor readings of both SWR and TDR underestimated the forest duff water content at low compacted levels, proving that the compaction of forest duff could significantly affect the measurement accuracy of both sensors. Experimental data also showed that the accuracy of the SWR sensor was higher than that of TDR according to the root mean square error (RMSE). Furthermore, low cost is another important advantage of the SWR sensor in comparison with TDR. This low-cost SWR sensor performs well in loose materials and is feasible for evaluating the water content of forest duff. In addition, the results indicate that decomposition of the forest duff should be taken into account for continuous and long-term water content measurement.

Sensor Failure Detection of FASSIP System using Principal Component Analysis

In the nuclear reactor accident of Fukushima Daiichi in Japan, the damages of core and pressure vessel were caused by the failure of its active cooling system (diesel generator was inundated by tsunami). Thus researches on passive cooling system for Nuclear Power Plant are performed to improve the safety aspects of nuclear reactors. The FASSIP system (Passive System Simulation Facility) is an installation used to study the characteristics of passive cooling systems at nuclear power plants. The accuracy of sensor measurement of FASSIP system is essential, because as the basis for determining the characteristics of a passive cooling system. In this research, a sensor failure detection method for FASSIP system is developed, so the indication of sensor failures can be detected early. The method used is Principal Component Analysis (PCA) to reduce the dimension of the sensor, with the Squarred Prediction Error (SPE) and statistic Hotteling criteria for detecting sensor failure indication. The results shows that PCA method is capable to detect the occurrence of a failure at any sensor.

SOC Estimation of Lithium-Ion Battery Based on Kalman Filter Algorithm for Energy Storage System in Microgrids

State-of-charge (SOC) is one of the vital factors for the energy storage system (ESS) in the microgrid power systems to guarantee that a battery system is operating in a safe and reliable manner for the system. Many uncertainties and noises, such as nonlinearities in the internal states of a battery, sensor measurement accuracy and bias, temperature effects, calibration errors, and sensor failures, pose a challenge to the accurate estimation of SOC in most applications. This study makes two contributions to the existing literatures. First, a more accurate extended Kalman filter (EKF) algorithm is proposed to estimate the battery nonlinear dynamics. Due to its discrete form and ease of implementation, this straightforward approach could be more suitable for real applications on the ESS. Second, its order selection principle and parameter identification method are illustrated in detail. It can accurately demonstrate the characteristics of the lithium-ion battery to show the feasibility and effectiveness of the algorithm for the ESS.

Continuous Remote Monitoring of Vital Signs in Pediatric Population

Background: Wearable sensor technologies coupled with secure patient portals allow for continuous real-time data acquisition from a patient in a hospital or home setting. This combination renders more effective health-management system with faster patient-recovery times and reduced healthcare costs. VitalConnect Inc. has developed a fully-disposable, FDA-cleared (for adults) wireless biosensor (VitalPatch®) that is worn on chest. VitalPatch captures multiple medical-grade biometrics and transmits the physiological data continuously (via Bluetooth) for up to 96 hours to a relay (tablet, wireless hub). Like adults, pediatric patients (5-17 years of age) could also benefit from such small and low-profile biosensor that can collect and stream vital signs uninterruptedly to a secure patient-portal. This data can then be monitored by a clinical triage center or healthcare-provider. Objective: Continuous remote monitoring of heart rate (HR) and breathing rate (BR) is critical during acute or chronic illnesses. The primary purpose of this study was to evaluate the performance of the VitalConnect platform in pediatric subjects during activities of daily living (ADL) to confirm accuracy of sensor measurements for HR and BR with respect to a clinical reference device, Capnostream20 (Oridion). Additionally, information on comfort and usability of VitalPatch at home was assessed for the total duration of wear. Methods: Thirty-five children were enrolled in the study (24 between 9-17 years, 11 between 5-8 years). All subjects participated in 96-hour wear-period of the VitalPatch biosensor and performed one hour of in-lab protocol on Day1 of the wear duration. Each participant underwent stationary breathing exercises (spontaneous, metronome), ADLs with postural maneuvers and treadmill walking. The study was conducted in presence of a nurse after approval from Institutional Review Board. The performance of heart rate, respiration rate, posture and number of steps were assessed for each subject separately using the mean absolute error (MAE) between the true and measured values. The reference for posture and step count was manual observation. Results: During the stationary condition, MAE (across 35 children) for HR and BR was 2.1±1.0 beats per minute (BPM) and 2.2±0.8 breaths per minute (BrPM) respectively compared to Capnostream20. During ADLs, MAE was 4.3±2.7 BPM for HR and 3.7±1.7 BrPM for BR. Accuracy of posture (standing, supine, walking) was >93% and step-count was >95% overall. Moreover, 80% participants rated wearing VitalPatch ‘comfortable’ without any itchiness during 96-hour wear. Conclusions: The VitalPatch biosensor demonstrated clinically-acceptable accuracy compared to a standardized reference device for both heart rate and breathing rate. It also provided sufficiently accurate measures for activity in terms of posture and number of steps. Furthermore, when used for up to 4 days at home, there were no adverse events (i.e. rashes, dermatitis, mechanical skin injury) and user experience was satisfactory. The accuracy of vitals and ease-of-use in the home environment in children aged 5-17 illustrate the potential of VitalPatch as a non-invasive and cost-effective vital sign monitoring alternative. VitalPatch biosensor can be integrated into state-of-art devices to monitor vital signs for pediatric patients with diseases like congenital heart abnormalities and adolescent fatigue. [iproc 2017;3(1):e5]

Capacitance variation measurement method with a continuously variable measuring range for a micro-capacitance sensor

Micro-capacitance sensors are widely applied in industrial applications for the measurement of mechanical variations. The measurement accuracy of micro-capacitance sensors is highly dependent on the capacitance measurement circuit. To overcome the inability of commonly used methods to directly measure capacitance variation and deal with the conflict between the measurement range and accuracy, this paper presents a capacitance variation measurement method which is able to measure the output capacitance variation (relative value) of the micro-capacitance sensor with a continuously variable measuring range. We present the principles and analyze the non-ideal factors affecting this method. To implement the method, we developed a capacitance variation measurement circuit and carried out experiments to test the circuit. The result shows that the circuit is able to measure a capacitance variation range of 0–700 pF linearly with a maximum relative accuracy of 0.05% and a capacitance range of 0–2 nF (with a baseline capacitance of 1 nF) with a constant resolution of 0.03%. The circuit is proposed as a new method to measure capacitance and is expected to have applications in micro-capacitance sensors for measuring capacitance variation with a continuously variable measuring range.