Dynamic Measurement Accuracy Research Articles

Research on Key Technologies of Powdery Material Dynamic Buoyancy Weighing System Based on Comparative Compensation Method

Dynamic weighing device is widely used in material processing and manufacturing engineering. In the weighing process, due to the viscosity of special powder material, it will produce vibration and be affected by vibration acceleration when adding weighing hopper. Its weighing reading will fluctuate, thus can not accurately carry out dynamic weighing. On the basis of dynamic buoyancy weighing system, the weight sensor and compensation sensor are added to construct the mass spring damping system. Through the analysis of transfer function, it satisfies the condition of using comparative compensation method and can be realized in the same vibration environment. Real-time tracking and compensation of low-frequency random vibration from outside the system (buoyancy) can be performed. In order to greatly improve the weighing accuracy of low frequency random vibration. The experimental results show that the dynamic measurement accuracy of the dynamic buoyancy weighing system can be less than ±0.5% after the comparison and compensation of the dynamic buoyancy weighing system, which can basically meet the weight measurement of powder material.

Large dynamic range Shack–Hartmann wavefront measurement based on image segmentation and a neighbouring-region search algorithm

The Shack–Hartmann wavefront sensor (SHWFS) has been used to measure wavefronts. However, the dynamic range and measurement accuracy limits the application of the SHWFS. A new centroid estimation algorithm based on image segmentation and related techniques to expand the dynamic range based on search strategy is presented in this paper. In this study, each spot is segmented from a spot array image and the centroid of each spot is calculated only in regions of segmented spots. To compute the slope between the spot centroid and the sub-aperture centre, the calculated centroids are assigned to their corresponding sub-apertures using a search method. The proposed method overcomes the limitations that the centroid must be calculated in its corresponding detection area and reduces the measurement errors caused by noise, expanding the dynamic range significantly without any change to the SHWFS setup as well as improving the measurement accuracy under strong noise. Moreover, the proposed method provides a unit linear coefficient response of centroid estimation. The dynamic range for the proposed method is evaluated by numerical simulations and experiments. Applications include measurement accuracy and linearity.

水下相位式激光测距定标方法

Based on the principle of phase laser ranging, the idea of using phase laser range finder for underwater ranging was proposed, and the feasibility of underwater phase laser ranging was analyzed in principle. Through the underwater distance measurement experiments, the feasibility of underwater phase laser ranging was verified, the range calibration algorithm for underwater phase laser range finder was completed, and the effects of water turbidity on the dynamic range and distance measurement accuracy of laser ranging were explored. The experimental results show that the average ranging error of underwater laser range finder after calibration is not more than 3 mm in the range of 3.5 m, and there is an exponential decay relationship between range and water turbidity. The underwater phase laser range finder provides a new method for the detection of underwater distance, which can achieve accurate ranging at short range of underwater target.

Flow field analysis and parameter optimization of main and measured nozzles of differential pressure type gas momentum instrument based on CFD

In honing online pneumatic measurement, the actual working conditions of honing have not been taken into account. While honing and online measurement of aerodynamic working environment is relatively small semi closed annular narrow space, various parameters will influence the movement characteristics of the measurement of gas, gas does not consider the previous online honing the actual working conditions of the dynamic measurement accuracy is hard to guarantee, does not meet the requirement of automatic processing of high precision. Through the combination of theoretical research and simulation experiment, through the study of honing, pneumatic measurement and aerodynamics, the characteristic equations of three working conditions under honing actual working conditions are obtained. Using fluid simulation software FLUENT to the actual working parameters of honing pneumatic measuring mechanism model is simulated, simulation results show that when the working temperature is less than the optimum value, to achieve amplification and linear range, complex parameter measurement, to meet the honing high dimensional accuracy and high shape precision and high automation requirements.

High-frequency small angle measurement using a dynamic autocollimator based on an improved k-means algorithm

An improved k-means algorithm is proposed to enhance the stability and dynamic measurement accuracy of high-frequency small angle measurement using a dynamic autocollimator. The improved algorithm incorporating an optimized initialization scheme is used to determine the accurate position of the light spot for angle calculation. Simulations executed on different datasets demonstrate the effectiveness of the algorithm. Experimental results indicate that the 30-min stability of 0.58 and 0.69 arc sec at the measurement frequencies of 5 and 10 kHz can be achieved by the improved algorithm, respectively. Also, the dynamic measurement accuracy of 0.99 and 1.25 arc sec under the rotation speeds of 1 and 20 deg / s, respectively, at the measurement frequency of 10 kHz can be obtained. It is confirmed that the improved algorithm is necessary and effective for the autocollimator.

Error Compensation Technique for a Resistance-Type Differential Pressure Flow Sensor

A flow sensor is designed based on resistance-type differential pressure flow (RDPF) method, and the flow data is measured during a coal gangue paste-filling process. The measurement error characteristics of a RDPF sensor are analyzed. Periodic and aperiodic errors are then modeled separately. The model for the periodic error is established by Fourier series approximation using least squares solution of an overdetermined equation to solve for the model parameters. The model for the aperiodic error is established using an online least squares support vector machine (LS-SVM) method. The cross-validation is used to solve model parameters. Simulations and experiments show that the dynamic measurement accuracy of the sensor is greatly improved by error compensation, thereby reducing filling material waste and improving the economic efficiency.

Power System Dynamic Frequency Measurement Based on Novel Interpolated STFT Algorithm

As the product of time and frequency resolution of the Short-Time Fourier Transform (STFT) constant, the dynamic frequency measurement accuracy provided by the STFT is reduced under asynchronous sampling. This paper proposes a novel Interpolated Short-Time Fourier Transform (IpSTFT) based on the Blackman window. The Blackman window is adopted to reduce the spectral leakage, and the spectral interpolation procedure is applied to eliminate the picket-fence effects. Results of simulations are provided to show that the proposed method can improve the accuracy of dynamic frequency measurement significantly with low time consumptions.

Frequency signal acquisition of scalar atomic magnetometer based on using TDC and FPGA

An improved equal precision frequency measurement method is presented for acquisition of frequency signal output from high sensitivity scalar atomic magnetometers. The frequency range to be measured is from 75 kHz to 350 kHz with a resolution better than 0.01 Hz, and the sampling rate should be at least 10 Hz. To meet the requirements on dynamic range, measurement accuracy and speed, at least eight significant digits must be kept. The TDC and FPGA are used to improve the traditional equal precision method. The FPGA acts as the controlling and computing centre, while the TDC measures the time deviation to eliminate the counting error of ±1 reference signal. A prototype frequency detector is fabricated and tested. The measured data show that the design is viable and further improvement is possible.

Experimental assessment of high sampling-rate robotic total station for monitoring bridge dynamic responses

Abstract High sampling-rate robotic total stations (RTS) are emerging tools for monitoring both semi-static and dynamic displacement responses of bridge structures, due to rapid advancements in data sampling rates and tracking speeds. However, the dynamic measurement accuracy of the RTS needs to be fully assessed, especially for different sighting distances. To this end, groups of static and dynamic evaluating tests were carried out on university campuses, and a further in-situ performance assessment with RTS was performed for monitoring dynamic responses of a long suspension bridge in Changsha, China, with a central span of 328 m. A standardized procedure was developed to process these RTS measurements. The background noise in RTS measurements for sighting-distances varying from 25 m to 400 m only results in minor errors which mainly distribute in a frequency range of less than 0.1 Hz. The vibration displacements of an oscillating platform between the RTS and an accelerometer are compared in both horizontal and vertical directions to demonstrate the sufficient accuracy of the RTS measurements. The in-situ experiment also leads to a similar conclusion. This study confirms that the feasibility of using high sampling-rate RTS for monitoring dynamic responses of bridges.

Development of an Unmanned Aerial Vehicle-Borne Crop-Growth Monitoring System.

In view of the demand for a low-cost, high-throughput method for the continuous acquisition of crop growth information, this study describes a crop-growth monitoring system which uses an unmanned aerial vehicle (UAV) as an operating platform. The system is capable of real-time online acquisition of various major indexes, e.g., the normalized difference vegetation index (NDVI) of the crop canopy, ratio vegetation index (RVI), leaf nitrogen accumulation (LNA), leaf area index (LAI), and leaf dry weight (LDW). By carrying out three-dimensional numerical simulations based on computational fluid dynamics, spatial distributions were obtained for the UAV down-wash flow fields on the surface of the crop canopy. Based on the flow-field characteristics and geometrical dimensions, a UAV-borne crop-growth sensor was designed. Our field experiments show that the monitoring system has good dynamic stability and measurement accuracy over the range of operating altitudes of the sensor. The linear fitting determination coefficients (R2) for the output RVI value with respect to LNA, LAI, and LDW are 0.63, 0.69, and 0.66, respectively, and the Root-mean-square errors (RMSEs) are 1.42, 1.02 and 3.09, respectively. The equivalent figures for the output NDVI value are 0.60, 0.65, and 0.62 (LNA, LAI, and LDW, respectively) and the RMSEs are 1.44, 1.01 and 3.01, respectively.

Dynamic measurements using digital image correlation

Digital image correlation (DIC), which enables non-contact measurement of displacements and strains, has seen widespread adoption within the geotechnical physical modelling community for the measurement of static displacements. Advances in high temporal resolution cameras now permit the use of DIC to calculate accelerations. However, it is currently unclear how the image acquisition rate and the choice of DIC algorithm influence the quality of this data. This paper describes the sources of error that affect the dynamic measurement accuracy. Numerical and physical experiments are used to demonstrate the relevance of (a) bias error in the sub-pixel interpolation scheme, (b) the ratio of sample rate to the frequency of the signal being monitored and (c) the signal-to-noise ratio on the accuracy and precision of DIC acceleration measurements. The results demonstrate that by using appropriate image texture, sampling frequencies and signal-to-noise ratios, measurements with an accuracy similar to accelerometers can be achieved. The displacement measurement error due to bias errors was found to be 0·0015 pixels. The error in the calculated velocity and acceleration was a function of the amplitude of displacement measurements with an optimum ratio between the sampling frequency to the signal frequency found to be between 25 and 50.

Real-time FPGA-based Kalman filter for constant and non-constant velocity periodic error correction

Displacement measuring interferometry has high resolution and high dynamic range, which is widely used in displacement metrology and sensor calibration. Due to beam leakage in the interferometer, imperfect polarization components, and ghost reflections, the displacement measurement suffers from periodic error, whose pitch is multiple harmonics of the Doppler frequency. In dynamic measurements, periodic error is usually on the order of nanometers, which impacts the dynamic measurement accuracy. This paper presents an approach to estimate and correct periodic error in real time based on an extended Kalman filter, which has the capability to deal with both constant and non-constant velocity motions. This algorithm is implemented on an application-specific hardware architecture in an FPGA, which has advantages in throughput and resource usage compared with conventional implementations. The measurement validation shows that this approach can effectively eliminate the periodic error for both constant and non-constant velocity motion, and the residual error reaches to the level of the background noise of the interferometer.

Research on the Sensor of Welding Seam Tracking Based on the Same Plane Electrode

Capacitive sensors have a wide range of applications, but its edge effect is severely restricted by the detection accuracy. In this paper, we put forward a kind of capacitance sensor based on the edge of capacitance. It has a wide range of static and dynamic measurement (mm) and high measurement accuracy. And its mathematical modeling, through the analysis proves that the model is correct and feasible.At the same time also used in the finite element analysis software ANSYS, three-dimensional model of the sensor was established, and the optimization and analysis of the sensor's output characteristic of sensor specific structural parameters, the final determination of the optimal structure parameters of the capacitive sensor. Finally, the experimental results show that the output signal of the sensor is good.

The Design and Control of Electromagnetic Actuator for Six-Axis Force Sensor Dynamic Calibration

In order to calibrate six-axis force sensor dynamic characteristics, double E-type electromagnetic actuator is operated by electric magnets. It is capable of sending sinusoidal excitation signal with variable amplitude and frequency continuously. The theoretical modeling and linearization is established. Repetitive control plus proportion control method is presented. And the stabilization is analyzed by small gain theorem. Simulation results show, compared to PID control method, the proposed method has higher trajectory accuracy, no steady-state error and the slightly smaller bandwidth. It has theoretical and practical value to improve six-axis force sensor dynamic characteristics measurement accuracy.

圆感应同步器系统误差的动态提取与补偿

As the precision of a photo-turntable control system using rotary inductosyn depends on the dynamic angular position measuring precision of a rotary inductosyn, this paper explores the system error of the rotary inductosyn. The error mechanism of rotary inductosyn was analyzed, and the system error of the rotary inductosyn was quantitatively and dynamically measured by using an experimental platform. Finally, the system error model of the rotary inductosyn was put forward based on the data processing and error mechanism, and the output signals from the rotary inductosyn were compensated by the error model. The software compensation method was verified and the experimental results for the rotary inductosyn with 720 poles, 12 bits show that the dynamic angle measurement accuracy is improved from 11.25″ to 1.17″, while the angular velocity estimation accuracy is improved from 0.72(°)/s to 0.09(°)/s. The test results show that the proposed method improves the dynamic measuring accuracy of the rotary inductosyn significantly and satisfies the accuracy demands of photoelectric platform pointing control systems. ©, 2015, Chinese Academy of Sciences. All right reserved.

Frequency-domain correction of sensor dynamic error for step response

To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly.

Dynamic behaviour and measurement accuracy of a bicycle brake hood force transducer

To measure road bike load inputs, it is customary to manufacture and instrument a bike component. The purpose of this paper is to investigate the influence of the dynamic behaviour of a brake hood force transducer on measurement accuracy. The majority of the studies reported in the literature on the development of transducers were designed with the objective of having high transducer stiffness in order to increase its first natural frequency to the highest possible degree. This paper shows that, in the case of force transmitted at cyclist's hands, this objective does not lead to the desired results. Rather, the best results are obtained when the natural frequency of the instrumented fabricated component matches that of its standard counterpart.

基于遗传优化小波神经网络逆模型的油水测量

As the traditional measuring method based on dielectric coefficients shows cross-sensitivity for multi-parameters in the measurement of oil/water two-phase flows,it can not meet the requirements of real-time optimization control for petroleum production.Therefore,this paper investigates a method to measure multi-parameters with cross-sensitivity by using multi-sensing technology.It presents an inverse model of wavelet neural network with genetic optimization and also researches its identification method.The model overcomes the blindness of initialization weight-value choice in traditional neural networks,provides the abilities of global optimization and nonlinear self-learning,and eliminates the cross-sensitivity of multi-factors.The simulation and experimental results demonstrate the validity and effectiveness of the proposed model and show that the correlation coefficient between the predicted values and calibration values is 0.999 6,which is better than that of BP-NN model.The method has strong generalized capability and robust convergence rate,and can effectively eliminate the influence of the cross-sensitivity of multi-factors and the nonlinearity of sensor self on the measuring precision,and improve the dynamic characteristics and measurement accuracy of sensor systems.

The Leicester Doppler Phantom—A Digital Electronic Phantom for Ultrasound Pulsed Doppler System Testing

Doppler flow and string phantoms have been used to assess the performance of ultrasound Doppler systems in terms of parameters such as sensitivity, velocity accuracy and sample volume registration. However, because of the nature of their construction, they cannot challenge the accuracy and repeatability of modern digital ultrasound systems or give objective measures of system performance. Electronic Doppler phantoms are able to make use of electronically generated test signals, which may be controlled precisely in terms of frequency, amplitude and timing. The Leicester Electronic Doppler Phantom uses modern digital signal processing methods and field programmable gate array technology to overcome some of the limitations of previously described electronic phantoms. In its present form, it is able to give quantitative graphical assessments of frequency response and range gate characteristics, as well as measures of dynamic range and velocity measurement accuracy. The use of direct acoustic coupling eliminates uncertainties caused by Doppler beam effects, such as intrinsic spectral broadening, but prevents their evaluation. (E-mail: john.gittins@uhl-tr.nhs.uk)

Full-scale measurements of dynamic response of suspension bridge subjected to environmental loads using GPS technology

Nowadays, there are many larger and taller engineering structures than in the past. These structures are commonly designed to be more flexible. Thus, they are sensitive to severe wind gust and earthquake tremor. For the dynamic response prediction, finite element (FE) modal updating and structural health monitoring, the dynamic characteristics of a structure are becoming increasingly important. The aim of this paper is to show an emerging tool-the real time kinematic (RTK) global positioning system (GPS), which is used to measure and monitor the low-frequency vibration of Dalian BeiDa Bridge, a medium span suspension bridge. The modal analysis is firstly performed on the developed three-dimensional FE model according to the original blue prints of the bridge to provide the analytical frequencies and mode shapes. The field ambient vibration tests using the accelerometers on the bridge deck are conducted just prior to the use of the GPS system in order to validate the FE model. And then, the calibration test is done to assess the dynamic displacement measurement accuracy of the GPS in three orthogonal directions. The GPS signal properties, such as the amplitude, standard deviations (STD), power spectral density (PSD), and probability density functions (PDF), are studied in details. After that, a structural health monitoring system based on the GPS is devised and installed on the bridge to provide real-time measurement of deck movement. The output-only modal parameter identification is carried out by using the Periodogram method to investigate the responses of the bridge. The result shows that the spectral densities of the displacements measured by the GPS correspond well with the results by the FEM analysis and the accelerometer vibration test. It is concluded that the GPS method is reliable and useful to clarify the ambient vibration response behaviors of the flexible structures. The integration of the GPS and accelerometer methods results in a hybrid arrangement that can help to eliminate some disadvantages of the two devices used separately.