Potential accuracy of methods of laser Doppler anemometry in the single-particle scattering mode

Potential accuracy of methods of laser Doppler anemometry is determined for the singleparticle scattering mode where the only disturbing factor is shot noise generated by the optical signal itself. The problem is solved by means of computer simulations with the maximum likelihood method. The initial parameters of simulations are chosen to be the number of real or virtual interference fringes in the measurement volume of the anemometer, the signal discretization frequency, and some typical values of the signal/shot noise ratio. The parameters to be estimated are the Doppler frequency as the basic parameter carrying information about the process velocity, the signal amplitude containing information about the size and concentration of scattering particles, and the instant when the particles arrive at the center of the measurement volume of the anemometer, which is needed for reconstruction of the examined flow velocity as a function of time. The estimates obtained in this study show that shot noise produces a minor effect (0.004–0.04%) on the frequency determination accuracy in the entire range of chosen values of the initial parameters. For the signal amplitude and the instant when the particles arrive at the center of the measurement volume of the anemometer, the errors induced by shot noise are in the interval of 0.2–3.5%; if the number of interference fringes is sufficiently large (more than 20), the errors do not exceed 0.2% regardless of the shot noise level.     

On-line measurement of particle size distribution and mass flow rate of particles in a pneumatic suspension using combined imaging and electrostatic sensors

This paper presents a novel instrumentation system that uses a combination of electrostatic and digital imaging sensors. An inferential approach is adopted for the mass flow measurement of particles, velocity and volumetric concentration of particles being measured independently. The velocity of particles is determined by cross correlating two signals derived from a pair of electrostatic sensors and the volumetric concentration of particles is obtained using a novel digital imaging sensor, which also provides particle size distribution data. The basic principles and limits of operation of the imaging sensor are discussed and explained. Results obtained from a pneumatic conveyor are presented which demonstrate good performance of the measurement system for both mass flow metering (accurate to about ±6%) and particle sizing (reliable to around ±2.5%). Particle size distribution results are also included and the insensitivity of particle sizing to changes in velocity and concentration is assessed. In addition, on-line sizing results are compared to off-line results, measured using an accepted laser diffraction based instrument, and good agreement is observed. In general, the results obtained are encouraging and the system shows great promise.     

A cross-correlation technique as a system evaluation tool; application to blood flow measurement in extra-corporeal circuits

Auto-correlation and cross-correlation techniques have been favored by engineers and scientists as powerful analysis tools, especially when noise is present in the system. Since cross-correlation and power spectral density functions are tightly coupled, cross-correlation is a well suited instrument for the analysis of time invariant systems. This paper discusses the conditions under which cross-correlation techniques can be used to identify a system model. Random signals, either arbitrarily generated or inherent in the systems, can be used as test signals for the purpose of identification. A real time cross-correlator is designed and used to evaluate blood carrying vessels for the purpose of flow measurement in extra-corporeal circuits. Naturally occurring random signals due to ‘impurities’ in the blood such as red and white blood cells are correlated by means of two pairs of ultrasonic sensors. The correlation functions obtained under different flow rates manifest themselves as unit impulse responses of the fluid system between upstream and downstream sensors. The results obtained were evaluated for accurate modeling of the fluid path and transit time flow measurement.     

Identification of impact force in thick plates based on the elastodynamics and time-frequency method (II)

The paper presents a novel experimental method for the determination of the impact load in the thick plate based on the theoretical Green’s function and the measured waveforms by the sensors arrayed on the surface on the plate. This method requires the location of the impact load. For the accurate estimation of location of impact source in a plate, the arriving time difference between sensors and the propagation velocity of acoustic waveform are necessary. Their measurements are difficult since the acoustic waveforms are dispersive with multi modes in the plate. The time frequency analysis for the acoustic waveform gives the information about the time difference for multi mode dispersive waveform. For the estimation of location of impact source in a plate, the information on the group velocity of the A0 flexible mode is important. In the paper, various time frequency methods are introduced and their methods are compared with simulated signals. The combined higher order time frequency (CHOTF) is employed for dispersive information for the A0 mode flexible mode. The location of impact source and the magnitude of impact load are well estimated based on the theoretical Green’s function and the CHOTF for the acoustic waveforms measured by three sensors arrayed on the plate.     

Comparative study of electrostatic sensors with circular and probe electrodes for velocity measurement of pulverised coal

This paper presents recent progress on the velocity measurement of pulverised coal in pneumatic pipelines using electrostatic sensors in combination with correlation signal processing techniques.A comparative study of electrostatic sensors with circular and probe electrodes was conducted on a 94 mm bore horizontal pipeline in a 4 MW furnace.The advantages and limitations of both sensors are discussed.Experimental results demonstrate that both sensors are capable of providing pulverised coal velocity measurement with excellent repeatability and dynamic response.     

Special signals in the calibration of systems for measuring dynamic quantities

The determination of errors generated by systems measuring dynamically changeable signals presents a difficult problem due to their unknown shape and the measurement duration. This paper presents a proposed solution to this problem by means of the signals maximizing chosen error criterion. Thus, it refers to the commonly applied methods for determining the accuracy class of systems intended for the measurement of static quantities.The method of determining a signal with one constraint, maximizing integral-square error, is discussed in this paper in detail. As an example, four acceleration sensors are considered and the maximizing signals from the range of one to twenty-five switchings are determined. It is worth underlining that the paper presents a solution obtained by an analytical method instead of using optimization methods, the application of which is necessary in the case of signals with an increased number of constraints.     

Analysis of jitter influence in fast frequency measurements

This paper presents a theoretical analysis of possible jitter impact in application of numeric criterion for fast measurement of frequency by coincidence principle. The primary goal is the generation of a signal containing a known amount of each jitter components. This signal was used for testing signals with regular pulse trains. Initially, jitter components are analyzed and modeled individually. Next, sequences for combining different kinds of jitter are modeled, simulated and evaluated. Jitter model simulation in Matlab is utilized to show the independence of frequency measurement results on the total jitter present in the reference and desired pulse trains independently. A good agreement between previously introduced theory of fast measurement of frequency and simulation in jitter presence is verified; these results allows to engineers use the numeric criterion for fast measurement of frequency in spite to interactions among jitter components in various applications for frequency domain sensors.     

Estimating random uncertainty of depth-averaged velocities measured by moving-boat acoustic Doppler current profilers

This paper presents a mathematical model for estimating the standard uncertainty of depth-averaged velocities measured by moving-boat acoustic Doppler current profilers. A general form of the presented uncertainty model was developed based on the law of propagation of variances and dimensional analysis. It was then calibrated using 30 datasets of stationary ADCP measurements, in which standard uncertainties were available from statistical analysis of the data. Because the model utilizes velocity data collected at a site, it accounts for all random error sources including ADCP system noise and ambient turbulence encountered at the site; it also accounts for the cross-correlation of ADCP depth cells in velocity measurements. The presented uncertainty model can be used in field surveys or data post-processing. It provides a useful tool for assessing the quality of ADCP measured depth-averaged velocities. A moving-boat ADCP measurement on the Mississippi River is presented as an application example. This paper also explores some insights on ADCP velocity profile and time series data.     

Electrical capacitance tomography for gas–solids flow measurement for circulating fluidized beds

Gas–solids flows in the risers of circulating fluidised beds (CFBs) and cyclones exhibit complex physical behaviour, such as local backflow and recirculation. The difficulties in accurate measurement of gas–solids flows stem from various flow regimes, which exist in multi-phase flows in pipelines and vessels. It is necessary to investigate the solids’ fraction profile, flow regime identification, image reconstruction, flow acceleration and flow velocity. Electrical capacitance tomography (ECT) is regarded to be a successful technology for imaging industrial processes containing dielectric materials. ECT would help understanding of gas–particle interaction, particle–boundary interaction and the influence of gas on the solids’ flow turbulence.The first part of this paper covers some new developments in ECT, i.e., algorithms for 3D image presentation and on-line iterative image reconstruction. The second part presents a novel non-intrusive technique for measuring axial and angular velocities. Theoretical and experimental studies, carried out using cross-correlation techniques in a cyclone separator dipleg, confirm the feasibility of on-line velocity measurement. Experimental results from various gas–solids flow facilities, CFB and cyclone, are presented.     

纵向多极阵列电导式两相流测量系统研究

针对优化后的纵向多极阵列电导式传感器,本文构建了基于DSP技术的两相流测量系统.整个测量系统包括激励信号发生电路、信号调理电路和基于DSP技术的数据采集卡及上位机软件,其中两相流流速测量采用基于DSP技术的频域直接相关方法来实现,数据采集卡由MSP430F149单片机和DSP5402构成,由单片机负责数据采集,DSP负责频域内相关运算,采用双口RAM实现两种处理器间数据通信与共享,单片机通过串口与上位PC机通信以实现数据的传输和采集系统设置.该测量系统在气水两相流流动环中取得了满意的动态试验效果.     

A signal model for cross-correlation flowmeters to analyse systematic measurement errors

For discussion of systematic errors of cross-correlation flowmeters, a general signal model is derived by means of system theory. Implementation of the model equations on a computer and simulation with different parameters show that the measured velocity can be higher or lower than the mean velocity, which makes calibration necessary.     

How to measure actual tire shape in the rolling condition using Scanning LDV

This work presents the development of a new method which makes use of Scanning Laser Doppler Vibrometry (LDV) for the indirect measurement of the shape of the tire sidewall in the rolling condition.Scanning LDV is widely adopted for the measurement of vibrational Operational Deflection Shape (ODS) in rolling tires using either the Eulerian or the Lagrangian approach. Residual effects of geometry are usually removed by an AC coupling.This paper presents a new approach in LDV velocity data processing that allows the processing of the velocity data obtained with a Scanning LDV in the Eulerian approach on a rolling tire in order to obtain not only ODS but also static shape.This technique does not require additional sensors or systems since it is based only on signal processing.The uncertainty of the obtained result is also evaluated and a comparison with a state-of-the-art solution in shape measurement is presented.     

Study and industrial evaluation of mass flow measurement of pulverized coal for iron-making production

This paper described a measurement system for mass flow measurement of pulverized coal in a blast furnace coal injection system. The system mainly consists of a volumetric concentration sensor and a velocity sensor. The concentration sensor is a capacitance sensor which has two pairs of concave electrodes placed axially on a piece of pipe of oxide of aluminum with different orientation to get being less affected by flow regime; the velocity sensor is also based on capacitance sensing principle, but uses “passing time difference method” which records the time at which each flowing cloud of coal powder passes through upstream and downstream sensor and then calculates the time difference to get the transit time for the cloud to travel between the two sensors. Both of the experiments in the laboratory and on the spot showed the measurement system has industrially acceptable performance.     

基于声波传感器的炉内温度测量方法研究

用具有强抗干扰能力的互相关测量技术，研制了一套基于声波传感器的炉内温度测量系统。在室温模拟环境下，对主要影响温度测量精度的炉内声波飞行时间的测量进行了实验研究。结果表明：该测量系统所采用的声源合理，互相关函数峰值明显，声波飞行时间测量准确，抗干扰能力强，能较准确测量声波路径上气体介质的平均温度，是一种很有前途的炉内温度测量方法。     

基于线阵CCD的空间目标外姿态测量系统

设计了9路线阵CCD相机组合的空间目标外姿态测量系统,它克服了采用面阵图像传感器用于姿态测量时存在的速度和精度的矛盾。该系统分别实时重构放置于被测物体上的点合作目标在世界坐标系下的三维坐标,经空间解算,确定被测物体的姿态角。着眼于合作目标和相机光学系统的相对位置及呼应,解决了多相机与多点合作目标一一对应时的目标干扰问题;设计了新的光学系统构架,提高了精度,节省了空间;实现了多相机测量系统的局部标定和全局标定。测试结果表明,该姿态测量系统可以实现对被测对象高精度、实时的测量,且具有合作目标简单,价格低廉等优点。     

基于虚拟仪器的互相关流速测量系统设计

采用计算机模拟与实验相结合的方式,建立了基于虚拟仪器平台的互相关测量系统。系统采用LabVIEW函数选板中信号运算部分提供的互相关和自相关函数模块,设计了使用函数互相关、极性互相关和差动自相关3种算法实现互相关流速测量的程序。使用随机信号对上述3种算法进行验证,并对计算结果进行比较,验证结果表明互相关和差动自相关算法较为理想。     

Lensed optical fiber sensors for on-line measurement of flow

This paper describes a system using lensed optical fiber sensors that are arranged in the form of two orthogonal projections. The sensors are placed around a process vessel for upstream and downstream measurements. The purpose of the system is for on-line monitoring of particles and droplets being conveyed by a fluid. The lenses were constructed using a custom heating fixture. The fixture enables the lenses to be constructed with similar radii resulting in identical characteristics with minimum differences in transmitted intensity and emission angle. By collimating radiation from two halogen bulbs, radiation can be obtained by the sensors with radiation intensity related to the nature of the media. Each sensor interrogates a finite section of the measurement section. Each sensor provides a view. Parallel sensors provide a projection. Signal processing is carried out on the measured data in the time and frequency domains to investigate the latent information present in the flow signals.     

Air velocity and flow measurement using a Pitot tube

The accurate measurement of both air velocity and volumetric airflow can be accomplished using a Pitot tube, a differential pressure transducer, and a computer system which includes the necessary hardware and software to convert the raw transducer signals into the proper engineering units. The incorporation of sensors to measure the air temperature, barometric pressure, and relative humidity can further increase the accuracy of the velocity and flow measurements. The Pitot tube measures air velocity directly by means of a pressure transducer which generates an electrical signal which is proportional to the difference between the pressure generated by the total pressure and the still air (static pressure). The volumetric flow is then calculated by measuring the average velocity of an air stream passing through a passage of a known diameter. When measuring volumetric flow, the ‘passage of a known diameter’ must be designed to reduce air turbulence as the air mass flows over the Pitot tube. Also, the placement of the pitot tube in the passage will influence how accurately the measured flow tracks the actual flow through the passage. Calibrating the measurement system in a wind tunnel can further increase the accuracy of the velocity and the flow measurements. This objective of this paper is to provide the field engineer with single, concise source of information on flow measurement using a Pitot tube.     

基于互相关检测的滚动轴承实时故障诊断方法

提出了一种易于用模拟电路实现的基于互相关检测的滚动轴承实时故障诊断方法,首先,用两个加速度传感器在不同测点采集轴承振动信号,将其分别送入相应通道的高Q带通滤波器来选择最优共振带;然后,将两路带通滤波器的输出信号进行互相关检测,将互相关检测得到的信号经低通滤波器,保留低频故障信号;最后,将低通滤波器输出的时域信号通过频谱分析仪显示滚动轴承故障特征频率的谱线以实现滚动轴承的实时故障诊断。用模拟电路的形式将该方法进行搭建,并在QPZZ-II实测平台完成滚动轴承的实时故障诊断。结果表明:该方法克服了单一信号源的局限性,能利用互相关函数削弱共振带内部噪声,使诊断结果具有更高的频谱辨识率,而且能够用结构简单、易于维护的模拟电路实现,对轴承实时故障诊断方法的应用与普及具有一定的参考价值。     

Accurate ultrasound speed measurement using an MLS-modulated continuous wave

The continuous wave shows greater potential than the pulse signal to achieve high-accuracy ultrasound speed measurement thanks to its stronger noise resistance. However, the accuracy of ultrasound speed measurement would deteriorate if echoes exist in the received continuous wave. This paper presents an applicable method using the maximum length sequence-modulated continuous wave. The present method improves the accuracy of ultrasound speed measurement further by resisting echoes. The time delay between the received signal and the transmitted signal is estimated accurately by combining the cross-correlation, parabolic interpolation and phase shift technique. Moreover, both the inherent delays induced by physical system and the path length of ultrasound are expediently corrected through least square estimation. As a result, accurate time of flight and ultrasound speed measurement are achievable. For example, the standard deviation of ultrasound speed measurement in distilled water is less than 0.003 m/s, and the deviation between the ultrasound speed measurement and the reference is less than 0.04 m/s.