Accurate distance measurement by an autonomous ultrasonic systemcombining time-of-flight and phase-shift methods

This paper presents an efficient algorithm for distance measurement, combining both the pulse time-of-flight method and the CW phase-shift method, It copes with a low-rate sampling technique allowed by the limited bandwidth of two ultrasonic transducers working in air at 30 kHz and with modest software resources of autonomous devices. The measuring system was implemented and tested on a compact Motorola MC68HC16-based platform, with a minimum of attached hardware. Experimental results show an accuracy better than 1 mm for a poor reflecting target at a distance of about 1 m     

Frequency switching time measurement using digital demodulation

A method for measuring frequency switching time in fast switching frequency synthesizers is described. The fast frequency switching waveform is digitized by an oscilloscope, and the switching transient is recovered by digital demodulation. The method can be used to measure the switching time for any fairly wide frequency steps within the acquisition bandwidth of the digitizing system, and it is insensitive to signal amplitude variations. Some results of measurements on a frequency agile signal simulator are presented     

Strain measurement of forming process using digital imaging

Abstract

An understanding of local strain behaviour during a metal forming operation can be important but maybe difficult to measure. A non-invasive digital imaging procedure has been developed to quantify local strain behaviour in metal forming. From digital images obtained during the forming process, discrete spatial data of the object profile was acquired. B-spline curve fitting was then applied to obtain a continuous profile. The deformation strains were calculated from the curvature of the continuous profile. The procedure was applied to an electric resistance welded pipe forming process. Strain gauge data was used to validate the proposed procedure.     

Absolute energy measurement of heavy ion beams using a resonant time-of-flight system

A resonant time-of-flight measurement system has been put into operation at the ATLAS facility for the determination of the energy of heavy ion beams. The system provides continuous, nondestructive monitoring of the beam energy. The system provides relative energy determination with a precision of . Absolute energy is determined to an accuracy of 10⁻³. A variety of beam tests have been performed to study the properties of the system.     

Accurate wood-chip water-content measurement

Translated from Izmeritel'naya Tekhnika, No. 3, pp. 56–57, March, 1988.     

数字波形匹配的导航信号载波精密同步方法

导航信号质量评估中,为了避免中频采样下变频处理带来的非线性失真,采用微波直接采样信号.但是由于数据量庞大,传统的载波同步方法实现困难.针对这个问题,提出一种采用匹配滤波技术的载波精密同步方法.首先,用大步进量产生一系列初相不同的伪随机码调制本地波形,伪随机码与导航信号相同,对采样的导航信号进行匹配滤波,根据匹配滤波输出结果确定导航信号载波相位的粗估计值,进行载波粗剥离.然后进行导航信号的伪随机码同步,以载波相位粗估计值为中心,在一定范围内以更精细的步进量进行载波波形匹配,实现载波精密同步.最后对算法进行仿真,仿真结果表明提出算法实际可行,载波同步精度高,载波频率为L波段时,选择合适步长,同步误差可小于0.01弧度.     

Accurate measurement of power system frequency using a digitalsignal processing technique

This paper describes the design, computational aspects, and implementation of a digital signal processing technique for measuring the operating frequency of a power system. The technique provides correct and noise-free estimates for near-nominal, nominal, and off-nominal frequencies in about 25 ms, and it requires modest computations. The proposed technique is implemented using a DSP-based board and has been extensively tested using voltage signals obtained from a dynamic frequency source and from a power system. Some test results are presented in the paper     

Digital time-of-flight measurement for ultrasonic sensors

Ultrasonic sensor measurements are mostly based on the determination of the time of flight (TOF). The development of a digital algorithm for pulse-echo measurement applications, based on the use of a cross-correlation function to determine the TOF, is presented. Some experimental results are presented, and the possibility to realize a low-cost real-time measurement system is considered     

数码相机的亮度分布测试研究

在数码相机测光原理和数字图像处理的基础上利用均匀亮度源对数码相机进行光学标定,获取数码相机采集到的图像灰度值与曝光量之间的确切关系,并以此来获得亮度回归公式.在均匀亮度源标定下数码相机的亮度回归曲线的相关系数R2达到了0.984 5.利用标定完的数码相机进行亮度测试时取得了很好的实验效果,并且在进行点目标物亮度测试时相对误差可以控制到5%左右,在进行面目标物亮度分布测试时整体误差基本上可以控制到10%左右.     

Accurate measurement of interferometer group delay using field-compensated scanning white light interferometer

Interferometers are key elements in radial velocity (RV) experiments in astronomy observations, and accurate calibration of the group delay of an interferometer is required for high precision measurements. A novel field-compensated white light scanning Michelson interferometer is introduced as an interferometer calibration tool. The optical path difference (OPD) scanning was achieved by translating a compensation prism, such that even if the light source were in low spatial coherence, the interference stays spatially phase coherent over a large interferometer scanning range. In the wavelength region of 500-560 nm, a multimode fiber-coupled LED was used as the light source, and high optical efficiency was essential in elevating the signal-to-noise ratio of the interferogram signal. The achromatic OPD scanning required a one-time calibration, and two methods using dual-laser wavelength references and an iodine absorption spectrum reference were employed and cross-verified. In an experiment measuring the group delay of a fixed Michelson interferometer, Fourier analysis was employed to process the interferogram data. The group delay was determined at an accuracy of 1×10(-5), and the phase angle precision was typically 2.5×10(-6) over the wide wavelength region.     

Accurate measurement of residual stress on any steel using the centre hole method

The centre hole method has been shown to be a simple and reasonably accurate method of measuring residual stress. With a 1.6 mm diameter hole, the method can be applied on operational plant and the equipment required is sufficiently portable for use on site. Its application has, however, been limited to use on low-strength steels, due to problems associated with forming the hole.
This paper describes the development of an air-abrasive technique for forming the hole, which allows the centre hole method to be used on any steel with a measurement accuracy of better than±8%.     

Thermal deformation measurement of flip-chip substrate using digital image correlation method

With the accelerated development of electronic products, flip-chip packaging has become one of the most prominently used and efficient designs in the integrated circuit (IC) industry. In daily application, the IC chip will be subjected to a temperature increase when it is in operation. With the rise in temperature, the chip is liable to a series of deformations which lead to possible malfunction of the IC unit. Therefore, the investigation of thermal deformation of flip-chip substrates is important. In this study, the thermal deformation of flip-chip substrates is measured with dual-camera digital image correlation technology, and with the measured data, a basis is established to predict the warpage conditions and strain tendencies of substrates due to thermal effect. Experiments were carried out with the substrates heated from room temperature to 200°C in a specialized vacuum-sealed oven. The topographic surface profile at higher temperatures can be obtained by adding the measured deformation to the surface profile of the substrates at room temperature. Experimental results show that the center area of the specimen had been warped up around 90?µm from the initial condition and the warpage effect of the substrate is obvious when the temperature increases to 200°C. The related maximum normal and shear strains are also discussed.     

4Pi spectral self-interference microscopy

Spectral self-interference microscopy (SSM) relies on the balanced collection of light traveling two different paths from the sample to the detector, one direct and the other indirect from a reflecting substrate. The resulting spectral interference effects allow nanometer-scale axial localization of isolated emitters. To produce spectral fringes the difference between the two optical paths must be significant. Consequently, to ensure that both contributions are in focus, a low-numerical-aperture objective lens must be used, giving poor lateral resolution. Here this limitation is overcome using a 4Pi apparatus to produce the requisite two paths to the detector. The resulting instrument generalizes both SSM and 4Pi microscopy and allows a quantification of SSM resolution (rather than localization precision). Specifically, SSM is shown to be subject to the same resolution constraints as 4Pi microscopy.     

基于LPC2136的精确温度测量

针对LPC2136片内ADC的分辨率较低,不能满足测量精度的需要,而外接高分辨率的ADC成本又较高的情况,提出了采用过采样和求均值的方法增加LPC2136片内ADC的分辨率。基于过采样技术提高模数转换器ADC转换分辨率的基本原理及电路模型,给出了一个应用过采样技术增加LPC2136片内模数转换器ADC的分辨率转换结果的实现示例及其软件实现方法,并进行了温度实测实验,结果表明测量分辨率明显提高,能满足测量精度的需要。     

Interlaminar shear strain measurement on angle-ply laminate free edge using digital image correlation

Because only coarse polishing is required in order for Digital Image Correlation (DIC) to be used, such a technique has been used to study interlaminar shear strain on the free edges of carbon/epoxy laminates. Pure UD and quasi UD have been considered. The measurement uncertainties are small when compared to measured fields. The correlation parameters of DIC have been optimized to highlight the strain gradients. DIC results for pure-UD samples show high interlaminar strain gradients with a non-linear behaviour and local damage close to inter-ply interfaces. Measurements of quasi-UD samples highlight the microstructure influence on the spatial repartition of free edge strain gradients.     

Simultaneous measurement of in-plane and out-of-plane displacement derivatives using dual-wavelength digital holographic interferometry

The paper introduces a method for simultaneously measuring the in-plane and out-of-plane displacement derivatives of a deformed object in digital holographic interferometry. In the proposed method, lasers of different wavelengths are used to simultaneously illuminate the object along various directions such that a unique wavelength is used for a given direction. The holograms formed by multiple reference-object beam pairs of different wavelengths are recorded by a 3-color CCD camera with red, green, and blue channels. Each channel stores the hologram related to the corresponding wavelength and hence for the specific direction. The complex reconstructed interference field is obtained for each wavelength by numerical reconstruction and digital processing of the recorded holograms before and after deformation. Subsequently, the phase derivative is estimated for a given wavelength using two-dimensional pseudo Wigner-Ville distribution and the in-plane and out-of-plane components are obtained from the estimated phase derivatives using the sensitivity vectors of the optical configuration.     

Development of multi-ESI-sprayer, multi-atmospheric-pressure-inlet mass spectrometry and its application to accurate mass measurement using time-of-flight mass spectrometry

The atmospheric pressure sampling nozzle (orifice, heated capillary, or inlet) of a high mass accuracy time-of-flight mass spectrometer (TOF-MS) was modified by replacing its single nozzle with multiple atmospheric pressure nozzles. This allowed multiple streams of liquids to be introduced into the MS in parallel (an electrosprayer for each nozzle), with minimum analyte interactions between the streams. The chemical contents of all liquid streams were analyzed concurrently using a single mass spectrometer. To obtain a higher mass accuracy by providing internal reference on each scan (acquisition) and to evaluate the suitability of TOF-MS for molecular-formula confirmation, a dual-ESI-sprayer, dual-nozzle version of this design was used. The accurate masses of tens of organic compounds in the mass range of 200-3000 Da were measured, and the results were compared with those obtained using dual-sprayer, single-nozzle TOF-MS. A significant improvement in mass accuracy was observed when the former technique was used. Comparison between the mass accuracy using dual-ESI-sprayer, dual-nozzle TOF-MS and that obtained using a double-focusing mass spectrometer operating under chemical ionization (CI) and fast atom bombardment (FAB) shows the suitability of the technique for elemental-composition confirmation. Approximately 85% of samples analyzed had mass errors of less than 5 ppm, and the other 15% had mass errors less than 8 ppm. Using a high-performance liquid chromatography (HPLC) as a device for introduction of one liquid stream (sample) and a syringe pump as a device for introduction of the second liquid stream (reference standard), the accurate mass of a tryptic digest of cytochrome c was measured. The range of mass errors was from -6.1 ppm to +3.6 ppm, a significant improvement over our previously reported mass accuracy for this digest using single-nozzle TOF-MS. The interactions between analytes in the liquid streams also were investigated using a variety of sample-introduction and nozzle-design combinations, including single-ESI-sprayer, single-nozzle; dual-ESI-sprayer, single-nozzle; dual-ESI-sprayer, Y-shaped inlet; and dual-ESI-sprayer, dual-inlet. The results demonstrated that the dual-ESI-sprayer, dual-inlet design provides reference peaks on every acquisition with minimum analyte-reference interaction and, therefore, higher consistent mass accuracy.     

大面阵数字航测相机的精密几何标定

通过将大面阵数字航测相机固定在二维内方位仪的高低轴内部,转动测量机架,使平行光管的点像目标依次成像在被测相机的CCD靶面上,结合相应的计算公式和测控软件,得出了大面阵数字航测相机的内方位元素及畸变值,解决了大面阵数字航测相机视场大、不易标定的问题.实践证明该方法是可行的。     

Three-dimensional displacement measurement for diffuse object using phase-shifting digital holography with polarization imaging camera

The amount of displacement of a diffused object can be measured using phase-shifting digital holography with a polarization imaging camera. Four digital holograms in quadrature are extracted from the polarization imaging camera and used to calculate the phase hologram. Two Fourier transforms of the phase holograms are calculated before and after the displacement of the object. A phase slope is subsequently obtained from the phase distribution of division between the two Fourier transforms. The slope of the phase distribution is proportional to the lateral displacement of the object. The sensitivity is less than one pixel size in the lateral direction of the movement. The longitudinal component of the displacement can be also measured separately from the intercept on the phase axis along the phase distribution of the division between two Fourier transforms of the phase holograms.