The effects of offset voltage on the amplitude and bandwidth ofkick-out pulses used in the nose-to-nose sampler impulse responsecharacterization method

The amplitude and bandwidth of kick-out pulses used in the nose-to-nose sampler impulse response characterization method were measured as a function of offset voltage. The measuring instrument was of similar bandwidth and its effects on the measurement were not removed. The amplitude is almost linear for offset voltages from -500 mV to 500 mV, except for values from about -50 mV to 50 mV. Slight changes in bandwidth were observed for offset voltages from -250 mV to 250 mV with significant bandwidth loss observed for offset voltages outside this range     

Nose-to-Nose校准技术的仿真研究

Nose-to-nose校准技术可以对任意带宽的取样示波器进行自校准．早期的研究工作集中在对关键信号hick-out脉冲的仿真．本文从不同的角度对微波二极管取样头电路进行了全面的仿真,得到了结论：hick-out脉冲是由于在取样电路的不平衡时选通脉冲的泄漏造成的．并对NTN校准技术从仿真实验到物理实验做了介绍．     

Quantifying the maximum phase-distortion error introduced by signalsamplers

Quantifying the errors introduced by signal sampler imperfections is of interest to people who are doing frequency domain measurements. The phase-distortion introduced by the sampler is hard to quantify and is usually neglected. In this article, upper bounds for this phase-distortion error are derived which are based upon simple assumptions, namely that the sampler weighting function is strictly positive, that it is limited in time, and that the function has only one local maximum. The theoretical limits are applied in order to specify the accuracy of a calibration procedure for broadband sampling oscilloscopes     

基于NTN技术的宽带取样示波器自动校准系统

与其它宽带取样示波器校准技术相比,NTN校准技术能够精确地获得取样示波器的冲激响应和复传递函数。但是,由于NTN校准技术要求两台取样示波器的输入端直接对接,这样就很难通过前面板对取样示波器进行操作。为此,介绍了一种基于NTN校准技术的宽带取样示波器自动校准系统,并详细介绍了系统的组成、功能及校准结果。该系统的整个校准工作是在PC机控制下完成的。     

New calibration technique for microwave moisture sensors

A new calibration technique was developed for implementation with microwave moisture sensors. The calibration permittivity function used for this purpose allows computation of moisture content in granular materials with significant differences in shape, dimensions, and composition, independent of bulk density and with temperature compensation. A 3D representation is used to plot the calibration permittivity function as it depends on temperature and moisture content in wheat and corn. For each material, data points form a plane surface. These planes have nearly the same coefficients, which can be utilized for the development of a “universal” calibration method for moisture sensing in natural and manufactured granular materials. Foundations of the method are discussed based on results obtained for wheat and corn over a wide temperature range and at moisture contents of practical interest     

压电式动态力传感器校准方法的研究

针对智能制造行业里压电式传感器的动态性能校准问题,介绍了针对传感器动态力参数的相关方法和脉冲力法校准装置,在装置上完成了试验验证和分析。介绍了两种常规的动态力校准方法,针对不同的校准方法建立了运动方程,做出了差异性分析。然后介绍了一种基于绝对法测量的压电式传感器脉冲力法校准装置,装置的结构包括基于刚体碰撞的脉冲力发生装置和基于外差式迈克尔逊干涉仪的测量系统,说明了工作原理和解算方法。最后利用建立的校准装置对典型压电式传感器进行动态力校准,进行结果分析和可靠性验证。     

一种基于残周期正弦拟合的冲击峰值计算方法

针对半正弦冲击波形峰值幅度的计算,提出了一种基于残周期正弦曲线拟合的最小二乘计算方法,通过在脉冲测量波形中截取峰值附近近似于半正弦部分的峰值波形,使用残周期正弦曲线拟合方法计算获得冲击峰值幅度。它具有操作简捷易行、收敛性好的特点,并可以通过拟合残差有效值来判定拟合效果的优劣。该方法直接使用截取的峰值波形原始数据进行计算,不需要用滤波器对波形数据进行预处理,从而避免了冲击计量中常用的数字滤波给峰值计算结果带来的影响,可以获得更加客观准确的校准结果。通过在实际校准实验波形上的计算,并与以往计算方法进行了比较,验证了所述方法的有效性和切实可行性。     

带有连接电缆的"NTN"校准技术

在利用“NTN”校准技术对取样示波器进行校准时，为保证校准精度，要求两台取样示波器的输入端直接对接。但在实际运用中，为方便起见，常常将两台取样示波器的输入端用电缆连接在一起。显然，电缆的接入。将对“kick-out”脉冲的响应波形产生影响，这就要求在数据处理中扣除电缆的影响。详细介绍了带有电缆的“NTN”校准技术的实验设置、数据预处理算法(包括去时基抖动处理、消除取样电路的非对称性的方法等)、“kick-out”脉冲的反卷积分离以及扣除电缆影响的算法。最后，给出取样示波器阶跃响应的波形并进行了评价。     

A/D converter characterization by spectral analysis in“Dual-Tone” mode

Analog-to-digital (A/D) converter performances are constantly improving, concerning both conversion speed and resolution. Consequently, characterization becomes harder as the limits of the testing instrumentation are reached. We tried to answer that problem by defining a test methodology based on “dual-tone” spectral analysis. In this paper we present both the basic principles of this method and also experimental results on A/D converters     

Measurement issues in quantitative ultrasonic imaging

Ultrasonic imaging of “flesh and blood” is vulnerable to the natural variability of these media: the speed of sound is not known, not constant, and not amenable to calibration using simply shaped manufactured samples. When images of high dimensional accuracy are needed, as for image guided surgery, the “average” or “typical” values used in diagnostic ultrasound may not be good enough. In this paper, we identify the main sources of uncertainty, and we suggest and model experimental approaches to in situ calibration     

New methods for accurate water dosage in concrete central mix plants

Online mixer measurements appear as being essential to the improvement of concrete manufacturing methods, as imposed by new economical and environmental demands. However, the lack of a well-established calibration procedure contributes to the poor reputation sometimes given to these measurements. The original in situ method developed and evaluated herein requires installing a sampler, yet only slightly disturbs the production process. By using this calibration method the mixing power becomes a reliable online indication of concrete water content (measurement standard deviation of 2.85 l/m³). A procedure for improving the regularity of water content in truck mixers has been presented to illustrate the benefit of well-calibrated online water content measurements in batch concrete in a central mix plant. The correction algorithms proposed herein have the potential to be automated and may improve up to 5 times the water content regularity in the truck mixers.     

Adapting second‐order response surface designs to specific needs

Experimental design strategies most often involve an initial choice of a classic factorial or response surface design and adapt that design to meet restrictions or unique requirements of the system under study. One such experience is described here, in which the objective was to develop an efficient experimental design strategy that would facilitate building second‐order response models with excellent prediction capabilities. In development, careful consideration was paid to the desirable properties of response surface designs. Once developed, the proposed design was evaluated using Monte Carlo simulation to prove the concept, a pilot implementation of the design carried out to evaluate the accuracy of the response models, and a set of validation runs enacted to look for potential weaknesses in the approach. The purpose of the exercise was to develop a procedure to efficiently and effectively calibrate strain‐gauge balances to be used in wind tunnel testing. The current calibration testing procedure is based on a time‐intensive one‐factor‐at‐a‐time method. In this study, response surface methods were used to reduce the number of calibration runs required during the labor‐intensive heavy load calibration, to leverage the prediction capabilities of response surface designs, and to provide an estimate of uncertainty for the calibration models. Results of the three‐phased approach for design evaluation are presented. The new calibration process will require significantly fewer tests to achieve the same or improved levels of precision in balance calibration. Copyright © 2008 John Wiley & Sons, Ltd.     

Energy conservative property of impulse‐based methods for collision resolution

Physical accuracy, numerical stability, and computational speed are critical factors in the simulation of collisions. The impulse‐based method models collisions in a system of rigid bodies in a relatively reliable and fast manner. In the present paper, evidence is presented for the energy‐conserving and momentum‐conserving properties of the method. Two different impulse‐based approaches are validated using numerical tests. A necessary condition is proposed for the impulse‐based method to be energy conservative. Results indicate that the impulse‐based method for collision simulation, which satisfies the proposed condition, is energy conservative. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimal realization of arbitrary forces in a magnetic stereotaxissystem

Very small implanted permanent magnets guided by large electromagnetic coils have been proposed previously as a method for delivering hyperthermia to or guiding catheters through brain tissue. This procedure is termed “magnetic stereotaxis”. Early efforts employed a single coil on a movable boom, a design that proved logistically difficult to use on human patients. The present work deals instead with a design where several stationary coils are employed to develop a force on the implanted magnet. The coil current-to-force relationship is developed for this type of machine, and several optimal solutions for realizing an arbitrary static force are presented for various constraints on the orientation of the implanted permanent magnet. Costs of the different solutions are compared in several examples using a mathematical model based on the Magnetic Stereotaxis System (MSS) developed by Stereotaxis, Inc., the University of Virginia, and Wang NMR     

基于出口调制的气体脉冲压力发生方法研究

针对航空航天领域对中低压气体脉冲压力测试与校准的需求,介绍了一种基于出口调制型方式的中低压气体脉冲压力发生方法,利用稳定气流源和旋转阀,通过控制电机运动方式可在固定容腔中产生中低气体脉冲压力。根据旋转阀运动状态和阀口流通面积变化情况,建立气体压力关系式,通过理论计算得到的结果验证了旋转阀产生气体脉冲压力的可行性。利用本装置进行实验,开展不同电机转速和进气压力条件的实验,实验表明:产生的脉冲压力幅值在4 MPa以下,脉宽在15 ms以内,并且装置结构对脉冲压力波形影响较为明显,未来可进一步通过装置结构优化得到更为理想的脉冲压力波形。     

A method for calculation of radiation quantities at all points in gamma radiation calibration fields

Radiation quantity values at all points of a known distance range of gamma radiation calibration fields were calculated using a mathematical method. The method is based on interpolation using Chi-square test on a set of experimental data at optional points of both collimated and un-collimated calibration set-ups by means of a reference instrument. In comparison with Monte Carlo calculations, the values that were calculated by this method differ by <1% for collimated and 2% for un-collimated calibration set-ups. Consequently, the radiation quantities at all points of gamma radiation calibration field set-ups can accurately be formulated and determined by this method. In addition, all points in the radiation fields can be regarded as test points.     

Uncertainty Evaluation and Validation of a Comparison Methodology to Perform In-house Calibration of Platinum Resistance Thermometers using a Monte Carlo Method

The uncertainty required by laboratories and industry for temperature measurements based on the practical use of platinum resistance thermometers (PRTs) can commonly be achieved by calibration using temperature reference conditions and comparison methodologies (TCM) instead of the more accurate primary fixed-point (ITS-90) method. TCM is suitable for establishing internal traceability chains, such as connecting reference standards to transfer and working standards. The data resulting from the calibration method can be treated in a similar way to that prescribed for the ITS-90 interpolation procedure, to determine the calibration coefficients. When applying this approach, two major tasks are performed: (i) the evaluation of the uncertainty associated with the estimate of temperature (a requirement shared by the ITS-90 method), based on knowledge of the uncertainties associated with the temperature fixed points and the measured electrical resistances, and (ii) the validation of this practical comparison considering that the reference data are obtained using the ITS-90 method. The conventional approach, using the GUM uncertainty framework, requires approximations with unavoidable loss of accuracy and might not provide adequate uncertainty evaluation for the methods mentioned, because the conditions for its valid use, such as the near-linearity of the mathematical model relating temperature to electrical resistance, and the near-normality of the measurand (temperature), might not apply. Moreover, there can be some difficulty in applying the GUM uncertainty framework relating to the formation of sensitivity coefficients through partial derivatives for a model that, as here, is somewhat complicated and not readily expressible in an explicit form. Alternatively, uncertainty evaluation can be carried out by a Monte Carlo method (MCM), a numerical implementation of the propagation of distributions that is free from such conditions and straightforward to apply. In this paper, (a) the use of MCM to evaluate uncertainties relating to the ITS-90 interpolation procedure, and (b) a validation procedure to perform in-house calibration of PRTs by comparison are discussed. An example illustrating (a) and (b) is presented.     

脉冲力校准中锤体质量块结构设计与受力方式对校准结果的影响分析

在脉冲力校准中,锤体质量块的力学性能会对校准结果产生较大影响。本文采用有限元手段,对锤体质量块的结构设计方案和受力方式进行分析,得出锤体质量块动态特性的影响因素,总结脉冲力校准中锤体质量块设计和使用时应遵循的规律,为动态冲击计量标准装置的研建提供借鉴。     

Generalized receptance‐based method for accurate and efficient modal synthesis

Modal synthesis plays an important role in efficient dynamic analyses of large structural assemblies. However, the numerical accuracy and the computational efficiency which existing modal synthesis methods have achieved to date are not quite satisfactory. This paper presents a new generalized receptance‐based modal synthesis method which is numerically very accurate and computationally very efficient. The method employs receptance data computed at just few frequency values to formulate a derived equivalent eigensys tem from which required eigenvalues and eigenvectors of interest can be solved. It provides mathematical generalization for existing mode‐based modal synthesis methods since modal data are essentially those receptance data at resonant frequencies. A normalization procedure is also presented which can be used to mass normalize computed mode shapes which are often required in practice. Compensation for the contribution of higher uncomputed modes to receptance data at lower frequency of interest is made to improve analysis accuracy by using lower calculated modes and known system matrices. Numerical results are presented to demonstrate the effectiveness of the proposed method. Copyright © 1999 John Wiley & Sons, Ltd.     

空间最佳N冲击过渡的系统方程

在时间任意的椭圆轨道过渡中,最佳过渡不是中间推力弧,而是冲击过渡。冲击过渡的研究,对于实际发射中选择最佳推力段有重要的指导意义。由Breakwell创立的极值曲线法利用现代控制理论,从端轨道出发建立起最佳N-冲击过渡的极值曲线场,是一种有力的数值手段。要把极值曲线法从平面推广到空间,关键是要解决两个问题:得到系统方程及相关的伴随系统积分。本文在所选五维相空间中,通过对经典公式,偏心率矢量及角动量方向单位矢量的分析及投影变换,导出了冲击过程中空间最佳N冲击过渡(时间任意)的系统方程,从而解决了两个关键问题之一。