磁悬浮转子真空计的研究历程

磁悬浮转子真空计被广泛应用于各个领域,在10^-4-1 Pa下具有相当高的精确度,以其优越的性能在其中占有重要地位,被广泛用于传递标准。然而,残余阻尼的存在严重影响了磁悬浮转子真空计的下限扩展,其中以涡流效应的影响最为显著,相对于涡流效应,测量产生的弛豫效应和科里奥利效应可以忽略不计。本文简要介绍了磁悬浮转子真空计的结构和原理,概述了其研究历程,重点阐述了残余阻尼和切向动量传递系数的相关研究,并分析并总结了一些重要因素对它们的影响。残余阻尼的相关研究主要从涡流效应、温度效应、弛豫效应、科里奥利效应和振动这几个方面进行了介绍;在切向动量传递系数方面上,主要说明了气体种类和压力对它的影响。最后提出了一些改进猜想及后续工作的研究方向。     

High-velocity impact experiment of aluminum foam sample using powder gun

Porous materials such as aluminum foam have been investigated for possible use as impact shock absorbers in transportation aeronautic applications. However, the response of aluminum foam during impacts at high velocities of more than 100 m/s is not yet fully understood. A high-velocity impact experiment was therefore carried out to clarify impact shock absorption properties of aluminum foam. A one-stage powder gun was used to accelerate an aluminum foam sample to impact a rigid wall. Velocity and deformation of the aluminum foam sample during impact was studied using a digital high-speed video camera, while the pressure wave in the aluminum foam sample was measured using a PVDF gauge. The experimental observations revealed uneven collapse of the aluminum foam sample structure during high speed impact with a general stress plateau effect, typical for cellular material structures when subjected to quasi-static loading.     

Quantitative measurement of oxygen content in Si targets

Enriched self-supporting targets of ^28,29,30Si are often used in the field of high resolution nuclear physics experiments. The Si targets were prepared by the thermal evaporation deposition or reduction-deposition methods. The targets, however, are always contaminated by oxygen as Si-material is easily oxidised. These contaminated targets lead to poor data with low S/N ratio. Thus it is very useful if one can estimate the amount of oxygen in the target quantitatively before experiments.In this work we have developed a method to estimate the amount of oxygen in the Si target. We used α-ray and β-ray thickness gauges, which have different sensitivity to oxygen atoms. Namely, the α-ray gauge is more sensitive to light elements such as oxygen compared to the β-ray gauge. Thus one can deduce the amount of oxygen by comparing the oxygen thickness measured by α-ray gauge with that of the β-ray gauge.Accuracy of a few percents can be obtained for the oxygen content in Si targets with a thickness of 1 mg/cm². The present method can also be applied to heavy elements such as Ta₂O₅.     

A thermocouple vacuum gauge for low vacuum measurement

The construction of a thermocouple vacuum gauge for the range of pressures from 200 to 800 mbar is reported. The gauge differs from similar ones that cover the medium vacuum region. The main difference is that the thermocouple is not fixed to the filament, as usual, but is placed at some distance from the filament.     

On the response of ballistic soap to one-dimensional shock loading

The effects of projectile penetration into soft tissue are often studied using the tissue simulant ballistic soap. Consequently, a full understanding of the high strain-rate response of ballistic soap is desirable. Using the plate-impact technique, key shock parameters have been measured for impacts in the range 81–968 m/s, allowing derivation of the Hugoniot equation-of-state for soap in the U_S–u_P and σ_X–u_P planes. A polynomial Hugoniot relationship was found in the U_S–u_P plane, with the general form U_S = 1.96 + 2.41u_P − 0.72u_P² (ρ₀ = 1.107 g/cc). Further, embedded lateral manganin stress gauges were employed to interrogate the evolution of lateral stress within the soap. A gradient in lateral stress, whose magnitude increased incrementally with impact stress, was apparent behind the shock for σ_X >1 GPa. It is proposed that at higher values of σ_X, increased compression of hydrocarbon chains acts to increase the materials resistance to shear, a phenomenon consistent with steric hindrance.     

Two‐dimensional guidelines for measurement system indices

In this paper, we review two common measurement system indices and a common process capability index. With some simple plots, it will be shown that the traditional guidelines for these measurement system indices can often misdirect improvement efforts. By taking advantage of the relationship between the measurement system indices and the process capability index, two‐dimensional guidelines that can be used as an alternative to the traditional guidelines are developed. These two‐dimensional guidelines are intended to help address adequacy of the measurement system and better direct improvement efforts to where there will be the most benefit. Copyright © 2010 John Wiley & Sons, Ltd.     

盘磨机磨盘间隙在线测量技术研究

介绍了国内外对于磨浆机磨盘间隙测量的研究现状,以及磨浆机磨盘间隙在线测量的改进方法,进一步探讨了电涡流传感器在磨浆机上齿盘边界特性、齿盘变转速响应特性、进退盘响应特性、齿盘的静动态响应性能、输出特性等最佳特性曲线拟合方程。优化了电涡流传感器结合超声波测厚仪对磨浆机磨盘间隙的实时在线测量方案。传感器安装与磨片边缘的距离大于2 mm、动盘外缘线速度大于360 m/min时,电压值稳定,进退盘响应及静动态输出特性变化总体趋于一致,最佳特性拟合曲线方程线性系数大于0.99。     

轧机AGC系统的Smith预估补偿

轧机厚度控制系统中厚度误差反馈信号的纯滞后影响了系统的稳定及响应速度。本文介绍了采用Smith预估器进行预估补偿的方法来克服纯滞后的影响,改善系统的动态特性。     

Measurement of Helium Leakage Rates through Closures of Dangerous Goods Packagings for the Assessment of Potentially Explosive Mixtures in Freight Containers

The objective was to find out whether an explosive atmosphere can be created in a freight container by gaseous leakage flow of vapour‐air‐mixture through leaks in the closures of dangerous goods packagings filled with hazardous liquids. Because of high temperatures during intercontinental carriage, there is a gauge pressure in the free vapour phase inside the packagings which can cause a gaseous leakage flow. Two different methods were applied: Helium limit leakage rates for 23 quantitatively important hazardous liquids concerning their lower explosion limit (LEL) were calculated for a worst case transport scenario (Method 1). Helium leakage rates of five closure types of dangerous goods packagings with volumes of approximately 6 l were measured using the pressure technique by accumulation (Method 2). All types of closures of steel packagings were uncritical. The maximum measured leakage was 33% of the limit leakage rate. The leakage rates of screw closures of plastic jerricans can exceed the LEL if there are production‐related patterns such as non‐concentricity of the closures and flashes on the neck. Especially for plastic packagings it is important to minimize gaseous leakage flow, because an explosive atmosphere can also be reached by permeation of the individual filling substance or by a combination of both effects. For the assessment of potentially explosive mixtures in freight containers, both mass transfer mechanisms have to be taken into account. Copyright © 2015 John Wiley & Sons, Ltd.     

A Method for Improving Multivariate Measurement Systems Assessment

Multivariate measurement systems analysis (MSA) is usually performed by designing suitable gauge repeatability and reproducibility (R&R) experiments, ignoring available data generated by the measurement system while used for inspection or process control. This article proposes an approach that, by using the data that are routinely available from the regular operation of the instrument, allows the measurement instrument's current precision to be compared against a benchmark. The proposed method may be appropriately used in an integrated and coordinated manner with the usual multivariate gauge study in the sense that it can be used to assess the stability or a possible deterioration in the precision of the measurement instrument while operational. Therefore, the complementary use of the proposed approach and the traditional multivariate gauge R&R studies can be a useful strategy for improving the overall quality of multivariate measurement systems. Furthermore, because it can be implemented at almost no additional cost, it may be effective in reducing the costs of a multivariate MSA performed with a certain frequency. Copyright © 2014 John Wiley & Sons, Ltd.