On a Class of Capacitively Tuned Transducer Oscillators

A class of transducer oscillators is characterized by a tuning method that exchanges short-term for long-term stability, and accepts both single and differential tuning sensor capacitances. When the tuning method is applied to a restricted class of RC oscillators, the relation between tuning capacitance and oscillator period can be made linear. The effect of amplifier phase shift and distortion is analyzed and a design procedure given. In one application, an oscillator used with an air-pressure sensor is tuned from 25 to 50 ms (corresponding to 40 to 20 Hz) with a differential tuning capacitance varying from -2 to + 7 pF. The short-term stability is 80 ppm when the average of 100 periods is measured. The deviation from linearity is less than 1.5 percent of the total range.     

Laser-produced plasma measurement of thermal diffusivity of molten metals

We have shown that a laser-produced plasma plume which is representative in elemental composition of the condensed phase target can be reproducibly generated if the movement of the surface due to evaporation is kept in pace with the thermal diffusion front propagating into the bulk. The resulting mass loss is then strongly controlled by the thermal diffusivity of the target matter, and this relationship has been exploited to measure the thermal diffusivity of metallic alloys. We have developed a novel RF Ievitator-heater as a contamination-free molten metal source to be used as a target for LPP plume generation. In order to determine the mass loss due to LPP excitation, a new high-sensitivity transducer has been constructed for measurement of the resulting impulse imparted on the specimen. The impulse transducer is built onto the specimen holder within the levitation-assisted molten metal source. The LPP method has been fully exercised for measurement of the thermal diffusivity of a molten specimen relative to the value for its room temperature solid. The results for SS304 and SS316 are presented, together with a critique of the results. A numerical modeling of the specimen heating in the molten metal source and the physical basis of the new method are also presented.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

An Induction Sensor for Liquid Interference Refractometers

The design and working principle are described for an induction-type displacement transducer for the automatic displacement of reflectors in a computer-controlled interference refractometer.     

The measurement of the relative density of homogeneous fluids bymeans of an optical technique

A transducer that uses an intensity-modulated optical method to measure the relative density of homogeneous fluids is described. An optical fiber is used in a special way as a refractometer, measuring index of refraction, which has a direct relationship with relative density. The method relies on the optical power loss exhibited by a fiber bent beyond a critical radius. For such a fiber the critical angle of reflection is a function of the refractive index of the surrounding medium. The latter will therefore determine the amount of leakage, which can be measured and related to the value of relative density     

一种新型差动位移变换器

本通过对三段式差动电感变换器轴向磁场分布的研究,找出了其非线性的根本原因,并针对这个问题提出一种新颖的差动式电感变换器的结构形式。实验测试证明,这种结构的变换器的线性范围较同样长度尺寸的传统三段式变换器宽,且灵敏度高、漂移小,精度能够达到要求,同时其结构和绕线工艺也较传统的三段式位移变换器简单,便于工厂进行大批量的生产。     

New high temperature phase transitions in cesium cupric chloride

Two new high temperature anomalies at 511 K and 538 K in CsCuCl₃ were investigated using different techniques such as differential thermal analysis, differential scanning calorimetry, thermal expansion, and reflectance measurements. These anomalies together with the Jahn-Teller effect of the copper ions suggest that these phase transitions can be explained as a Jahn-Teller induced transition in the case of an antiferro-distortive ordening.     

《一种新型电—热—声转换装置的特性研究》

设计制作了一高频电—热—声转换装置，装置由电热层、绝缘层和导热层组成。将交变的电信号接入电热层，会产生交变的热信号，促使电热层表面附近的气体压力产生交变的振荡，形成相应的声波。装置产生了可测频率在3 kHz-25 kHz的热声现象。装置作为小型高频发声器具有频带宽、频响平坦、无运动部件等优点。     

Phase aberration correction using ultrasound radiation force and vibrometry optimization

We describe a phase aberration correction method that uses dynamic ultrasound radiation force to harmonically vibrate an object using amplitude modulated continuous wave ultrasound. The phase of each element of an annular array transducer is adjusted to maximize the radiation force and obtain optimal focus of the ultrasound beam. The maximization of the radiation force is performed by monitoring the velocity of scatterers in the focus region. We present theory that shows focal optimization with radiation force has a well-behaved cost function. Experimental validation is shown by correction of manual defocusing of an annular array as well as correcting for a lens-shaped aberrator placed near the transducer. A Doppler laser vibrometer and a pulse-echo Doppler ultrasound method were used to monitor the velocity of a sphere used as a target for the transducer. By maximizing the radiation force-induced vibration of scatterers in the focal region, the resolution of the ultrasound beam can be recovered after aberration defocusing.     

GNSS接收机伪距和载波相位测量噪声直接估计方法

基于微分法的思想,提出了一种可以直接估计伪距和载波相位观测噪声的方法。通过对二阶系统求三阶导数,隔离系统本身的影响,通过对非差、单差、双差的残余观测噪声序列的分析,直接估计伪距和载波相位的观测噪声和接收机钟差的高阶噪声。由于该方法可以在线工作,对大量的GNSS集成系统,用该方法估计先验观测方差非常方便。     

焦炉集气管压力自动控制方法及其实现

通过对焦炉煤气集气管压力系统的分析研究,建立控制系统的集气管压力协调控制方案,使得系统在传统PID控制的基础上,能够按照系统实际运行状况智能选择控制策略.通过SUPCON JX-300X DCS集散控制系统,实现压力变送器、电动执行机构、调节阀、热电阻等等监测信号在DCS中达到计算机实施监控和控制,在上位机上,均可进行监控和数据程序的管理.     

Depth-Resolved Surface Thermophysical Property Measurement by Laser-Produced Plasmas

A new laser-based method for real-time in situ measurement of thermophysical properties of materials has been developed. It entails production by a high-power laser pulse of a plasma plume from the surface of a condensed-phase specimen and simultaneous measurement of a material's response to the excitation. The specimen may be a solid or in a molten state at high temperatures. It has been shown that the thermal diffusivity can be determined, for instance, from the mass loss due to laser excitation. In one implementation the mass loss is determined from the impulse imparted on the surface by the ablated matter which is measured by an impulse transducer. In this paper, we present a new spectroscopic method for measurement of the mass loss, facilitating in situ non-contact measurement of the thermal diffusivity for the first time. An implementation of this method is described, whereby the thermal diffusivity of a complex layered surface is determined as a function of depth with resolutions as small as 13 nm.     

Evaluation of fibre optic sensors for structural condition monitoring

This paper presents fibre optic sensing technology for strain monitoring of engineering materials and structures. The research program consisted of laboratory tests including thermal tests, tensile tests and flexural tests, and a field application on a concrete bridge deck (Joffre Bridge) reinforced partly with fiber reinforced polymers (FRP). Four types of Fabry-Perot fibre optic sensors were investigated and compared to other types of strain gauges including Bragg fibre optic sensors and resistance strain gauges. Typical field monitoring results from the static and dynamic tests using calibrated-truck loads on the Joffre Bridge are also presented in this paper. Experimental and field monitoring results show that Fabry-Perot fibre optic sensors perform linearly and show good response to thermal variations and mechanical loading conditions. The fibre optic sensing technology shows an enhanced accuracy and has potential for significant improvement in the long-term monitoring of strain levels in field applications over conventional strain gauges. It is a promising technique for long-term ‘health’ monitoring of new and rehabilitated structures.     

An Experimental Technique for Liquid/Solid Thermal Conductivity Measurements at the Melting Point

Based upon the theory that the thermal conductivity can be determined by measuring the speed of the propagation of the solid/liquid phase interface during a phase transition, a system was developed to investigate the thermal conductivity of metals and alloys at the liquid/solid phase transformation point. Furthermore, a mathematical method was applied to represent the melting and solidifying process in the phase transformation chamber, by which the error could be analyzed. In order to test the feasibility of the method and the measuring system, a series of verification experiments on lead have been performed to estimate the precision and the applicability of the measuring system. From comparisons with recommended data from the literature, the uncertainty of the experimental results is estimated to be about 5% which means the measuring method is suitable to determine the thermal conductivity of eutectic alloys and metals at the liquid/solid phase transformation point. This work provides a relatively precise method for thermal conductivity measurements on new materials such as lead-free solders.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China     

Method of determining the relative sensitivity of thermal vacuum gages to different gases

A new method is described for determining the relative sensitivity of thermal vacuum gages and their sensors (tranducers) to different gases. The method is based on compensation for the change in the transducer signal caused by the use of a gas other than nitrogen or air and by variation of the volume of the measurement chamber. This approach makes it possible to avoid some of the errors intrinsic to measurements of low pressures and small increments in the transducer signal. A vacuum system configuration that allows the given method to be realized is described. Translated from Izmeritel'naya Tekhnika, No. 1, pp. 31–32, January, 1997.     

低频标准角振动台

低频标准角振动台产生标准角位移、角速度和角加速度,用正弦信号对角位移传感器、角速度传感器(陀螺、转速表等)和角加速度计进行幅频和相频特性校准。简要介绍了低频标准角振动台的工作原理,并应用其对角运动传感器进行校准。校准范围为0.1~100H z;幅值灵敏度不确定度优于1%;相移不确定度小于1°。     

Determination of thermal stress in concrete pavements by means of measurement of in-situ strains

A new method of determining the thermal stress of concrete pavement in-situ has been developed and applied to engineering practice with success. It consists of three parts:
1. A system of theorems was established on the basis of mathematical modelisation that both temperature and thermal strain were sine functions of t, the time of observation, owing to the daily fluctuations of temperature and consequently the corresponding thermal strain. It was found that there exist a time phase and an angle of axes rotation between temperature and thermal strain.
2. A bridge circuit with a strain block and specially designed equipment 'free body' was introduced. The strain transducer for every test point consists of one strain gauge in the strain block and one in the 'free body', the former is used as the active gauge in the bridge circuit and the latter as the dummy. A temperature probe of resistance type was inserted nearby each of the gauges. Arrangement of observations and procedure of the data treatment were stated.     

Stress analysis in thermal barrier coatings subjected to long-term exposure in simulated turbine conditions

In recent years, ruby fluorescence spectroscopy has been demonstrated as a powerful technique for monitoring residual stress evolution in the thermally grown oxide scale in thermal barrier coating (TBC) systems. The measured residual stresses, in turn, can be used to monitor evolution of damage in the coatings. Effective use of this technology for real-time damage monitoring requires the identification of trends in measured stresses that can be used as indicators of damage evolution. The present work focuses on studying the evolution of residual stresses in TBC systems during long-term exposure to turbine operating conditions. The coatings are electron beam physical vapor deposited (EBPVD) and atmospheric plasma sprayed (APS) zirconia. The stress evolution in both EBPVD and APS coatings is analytically modeled by an approach that takes into consideration contributions due to both thermal mismatch and oxide growth. Microstructural changes in the TBC system are correlated with measured stress trends through comparison with the modeled stresses. The stress measurements and modeling provide insight into failure modes and mechanisms, and to identify critical features in the measured stress data that can be used as indicators of failure in TBCs.     

太阳能建筑用石蜡/CNTs相变乳液的制备及光-热性能研究

结合建筑结构在太阳能领域的蓄热控温特点,采用"两步法"制备出适用于太阳能蓄热的新型石蜡/CNTs相变乳液,通过纳米粒度电位仪和布鲁克旋转黏度仪分析了CNTs掺量对相变乳液技术性能的影响,确定最佳CNTs掺量;再采用差示扫描量热仪、导热系数测定仪、自制太阳光-热转换装置及紫外/可见/近红外分光光度计探究相变乳液的热物性能和光-热转换性能。结果表明,随着CNTs掺量的增大,相变液滴的粒径分布和运动黏度发生较为明显的变化,综合考虑相变乳液的稳定性及泵送性,推荐石蜡相变乳液中CNTs的最佳掺量控制为0.6%。由于石蜡具有较高的相变储热性能及CNTs具有较大的导热系数,掺加石蜡/CNTs能够显著增强相变乳液的导热性能和光-热转换能力,完全可用于建筑结构中以达到对太阳光辐射的蓄热与调温作用。     

光电集成加速度地震检波器中声光波导相位调制器的设计与实验

提出了一种新型的光电集成加速度地震检波器,这是一种全新的微光机电系统(MOEMS),为实现硅基底上的光波导M-Z干涉仪的相位调制,采用了声光相位调制的方法,该相位调制器利用叉指换能器(IDT)激发出声表面波(SAW)实现对光波导的相位调制,在对光波导声光相位调制机理深入研究的基础上,设计并制作了器件,实验结果与理论相一致。