电容式物位计中挂料问题的研究

传统电容式物位传感器在测量导电介质时,无法消除电极挂料对测量的影响,本通过分析电极挂料的等效电路,提出了带有电极挂料的物位计测量电路,并指出一定的初始条件和测量条件下,测量电路的输出电压仅与物位电容有关,而与电极挂料无关,这为今后进一步研制开发新型电容式物位计,消除电极挂料的影响提供了理论依据。     

射频导纳原理在料位测量中的应用

固态、液态（包括浆体）料位测量技术广泛应用于石油、化工、能源、食品、矿山、储运等工业生产领域，95％以上的容量测量也是通过料位测量得到的。传统料位测量方法多种多样，如电容式、放射线式、机电式、声波式等，其中又以电容式（又称做射频式）应用最为广泛。它耐腐蚀、抗高温、抗高压，但有一个致命的缺陷，即测量黏附性导电物料时，物料会黏附在传感电极的外套绝缘罩上（挂料），形成虚假物位，产生很大的测量误差，使仪表无法工作。正是这一点妨碍了电容式物位仪表的更广泛推广应用。应用射频导纳技术，对传统的电容式物位仪表进行…     

一种电容层析成像系统电极组合激励测量方法

针对电容层析成像图像重建具有非线性不适定性的问题,提出了8组24电极旋转激励测量方案,并与传统12电极电容层析成像传感器进行了对比分析,包括电容值大小及其动态范围、敏感场分布均匀性以及重建图像质量。应用COMSOL软件及Matlab软件对两种传感器激励模式进行仿真,结果表明:所提出的8组电极旋转激励测量模式,其电容独立测量数与传统12电极传感器相近,可较好地保证实时成像速度,测量电容值较大且动态范围较小,降低了信号检测电路设计难度,测量区域灵敏场均匀性有所改善,对中心物体的成像质量明显提高。     

物位传感器的原理及其应用

物位传感器可以分为两类：一类是连续测量物位变化的连续式物位传感器：另一类是以点测为目的的开关式物位传感器（即物位开关）。目前,开关式物位传感器比连续式物位传感器应用更为广泛。开关式物位传感器主要应用于过程自动控制的门限、溢流和防止空转等。连续式物位传感器主要应用于连续控制和仓库管理等方面．有时也可以应用于多点报警系统中。     

氦液面测量用电容传感器的设计研究

本文主要介绍了“YR—80—Ⅱ型电容式低温液面计”的一次敏感元件——电容传感器的研制和设计情况。对电容传感器的工作原理、结构设计、装配工艺等方面做了比较详细地叙述。电容传感器探头外径为φ10mm、测量范围0～1000mm、漏热对液氦的损耗量为0.75 1/24h、内电极,外电极以及零位电容补偿线之间的绝缘电阻大于20MΩ。在内电极引出管中,增加了零位电容补偿线,较好地克服了内电极引线分布电容变化对液面测量的影响;在外电极(外管)与八芯密封插座之间,采用了导热系数小的尼龙材料做连接座,减小了电容传感器上部漏热对液氦的损耗。     

电容薄膜规规管零漂的改善

从1949年开始到现在,国外已研制出四代电容薄膜压力传感器.第一代是差压式双边对称电极的传感器;第二代是绝对式单边双电极的传感器;第三代在测量线路上有了很大的改进;第四代是对式单边单电极的传感器,首先分析了造成电容压力传感器稳定性差的6种原因。认为环境温度的改变和规管焊接应力是造成规管零漂的主要因素。并对这两种主要因素提出了相应的解决办法.温度变化的影响采用恒温的方法来解决.焊接应力的影响采用以粘代焊的方法来消除.采用这两种措施以后,电容薄膜规的稳定性有了较大的改善.     

三维电容层析成像组合电极激励测量模式

针对3层电容阵列电极传感器,基于三维仿真,研究了两种组合电极激励测量模式,并与传统的单电极激励单电极测量模式进行了比较,包括电容测量值大小及其动态范围、敏感场分布均匀性以及重建图像质量。基于COMSOL软件及Matlab软件进行了仿真实验,结果表明:相较于传统的单电极激励单电极测量模式,组合电极激励测量模式所得图像重建效果更好,测量电容值较大且动态范围较小,敏感场分布更加均匀,对中心物体的成像质量明显提高。     

基于V/T变换的电容传感器新型电容测量电路

提出了一种基于V／T变换的用于电容传感器的电容测量电路。它将被测微小电容变化量转换成时间信号并由单片机进行处理，电路结构简单，电路中没有影响测量稳定性和产生零点漂移的元器件，大幅度地降低了测量过程中的噪声。     

电容传感器新型电容测量电路设计

提出了一种基于V／T变换的用于电容传感器的电容测量电路。它将被测微小电容变化量转换成时间信号并由单片机进行处理，电路结构简单，电路中没有影响测量稳定性和产生零点漂移的元器件，大幅度地降低了测量过程中的噪声。     

线面式电容传感器结构设计与传感特性研究

提出了一种基于自阻尼垂向测量参考的线面式电容传感器,对垂向运动中的残留水平位移进行精确测量。线面式电容传感器利用细丝电极作为直接垂向测量参考,消除了间接参考在其转换过程包含的系统误差;同时采用细丝末端的液体阻尼器保证细丝电极的稳定性。实验表明:在0.38~0.4pF范围内,线面式电容传感器的分辨力优于0.05μm,短期稳定性约为0.1μm。     

Characterization of Capacitive Array for NDE Applications

Abstract

We have developed a capacitive array sensor which responds to the complex dielectric constant of an interrogated material. The sensor requires only single-sided access and operates in a differential mode for detection of discontinuities in the relative dielectric constant, ε _r , or in the absolute mode where the interest is in absolute quantities. The device in general is noncontacting but can be fabricated as an embedded sensor.

Various proof-of-concept studies have been performed to explore possible applications of the device. In the differential mode, small surface features (notches) were detected in a conductor; in dielectrics, both surface and subsurface features were detected. The probe was sensitive to change in impedance caused by a curing epoxy, viewed through a graphite-epoxy composite panel.

A study was performed to assess the use of the probe for noncontact characterization of sintering of ceramics. In this (absolute) mode, the effects of liftoff and dielectric constant must be separated. We propose a scheme based on the ability to multiplex the capacitive array probe to accomplish this. Preliminary investigation shows that the effect of parasitic capacitance between the probe and ground points in the environment must be suppressed.     

Characterization of capacitive array for NDE applications

We have developed a capacitive array sensor which responds to the complex dielectric constant of an interrogated material. The sensor requires only single-sided access and operates in a differential mode for detection of discontinuities in the relative dielectric constant, _r , or in the absolute mode where the interest is in absolute quantities. The device in general is noncontacting but can be fabricated as an embedded sensor.Various proof-of-concept studies have been performed to explore possible applications of the device. In the differential mode, small surface features (notches) were detected in a conductor; in dielectrics, both surface and subsurface features were detected. The probe was sensitive to change in impedance caused by a curing epoxy, viewed through a graphite-epoxy composite panel.A study was performed to assess the use of the probe for noncontact characterization of sintering of ceramics. In this (absolute) mode, the effects of liftoff and dielectric constant must be separated. We propose a scheme based on the ability to multiplex the capacitive array probe to accomplish this. Preliminary investigation shows that the effect of parasitic capacitance between the probe and ground points in the environment must be suppressed.Contribution of the National Institute of Standards and Technology (formerly National Bureau of Standards); not subject to copyright.     

Effect of crystallization on humidity sensing properties of sol-gel derived nanocrystalline TiO2 thin films

In the present work, we describe the effect of crystallization on humidity sensing properties of nanocrystalline TiO₂ thin films prepared by sol-gel techniques. Here, we report an enhancement in the relative humidity (RH) sensitivity just after the crystallization at 375 °C, which is attributed to increased surface activity near crystallization and lower crystallite size. After crystallization, the RH sensitivity was found to decrease with increasing grain size. The complex impedance of the sensor, measured using impedance spectroscopy, fits well with an equivalent circuit consisting of inter-granular resistance and capacitance in parallel. It was found that with the change in RH, only resistance changes significantly, when compared with the capacitance.     

Mobile patient monitoring based on impedance-loaded SAW-sensors

A remotely requestable, passive, short-range sensor network for measuring small voltages is presented. The sensor system is able to simultaneously monitor six small voltages in millivolt-range, and it can be used for Holter-electrocardiogram (ECG) and other biopotential monitoring, or in industrial applications. The sensors are based on a surface acoustic wave (SAW) delay line with voltage-dependent, impedance loading on a reflector interdigital transducer (IDT). The load circuit impedance is varied by the capacitance of the voltage-controlled varactor. High resolution is achieved by developing a MOS-capacitor with a thin oxide, low flat-band voltage, and zero-voltage capacitance in the space-charge region, as well as a high-Q-microcoil by thick metal electroplating. Simultaneous monitoring of multiple potentials is realized by time-division-multiplexing of different sensor signals.     

气敏材料及传感器特性检测系统

讨论了在气敏材料及气敏传感器检测中遇到的问题和解决方法，并设计实现了新型检测系统，通过采用动态配气技术，结合计算机软硬件技术，采用按需设计测试流程的方法实现气敏传感器和气敏材料多方面性能的灵活检测，满足科研、生产中的不同检测需要。     

Impedance Resonance: A Novel Technique for Signal Acquisition From Interdigitated Electrodes (IDE) in Sensor Applications

A simple and useful modification to the common method of acquiring the impedance spectrum of modified interdigitated electrodes consists of including an appropriately sized induction coil connected in parallel with the interdigitated electrode (IDE). The resulting impedance behavior of the IDE/coil combination transforms the customary Bode plot of total impedance versus frequency data from a broad, complex curve to a simple resonance peak which can serve as the basis for a sensor output signal. The exact frequency and amplitude of the impedance resonance peak are a function of both the fixed induction characteristics of the coil and the experiment-dependant capacitance of the modified IDE. Quantifiable changes in the impedance resonance peak have been correlated with experimental parameters such as the electrical characteristics of polymer coatings on the IDE array leads, exposure of the IDE to aqueous solutions of varying composition, and molecular mobility factors in curable polymer resins.     

Improved Sensitivity in the Impedance Method of Determining the Resonant Frequency of a Piezoelectric Detector

Connecting a piezoceramic capacitor into an arm of a capacitance bridge allows one to use an impedance method to determine the resonant frequency of a low-sensitivity piezoelectric sensor.     

Local behavior of complex materials: scanning probes and nano structure

Understanding the behavior of complex materials such as organic self-assembled monolayers, molecular and nano wires, and transition metal oxide thin films, is facilitated by probes of local properties. Recent extensions of scanning probe microscopies that extract electrical potential, capacitance, dielectric constant, electromechanical coupling coefficients and impedance, are described. In most cases, these complex properties are accessed by stimulations and/or response function detection with multiple frequency modulations. Several illustrative examples include determination of the electronic structure of individual defects in a carbon nanotube, ferroelectric domain interactions in oxide thin films, and electric potential of an alkanethiol on metal.     

SnO2气敏元件灵敏度及选择性的复阻抗分析

运用复阻抗谱方法,在不同浓度乙醇与汽油气体中,测试ＳｎＯ２厚膜气敏元件的电抗－频率关系曲线,由电抗的变化来标定元件的灵敏度。与以往的测试采用直流电参量标定灵敏度相比,复阻抗测试不仅提高了元件的灵敏度,而且显著改善了选择性。该结果表明复阻抗测试不仅反映元件在气体吸附或解吸时晶粒间界处晶界电阻的变化,也反映了晶界电容的变化,因而更能体现气敏机制的本质。