高精度石油水分在线测量技术的研究

提出了一种新的高精度石油水分在线测量技术———基于实时温度补偿的电容式水分测量技术,并提出了电容测量电路参数的最小二乘估计方法。介绍了电容传感器的工作原理、结构及函数模型,给出了电容测量原理及方法,推导了温度补偿的二元线性拟合算法。实验结果表明:在0~10%的含水率范围内,本方法的测量误差≤±0.1%,测量周期为1 s,能够实现低含水率情况下石油水分的高精度在线测量。     

电容式水分仪的开发

电容式水分仪是一种利用介电常数原理测量物质含水量的检测仪,文章系统分析了单片式电容传感器的检测原理,设计了微弱信号采集、滤波、放大电路及数据采集、处理系统。实践表明,所研制的水分仪能有效地检测建筑物内供水管线的漏损。     

电容式振动传感器谐波失真自检测接口ASIC设计

为实现电容式振动传感器的谐波失真测量,针对电容式振动传感器表头设计出一种开关电容型接口ASIC芯片,采用相同电极分时复用的方法,从而避免电容敏感与静电力反馈的馈通现象.对传感器敏感电容上下极板与中间质量块间的杂散电容导致的谐波失真进行了原理分析,可知传感器二次谐波与寄生电容成正比,三次谐波与寄生电容无关.提出采用电容阵列补偿、静电力平衡反馈式闭环电路结构进行传感器谐波失真抑制,并基于静电力原理提出一种新的电容式振动传感器谐波失真自检测方法,该方法无需精密振动台,仅需要低失真度电压信号源.实际测试结果显示,谐波失真检测精度可达到-83 dB.ASIC芯片采用2μm CMOS工艺流片,刻度因子为1.2 V/g（g为重力加速度,g=9.8 m/s2）,量程为±2g,噪声密度为3×10-6g/（Hz）～（1/2）,静态功耗为40 mW.测试结果证明,该电路达到高精度微加速度计系统设计要求,可以应用到地震监测、石油勘探等领域中.     

电容式触觉传感器信号检测系统的设计

信号检测系统对电容式触觉传感器的分辨力、稳定性和信噪比都有重要影响.设计了一种基于PCap01电容数字转换芯片的电容式触觉传感器的信号检测系统,采用FPGA控制多路开关选通电容式触觉传感器的触觉单元并进行阵列式扫描,通过SPI通信读取PCap01的测量结果后通过USB通信将数据传输给上位机,在上位机中以三维柱状图和曲面图动态显示电容式触觉传感器表面的受力情况,系统的采样速率可达15帧/秒.实验结果表明,设计的信号检测系统可以满足电容式触觉传感器的需求,通过采集的数据可以获取电容式触觉传感器表面的受力信息.     

土壤湿度传感器非线性误差补偿方法

PHSL-S土壤湿度传感器具有高度非线性,严重影响土壤水分含量的测量准确性。本文介绍了一种基于最小二乘法和多项式拟合的土壤湿度传感器非线性误差补偿方法。首先介绍了非线性误差补偿原理,构建了基于多项式拟合的土壤湿度传感器非线性误差补偿器(即传感器逆模型),通过综合评价拟合函数性能参数,确定补偿器的阶数;利用最小二乘法,求解出了传感器补偿器的参数。利用PHSL-S传感器土壤湿度检测系统进行实验,结果表明,这种基于最小二乘法和多项式拟合的土壤湿度传感器非线性误差小于5%,证实了该方法的有效性。     

浅谈食品水分含量快速检测法

本文从电容法、电阻法、微波法及红外线法水分检测技术出发,阐述了常用食品水分含量快速检测法的测量原理和测量特点,提出了食品水分含量快速检测的发展方向.     

用于生物力学测量的新型电容式三维力传感器

针对生物力学测量的应用需求,考虑到电容型传感器温度特性好、功耗低等特点,研制了一种新型电容式三维力传感器。该传感器基于一种新颖的弹性体结构,以聚氨酯泡沫作为介质构成了3组电容,使得传感器能够同时感知3个维度的输入力分量并转化为3个通道的电容变化,利用ANSYS有限元分析确定了传感器的尺寸,使其各维度的量程达到±200N,安全过载大于150%。设计了由电容采集模块和信号处理模块组成的测量系统,嵌入传感器内部,一体化的设计实现了测量数据的实时解算和输出。此外,针对电容式传感器存在的迟滞效应和维间耦合干扰问题,建立了迟滞补偿与解耦模型。通过实验验证,该传感器的Ⅰ类误差低于2.8%,Ⅱ类误差低于4.6%。     

压电陶瓷振动传感器的迟滞非线性误差补偿研究

针对振动测试中压电陶瓷传感器的迟滞非线性会影响检测精度的问题,分析了压电陶瓷的微观极化机理,解释了压电陶瓷传感器产生迟滞非线性的原因。为了有效补偿压电陶瓷的迟滞非线性,提高检测精度,提出了一种可以反映压电陶瓷传感器非对称迟滞特性的改进Bouc-Wen模型,研究并给出了模型参数对迟滞曲线的大小、形状及平稳性影响关系和逆模型的求取方法。利用改进Bouc-Wen逆模型作为补偿器来补偿压电陶瓷传感器的迟滞非线性,实验验证结果表明:采用逆补偿后,校正位移总是能够很好跟踪传感器的实际输入位移,有效保证了检测精度。     

电容式微含水量检测系统设计

针对在线检测火药含水量的实际要求,设计平板电容水分检测传感器,利用水的相对介电常数远大于被检物料的相对介电常数的原理,构建和电容传感器相关的交流电桥和测量电路,并设计自补偿电路,使得桥路输入为零时输出也为零。由于所测含水量范围为0.5%~3.5%,测量准确度为0.1%,为提高系统的测量准确度,分别对影响含水量的温度、湿度和重量容积比加以考虑,建立多参数校正的水分在线检测系统。经过大量实验验证:该系统性能稳定,测量精度高,具有很好的实用价值。     

基于ANSYS的电容式测压器的数值模拟

针对目前火炮膛压测试中传感器安装结构与测压器小体积之间的矛盾,设计了一种壳体电容式压力传感器.介绍了测压器的结构及基本原理,并利用有限元分析软件ANSYS对测压器的壳体进行了静态及瞬态分析,由静态分析的结果对壳体电容进行最小二乘法拟合,拟合相关系数为0997 5,并绘制出电容式测压器的静态灵敏度曲线,在模拟膛压发生器上进行动态实验,采用上升沿校准的方法对膛压曲线进行分析.结果表明:该测压器具有良好的非线性,静态灵敏度随压力载荷的增加而增加;该设计方案是可行的,值得推广.     

The influence of electric-field bending on the nonlinearity ofcapacitive sensors

Three-layered electrode structures are often employed in multiple-electrode capacitive position sensors. Even when advanced algorithms and well-designed guarding electrodes are used, the electric-field-bending effect is still one of the major contributors to the nonlinearity of capacitive position sensors. In this paper, the effects of electric-field bending on linearities of five capacitive linear-position sensors have been studied based on a physical model of the capacitive sensor. It is shown that the effect of electric-field bending on linearities strongly depends on the sensor structures, and that it is significantly reduced when advanced sensor structures and algorithms are used. The results are very useful for optimizing the sensor structure according to its application     

The application of the capacitor's physics to optimize capacitiveangular-position sensors

The distributions of the potential and charge density in a capacitive angular-position sensor with three electrode disks in an axis-symmetrical configuration have been found by creating a suitable physical model and solving Laplace's equation. The influences of geometrical parameters on the nonlinearity, which originates from the electric-field-bending effect, are discussed in detail for a capacitive angular-position sensor. The approximately analytical results are verified by a numerical analysis and are found to be very useful to predict the influences of geometrical nonidealities. The calculations are experimentally verified by using a novel, absolute angular-position sensor with a nonlinearity of less than ±17" and ±50" over measurement ranges of 15° and 90°, respectively     

Performances and potentialities of a very simple self-compensatedpressure sensor demonstrator

A pressure sensor demonstrator has been designed and mounted using a simple analog-digital BiCMOS converter and a capacitive silicon-Pyrex sensing cell. The measurements as a function of pressure and temperature have enabled the authors to evaluate the efficiency of a ratiometric scheme to self-compensate thermal drifts and nonlinearities. The best demonstrator is characterized by a thermal coefficient of offset smaller than 20 ppm/K and a nonlinearity lower than or equal to ±1.2% FS. The essential features of the sensor have been modeled by a simple analytical expression. The model specifies the potential gains in pressure sensitivity and nonlinearity. The best design is based on a quasisymmetrical architecture in which stray capacitors are minimized. This study demonstrates the feasibility of self-compensated capacitive sensors characterized by an overall accuracy of the order of a few percent of the measurement scale over a temperature range of 100 K at very low cost     

A Differential Capacitive Torque Sensor With Optimal Kinematic Linearity

This paper presents a new design for a torque sensor based on a differential capacitive technology. An arc-radial mechanism is adopted to achieve high rotary/radial motion linearity. Kinematic model of this assembly is derived via vector loop equations. A nonlinearity index is formulated and practical kinematic constraints are imposed. Results show that very high kinematic linearity could be achieved by this new device     

Intelligent sensors using computationally efficient Chebyshev neural networks

Intelligent signal processing techniques are required for auto-calibration of sensors, and to take care of nonlinearity compensation and mitigation of the undesirable effects of environmental parameters on sensor output. This is required for accurate and reliable readout of the measurand, especially when the sensor is operating in harsh operating conditions. A novel computationally efficient Chebyshev neural network (CNN) model that effectively compensates for such non-idealities, linearises and calibrates automatically is proposed. By taking an example of a capacitive pressure sensor, through extensive simulation studies it is shown that performance of the CNN-based sensor model is similar to that of a multilayer perceptron-based model, but the former has much lower computational requirement. The CNN model is capable of producing pressure readout with a full-scale error of only plusmn1.0% over a wide operating range of -50 to 200degC.     

Modeling of the front end of a new capacitive finger-typeangular-position sensor

A robust capacitive finger-type angular-position and angular-speed sensor for automotive and metrology applications is presented. The advantages of the capacitive sensor principle are simplicity, high response speed and resolution (±0.04°), compact sensor outlines, and insensitivity to dirt and condensation. Additionally the presented finger-type geometry allows easy mounting and replacement. The paper describes the working principle, the design and the layout of a prototype sensor. It models the front-end topology and derives the transfer function of the input circuit. The required relationships for computing the angular rotor position are presented, and measurement results obtained from a prototype sensor are discussed     

A switched-capacitor interface for capacitive pressure sensors

A switched-capacitor interface for a capacitive pressure sensor is developed which provides a linear digital output. It consists basically of a sample/hold circuit followed by a charge-balancing analog-to-digital converter. The sensor capacitance changes hyperbolically with an applied pressure. To convert the nonlinear capacitance change into the linear digital output, two linearization methods are investigated. In either method, a linear digital output with an accuracy higher than 8-b is obtained. Because of its high-accuracy capability and compatible fabrication process, the interface described is best suited for a smart silicon capacitive pressure sensor     

A solid-state relative humidity measurement system

The implementation of a solid-state capacitive relative humidity (RH) sensing system which employs a polymer as the moisture-sensitive material is discussed. The sensing mechanism is based on the fact that the dielectric permittivity of the insulating polymer, polyimide (PI), is linearly related to the ambient relative humidity. Therefore, the capacitance of a parallel-plate device using PI as the dielectric is a linear function of ambient RH (because PI does not swell during moisture absorption). Standard IC processing techniques are used to fabricate the PI-based integrated sensor capacitor. In order for such as sensor to be useful in the field, a voltage, current, or frequency output is desirable. A discrete capacitance-to-voltage converter circuit using this sensor capacitor has been constructed. The performance of this system is reported     

Fringing Field Capacitance Sensor for Measuring the Moisture Content of Agricultural Commodities

A fringing field capacitive sensor is described for measuring the moisture content (MC) and temperature of agricultural commodities. Sensor performance was characterized by mounting the device on handheld probes and in acrylic canisters to determine the dielectric constant and MC of wheat and corn. The handheld probes demonstrated a promising capability to measure the MC of grain in hoppers, truck beds, and cargo holds. It is proposed that the sensors be supported on cables in grain silos and storage bins to acquire in situ data for grain storage management and control of aeration systems. The sensor is watertight and constructed with corrosion resistant materials which allow MC measurements to be made of industrial materials, chemicals, and fuels.     

Measurement of the moisture content of fiber in a layer of variable thickness

Conclusions The experiment showed that the joint use of two fundamentally different methods (in this case radioactive and capacitive) allows contactless measurement of the moisture content of wool and staple fiber in a layer of variable thickness; the root-mean-square error of measuring the moisture content of the fiber upon a change of the bulk thickness of the layer from 0.1 to 0.6 g/cm². was ±1%. The accuracy can be greatly improved by measuring the capacitance of the transducer at higher frequencies, 1.5–10 MHz. By using a comparatively simple computer the method permits automating the operation of the drier and obtaining information not only on the moisture content but also on the dry weight of the specimen. We can assume that (9) is applicable both for determining the moisture content of capillary-porous colloid materials in a layer of variable thickness (cloth, paper, cardboard, leather, food products) and for other cases where capacitive methods of measuring moisture content are used, but a change of the bulk thickness of the layer being monitored introduces substantial errors.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 78–79, September, 1970.