Compensation of Angular Errors Using Decision Feedback Equalizer Approach

Speed and position measurements of rotating shafts are very important in the field of mechanical engineering. In automotive applications, magnetic field sensors for such measurements (camshaft, crankshaft, anti-lock braking system, windshield wiper, etc.) have the largest market share of all sensor types. Camshaft applications are challenging due to their requirements on high angular accuracy under harsh environmental conditions. Due to mounting and packaging tolerances, the magnetic field at the sensors position varies, resulting in angular measurement errors for sensor concepts in use today. Mounting and packaging tolerances cannot be avoided; however, they can be compensated by a new filter structure which is described in this paper. The decision feedback equalizer (DFE)—known from digital communication—was analyzed and modified for the use in angular measurement applications. A new filter structure, using data prediction and an adaptive algorithm based on a physical model, is proposed. This filter calculates and compensates angular errors caused by mounting and packaging tolerances.      

Real-time position and attitude sensing using CCD cameras inmagnetic suspension system applications

A position measurement system using CCD cameras is designed for large-gap magnetic suspension applications. White dots are placed on a magnetically suspended model, which is then scanned by CCD cameras against a black background. A real-time hardware system is applied to detect the coordinates of these white dots and generate corresponding attitude data for the suspended model by the lookup-table method. Circuit hardware is designed and implemented with efficient algorithms to accomplish the objective. The purpose of the real-time measurement system is to detect the position and attitude of the magnetically suspended model and to feed this information to the control circuit. System analysis and test results are presented     

磁浮列车磁场测量系统中运动控制平台的设计

磁浮列车气隙磁场的测量可以为列车电磁系统的设计和控制提供重要依据．本文对气隙测量系统中磁传感器运动控制平台的设计进行了详细介绍,阐述了运动控制平台的工作原理和光栅尺信号的处理方法．采用双计数器鉴相法消除了光栅尺抖动的影响,提高了传感器的定位精度．同时采用电流矢量恒幅旋转的细分方法实现了步进电机恒转矩均匀细分控制,提高了步进电机的分辨率和运行稳定性．所设计的运动控制平台的定位精度可以达到1μm．     

Focal plane detector for the Oxford MDM-2 spectrometer

A “hybrid” focal plane counter comprising a gridded ionization chamber with position sensitive proportional counters, 300 mm long, 510 mm deep and with an active height of 60 mm, is described. The detector is designed for use with the Oxford MDM-2 magnetic spectrometer and is suitable for both light and heavy ions. Typical results obtained are 0.6 mm position resolution and 1% total energy resolution. Two energy loss, a veto and two position signals are available as well as provision for height and timing signals. Techniques are described for the reduction of capacitive noise, correction of electric field nonuniformities, and the reduction of interference from positive ions on the ionization signals.     

Integrated optics magnetic sensor from 2 kHz to 9 GHz

A new type of integrated optical magnetic field sensor is presented in this paper. The proposed sensor consists of a Mach-Zehnder waveguide interferometer and a doubly loaded loop antenna. Such a structure can successfully avoid detection of the undesired electric field signal. The size of the sensor is 35 mm×6 mm×1 mm. The measurements show that the frequency response is from 2 kHz to 9 GHz, the dynamic range is 98 dB, and the minimum detectable magnetic field is 51.8 μA/m at 1 GHz. Therefore, this sensing system can be used in electromagnetic compatibility measurements.     

Measurement of the transition temperature distribution and magneticfield profile of large superconducting films

A novel apparatus has been developed to measure the transition temperature (T_c) distribution and magnetic field profile of large superconducting films. Two techniques were used. The first one is an ac inductive method which provides a contactless measurement of T_c. The second technique employs a Hall device to measure magnetic field. Driven by two step motors, the measuring probe, either a two-coaxial-winding coil or a Hall sensor, can move over the sample on a polar plane. As the probe scans the sample step by step, various points on the sample are measured one by one. Experiments were carried out on a 30 mm diameter YBa₂Cu₃O_7-δ thin-film. The T_c distribution and the surface profile of trapped magnetic field were obtained     

A single-layer flat-coil-oscillator (SFCO)-based super-broadband position sensor for nano-scale-resolution seismometry

A new class super-broadband, nano-scale-resolution position sensor is tested. It is used as an additional sensor in seismograph. It enables to extend the band and enhance the sensitivity of the available technique by at least an order of magnitude. It allows transferring of mechanical vibrations of constructions and buildings, with amplitudes over 1 nm, into detectable signal in a frequency range starting practically from quasi-static movements. It is based on detection of position changes of a vibrating normal-metallic plate placed near the flat coil—being used as a pick-up in a stable tunnel diode oscillator. Frequency of the oscillator is used as a detecting parameter, and the measuring effect is determined by a distortion of the MHz-range testing field configuration near a coil by a vibrating plate, leading to magnetic inductance changes of the coil, with a resolution 10 pH. This results in changes of oscillator frequency. We discuss test data of such a position sensor, installed in a Russian SM-3 seismometer, as an additional pick-up component, showing its advantages compared to traditional techniques. We also discuss the future of such a novel sensor involving substitution of a metallic coil by a superconductive one and replacement of a tunnel diode by an S/I/S hetero-structure-as much less-powered active element in the oscillator, compared to tunnel diode. These may strongly improve the stability of oscillators, and therefore enhance the resolution of seismic techniques.     

混合型主动悬架电磁反力作动器的匹配研究

针对由电磁反力作动器与被动悬架构成的混合型主动悬架系统,建立了1/4车辆模型,在Matlab环境下计算动力吸振器分别安装在悬挂质量和非悬挂质量时的车身响应特性,以分析作动器参数及不同安装位置对平顺性的影响。结果表明:电磁反力作动器布置在非悬挂质量环节比较有利。对作用在非悬挂质量环节的作动器,以吸振器状态进行了参数优化,并就混合型悬架与被动悬架的车身幅频特性进行了比较,分析混合型主动悬架作动器与轮胎之间的力传递特性,指出用车辆不同路面下被动悬架的轮胎最大动载荷,作为选择作动器控制能力的参考依据。     

Noncontact Laser Inspection Based on a PSD for the Inner Surface of Minidiameter Pipes

A new noncontact laser-inspection technique based on a position-sensitive detector (PSD) to inspect the inner surface of minidiameter pipes is proposed, and the corresponding sensor is developed. A light spot is projected onto the pipe inner wall after the laser beam is reflected by two mirrors. At the same time, four current signals are produced when the light spot is read by the 2-D PSD. According to the magnitude of the current signals and the structure parameters of the sensor, the spot position on the inner wall can be calculated in a local 3-D coordinate system. With a micromotor, the surface of the whole inner wall can be scanned by the laser beam. This way, the coordinates of all the sample points in the section are obtained. After that, several reasonable data-processing methods are used, such as data segmentation and least squares fitting. Finally, the section curve can be reconstructed. The radius and defects of the section can also be obtained. Driven by a micropipe robot, the sensor can inspect a long curved pipe. The inspection system based on this technique can detect the inner surface of minidiameter pipes, which has an inner diameter of 9.5–10.5 mm and a curvature radius of more than 100 mm. The measurement accuracy of this inspection system for the inner diameter and surface defect reaches $pm$0.1 mm.      

High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing

Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large angular measurement range and allows the use of a probe that is small in comparison with the measurement volume. We review PSD characteristics and quantitative resolution limits, consider the lock-in amplifier measurement system as a communication link, discuss the application of FDM to PSDs, and make comparisons with time-domain techniques. We consider the phase-sensitive detector as a multirate DSP problem, explore parallels with Fourier spectral estimation and filter banks, discuss how to choose the modulation frequencies and sample rates that maximize channel isolation under design constraints, and describe efficient digital implementation. We also discuss hardware design considerations, sensor calibration, probe construction and calibration, and 3-D measurement by triangulation using two sensors. As an example, we characterize the resolution, speed, and accuracy of an instrument that measures the position and orientation of a 10 mm $times$ 5 mm probe in 5 degrees of freedom (DOF) over a 30-mm cube with 4-$mu hbox{m}$ peak-to-peak resolution at 1-kHz sampling.      

Calculation of Skin Depths and Eddy-Current Power Losses for Magnetic Position Sensors

1. IntroductionIn a quasi-stationary magnetic field, eddy-currelltfrom an alternating-current excitation induces secondary currents and fields between magnetic material and position sensor. The skin depths and eddycurreat losses are also induced in a conductor whenan alternating external magnetic field is applied tothe conductor[1]. For a magnetic position sensort ifthe position of the moving sensor is given, the waveform of the output voltage induced by eddy-currentcan be used as an index to …     

Advances of Barkhausen Emission Measurement

Barkhausen emission (BE) is a well-known phenomenon used in nondestructive testing techniques of ferromagnetic materials. The weaknesses of methods based on BE are related to the difficulties of ensuring measurement reproducibility because of the influence of the specimen on the measurement channel. In this paper, we propose a method of sensor calibration prior to measurement. To implement the calibration, a BE sensor is equipped with an additional calibration coil. The electrical pulse induced in the calibration coil is then used to reconstruct measured magnetic field pulses at the specimen surface.     

A novel sensor for monitoring acoustic cavitation. Part I: Concept, theory, and prototype development

This paper describes a new concept for an ultrasonic cavitation sensor designed specifically for monitoring acoustic emissions generated by small microbubbles when driven by an applied acoustic field. Its novel features include a hollow, open-ended, cylindrical shape, with the sensor being a right circular cylinder of height 32 mm and external diameter 38 mm. The internal diameter of the sensor is 30 mm; its inner surface is fabricated from a 110 /spl mu/m layer of piezoelectrically active film whose measurement bandwidth is sufficient to enable acoustic emissions up to and beyond 10 MHz to be monitored. When in use, the sensor is immersed within the liquid test medium and high frequency (megahertz) acoustic emissions occurring within the hollow body of the sensor are monitored. In order to shield the sensor response from events occurring outside the cylinder, the outer surface of the sensor cylinder is encapsulated within a special 4 mm thick polyurethane-based cavitation shield with acoustic properties specifically developed to be minimally perturbing to the 40 kHz applied acoustic field but attenuating to ultrasound generated at megahertz frequencies (plane-wave transmission loss >30 dB at 1 MHz). This paper introduces the rationale behind the new sensor, describing details of its construction and the materials formulation program undertaken to develop the cavitation shield.     

用于心磁传感器测试系统的三轴向亥姆赫兹线圈的设计与仿真

心磁检测对于心脏相关疾病的诊断具有独特优势，在用于测量心脏磁场的传感器(下称心磁传感器）的研制过程中，需要在模拟心磁的磁场环境下进行测试工作。基于此，设计了一个用于心磁传感器测试系统的亥姆赫兹线圈，它可以产生磁感应强度为pT级的动态磁场，模拟心磁环境，以满足心磁传感器测试的需求。根据亥姆赫兹线圈的磁场产生原理，使用磁屏蔽筒对环境磁场进行屏蔽，通过计算确定了线圈尺寸、线圈匝数、导线长度及导线横截面直径等参数。使用COMSOL Multiphysics仿真软件对亥姆赫兹线圈产生的静态磁场的分布均匀性以及通入线圈电流变化时磁场的动态特性进行仿真分析。仿真结果表明，所设计的亥姆赫兹线圈满足设计要求，能够产生磁场强度为100 pT左右、均匀度小于5%、波形实时性好的类心脏磁场波形，为心磁传感器的测试提供了良好的测试环境。所设计的亥姆赫兹线圈能够用于心磁传感器的测试工作，为心磁传感器的实际应用奠定了基础。     

Investigation of cryogenic level sensors for LN2 and LOX

Investigations of two different types of cryogenic level sensors (capacitance and High Temperature Superconductor (HTS) for level measurement of liquid nitrogen (LN₂) and liquid oxygen (LOX) are presented here. They were tested for an active length of 400 mm in LOX and LN₂. A discrete diode array level sensor was used as a primary standard for calibrating these sensors. Comparative studies on linearity, sensitivity and other parameters at the operating temperatures are presented.     

Fabrication of grouped magnetic heads

A new magnetic transducer has been developed for use in the measurement of mechanical displacement. Experiments suggest that the transducer could be used for various purposes: for instance, readout information from magnetic drums or disks of computers, nondestructive readout from thin-film memories, magnetic pattern recognition, and an unconventional flux sensor. The transducer is composed of flux-sensitive magnetic heads which are fabricated from a sheet of ferromagnetic thin film by photoetching process. By using the etching process, a large number of heads are produced simultaneously, and the heads are operated in a group. The characteristics, performances, and an application of grouped magnetic heads are described in this paper.     

Micromachined optical fiber current sensor

We describe a micromachined optical fiber current sensor. The sensing element consists of a squared silicon membrane (8 mm long and 20 mum thick) that has a cylindrical permanent magnet (NdFeB alloy, 3-mm diameter, 1.5 mm high) fixed on its central region. This structure allows the permanent magnet to vibrate in the presence of the magnetic field gradient generated by an ac. A linear relation between the electrical current and the magnet displacement was measured with white-light interferometry with an optical fiber low-finesse Fabry-Perot microcavity. A measurement range of 0-70 A and a minimum detectable intensity of 20 mA were obtained when distance D between the membrane and the electrical power line was 5 mm. The output signal directly shows a linear response with distance D.     

A high performance, variable capacitance accelerometer

A variable capacitance acceleration sensor is described. Manufactured using silicon microfabrication techniques, the sensor uses a midplane, flat plate suspension, gas damping, and overrange stops. The sensor is assembled from three silicon wafers, using anodic bonds to inlays of borosilicate glass. Typical sensor properties are 7-pF active capacitance, 3-pF tare capacitance, a response of 0.05 pF/G, a resonance frequency of 3.4 kHz, and damping 0.7 critical. It is concluded that this sensor, with appropriate electronics, forms an accelerometer with an order-of-magnitude greater sensitivity-bandwidth product than a comparable piezoresistive accelerometer, and with extraordinary shock resistance     

Laser Doppler field sensor for high resolution flow velocity imaging without camera

In this paper we present a laser sensor for highly spatially resolved flow imaging without using a camera. The sensor is an extension of the principle of laser Doppler anemometry (LDA). Instead of a parallel fringe system, diverging and converging fringes are employed. This method facilitates the determination of the tracer particle position within the measurement volume and leads to an increased spatial and velocity resolution compared to conventional LDA. Using a total number of four fringe systems the flow is resolved in two spatial dimensions and the orthogonal velocity component. Since no camera is used, the resolution of the sensor is not influenced by pixel size effects. A spatial resolution of 4 microm in the x direction and 16 microm in the y direction and a relative velocity resolution of 1x10(-3) have been demonstrated up to now. As a first application we present the velocity measurement of an injection nozzle flow. The sensor is also highly suitable for applications in nano- and microfluidics, e.g., for the measurement of flow rates.     

Single-crystal magneto-optic sensor with electrically adjustable sensitivity

A novel magneto-optic sensor with electrically adjustable sensitivity is proposed that is based on the approximate multiplication correlation between the linear electro-optic phase retardation and the Faraday magneto-optic rotation angle in a single bismuth germanate crystal. The measurement sensitivity and its temperature stability, linear and monotonic measurement ranges of the proposed sensor can be controlled in real time by adjusting the modulating voltage applied to the sensing crystal. In particular, the proposed sensor can be used for the precise measurement of dc magnetic field or dc current. The basic sensing performance is theoretically analyzed and experimentally demonstrated by dc current measurement.