基于跨导放大器的晶振频率及阻抗测量系统的设计与实现

基于国内普遍采用的晶体谐振器参数测量方法--阻抗计法的原理,针对跨导放大器的特点以及晶体参数测量的要求,设计了一套基于跨导放大器的新型晶振参数测量系统,同时分析了系统的组成和振荡原理等问题.该系统根据跨导放大器电压转换电流的特性和偏置电流端特性,去除了原阻抗计法中峰值检测电路,简化了电路.实验结果表明,不仅简化了电路,...     

高性能交流恒流电路模拟与实测

采用信号发生器、集成运算放大器及仪表放大器等多个模块设计高性能交流恒流源电路,用于工业在线电极电导仪对溶液电导率的准确测量。采用4个挡位电阻控制电流输出,提供40μA~40m A的输出电流。分析负载电阻与挡位电阻和测量电压的关系,为电导率仪的进一步设计提供了高效的电路基础。模拟与实例测试结果表明:该恒流电路有较好的恒流输出稳定性,精度高、数字调整功能可靠。     

RD1460型SO2分析仪的使用与维修

介绍RD1460型SO2分析仪的测量原理、传感器结构、温控电路、测量电路及标定程序.重点论述在硫酸装置实际使用过程中遇到的典型故障的分析和处理,强调恒定的气体流量、桥路电流、桥路温度是确保分析仪正常工作的三大重要因素.     

RDl460型SO2分析仪的使用与维修

介绍RDl460型S02分析仪的测量原理、传感器结构、温控电路、测量电路及标定程序。重点论述在硫酸装置实际使用过程中遇到的典型故障的分析和处理，强调恒定的气体流量、桥路电流、桥路温度是确保分析仪正常工作的三大重要因素。     

应用嵌入式技术开发智能检测配电终端

基于准同步采样技术,研究0.4k V低压配电系统三相电压、三相电流等电气参数的采样方法,结合DSP计算引擎提供的DFT算法,实现高精度电流、电压、频率、有功功率、无功功率、总谐波畸变率及2~31分次谐波含量等的测量和计算。基于电子设计自动化技术实现装置电流参数信号采样电路、电源电路、LCD显示电路的设计开发,实现底层硬件平台的单元测试、系统测试和安装运行。     

微安培检测器的研制

安培检测器的设计中,电化学池通电后产生的微电流信号极其微弱,往往淹没在噪声中很难采集识别.根据安培检测和恒电位器原理,利用数据放大器采集放大微弱信号,研制了一种新型微安培检测器.微安培检测器电路性能稳定,实验测试的结果与理论值符合很好,其中微电流测试电路不仅可应用于微安培检测器中,还可配上不同的传感器用于其它测量微弱电流信号的场合.     

电流分布对圆柱件酸性镀铜层厚度的影响

通过生产对比试验研究了电流分布对圆柱件酸性镀铜层的影响，结果表明，生产实践中象形阳极，电路屏这两种措施的使用效果存在相互关系，只有联合使用，同时阴极以一定转速卧式电镀，才能最大限度消除因电流分布对镀层造成的不良影响。     

低频电流下人体阻抗特性的研究

目的探讨在低频电流(f<1000Hz)下人体阻抗的的特性。方法采用串联电路法测量94名男性和122名女性在不同频率电流下的人体手臂阻抗的大小。结果随着电流频率的增加,人体阻抗呈现下降的趋势;同等频率下,人体阻抗男性略大于女性。结论人体阻抗具有容抗的特点;皮肤阻抗远大于皮肤下其他组织阻抗。     

用电流互感器测直流电流的探讨

对整流设备输出直流电流的测量,过去采用直流电流互感器,它的一次传感器用磁饱和原理构成,铁芯较笨重。二次仪表常用盘装式磁电型电流表。直流互感器有明显的缺点,如不易进行现场校验,易受周围磁场干扰,易损坏,尤其因磁路特性以及相关联的电路特性难以保证整个测量范围的线性度,使测量的准确度受到影响,特别是低读数区的误差比较大。     

硅压阻式轮胎气压传感器电路设计

分析硅压阻式压力传感器工作原理并比较电流源和电压源供电方式下温度变化时的测量效果,指出电流源供电电路所测结果不受温度变化的影响,可保证检测结果的真实性。硅压阻式压力传感器前置放大电路采用同相并联差动放大及级联对称全耗尽CMOS运放,具有较高增益和共模抑制比、低功耗及可在高温环境下稳定工作的特点。采用硅压阻式压力传感器可以满足轮胎气压检测的要求。     

Local mass transport effects in the FM01 laboratory electrolyser

A number of patterns of segmented line electrodes have been manufactured using copper printed circuit board technology. These segmented electrodes have been used to investigate local mass transport effects in ICI's FM01-LC parallel plate electrolyser. It is shown that in the absence of a turbulence promoter the current distribution is uneven. Along the direction of electrolyte flow, a tertiary current distribution is observed. In addition, close to the cell entrance, an uneven current distribution occurs perpendicular to the direction of electrolyte flow; this reflects the design of the electrolyte distributor. With a turbulence promoter the current distribution is more even and the entry effects are much reduced. The turbulence promoter can, however, impose its own pattern on the current distribution perpendicular to the flow.     

Experimental study on the effect of reactant flow arrangements on the current distribution in proton exchange membrane fuel cells

Current distribution in a proton exchange membrane fuel cell (PEMFC) is significantly influenced by reactant flow configurations. In this study, the current distribution has been measured experimentally using a segmented flow-field plate and printed circuit board (PCB). Local current distributions for a PEMFC with serpentine flow field and three different flow arrangements including co-flow, cross-flow, and counter-flow arrangements for the anode and cathode streams are investigated along with the effect of flow channel orientation. It is shown that the counter-flow arrangement yields most uniform distribution for the current density, whereas the co-flow arrangement results in a considerable variation in the current density from the reactant gas stream inlet to exit. Flow channel orientation can also impact the cell performance and the current distribution appreciably. The limiting hydrogen concentration at the anode side due to the low stoichiometry condition can have a predominant effect on the current distribution and cell performance.     

基于FPGA与AD7985的脉冲电源数据采集设计

为了满足精密电镀的控制需求,设计了一种基于FPGA和AD7985的高速高精度的数据采集系统,该数据采集系统可应用于高精度的脉冲电镀电源中,用于采集输出脉冲的电流和电压参数并用于电流调控.首先设计分析了采集系统的主要硬件电路,包括隔离放大电路、电压跟随电路和AD转换电路;然后对AD7985的控制时序进行了研究,给出了控制...     

基于单片机的按摩机传动数字控制电路设计

对基于单片机的按摩机传动控制电路进行设计。以单片机为核心控制芯片．以直流电机PWM调速技术为基础设计电源电路、复位电路、电机和指示灯控制电路、按键及显示电路等部分,利用软件编程实现人机交互及按摩功能。按键操作选择按摩机工作状态,报警装置示警或提示按摩完成,指示灯显示当前工作状态,LED数码管显示当前电机转速。经过理论分析及实验研究,该系统能够实现基本的按摩功能,结构简单、性价比高、体积小,可较好地满足人体腰部、足部以及颈部的按摩需要。     

Using electrochemical impedance spectroscopy to compensate for errors when measuring polarisation curves during three-electrode measurements of solid oxide fuel cell electrodes

The use of three-electrode techniques involving an independent reference electrode is invaluable in determining the overpotential losses at solid oxide fuel cell (SOFC) electrodes. However, there are numerous barriers to achieve the accurate measurement of such overpotentials in an SOFC. Furthermore electrochemical impedance spectroscopy (EIS) is commonly used to analyse the processes occurring on SOFC electrodes, and there has been considerable work in establishing viable three-electrode techniques for EIS experiments under open circuit conditions. However, the three-electrode techniques currently developed for EIS experiments are not well suited for conditions of high load, or changing gas compositions; either intentionally or under diffusion limiting conditions. This paper reports a solution for commonly used pellet cells, which mitigates these problems. The paper presents a method using EIS to correct for errors when measuring the working electrode overpotential during polarisation arising from a shift in the electrolyte current distribution from the primary to the secondary current distribution under load. This technique enables meaningful overpotentials to be calculated using experimentally simple cell geometries under conditions where they cannot normally be accurately measured.     

A printed circuit board approach to measuring current distribution in a fuel cell

A new method of measuring current distribution in a polymer electrolyte fuel cell of active area 100cm2 has been demonstrated, using a printed circuit board (PCB) technology to segment the current collector and flow field. The PCB technique was demonstrated to be an effective approach to fabricating a segmented electrode and provide a useful tool for analysing cell performance at different reactant gas flow rates and humidification strategies. In this initial chapter of work with the segmented cell, we describe measured effects on current distribution of cathode and anode gas stream humidification levels in a hydrogen/air cell, utilizing a NafionTM 117 membrane and single serpentine channel flow fields, and operating at relatively high gas flow rates. Effects of the stoichiometric flow of air are also shown. A clear trend is seen, apparently typical for a thick ionomeric membrane, of lowering in membrane resistance down the flow channel, bringing about the highest local current density near the air outlet. This trend is reversed at low stoichiometric flows of air. At an air flow rate less than three times stoichiometry, the local performance starts to drop significantly from inlet to outlet, as local oxygen concentration drop overshadows the lowering in resistance along the direction of flow.     

高职院校开设集成电路相关专业的可行性研究

集成电路是科技、知识密集型产业,是各国科学技术竞争的必争领域。从我国集成电路产业面临的困境和国家推动政策入手,分析我国集成电路产业分类、产业现状和产业人才需求情况,通过调研我国本科和高职院校集成电路产业人才培养现状,提出我国高职院校的集成电路相关专业建设建议,供高职院校参考,从而为我国集成电路产业发展做出贡献。     

一种可关断晶闸管(GTO)直接门极驱动电路的研究

可关断晶闸管(GTO)要求其驱动电路提供的驱动电流的前沿应有足够的幅值和陡度,且一般需要在整个导通期间施加正门极电流,关断需施加负门极电流,幅值和陡度要求更高.主要结合GTO门极驱动的要求,提出一种新型的直接门极驱动电路,这种新型门极驱动电路结构简单,电感值低,因此可以为GTO提供快速的门极脉冲.每个GTO门板驱动完全独立,一定数量的GTO就可以串联使用来适应高压需要.     

Optimization of cathode catalyst layer for direct methanol fuel cells: Part I. Experimental investigation

The cathode catalyst layer (CL) in direct methanol fuel cells (DMFCs) has been optimized through a balance of ionomer and porosity distributions, both playing important roles in affecting proton conduction and oxygen transport through a thick CL of DMFC. The effects of fabrication procedure, ionomer content, and Pt distribution on the microstructure and performance of a cathode CL under low air flowrate are investigated. Electrochemical methods, including electrochemical impedance, cyclic votammetry and polarization curves, are used in conjunction with surface morphology characterization to correlate electrochemical characteristics with CL microstructure. CLs in the form of catalyst-coated membrane (CCM) have higher cell open circuit voltages (OCVs) and higher limiting current density; while catalyzed-diffusion-media (CDM) CLs display better performance in the moderate current density region. The CL with a composite structure, consisting both CCM and CDM, shows better performance in both kinetic and mass-transport limitation region, due to a suitable ionomer distribution across the CL. This composite cathode is further evaluated in a full DMFC and the cathode performance loss due to methanol crossover is discussed.     

整流设备动态均流技术

叙述了影响晶闸管均流的因素,包括元件通态特性、元件开通特性、母排连接方式等。分析了动态均流的主要电路构成,指出实现动态均流的基本原理是立足于控制回路,通过自动调节实现同相桥臂元件通态平均电流趋于相同。通过对桥臂电流波形的分析,论证了动态均流方法的有效性。采用此方法在较宽的电流范围内能保证均流系数大于95%。