7 1／2位A／D转换器的研制

为满足高精度电压测量的要求，研制了电荷平衡与单斜相结合的多斜式模数转换器。分析了复合运放提高性能的原理，利用两运算放大器设计了高性能复合放大器，以构成理想的积分电路。在对输入电压积分的同时，不断释放标准单位电荷量，以形成模数转换器的电荷平衡过程，并通过计数取得高位读数。断开输入后，连续释放剩余电荷以形成单斜过程，并取得低位读数。通过高低位读数的合成及采用合理的校正措施，模数转换器的分辨率达到七位半以上。     

基于电荷平衡原理的微弱电流测量研究北大核心CSCD

针对电离室输出宽量程双极性微弱电流的测量需求,在积分电路的基础上,研究了基于电荷平衡原理的多斜积分电路测量系统。在对输入电流的积分过程中,通过切换正负参考电源实现对电容的充电或放电,电容充电和放电所占的周期数形成测量系统的高位读数。利用一个测量周期开始和结束时电容电压的差值,形成测量系统的低位读数。通过标准电流源进行测试,该测量系统能够实现±24.5 nA的双极性微弱电流测量,满量程的最大线性误差为0.014 3%。重复测试100 pA输入电流,得到标准差分为0.088 97。实验结果表明:测量系统的线性度和重复性很好、精度高、量程广,能满足实际测量的需求并且应用领域广泛。     

美国模拟器件公司仪表专用电路简介

美国模拟器件公司创建于1965年,当时正是集成电路蓬勃发展的时期。为了竞争国内外市场,他们以模数和模数转换器为核心发展了一系列模拟器件。该公司的主要成就是把工业信号输送到计算机这一系列的接口电路集成化、标准化和系列化,让工业现场到计算机形成了通道。从1970年到1980年间,经过了十年的发展,它从一个美国的小公司发展成为一个世界性的大公司。产品从混合电路的模数和模数转换器扩大到十八个大的类别,营业额增至一亿美元。下面就这几类产品进行介绍。一、放大器1.运算放大器它共有25种,其中高精度低漂移运算放大器(简称运放,下同)6种;场效应输入级的高阻抗运放6种;高速电路6种;斩波稳零运放两种;通用型两种,高输出电压(高达士140伏)放大器一     

数字式贝克曼温度计的研制

介绍了以高精度高集成性的放大器TLV2322、高精度的多路模数转换器TLC2543为核心，以8031为CPU的数字式贝克曼温度计功能样机的硬件和软件设计方案，它比起玻璃式贝克曼温度计有诸多优点，克服了玻璃式贝克曼温度计操作复杂、读数误差大的主要缺点。     

通用型高增益运算放大器的试制

一、电路的特点和简单工作原理仿μA741是一种通用型高增益运算放大器,与一般运算放大器比较,这种放大器具有增益高、输入阻抗高、补偿简单(只需外接一只30Pf电容)、共模电压范围大和输出幅度大等特点,所以使用方便、可靠。它可用于各种运算电路、电压比较器、直流放大器、电压电流变换器、伺服控制放大器、模数转换器、锁相环直流放大器及各种有源滤波器等,因此使用方便,用途较广。目前在Ⅲ型电动单元组合仪表上已推广使用。此电路基本上可分为四个组成部分,即差分输入级、中间放大级、输出级,以及供给各级偏置电流的偏置电路。输入级由T_1T_3和T_2T_4组成差分对,T_1和T_2是NPN型组成的射极输出器,T_3和T_4是     

数字式贝克曼温度计功能样机的研制

本文介绍了以高精度高集成性的放大器TLV2322、高精度的多路模数转换器TLC2543为核心,以8031为CPU的数字式贝克曼温度计功能样机的硬件和软件设计方案,该样机比起玻璃式贝克曼温度计有诸多优点,克服了玻璃式贝克曼温度计操作复杂、读数误差大的主要缺点。     

高频反馈控制电路的分析与探讨

在现代通信系统和电子设备中,为提高其技术性能指标,或符合特定要求,广泛采用了反馈控制电路。而负反馈放大器为其典型实例。放大器的输出信号通过负反馈网络反馈到其输入端,与输入信号相减,当输出电压增大,则反馈电压也增大,反馈信号与输入信号相减后,使实际输入信号减小,从而减小了放大器的输出电压,使输出电压幅度保持不变,提高了电路的稳定性。     

压电式微固体模态谐振器电荷放大器负载效应的研究

文中采用串联电阻的方法,解决了传统的阻抗分析仪很难满足共振激励需求的问题,研究一种具有特殊电压激励方式的压电式微固体模态谐振器等效电路。通过绘制压电谐振器的导纳圆图,分析并获得压电谐振器在共振频率附近的等效电路参数。通过比较有无电荷放大器作为负载接入压电谐振器的实验结果,发现带有电荷放大器的压电谐振器等效电路的谐振频率从346.119 k Hz降低至344.979 k Hz。得出结论:如果电荷放大器作用于压电谐振器负载端,应该关注它对谐振频率的影响。     

杂散电容对交流法微电容测量电路噪声特性影响的分析

对电容成像交流法微电容测量电路由杂散电容导致的测量噪声进行了研究.利用运算放大器的噪声模型,对运算放大器输入电压噪声、输人电流噪声以及周边电阻元件的热噪声通过杂散电容作用于交流法微电容测量电路输出的影响进行了理论分析,给出了测量电路输出中噪声峰峰值的理论计算公式并进行了实验验证.理论分析及实验结果表明:交流法微电容测量电路前级运算放大器输入电压噪声通过测量端与地之间的杂散电容形成的噪声是该微电容测量电路输出噪声的主要来源.最后给出了电容成像系统前级运算放大器选型的指导原则.     

新型的高性能交流稳压电源

在电源的输入与负载之间串连一只阻抗器,通过接入反馈控制网络自动调整阻抗器的电阻值,来稳定输出电压,就形成了串连稳压器,形成这只阻抗器的电路由场效应管,运算放大器,晶体管和整流桥组成,这只阻抗器的等效电阻是纯电阻,所以在调电压的过程中不会产生谐波,也就是不会产生正弦波失真,反馈控制网络有极稳定的基准电压,比较是增益很高的运算放大器,电路有非常好的转换线性,因此该装置有很高的稳压精度。     

Electron and light microscopy studies on the domain structures of Zn3B7O13Cl, Zn3B7O13Br and Zn3B7O13I ferroic boracites

The domain structures of Zn₃B₇O₁₃Cl, Zn₃B₇O₁₃Br and Zn₃B₇O₁₃I boracite single crystals were studied by means of polarized light in conjunction with electron microscopy. Single crystals of the three compositions were grown by chemical transport reactions in closed quartz ampoules, at a temperature of 900 °C and were examined by polarizing optical microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For both PLM and SEM, the same as‐grown samples were used without having to resort to metallization of the crystal faces. For TEM the single crystals were crushed and mounted on holey carbon films. Comparative electron microscope images were useful for revealing the domain structure of these ferroelectric/ferroelastic materials previously observed between the crossed polars of an optical microscope. X‐ray diffraction analysis of the pulverized crystals was performed for this triad of halogen boracites containing zinc as a common metal.     

Cylindrical specimens for KIC of rocks

Stress intensity factors for pairs of diametrically opposite radial cracks on the inside of a jacketed pressurized hole in a thick cylinder have been calculated by using finite element technique. Burst tests on thick cylinder rock samples under above conditions have been performed and the K_IC values for Antrim Shale and Limestone determined. The method is very convenient for rocks whose samples are often available in form of cylindrical bars drawn as cores from underground drilling.     

GT/CAD/CAPP/PDM/ERP系统集成研究

研究ETO生产方式下以成组技术为基础的CAD/CAPP/PDM/ERP的集成方法,包括面向CAD/CAPP/PDM/ERP的集成的成组信息编码,基于成组编码的CAD/PDM集成、CAPP/PDM集成和PDM/ERP集成.提出了基于成组技术的CAD/CAPP/PDM/ERP集成框架,研究了贯穿于CAD、CAPP、PDM与ERP系统的统一的成组编码方案和信息编码方案.     

基于太赫兹光谱的人参和西洋参鉴别

为了快速区分人参和西洋参,依据两者所含的人参皂苷在太赫兹波段具有不同指纹光谱,提出了一种基于人参皂苷的太赫兹光谱鉴别人参和西洋参的方法。采用MATLAB软件识别人参和西洋参的太赫兹光谱,同时根据太赫兹光谱特征并通过标准的主成分分析(PCA)区分出人参、西洋参。实验结果表明,基于太赫兹光谱的主成分分析可精确区分出人参、西洋参,并且还可以应用于其他类似物质的区分中。     

Analysis of the Rk surface roughness parameter proposals

European manufacturers have proposed a set of surface roughness parameters based on an examination of the variation in slope of the bearing ratio curve of a surface profile. It is shown, that the proposed procedure provides no useful information, and indeed is misleading, since the bearing ratio curve of even a normally-distributed random surface profile exhibits the expected variation in slope when plotted on rectangular coordinates. On the other hand, the desired information is readily obtained by a similar examination of the cumulative height distribution of a surface profile (the unity complement of the bearing ratio) when it is plotted on normal probability coordinates.     

永磁同步电机积分滑模观测器控制

对永磁同步电机观测器控制进行研究,针对传统滑模观测器存在控制精度低、系统抖振较大的不足,设计了一种永磁同步电机积分滑模观测器控制。积分滑模控制具有控制精度高、系统抖振小的特点。积分滑模观测器可以有效提高电机控制精度,增强控制系统抗干扰能力。采用饱和函数代替符号函数进行滑模控制律设计,降低控制系统固有抖振,使滑模控制动态性能提高。通过仿真验证了积分滑模观测器控制策略的可行性。     

Characterization of cast Al86Mn3Be11 alloy

An Al₈₆Mn₃Be₁₁ alloy cast into copper mould was subjected to metallographic investigation. The as-cast microstructure consisted of a quasicrystalline icosahedral phase (i-phase), Be₄AlMn phase and, occasionally, a hexagonal phase. Al-rich solid solution represented the dominant phase. The chemical compositions of phases were determined using AES. The composition of the Be₄AlMn slightly deviated from the stoichiometric composition, whereas the composition of the i-phase was approximately Al₅₂Mn₁₈Be₃₀, containing an appreciable amount of Be. The average composition of the hexagonal phase was Al₆₆Mn₂₁Be₁₃. Deep etching and particle extraction provided a deep insight into the three-dimensional morphology of the i-phase and the hexagonal phase, whereas Be₄AlMn was slightly attacked by the etchant. The i-phase was present predominantly in the form of dendrites and a rodlike eutectic phase. The hexagonal phase was primarily in the form of hexagonal platelets, whereas Be₄AlMn was rather irregular in shape. The morphology of the i-phase can be explained by predominant growth in 3-fold directions and the lowest energy of the 5-fold planes, leading to the faceting and adopting a pentagonal dodecahedron shape. The brightnesses of phases in the backscattered electron images were rationalized by determining their backscattering coefficients. TEM investigation showed considerable phason strain in the i-phase, and the polycrystalline nature of the Be₄AlMn phase.     

Investigation on the impact behavior of Al2O3-SiC-MgO nanoceramic/metal laminated composite

Lightweight laminated composites containing a ceramic front layer and a metallic backing layer were used in order to protect people, moving equipment, and mobile vehicles from high velocity impact and the increased mobility of mobile vehicles. In this study, by adding10 vol% SiC and 500 ppm MgO nanoscale particles on the microstructure of Al ₂ O ₃ matrix and applying optimum sintering conditions, ceramic performance against high-speed projectile impact was improved. To perform this investigation, a number of target samples with two different types of front layers (alumina and Al ₂ O ₃-SiC-MgO nanocomposite ceramic) were produced. Impact tests were conducted on these samples using 7.62 mm projectiles with a velocity of 820 ± 15 m/s. The amount of bulge and bending of the backing layer caused by impact tests was measured. The results of the impact tests on the samples made of Al ₂ O ₃-SiC-MgO nanocomposite ceramics and alumina were also compared and analyzed. The results indicate that the substitution of Al ₂ O ₃-SiC-MgO ceramic layer — which is proffered in this paper — instead of pure alumina ceramic layer, decreases the areal-density of the samples by at least 30% and improves mechanical properties by about a 60% increase in flexural strength and 100% growth of the energy distribution factor, which impressively increases impact energy absorption.     

Electron microscopy of crack/particle interactions in Al2O3/SiC nanocomposites

Crack/particle interactions in alumina/silicon carbide nanocomposites have been investigated by scanning electron microscopy and transmission electron microscopy, with cracks induced by Vickers microindentation. Intergranular cracks are frequently deflected into grains by SiC particles on grain boundaries inclined to the average direction of crack propagation. This mechanism is proposed to explain the change in the fracture mode from intergranular fracture for monolithic alumina to predominantly transgranular fracture for the nanocomposites. Neither stress-induced microcracking around SiC particles nor significant crack deflection by intragranular particles was found to occur in the nanocomposites. It is argued that an addition of nanoparticles may not be a promising approach for increasing the toughness of alumina.     

Near-field second harmonic imaging of the c/a/c/a polydomain structure of epitaxial PbZrxTi1–xO3 thin films

Near-field optical second harmonic microscopy has been applied to imaging of the c/a/c/a polydomain structure of epitaxial PbZr _x Ti_{1– x} O₃ thin films in the 0 <  x  < 0.4 range. Comparison of the near-field optical images and the results of atomic force microscopy and X-ray diffraction studies show that an optical resolution of the order of 100 nm is achieved. Symmetry properties of the near-field second harmonic signal allow us to obtain good optical contrast between the local second harmonic generation in c- and a-domains. Experimentally measured near-field second harmonic images have been compared with the results of theoretical calculations. Good agreement between theory and experiment is demonstrated.