基于LabVIEW的单臂、双臂电桥仿真实验系统开发

针对大学物理实验中的直流电桥测电阻实验,统一了单臂电桥和双臂电桥中流过检流计的电流强度计算公式.以Lab VIEW为开发工具,设计了一套集直流单臂、双臂电桥测试功能于一体的虚拟仿真实验系统,实现了单臂电桥测量中值电阻和双臂电桥测量低值电阻的全部功能.在大学物理实验教学中,将虚拟仪器用于实验教学,辅助讲解教学难点,有效地提高了教学质量;将虚拟仿真实验通过VI生成应用程序(EXE)放在校园网上,用于信息化教学,为学生预习、复习提供了自主学习空间.     

热敏电阻测温仪探讨

探讨采用伏安法及电桥法测量热敏电阻的温度特性,用非平衡电桥的原理设计热敏电阻测温仪。     

一种基于运算放大器的高灵敏度惠斯通电桥

关于如何提升惠斯通电桥灵敏度一直是惠斯通电桥研究的热门话题.运算放大器组装成为的差分放大电路在一定范围内可以线性放大输入电压.但是,使用运算放大器提高电桥灵敏度的方法并未被采用.本文采用LM358N型运算放大器来提高电桥两端电势差的测量精度,从而提升惠斯通电桥的灵敏度.我们使用Multisim软件对该方案进行仿真,结果表明如果将放大倍数调至20倍,那么实际误差将小于2%.经过对改进电桥进行实际测量,实验和理论结论符合得很好.采用此方法可以得到一个易操作、低成本、高灵敏度的惠斯通电桥.     

箱式电桥示教板

电桥是电测量中的基础电路之一,在实验课中除了有训练实验技术的意义之外,结合我们学校的专业特点,还有多方面的实际应用.例如电导仪、水分测定、电阻地温计、电阻风速计、光敏电阻比色计等等,都与电桥有关.以前这方面的教学并没有收到预想的效果.其原因之一是学生对箱式电桥的电路结构原理不易了解,在使用中缺乏信心. 我们教研组在这次教学改革中,做了一个简单的箱式电桥示教板,它的电路     

探讨热敏电阻温度计的制作及其要领

电桥测电阻实验是高校普通物理教学中的传统电学实验之一.目的是让学生验证电桥平衡原理,掌握电桥的使用方法.实验中学生要做的就是反复多次测量电阻阻值,实验内容比较简单,很快就能完成.针对这种情况,我们对此实验做了适当的改进.让学生在熟悉电桥的使用方法后,利用电桥的功能及热敏电阻的特性,制作一个简易的热敏电阻温度计.热敏电阻是一种广泛应用于温度测量、温度控制、温度补偿等方面的元件,当其温度发生微小变化时,它的阻值就要发生相应变化.通过这个小制作,不仅充实了电桥实验的内容,也可以使学生了解热敏元件的一些特性,同时也提高了学生做实验的兴趣.     

一种基于运算放大器的高灵敏度惠斯通电桥

关于如何提升惠斯通电桥灵敏度一直是惠斯通电桥研究的热门话题.运算放大器组装成为的差分放大电路在一定范围内可以线性放大输入电压.但是,使用运算放大器提高电桥灵敏度的方法并未被采用.本文采用LM358N型运算放大器来提高电桥两端电势差的测量精度,从而提升惠斯通电桥的灵敏度.我们使用Multisim软件对该方案进行仿真,结果表明如果将放大倍数调至20倍,那么实际误差将小于2%.经过对改进电桥进行实际测量,实验和理论结论符合得很好.采用此方法可以得到一个易操作、低成本、高灵敏度的惠斯通电桥.     

惠斯登电桥测量灵敏度的实验研究

探讨惠斯登电桥测量灵敏度与电桥端电压、电桥桥臂电阻值、电桥平衡监测仪表内阻以及电桥桥臂电阻比率的关系,实验结果与理论分析相符。     

直流电桥测自感系数

自感系数(簡称自感)的測定,一般采用交流电桥,作者設計了一种使用直流电源的电桥测定方法,此法簡单,而且比較直观。茲介紹如下,供参考: 测量电路如图1所示,測法如下: 一、閉合开关K,調D的位置,使电桥平衡(即使通过电流計G的电流等于零)。     

简单价廉的电桥线性化

电桥的一个臂接上电阻型传感器构成非平衡电桥,能实现非电量转化为电量.这种电路广泛应用于各种测量之中.传感器的电阻值R_1随被测量变化时,电桥的输出一般不和R_1成线性关系.由非线性输出变为线性输出,可以有多种途径,如可采用数据处理方法使其线性化;也可以利用运放电路检测电桥的输出电压,再设法用运放电路的输出电压改变三极管或其它器件的导通电阻,以控制电桥的工作电压.但此法受运放电路及外围元件的精度、稳定性的影响较大,使非线性     

影响惠斯通电桥灵敏度因素的实验验证

介绍了惠斯通电桥测电阻的原理,给出了电桥灵敏度的定义和公式。利用电桥测量了未知电阻的阻值和电桥灵敏度,用实验分析和验证了影响电桥灵敏度的因素。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.