提高数字电压表的抗干扰能力

现代生产技术中,必须测量和控制多种连续变化的物理量,如温度、压力、电压、电流等。直流数字电压表除了能直接测直流电压外,还能间接地测量多种物理量,原因是很多物理量通过各种变换器均能很容易地转换成直流电压。在许多场合下,这些物理量的测量,不仅要用数字来显示其读数,而且要求显示的读数以一定的代码方式(如目前广泛使用的8、4、2、1编码形式)作为信息输出到机外,以提供打印机打印记录读数,或者参与某个系统的控制。但是,在实际的应用中,由于存在各种各样的干扰信号,以各种方式从各个途径来影响直流数字电压表的准确测量,这种干扰在电压表带有代码信息输出时,就显得格外严重。这是由于外接的处理代码信息的各种外部设备,都很容易引进这样那样的干扰信号,这些干扰信号中以共模     

Optical emission spectroscopy study on depositionprocess of microcrystalline silicon

This paper reports that the optical emission spectroscopy (OES) is used to monitor the plasma during the deposition process of hydrogenated microcrystalline silicon films in a very high frequency plasma enhanced chemical vapour deposition system. The OES intensities (SiH\sj{*}, H微晶硅 VHF-PECVD 发射光谱学 薄膜物理学microcrystalline silicon, VHF-PECVD, optical emission spectroscopy2005-11-092005-11-092005-12-12This paper reports that the optical emission spectroscopy （OES） is used to monitor the plasma during the deposition process of hydrogenated microcrystalline silicon films in a very high frequency plasma enhanced chemical vapour deposition system. The OES intensities （Sill^＊, H^＊ and H^＊β） are investigated by varying the deposition parameters. The result shows that the discharge power, silane concentrations and substrate temperature affect the OES intensities. When the discharge power at silane concentration of 4% increases, the OES intensities increase first and then are constant, the intensities increase with the discharge power monotonously at silane concentration of 6%. The SiH^＊ intensity increases with silane concentration, while the intensities of H^＊α and H^＊β increase first and then decrease. When the substrate temperature increases, the SiH^＊ intensity decreases and the intensities of H^＊α and H^＊β are constant. The correlation between the intensity ratio of IH^＊α/ISiH^＊ and the crystalline volume fraction （Xc） of films is confirmed.     

甲醛在脯氨酸膜修饰电极上的电催化氧化

应用电化学法和光谱电化学法研究了脯氨酸膜修饰电极的制备 ,用循环伏安法探讨了该膜的电化学性质及其对甲醛的催化氧化 .该电极催化稳定性良好 ,在NaOH溶液中 ,掺杂Ni (Ⅱ )后的脯氨酸膜修饰电极对甲醛和乙醇的氧化均有一定的催化活性 ,但对甲醛的催化活性更佳     

怎样制作精美的印制板

使用电脑绘制印制板底图观已日益推广普及。但是,电子爱好者在单件及少量制作时,仍常用手工制图。本文介绍怎样将印制板制作得精美实用。1.将元器件备齐,根据电气性能要求(如哪些元器件因发热等原因要装散热器,哪些元器件需要防电磁干扰等),合理安排好位置。然后,按原理图画出元件位置排列图及走线     

基于ESPI和DIC技术的混凝土断裂特性研究及对比分析

采用电子散斑干涉(ESPI)技术和数字图像相关(DIC)技术对带预制裂缝的三点弯曲混凝土梁进行了测量,研究了普通混凝土(混凝土强度f_(cu)=33.2MPa)和高强混凝土(f_(cu)=65.1MPa)的断裂特性。结果表明:各组试件的P-δ曲线离散性较大,但P-CMOD曲线吻合度较高,在峰值荷载处,临界裂缝尖端张开位移(CTOD_c)分别为21mm和29mm;从试验裂缝张开位移(COD)曲线确定裂缝扩展长度,两种混凝土的裂缝扩展长度与韧带高度之比分别为1∶4和1∶3。分析了两组试件的荷载-裂缝扩展长度关系规律。与夹式位移计测量结果对比发现,ESPI和DIC均可替代传统测量仪器得到比较准确的测量结果,当试件变形较大(CMOD0.25mm)时,ESPI的测量误差较大,而DIC误差一直保持在0.03mm以内。分析了两种技术测量误差产生的原因,对降低实验误差提出了一些建议。     

NUMERICAL PREDICTION OF PROCESS-INDUCED RESIDUAL STRESSES IN GLASS BULB PANEL

A numerical simulation model for predicting residual stresses which arise during the solidification process of pressed glass bulb panel was developed. The solidification of a molten layer of glass between cooled parallel plates was used to model the mechanics of the buildup of residual stresses in the forming process. A thermorheologically simple thermoviscoelastic model was assumed for the material. The finite element method employed was based on the theory of shells as an assembly of flat elements. This approach calculates residual stresses layer by layer like a truly three-dimensional calculation, which is well suited for thin pressed products of complex shape. An experimental comparison was employed to verify the proposed models and methods.     

3DS MAX软件应用之模拟三维场景

计算机三维建筑动画制作,在当今的建筑行业,被越来越广泛的应用,其逼真的现场模拟,对于帮助用户直观的理解设计者的思想与建筑的最终效果,有着莫大的帮助。而其制作的关键,是先要有数字化模拟的场景。本文主要就这样的虚拟场景制作,提出些制作经验。     

Large eddy simulations of a circular orifice jet with and without a cross-sectional exit plate

The effect of a cross-sectional exit plane on the downstream mixing characteristics of a circular turbulent jet is in- vestigated using large eddy simulation （LES）. The turbulent jet is issued from an orifice-type nozzle at an exit Reynolds number of 5 ×104. Both instantaneous and statistical velocity fields of the jet are provided. Results show that the rates of the mean velocity decay and jet spread are both higher in the case with the exit plate than without it. The existence of the plate is found to increase the downstream entrainment rate by about 10% on average over the axial range of 8-30de （exit diameter）. Also, the presence of the plate enables the formation of vortex rings to occur further downstream by 0.5-1 .Ode. A physical insight into the near-field jet is provided to explain the importance of the boundary conditions in the evolution of a turbulent jet. In addition, a method of using the decay of the centreline velocity and the half-width of the jet to calculate the entrainment rate is proposed.     

有线电视HFC网络的日常维护研究

HFC网络是一种经济实用的数字接入技术,传输容量大、双向传输能力强,在我国得到了普遍应用。但HFC网络的维护与早期CATV同轴电缆网络有很大区别,需要从多个方面入手才能保证系统的正常运行。笔者从实践出发,就有线电视HFC网络的日常维护进行了探讨,对HFC网络维护实践有着一定的借鉴意义。     

Analytical investigation velocity fields on mean and turbulent of a plane jet

This paper analyses the downstream developments of the mean and the turbulent velocity fields of a plane jet. Based on the conservation of mass and the conservation of momentum, the mean-velocity half width （reflecting the jet spread rate） and the relative mass flow rate （jet entrainment） are related to the decay rate of the centreline mean velocity. These relations are not subject to self-preservation. Both analytical and experimental results suggest that the jet spread rate （K1） and the entrainment rate （K3） （and thus the decay rate K2） can be well estimated from the centreline velocity, i.e., K1 ≈ 0.6K2 and K3 ∝K2. The effect of initial mean velocity and RMS velocity profiles on the downstream mean velocity field appears to be embodied in the constants K1 K2 and K3. The analytical relationship for the self-preserving Reynolds shear stress, obtained for the first time, works well.