低压差线性电压调整器噪声电压测试方法

低压差线性电压调整器在便携应用中除需要实现电压转换功能外,还必须满足专用电路的噪声要求。噪声电压作为低压差线性电压调整器的关键指标之一,它限制电路能够处理的最小信号电平。为适应新型低压差线性电压调整器的低噪声测量需求,该文提出采用电池供电与实时信号分析仪相结合的噪声电压测试方法,该方法通过降低低压差线性电压调整器输入噪声对输出噪声的影响,具有测量精度较高、测试灵活、平台搭建简单等特点。文中对比分析采用直流电源供电与采用电池供电的噪声电压测试方法,实验结果表明:采用电池供电的噪声电压测试方法可以满足10μV量级的噪声电压测试需求,达到对低压差线性电压调整器噪声电压进行准确考核的目的。     

频谱分析法在测量封闭式制冷压缩机转速中的应用

采用频谱分析法测量封闭式压缩机的实际转速:通过电流互感器将变频器输出端电流信号转变成电压信号,对该电压信号进行数据采集并进行快速傅立叶变换获得定子电流的激磁分量频率和转子电流在定子电流中的反馈"负载分量"的频率,根据这两个频率计算出封闭式压缩机的实际转速.由于受外界磁场和噪声等的干扰,对所采集到的数据进行低通滤波处理.     

使用低磁场的分布溅射离子泵

1、引言 在电子储存环中,一般地为了解决受通导限制长真空室的抽气,在弯转磁铁磁场中装置线性的离子泵～〔1〕。这些泵构成真空室的一部份,并且伸展到所有容易受同步辐射光解吸作用的真空室部份。LEP真空系统已经计划采用整套的离子泵～〔2〕。然而,特殊问题是这些泵必须运用在典型值为0.02泰斯拉(1泰斯拉=10～4高斯—译注)的特别低的注入磁场中。 我们首先研究了给定尺寸的一个泵单元,维持点燃放电的最低磁场与压强及阳极电压的关系。泵性能的测量以放电强度 I/P即泵电流与压强之比。其次,采用一个校准测试罩,测量了各种泵型的抽速与压强…     

用于低功耗微型磁通门的Co77Fe2.5Mn1.4Mo2.1Si13B4非晶薄膜研究

采用直流磁控溅射方法制备了一种适用于微型磁通门的Co77Fe2.5Mn1.4Mo2.1Si13B4非晶软磁铁芯薄膜,并对薄膜进行了200℃外加面内横向磁场的真空退火。利用振动样品磁强计(VSM)、X射线扫描仪(XRD)以及扫描电子显微镜(SEM)测试了薄膜的磁滞回线、相组成、表面形貌并进行了成分分析;使用制备得到的薄膜作为双铁芯磁通门的铁芯,测试了磁通门的激励电流、灵敏度和线性范围。结果表明,制备得到的薄膜主要呈非晶态,具有较大的相对磁导率并且磁滞回线在小磁场下出现明显的拐点;用作磁通门铁芯薄膜时,能得到类似使用Co基非晶带材铁芯时的明显的磁通门信号;工作在40kHz时,磁通门传感器能以有效值22mA的激励电流获得2700V/T的输出电压灵敏度。因此,制备得到的薄膜适用于低功耗、高灵敏度微型磁通门传感器。     

PbBi/SiO多层交迭膜的制备和分析及其超导性质

以交替的超导/绝缘薄膜作为模型系统。用真空蒸发方法制备了样品并对其层状结构用俄歇谱仪作了检测。低温测试装置具有可控制的温度和强度与方向可调的磁场。测量了超导转变温度及临界电流与温度、磁场的关系。实验结果与钉扎理论的处理很好地一致。     

可编程交流电压比率标准的研究

提出了1种基于双级感应分压器和乘法型数模转换器(mDAC)组合分压的宽频可编程交流电压比率标准，实现工作频率范围内的高精度任意交流电压比率的输出。比率标准采用自锁型继电器开关实现双级感应分压器的可编程控制，使用注入电压法实现mDAC分压模块与双级感应分压器输出电压的组合分压。提出了mDAC宽频比率误差修正方法，将比率标准分压精度优化了1个数量级。提出1种交流电压精密比较测量系统，对比率标准的性能进行了测试。可编程交流电压比率标准输出分辨率优于1μV/V,在工作频率50 Hz～10 kHz范围内比差优于0.2μV/V,在1 kHz频率下角差优于1μrad。     

C布预制体C/C复合材料磁电阻特性研究

C布预制体C/C复合材料试样经不同温度石墨化处理后,通过X射线衍射法标定其石墨化度,研究其磁电阻特性。结果表明:随着石墨化度的提高,C/C复合材料的磁电阻增大;石墨化度对C/C复合材料磁电阻-位向关系无影响,磁电阻-位向关系是材料本身的特性,不随石墨化度、磁场强度、测量温度等因素的变化而变化,实验用材料最大磁电阻出现在90°位向处;固定磁场强度,不同石墨化度试样的最大磁电阻随测量温度(5～300K)的增加线性降低;测量温度高于5K,外加磁场小于1.2T时,磁电阻随磁场强度的增大线性增大,场强高于1.2T后,磁电阻不再随磁场强度的增加而变化;测量温度在4.2K时,磁电阻随外加磁场的变化会出现量子化平台。     

测微仪到A/D板放大倍数的确定

利用测微仪把机械量变成模拟量是常用的方法。由于测微仪输出电压以毫伏计,而A/D板输入电压需达±5V(对双极性A/D转换),二者连接必须有放大器。放大器的放大倍数如何确定呢?如果测微仪满量程时,输出电压为±50mV,那么对应A/D板输入电压±5V的放大倍数是否就取100倍呢?这样确定是不合理的。因测微仪在与A/D板连接后要保证测量结果为最大值时,一方面使对应的A/D板电压不超过±5V才能保证A/D板不受损坏,另一方面又不会降低分辨率。所以在测微仪满量程时,A/D板的电压以4V左右为宜,这     

压力变送器测量结果的不确定度评定

<正>压力变送器是一种将压力变量转化为可传送的标准化输出信号的仪表,而且其输出信号与压力变量之间一般存在线性函数关系。1测量过程测量依据:JJG 882—2004《压力变送器检定规程》JJF 1059—1999《测量不确定度评定与表示》环境条件:温度(20±5)℃,相对湿度45%～75%测量标准:0.05级(0～60)MPa活塞压力计电流标准:便携式压力校验仪Druck DPI601测量范     

简易数控充电电源的设计

以C8051F为控制核心,采用电压电流串联负反馈实现数控充电电源恒压恒流输出,实时测量负载电压电流信号,并通过LCD显示。通过测量负载两端电压信号,实现数控充电电源恒流输出到恒压输出的切换。在恒流输出模式下,改变负载电阻,输出电流变化的绝对值≤3mA,纹波电流≤1mA;在恒压输出模式下,改变负载电阻,输出电压波动小于0.2V,纹波电压小于6mV。此外,通过温度传感器,系统实现对温度的检测,当温度异常时,系统进行报警并开风扇,实现系统过热保护,当温度恢复正常时,系统可以实现自恢复。     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.     

Tc trend in high-Tc superconductors

In our previous works, we have shown that most existing ceramic superconductors can be considered to be built of superconductor-semiconductor composite and we have estimated the change in phonon spectrum of the intrinsic superconductor unit if a semiconductor unit is attached to it. Moreover, the proximity effect under the size quantization condition has been examined in the superconductor-semiconductor composite. Each of the stated effects by itself could causeT _c enhancement in general as more semiconductor blocks are added to the system. We extend our study in this paper to analyze the combined actions of phonon spectral change and proximity effect without size quantization condition onT _c variation in members of the Tl₁ series of high-T _c superconductors. Our results indicate that an optimumT _c is obtained if the stated effects are included in the idealized unit cells of the superconductors made up of a superconductor-semiconductor array.     

Anomalous Hall Effect in Sn1?x?yMnxEuyTe and Sn1?x?yMnxEryTe Mixed Crystals

The Anomalous Hall Effect (AHE) was investigated in IV–VI ferromagnetic semimagnetic semiconductors of Sn_1–x Mn _x Te codoped with either Eu or Er. The analysis of experimental data is as follows. Hall resistivity and magnetization showed that AHE coefficient R _s depends on temperature and its value decreases with thetemperature increase. We observe that above ferromagnet–paramagnet transition temperature R _s changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of R _s , particularly change of the sign.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Effect of pressure onTc in La2-xBaxCuO4 withx=0.125

The superconducting transition temperature,T _c , of La_2–x Ba _x CuO₄ has been measured under high pressure up to 8 GPa.T _c is found to change drastically at the pressure where the structural phase transition takes place. This finding clearly indicates that there exists an intimate relation between the crystal structure and superconductivity.