基于SNS型双路约瑟夫森结阵驱动方法研究

根据SNS型双路约瑟夫森结阵的驱动原理以及结阵分段特点,提出了平衡三进制驱动算法,实现了双路约瑟夫森结阵偏置状态的快速计算。根据约瑟夫森结阵的偏置状态以及组合方式,采用节点电压法,准确合成了双路阶梯波交流量子电压的台阶电压值,最终实现了最小分辨率为2个结,有效位为15位的交流量子电压输出。双路交流量子电压互测实验结果表明,合成交流量子电压的最大误差为0.06 μV,双路信号同步性测试实验中,两个通道的相位差为-0.01 μrad,证明了合成双路交流量子电压具有较高的幅值准确度和相位同步性。     

基于约瑟夫森量子电压的交流功率测量系统及方法研究

基于约瑟夫森量子电压标准设计了交流功率差分测量系统。通过分析差分采样系统的误差分布及误差传递函数,提出换向差分测量方法,减小了差分采样系统的增益误差,提高了电压幅值测量准确度;通过分析衰减系数η,证明了采用换向差分测量较容易实现10-7量级电压幅值测量。通过评估差分采样系统零相位,结果证明了差分采样系统具有较好的相位测量稳定性。分析了交流功率差分测量系统的不确定度分量,评估了功率因数为1.0,0.5 L和0.5 C时的功率测量不确定度,通过与国家交流功率基准装置进行实验比对,证明了基于约瑟夫森量子电压交流功率测量系统不确定度评估的合理性。     

基于Matlab/Simulink的电压暂降仿真与分析

介绍了检测电压暂降的有效值算法和傅里叶变换(FFT)算法,在Matlab环境下,针对四种冲击性负荷引起的电压变化进行仿真,并将有效值算法和傅里叶变换(FFT)算法相结合,检测了电压暂降的幅值、持续时间和相位跳变,验证了这两种算法的有效性。仿真结果表明,在正常负荷相同的条件下,冲击性负荷的有功功率对于电压暂降的幅度和相位跳变均有明显的影响;而冲击性负荷的无功功率则主要影响电压暂降的幅度,对于相位跳变的影响很小。     

面向瞬态EMI测试的FFT-SCZT算法研究

针对传统接收机电磁干扰(electro-magnetic interference,EMI)测试实时性差,难以实现瞬态EMI信号测量的问题,提出基于快速傅里叶变换(fast Fourier transform,FFT)与分段线性调频Z变换(segmented chirp-Z transform,SCZT)结合的瞬态EMI测试方法。首先采用FFT对整个频谱进行初扫得到范围更小的特征频带;其次,基于SCZT时间复杂度低的特点,采用SCZT对特征频带进行频率细分;最后,应用FFT-SCZT测量对幅值动态变化、频率动态变化信号进行测量验证。实验结果表明:FFT-SCZT对幅值动态变化信号的频率、幅值测量相对误差分别小于0.004 5%、2.4%,对频率动态变化信号的频率、幅值测量相对误差分别小于0.004 7%、0.25%;FFT-SCZT算法可准确测量瞬态信号。     

基于阶梯波的周期非正弦电压精密测量——阶梯波研究之四

经典傅里叶变换要求采样数据必须布满整个周期。以周期非正弦波分析为例,提出一种利用规则分布的部分采样数据仍可进行傅里叶变换的新方法。以阶梯波为参考的差分测量用于周期非正弦波,在每个阶梯波台阶上丢弃起始和结束部分的采样以克服过渡过程和吉布斯现象后,高频分量的傅里叶变换将产生明显偏差。为克服这种偏差,将傅里叶变换的基函数(三角函数)作同样的离散,组成相应的影响矩阵,其逆矩阵将能恢复准确结果。由于影响矩阵的阶次是最高谐波次数的2倍,一般情况下求逆十分困难,并需要较大存储空间。提出了使影响矩阵成为稀疏因而简化运算的条件。进一步讨论了基于阶梯波的差分采样所需要的限幅条件在周期非正弦电压下的表现及其应对方法。模拟和演示实验结果表明,该方法可极大减少计算量,仍具有较高准确度。最后探讨了该方法扩展到一般采样缺失情况下的可能性。     

我国量子电压基准装置与国际比对取得成功

本刊讯最近，国际计量局（BIPM）专家T．Wite博士和D．Reymamn博士携带该局可搬运式IV量子电压标准装置（即约瑟夫森结阵电压标准）到中国计量科学研究院，与我国量子电压基准装置进行了比对。两套装置通过汞电池过渡标准的间接比对和两个约瑟夫森结阵电压的直接比对后，又通过分别测量同一个标准电池进行了间接比对，取得了好的结果。这是迄今为止BIPM与各国进行的15次比对中所取得的最好结果之一。通过汞电池过渡标准的比对，表明我国基准装置与BIPM同类装置测量结果的差仅为0．06nV（即相对差为6×10-11），平均值的标准偏差为1…     

基于小波降噪和短时傅里叶变换的主轴突加不平衡非平稳信号分析

针对主轴运行过程中突加不平衡而产生的非平稳信号无法采用传统的傅里叶变换对信号进行分析处理的问题,提出一种采用小波降噪与短时傅里叶变换相结合对主轴振动特征信息进行准确提取的方法,该方法利用小波降噪技术对非平稳信号进行滤波处理,再对滤波处理后的信号进行重构,最后通过短时傅里叶变换精确获取主轴振动幅值,通过仿真和实验验证了该方法的有效性。     

基于希尔伯特-黄变换提取车辆轨道耦合系统时频特性

为研究各种激扰对车辆轨道耦合系统动力学响应时频特性影响,将基于改进经验模态分解（EMD）的希尔伯特-黄变换（Hilbert-Huang Transform）应用于车辆轨道耦合动力学振动信号分析中。运用改进EMD方法提取耦合系统振动响应的固有模态函数（IMF）,并对其进行希尔伯特-黄变换,得到振动响应的希尔伯特时频幅值谱和边缘谱。分析表明：希尔伯特-黄变换较傅里叶变换的分辨率与精度高,能有效捕捉车轮缺陷及轨道谐波不平顺激励下车辆轨道耦合系统的调制信号;车体垂向振动加速度随轨道不平顺波长、幅值非线性变化,振动信号的轮周激励成分为调制信号,且随轨道不平顺幅值增大而减小,随轨道不平顺波长增大非线性变化。     

转子动平衡检测中不平衡信号幅值与相位的计算方法

本文主要论述了在旋转机械的动平衡检测中，采用转速脉冲信号触发A／D进行整周期采样，然后通过对采集到的整周期信号进行离散傅里叶变换，从而得到不平衡信号的幅值与相位。     

傅里叶与小波变换的电力谐波测试性能研究

简述傅里叶变换和小波变换的基本原理,在Matlab平台上设计傅里叶变换模块和小波变换模块。针对含有突变干扰、白噪音干扰等常见工程电力信号,通过实验系统研究傅里叶变换、小波变换的频域和时频分析特性。实验结果表明,傅里叶变换能较好地测试出信号的谐波成分,小波变换具有良好的信号频段分析特性。根据这些特点,探讨傅里叶变换、小波变换各自的适用场合,以便高效利用这两种方法分析电力谐波成份,为治理谐波奠定基础。     

1V脉冲驱动型交流量子电压源研究

脉冲驱动型交流量子电压标准ACJVS通过高速脉冲序列驱动约瑟夫森结阵芯片的方式实现宽频带交流量子电压的合成,相比于可编程型交流量子电压标准PJVS,具有免台阶切换、频谱纯净、频带宽等优点。搭建的系统主要包括8位高速脉冲码型发生器、微波放大器、直流阻断、约瑟夫森结阵芯片等。通过驱动包含4个子阵列,每个子阵列含12810个约瑟夫森结的结阵芯片,并结合4通道联合低频补偿的方式,成功产生了1V有效值的脉冲驱动型交流量子电压,为进一步建立交流量子电压基准打下了坚实的基础。最后,展望了脉冲驱动型交流量子电压在量子阻抗桥、交流量子功率源、交流量子功率表方面的应用价值。     

Systematic-Error Signals in the AC Josephson Voltage Standard: Measurement and Reduction

We investigate the dominant frequency-dependent systematic-error signals (SESs) in the AC Josephson voltage standard. We describe our error measurement technique and a number of methods to reduce the errors. Most importantly, we found that a small change in on-chip wiring significantly reduces the SES, improves SES measurement stability, and enables a suitable bias correction method. We show that direct analog-to-digital converter measurements of the SES of two on-chip Josephson arrays are in very good agreement with errors inferred from AC-DC transfer standard measurements. Finally, we demonstrate that the reduction of the SES using these techniques greatly improves the agreement between the AC-DC differences of the two arrays as well as the absolute AC voltage accuracy.     

Progress Toward a 1 V Pulse-Driven AC Josephson Voltage Standard

We present a new record root mean square (rms) output voltage of 275 mV, which is a 25% improvement over the maximum that is achieved with previous ac Josephson voltage standard (ACJVS) circuits. We demonstrate the operating margins for these circuits and use them to measure the harmonic distortion of a commercial digitizer. Having exceeded the threshold of 125 mV rms for a single array of Josephson junctions, we propose and discuss the features of an eight-array circuit that is capable of achieving 1 V rms. We investigate the use of a resistive divider to extend the ACJVS voltage accuracy to higher voltages. By the use of a switched-input measurement technique, an integrating sampling digital voltmeter, a resistive voltage divider, and ACJVS synthesized sine waves as reference voltages, we characterize the stability of a commercial calibration source for a few voltages up to 2.7 V.      

Error and Transient Analysis of Stepwise-Approximated Sine Waves Generated by Programmable Josephson Voltage Standards

We are developing a quantum-based 60 Hz power standard that exploits the precision sinusoidal reference voltages synthesized by a programmable Josephson voltage standard (PJVS). PJVS systems use series arrays of Josephson junctions as a multibit digital-to-analog converter to produce accurate quantum-based dc voltages. Using stepwise-approximation synthesis, the system can also generate arbitrary ac waveforms [i.e., an ac programmable Josephson voltage standard (ACPJVS)] and, in this application, produces sine waves with calculable root mean square (rms) voltage and spectral content. The primary drawback to this ACPJVS synthesis technique is the uncertainty that results from switching between the discrete voltages due to finite rise times and transient signals. In this paper, we present measurements and simulations that elucidate some of the error sources that are intrinsic to the ACPJVS when used for rms measurements. In particular, we consider sine waves synthesized at frequencies up to the audio range, where the effect of these errors is more easily measured because the fixed transition time becomes a greater fraction of the time in each quantized voltage state. Our goal for the power standard is to reduce all error sources and uncertainty contributions from the PJVS-synthesized waveforms at 60 Hz to a few parts in 10⁷ so that the overall uncertainty in an ac power standard will be a few parts in 10⁶.     

基于经验模态分解的聚焦超声非线性声场检测

为精确检测聚焦超声声场中的谐波成分并得到谐波分布规律,开展了对聚焦超声非线性声场检测的研究,提出基于经验模态分解的聚焦超声谐波检测方法。首先对声场信号进行经验模态分解;然后利用噪声判断准则判断出固有模态函数（IMF）中的噪声分量,滤除噪声分量后将剩余的IMF分量予以重新组合;最后对新信号进行傅里叶变换,得到各次谐波的幅值。结果表明:它能较好地抑制噪声,相比于传统的检测方法可获得更平滑的谐波分布;该方法对开展谐波成像、医学超声检测具有重要意义。     

正弦波电压差分测量与多周期策略——阶梯波研究之三

将片段采样概念应用于正弦波电压的差分测量,把多周期策略施加于被测正弦波的频率扩展,通过实验演示上述测量的具体过程,验证方法的可行性。分析了阶梯波差分测量的特点。为适应这个特点,提出了限幅片段采样的概念及相应的方法。由此提出将交流量子电压基准的准确度提高一个数量级至10^-8水平的建议,叙述了它的原理及具体的方法,指出了所需要的条件。     

Precision Differential Sampling Measurements of Low-Frequency Synthesized Sine Waves With an AC Programmable Josephson Voltage Standard

We have developed a precision technique to measure sine-wave sources with the use of a quantum-accurate ac programmable Josephson voltage standard. This paper describes a differential method that uses an integrating sampling voltmeter to precisely determine the amplitude and phase of high-purity and low-frequency (a few hundred hertz or less) sine-wave voltages. We have performed a variety of measurements to evaluate this differential technique. After averaging, the uncertainty obtained in the determination of the amplitude of a 1.2 V sine wave at 50 Hz is 0.3 $muhbox{V/V}$ (type A). Finally, we propose a dual-waveform approach for measuring two precision sine waves with the use of a single Josephson system. Currently, the National Institute of Standards and Technology (NIST) is developing a new calibration system for electrical power measurements based on this technique.      

Maintaining the Unit of Voltage at PTB via the Josephson Effect

In Section I a report on high precision voltage comparisons between the mean EMF of the former PTB voltage standard (consisting of a group of 39 saturated Weston cells) and the Josephson reference voltage is presented. The experiments were carried out with a total uncertainty (1 ?) of 4 parts in 108. The measured rate of change of the mean EMF during a 1?year period was - 1.3 X 10-7 V per year. This voltage stability is sufficient to maintain the unit of voltage by this group of standard cells for several months until a new comparison with the Josephson reference voltage becomes necessary. Due to the effects of thermal EMF's in the millivolt circuit of the measuring system used at present, the Josephson reference voltage (?3 mV) is only stable during a short time. In Section II a prototype cryogenic voltage standard developed at PTB is described. By immersing the main measurement components into the superfluid liquid helium bath, a long term voltage stability can be achieved. These components include the cryogenic resistive divider, consisting of a new copper alloy, and the SQUID null detector. The resistance ratio of the cryogenic resistive divider of 320:1 is determined by a ten-decade inductive voltage comparator operating at 84 Hz. The effects of power dissipation introduce only errors of second order because the currents in the calibration mode and the measurement mode are the same.