A Low-Frequency Current Probe System for Making Conducted Noise Power Measurements

The two current probe technique of measuring conducted radio-frequency interference is a radical departure from conventional measurement techniques. The technique evolved from a dissatisfaction with present techniques, due to the lack of sufficient information obtained from measurements concerning the source of the interference. Normally, the wires concerned when testing for conducted interference are 60-Hz power lines of the two conductor type. If a pair of conductors comprising a power cord is considered as a transmission line, the factors which determine its performance at radio frequencies are primarily the wire length and loading. In practice, power lines do not have readily described configurations, which makes a transmission-line analysis extremely difficult. As a result, no attempt to analyze the situation is made at all. Usually, a line impedance stabilization network (LISN) is inserted into the line and the noise voltage developed is measured across a 50-ohm internal resistor which is effectively placed across the line. Thus, the only information obtained is a noise voltage which existed across a resistor at the time of measurement, but is nonexistent after the test. The noise voltage existing across the line after the LISN has been removed remains unknown. As a matter of fact, it cannot even be calculated, since the line characteristics are unknown. Thus insufficient information is the reason for pursuing the current probe techniques. The two current probe technique of measuring conducted interference overcomes the limitations of the LISN technique by supplying more information about the line.     

电子电压表各档量程选择与测量误差分析

用电子电压表进行测量时会带来一定的误差.正确了解电子电压表的特点以及误差形成原因,掌握正确的测量技术和方法,就可以减小测量误差.     

Semiconductor surface study by transverse acoustoelectric voltage using surface acoustic waves

Electrical properties of semiconductor surfaces can be determined by measuring the transverse acoustoelectric voltage. This voltage is produced by the interaction of the surface acoustic wave propagating on a piezoelectric substrate and the carriers on semiconductor surface placed in proximity. Using 110 MHz LiNbO₃ delay lines, the transverse acoustoelectric voltage has been measured across CdS and Si, the surface properties of which are varied by different light illumination. Detailed study of the voltage waveform reveals the type of traps and the amount of charge in the traps. The method is simple, needs no contacts to the sample, and is sensitive.     

Analysis of radio paging errors in multitransmitter mobile systems

Many mobile telephone and personal paging systems require signaling simultaneously from multiple transmitters. This paper analyzes the factors that cause paging errors due to interference when the signaling format consists of audio tones sent simultaneously from two FM transmitters. The factors considered are: drift in carrier and modulation frequencies, and misequalization of land-line amplitude and audio delay. The following results are shown: 1) the interference errors are eliminated if the land lines are amplitude and phase equalized, 2)if the lines are not equalized but the modulation frequencies are equal, then the interference errors can be decreased by an order of magnitude if the transmitters are mistuned such that their difference carrier frequency is just greater than the modulation tone filter bandwidth in the receiver, and 3) if the modulation frequencies are slightly different, then the interference errors can be decreased somewhat by misequalizing the modulation indicies. It is then concluded that if the land lines are not equalized and the signaling tones are not exactly equal, the interference errors cannot be eliminated, but can be decreased by properly aligning the system.     

Analysis of Radio Paging Errors in Multitransmitter Mobile Systems

Many mobile telephone and personal paging systems require signaling simultaneously from multiple transmitters. This paper analyzes the factors that cause paging errors due to interference when the signaling format consists of audio tones sent simultaneously from two FM transmitters. The factors considered are: drift in carrier and modulation frequencies, and misequalization of land-line amplitude and audio delay. The following results are shown: 1) the interference errors are eliminated if the land lines are amplitude and phase equalized, 2)if the lines are not equalized but the modulation frequencies are equal, then the interference errors can be decreased by an order of magnitude if the transmitters are mistuned such that their difference carrier frequency is just greater than the modulation tone filter bandwidth in the receiver, and 3) if the modulation frequencies are slightly different, then the interference errors can be decreased somewhat by misequalizing the modulation indicies. It is then concluded that if the land lines are not equalized and the signaling tones are not exactly equal, the interference errors cannot be eliminated, but can be decreased by properly aligning the system.     

分布式阵列雷达基线位置和相位误差的卫星标校方法

在采用相位干涉测角的分布式阵列雷达系统中,系统阵面相位中心位置误差和相位误差对测角精度影响很大,且阵面相位中心位置与物理中心位置通常不一致,因此需要对其进行精细标准补偿。传统的雷达系统误差校正方法通常采用远场辐射源来对雷达进行校正,但是对于单元间距很大的分布式阵列空间目标监视雷达而言,要实现远场辐射校准往往很难。该文提出一种利用多弧段的精轨卫星精密星历对阵面相位中心位置误差引起的相位误差进行白化,然后搜索相位中心坐标和相位差使匹配方差最小的校正方法,无需使用特定仪器测量,且能很好地标定误差;计算机仿真以及实测数据验证了使用该文校正方法后,测角精度得到了显著提升。     

多回高压输电线路产生的无线电干扰分析

在规划设计，中关村软件园东侧将建设包括4回220kV四分裂导线，6回110kV单导线构成的10回高压输电线路，为了评估该高压线路走廊对软件园的电磁环境影响。在简述高压输电线路由于电晕产生的无线电干扰的基础上，分析单回220kV四分裂导线。220kV不采用分裂导线两种情况下的无线电干扰水平，由此估计该10回输电线路产生的无线电干扰水平，结果表明，该高压线路走廊产生的无线电干扰水平符合国家标准GB15707-1995《高压交流架空送电线无线电干扰限值》相应的要求。     

Comparative Radio Noise Levels of Transmission Lines, Automotive Traffic, and RF Stabilized Arc Welders

Radio interference data that have been measured throughout the frequency range of 30 Hz to 1 GHz on power transmission lines, automotive traffic, and RF stabilized arc welders by many investigators have been assembled, converted to a common system of units, and collectively plotted. The resulting composite presentations permit an assessment of the relative interference levels produced by the three types of radio noise sources. It is concluded that below 25 MHz, lower voltage transmission, lines and RF stabilized arc welders are the major incidental radio noise sources when the observer is within 100 feet of the source. Above 40 MHz, automotive traffic and lower voltage transmission lines are the major radio noise sources with neither appearing to be consistently the greater when an observer is within 50 feet or less of the source.     

An accurate experimental method for characterizing transmission lines embedded in multilayer printed circuit boards

We have developed an accurate method for measuring the complex propagation constant and characteristic impedance of transmission lines embedded in multilayer printed circuit boards. It is based on mathematical error-removal schemes using two different length transmission lines and an advanced via-hole structure that minimizes coupling. Consequently, associated errors, due to discontinuities and interference can be effectively eliminated, and the frequency dependencies of the transmission line parameters can be clarified in wide frequency bandwidths. We verified the validity of this method in frequency ranges up to at least 18 GHz, by comparing the determined values with the theory derived from transverse electromagnetic (TEM) approximations.     

Behaviour of power-factor meters under non-sinusoidal current and voltage

Different types of analogue and digital power-factor meters used for low frequencies are studied. Their errors are calculated when the current or voltage waveform is distorted. It is shown that large errors appear under these working conditions. A new measuring instrument is proposed. It has very small errors, even under highly distorted waveforms, having low-pass filters at the inputs to prevent errors generated by high frequency harmonics.     

Instrumentation Problems Encountered Making Man-Made Electromagnetic Noise Measurements for Predicting Communication System Performance

One of the factors involved in communication system performance is the electromagnetic interference environment (broad-band radiated electronic noise). Attempts are often made to use commercially available radio-frequency interference field intensity meters for these measurements. Measurements made with these instruments are of limited use since detector functions like peak and quasi-peak are not useful parameters in statistical communication theory. It is recommended, instead, that rms voltage be measured simultaneously with average voltage and average logarithm of the voltage. These latter three parameters may be used to infer the amplitude probability distribution, which is a required statistic for predicting the performance of communication systems. Data are given on dynamic range requirements for accurate measurement of these statistical parameters for a given man-made noise sample. An Appendix contains several hardware solutions to the problems posed in this paper.     

Error analysis of tissue resistivity measurement

We identified the error sources in a system for measuring tissue resistivity at eight frequencies from 1 Hz to 1 MHz using the four-terminal method. We expressed the measured resistivity with an analytical formula containing all error terms. We conducted practical error measurements with in-vivo and bench-top experiments. We averaged errors at all frequencies for all measurements. The standard deviations of error of the quantization error of the 8-bit digital oscilloscope with voltage averaging, the nonideality of the circuit, the in-vivo motion artifact and electrical interference combined to yield an error of +/- 1.19%. The dimension error in measuring the syringe tube for measuring the reference saline resistivity added +/- 1.32% error. The estimation of the working probe constant by interpolating a set of probe constants measured in reference saline solutions added +/- 0.48% error. The difference in the current magnitudes used during the probe calibration and that during the tissue resistivity measurement caused +/- 0.14% error. Variation of the electrode spacing, alignment, and electrode surface property due to the insertion of electrodes into the tissue caused +/- 0.61% error. We combined the above errors to yield an overall standard deviation error of the measured tissue resistivity of +/- 1.96%.     

微纳米加工表面和表层的完整性评价

对近年微纳米表面和表层的完整性评价技术和检测方法作了综合性概述,并且应用现有的高精度现代化测试设备,对超精密加工的硅、锗、玻璃、硬质合金、铝等材料的几种性能进行了实验研究,证明了这些手段和评价方法的可行性。     

Computation of Radio Interference Levels in High Voltage Transmission Lines with Corona

In this article, an analysis of radio interference levels due to high voltage transmission lines with corona is presented. A method to predict radio interference levels, which based on Gary's method and modal decomposition theory, is described and presented, considering also the skin effect in conductors and in the ground plane. Several application examples for 3-phase lines are presented and the results are compared with measurements published elsewhere.     

Circuit for Impulse Testing of Gas-Tube Lightning Arresters

Telephone lines may be protected from lightning-induced surges by gas-tube lightning arresters. Typical arresters break down at 250-400 V dc. Breakdown voltage increases with the rate of rise of the applied voltage and may be two or three times the dc value at a rate of rise of 10 kV/μs. Lightning surges on telephone lines approach this rate of rise. The circuit described in this paper generates and measures ramps with linear rates of rise from 0.5 to 10 kV/μs chopped at 500-1500 V. In order to achieve ramp linearity and to minimize oscillations after the chop, stray capacitances and inductances must be made as small as possible. Construction and layout required to achieve this are described in some detail and typical test oscillograms at 0.5 and 10 kV/μs are presented in corroboration. Measurement accuracy is analyzed and maximum errors are estimated to be, for breakdown voltage, 3 and 10 percent at 0.5 and 10 kV/μs, respectively; and for rate of rise, 5 percent for all ramps. If greater accuracy is required, it can be obtained by correction for divider time constant errors and by further study of carbon resistor voltage coefficients.     

利用楔形薄膜干涉测定液体的折射率

介绍一种利用上下分界面反射率不同的楔形薄膜干涉测量液体折射率的方法，并进行了实际测量，且分析了产生误差的原因。该方法具有待测量少、简便易行、精度高等优点。     

塔康地面信标半幅探测电路对测距精度的影响分析

在分析塔康信标半幅探测电路工作原理的基础上,重点讨论了影响塔康系统测距精度的主要因素,一方面推导出半幅探测脉冲的定时误差与参考电压的幅度误差之间的定量关系μs(??ut 3)V(/)?,另一方面讨论了当多径干扰造成测距脉冲波形展宽而导致定时误差时,提出了一种通过测量半幅探测脉冲的实际宽度T来间接得出定时误差?t,从而控制延时时间减小定时误差的补偿方法,达到提高测距精度的目的。     

线性光耦HCNR201原理及其在轴承故障检测中的应用

因铁路货车轴承故障检测现场工况复杂,各种电磁干扰信号极易随被测信号进入测量系统.针对这个问题,设计了用高线性度模拟光耦HCNR201和运算放大器实现的电压隔离硬件电路.该电路中,线性光耦的前端用一个运算放大器构成一个负反馈放大器,用来检测模拟电压信号;线性光耦后端的运算放大器进行电流与电压之间的转换,最终输出电压信号,实现电压信号的1：1隔离传输.实验结果表明：该方法测量电压线性度好、精度高.     

Transient field coupling and crosstalk in lossy lines witharbitrary loads

We extend the transient scattering analysis of a lossy multiconductor transmission line to the evaluation of the interference produced by a field illuminating the line. The external interference is described by suitable voltage wave sources that are readily computed in the time domain and do not affect the structure of the transient scattering equations. The proposed formulation fully exploits the advantages of the transient analysis based on the line matched scattering parameters, dealing effectively with low-loss lines and helping the understanding of the interference mechanism through the physical interpretation of the results. The simplicity and efficiency of our approach is evidenced by means of a numerical example of the external interferences on a realistic nonlinearly loaded highly mismatched 3-conductor interconnect     

Reduction of the electrical potential of interfered pipelines due to currents of high voltage power lines and electric railways

Inductive interference of natural gas-, oil-, district heating- and water-pipelines due to short circuit and operation currents of high voltage lines and electric railways is a noticed problem since influencing and influenced systems are constructed very close together in the same so called "energy route". The measurement of the pipe potentials against remote earth at defined pipeline locations as well as the calculation of the induced voltage along an interfered pipeline is very important to identify critical sections on the pipeline to reduce the risk of hazard on the one hand and the a.c. corrosion possibility on the other hand. A.c. corrosion, which already begins at induced voltages in the range of 4–10 V depending on the specific soil resistivity can lead to pipeline leakages in worst case. This paper delivers some insights into an actual interfering situation regarding a new built 400 kV overhead line and an existing natural gas pipeline. The methods of measuring and simulation are described separately. Afterwards the results are compared and discussed. Finally, common potential mitigating measures such as a.c. earthing systems and galvanic separations by insulating joints in the course of the pipeline, as well as some alternative measures like the connection to low impedant operational earths of in Austria applied low voltage TN-systems and the use of surge arrestors, are shown.