Effects of Measurement Devices on Conducted Interference Levels

Measurements of power line conducted interference voltages are commonly made throughout the 150 kHz to 30 MHz frequency range on military, industrial, and consumer equipment using line impedance stabilization networks (LISN) and, more recently, current probe techniques. This paper presents some brief background information concerning power line conducted interference measurements and the results of a study to assess the effects of LISN and current probe measurement devices on the level of measured conducted interference. A model is defined which facilitates prediction of the effects. The model concept allows the procedures described in this paper to be extended to equipment of other impedance definitions. A comparison of the calculated and empirical differences is made and suggests an analytical approach in sizing the effects upon the conducted interference levels.     

Power Line Conducted Interference Measurement Differences Using U. S. and CISPR Line Impedance Stabilization Networks

Measurements of power line conducted interference are commonly made on commercial equipment throughout the world using line impedance stabilization network (LISN's) in accordance with industrial and governmental procedures. Procedures in the United States applying to the 0.15-30 MHz frequency range specify an LISN that presents a frequency-dependent RF impedance to the equipment under test (EUT) whereas other national practices specify as LISN having an invariant 150-ohm impedance. This paper explores the expected measurement differences resulting from use of the two LISN's for power line interference measurements. Calculated difference factors, which depend on the EUT power line RF-input impedance, are developed. The factors have utility in assessing expected conducted interference levels in one LISN measurement configuration, given the interference levels and impedance parameters of the other. Measurement differences, in addition to those introduced by the LISN, which are attributed to variations in specified field strength meter parameters (i. e., detector, bandwidth, mechanical time constants, etc.) are beyond the scope of this paper.     

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

A technique for accurately measuring conducted radio frequency interference has been developed at the U.S. Naval Civil Engineering Laboratory. The technique involves the use of two current probes simultaneously to determine the impedance levels of the lines or equipment under measurement. The noise currents of the lines or electrical equipment are measured directly using one of the two probes. Knowing the noise currents and the impedances through which it flows provides the necessary information for computing noise voltages and noise power. Further, it allows prediction of the noise power delivered by the measured device into any known impedance connection. The bandwidth covered by this technique is 20KC-30mc. This range is covered by two instruments, the first covers 20KC-2mc and the second 2mc-30mc. The high frequency instrument has been described before and will not be discussed here. The low frequency instrument is new and has several unique features. The main feature being a direct read out of both the impedance magnitude and the phase angle of the system being measured. This is accomplished by transistorized circuits which drive two front panel meters, one for impedance magnitude and one for phase angle and its polarity. By providing the phase information it is possible to specify the noise observed in terms of noise power. This technique removes the many ambiguities which are normally associated with conducted noise measurements using line impedance stabilization networks.     

A DC current transformer for large bandwidth and high common-moderejection

A review of known magnetic-coupled current-sensing techniques is presented, Subsequently, a novel technique is introduced, based on a configuration discussed in a previous paper. The previous technique made use of a galvanomagnetic device (Hall effect sensor) to sense the magnetization of a current transformer core, so that the sum of the Hall voltage and the voltage across the secondary shunt resistor would yield a faithful copy of the input current. The technique described in this paper makes use of the same principle to obtain a high bandwidth (from DC to 1 MHz) and very high common-mode rejection current transformer, without the need for a Hall effect probe. This is achieved by subtracting the high-frequency components, detected across the secondary shunt resistor, from the voltage across a primary shunt resistor connected in series with the primary of the current transformer. The resulting signal is an accurate image of the transformer magnetizing current, which is then transferred to the secondary side by means of a low-bandwidth isolation amplifier. The high-frequency components are subsequently added, to the amplified and filtered low-frequency components, by means of a third transformer winding, the number of turns of which is chosen to be equal to the gain of the low-frequency amplifier     

Statistical Correlation Between Conducted Voltages on the Powerline and Those Measured with a Line-Impedance Stabilization Network

In measurements of physical parameters, it is not always possible to obtain consistent results because of the dependence on and interaction of a significantly uncontrolled variable element in the measurement. For consistent results to be obtained, the variation in the element may be eliminated by replacing the element with a simulated representative constant. Measurement of conducted powerline noise from electric/ electronic equipment is subject to such variation. Conducted-noise measurement procedures used in the United States, and also internationally, typically employ line-impedance stabilization networks (LISN's) which, in theory, eliminate the effects of variations in the ac power-distribution-network impedance on the measurement. The LISN is designed to be representative of the actual power-distribution- network impedance presented to equipment connected to the network. The LISN and power-network impedances are both frequency variant. Power-network impedances can assume a wide range of values at a fixed frequency, whereas the LISN impedance, assuming that any line-impedance effects are small, is a single value. This paper explores the correlation between conducted noise voltages measured in a LISN configuration and the actual noise voltages expected to be impressed on the power distribution system. The analysis is conducted at 1 MHz. The paper analytically relates the impedances of the LISN, power distribution system, and equipment. A LISN of the type used in the United States is used in the development; however, the concept and procedure presented is applicable to any LISN, frequency, and equipment.     

利用探针检测开关电源传导干扰

利用电压探针、电流探针和功率探针分别研究了开关电源的电压、电流和功率传导干扰的检测技术，阐述了其测量方法和经验。最后列举了几种开关电源的电压、电流和功率的谐波含量。     

Power line filter design for conducted electromagnetic interference using time-domain measurements

A time-domain technique for the design of passive power line conducted electromagnetic interference (EMI) filters in the frequency range 150 kHz-30 MHz is described. A digital storage oscilloscope (DSO) with adequate sampling, storing and processing features is sufficient for the design using the proposed technique. Accordingly, Agilent's Infiniium Oscilloscope (Model 54810A) has been used. The signals from LISN are directly fed into the two channels of the DSO where they are added and subtracted to separate the CM and DM components, thereby eliminating the need for common-mode-differential mode (CM-DM) separator. These components are stored in the DSO. A specially designed filter design software (FDS), residing in the DSO, estimates the noise spectrum by computing the Bartlett and Welch periodograms. It also computes the filter component values. Thus, the sampling of the conducted noise, separation of CM and DM components, signal processing, and filter value computations are all done using one DSO. A spectrum analyzer is not required. Bartlett periodograms have been preferred over Welch periodograms due to low memory storage requirements of the former. The proposed technique has been applied to the design of power line filter for a switched mode power supply (SMPS), and satisfactory results have been obtained. The proposed measurement scheme is compact, economical, and convenient. All the details of this work are presented.     

Essential-coupling-path models for non-contact EMI in switching power converters using lumped circuit elements

This paper proposes a simple lumped circuit modeling approach for describing noncontact EMI coupling mechanisms in switching power converters. The resulting model assumes a minimum number of noise sources and contains essential coupling paths that allow easy physical interpretations. Essentially, all capacitive couplings are represented by an equivalent noise voltage source and six coupling impedances, whereas all inductive couplings are represented by an equivalent noise current source and three coupling impedances. The resulting coupled noise appears as currents flowing into the terminals of the line-impedance-stabilization-network (LISN). The equivalent voltage source can be conveniently approximated as the switching-node-to-zero voltage, which is typically a rectangular pulse of a few hundred volts. The equivalent current source can be modeled as the current flowing around a loop containing the equivalent voltage source and parasitics such as winding capacitance of the power transformer, the snubber capacitance and connection inductances. Also, the coupling impedances can be estimated by making simplifying assumptions about the geometry of the components and tracks, or by direct measurements. Simulations and experiments verify how inductive and capacitive couplings through each path may produce substantial EMI measured by the LISN. Being based on a lumped circuit approach, the proposed model is easy to apply in practice for understanding, diagnosing and approximating EMI behaviors.     

Measurement of conducted electromagnetic emissions in PWM motordrive systems without the need for an LISN

This paper presents a technique for measuring the conducted electromagnetic emissions produced by pulse-width modulated (PWM) inverter induction motor drive systems. The method does not require an artificial line-impedance stabilizing network (LISN) but does, however, allow the emission levels to be calculated as if an LISN were present. Testing can be performed when an LISN is either unavailable, prohibitively expensive, or impractical to include in the supply. This is often the case for large drive systems or for systems already installed in the field. A normal RF voltage probe and a spectrum analyzer are used to measure the spectra of the common-mode and differential-mode excitation sources due to the inverter switching. Line inductors for high-frequency (HF) isolation are required for some of the tests, but the cost and complexity of these compared to an LISN is low. Common-mode and differential-mode Thevenin equivalent circuits are then derived from measured impedances. The emissions for any defined supply impedance (including an LISN) can then be determined. A laboratory test on a 15 kW PWM drive system is carried out to verify the accuracy and effectiveness of the proposed method     

Passive cancellation of common-mode noise in power electronic circuits

It is well known that common-mode (CM) conducted electromagnetic interference (EMI) is caused by the common-mode current flowing through the parasitic capacitance of transistors, diodes, and transformers to ground in the power circuit. Because of the potential for interference with other systems it is necessary to attenuate this noise. Ordinarily this is accomplished by using a magnetic choke across the input power lines, resulting in penalties to the overall size and cost of the completed system. In order to lessen the requirement for this magnetic choke, there has been a desire to introduce noise cancellation techniques to the area of EMI. This text introduces a method of canceling the common-mode EMI by using a compensating transformer winding and a capacitor. Compared with other cancellation techniques, it is much simpler and requires no additional transistors and gate-drive circuitry since it merely adds a small copper winding and a small capacitor. By using this technique the size of the EMI filter can be reduced, especially for applications requiring high currents. In this paper, the new method for passive noise cancellation is applied to many popular converter and inverter topologies. The method, results, and ramifications of this technique are presented in order of appearance.     

Technique for measurement of powerline impedances in the frequencyrange from 500 kHz to 500 MHz

A method for measuring power line impedances using two current probes is examined. This method is characterized by good isolation of the measurement equipment from the power line voltage and by the capability of measuring power line impedances between any pair of power-plug terminals. The use of this two-current probe method with the model described is effective in measuring power line impedances from 0.5 MHz to 100 MHz. Using purely resistive loads for calibration, the error is less than 5% for frequencies below 100 MHz, and less than 20% for frequencies between 100 MHz and 500 MHz. The error in an impedance measurement increases with the magnitude of the load impedance     

微型电场传感器在工频电场测量中的应用研究

该文基于高性能的MEMS电场敏感芯片研制出一种新型的工频电场测量系统。针对芯片调制被测电场后其输出信号的特征,采用正交相关检测原理提出一种可抑制背景干扰噪声的工频电场解调算法,设计出小型化、空间分辨力高的工频电场测量探头,并在基础上提出MEMS工频电场测量系统的系统级设计方案,成功实现了MEMS电场敏感芯片输出信号的无线采集、滤波、以及电场信号的高精度解调。高压输电线路下工频电场测量结果表明,MEMS工频电场测量系统与传统电场测量仪的测量结果具有良好的一致性。     

The pyroelectric detector of infrared radiation

The pyroelectric detector is a thermal sensor of infra-red radiation requiring no bias. While in principle a pure capacitor (hence theoretically noiseless), the detector has a varying noise contribution as a function of frequency due to a load resistor, series loss resistance, and amplifier. The actual sensor is a pyroelectric crystal exhibiting spontaneous polarization. The spontaneous polarization and dielectric constant of the crystal are temperature-dependent. A change in incident power raises the detector temperature causing an electric charge to appear across the electroded surfaces cut perpendicular to the crystal's ferroelectric axis. Under open circuit conditions, a voltage is obtained which is ultimately neutralized by current flow through the leakage resistance or load resistor. The evacuated detector package incorporates an electroded flake of triglycine sulfate mounted on a substrate of low thermal and electrical conductivity, a field effect transistor, load resistor, and an infrared transparent window. Data on the detectivity, responsivity, and noise as a function of frequency and area are presented. Polycrystalline pyroelectric detectors of TGS are feasible and simplify the construction of arrays and mosaics. Applications of the pyroelectric detector to date have been in a multielement line scanner, thermal imaging camera, spectrometer, and laser calorimeter.     

Characterization of power electronics system interconnectparasitics using time domain reflectometry

The significance of interconnect parasitics of power electronics systems is their effects on power converters' electromagnetic interference (EMI)-related performances, such as voltage/current spikes, dv/dt, di/dt, conducted/radiated EMI noise, etc. In this paper, a time domain reflectometry (TDR) measurement-based modeling technique is described for characterizing interconnect parasitics in switching power converters. Experiments are conducted on power components of a prototype high-power inverter, including insulated gate bipolar transistor (IGBT) modules, busbar and bulk capacitors. It is shown that the interconnect inductance of the IGBT module can be extracted completely using TDR. It is also shown that the busbar equivalent circuit can be modeled as transmission line segments or L-C filter sections, and the bulk capacitor contains a significant equivalent series interconnect inductance     

Thermal noise in a finite bandwidth

In a practical circuit, the output noise due to the thermal noise of a resistor will depend on the actual transfer function of the noise source. The bandwidth will never be infinite because the transfer function of either the noise source or the device measuring the output noise will cause limitations. Consequently, the thermal noise voltage of a resistor in a finite bandwidth is maximum for a given resistor value. That maximum thermal noise voltage depends on the stop frequencies and decreases for both smaller and larger resistor values     

Reduction of CM Noise Emissions From PLC Modem Using Optically Coupled Signaling

This paper investigates the feasibility of implementing an optical coupler in the analog front-end (AFE) circuit of a power line communication (PLC) modem to reduce the common mode (CM) noise coupling onto the power lines. Based on a two-current-probe measurement approach, an equivalent CM circuit model is developed to predict the expected CM current generated by the PLC modem when it is plugged onto the power line network. The model provides insight into the CM noise coupling mechanism from any PLC modem onto the power line network, so that the effectiveness of using an optical coupling technique in reducing the CM current from the power line network can be properly quantified     

Estimation of RF PA Nonlinearities after Cross-correlating Current and Output Voltage

The estimation of 1 dB compression and third-order intercept points can be obtained after the cross-correlation between dynamic current and output voltage of radio frequency power amplifiers. This estimation is performed using actual power measurements and not power inferred from voltage values. The underlining theory and a correlator that allows implementing this measurement on-chip are presented. The trade-off between measuring voltage and the actual power is also discussed and it is shown that different information concerning the output load is obtained when observing the PA’s output voltage and power. Simulation results, obtained with the model of a prototype demonstration chip, show that good accuracy can be obtained with relatively simple measurement conditions. These results include the analysis of optimum stimuli amplitudes and the effect of noise in estimation accuracy.     

数字式电子人工耳专用集成电路设计

本文设计了一个数字式电子人工耳专用植入芯片.芯片的刺激通道为17个,能提供多达4种刺激模式,并具有电源电压、电极间电阻以及电极间窜扰的实时测量能力,因而能够适应临床上研究各种不同的语音编码算法的需要.芯片内设有缓冲寄存器,能在进行当前帧刺激的同时接收下一帧数据,提高了刺激率.这是一块数模混合的芯片.工作电压12V,最大功耗＜50mW,采用2μm N阱CMOS工艺制造,芯片面积20mm².     

飞机开关负载传导干扰的测量方法

开关负载在飞机交流电网的导线上产生的干扰主要是传导干扰.对使用射频电流探头和线性阻抗稳定网络测量开关负载传导干扰的方法进行了介绍,并用matlab对线性阻抗稳定网络测量方法进行了仿真.这两种方法能够容易地测出共模与差模干扰.