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.     

Technical Considerations for Establishing Requirements Pertaining to Broad-Band EMI from Data-Processing Equipment and Office Machines

This paper extends the scope of earlier narrow-band work to include control of broad-band emission sources which can exist independently of, or in conjunction with, narrow-band sources in electronic data-processing (EDP) and office-machine (OM) equipment (products). While both narrow-band and broad-band noise sources have the potential for RF interference with communication services, our experience with broad-band problems has shown this class of sources to be much less significant than the low incidence of actual narrow-band component EDP interference problems examined in the initial paper [1]. Limits are discussed considering the empirical data base and need for international harmonization of interference requirements     

Technical Considerations for Establishing Narrow-Band EMI Requirements for Data-Processing Equipment and Office Machines

Technology studies of the electromagnetic emanation charactersitics of electronic data processing (EDP) and office machine (OM) equipment was initiated within IBM about a decade ago. Since then, experimental and theoretical studies have been made of both radiated and conducted modes of electromagnetic propagation, and, in particular, the relationship of this propagation to communication receiver interference has been explored. This paper focuses on: 1) development of a worst-case narrow band interference model for most classes of communication services in the United States, and 2) a general approach to narrow band radiated and conducted limit setting. The low incidence of narrow band EDP interference problems is examined, and a statistical estimate of EMI is made for TV services (radiated) and AM radio (conducted). The significance of various limit levels is then discussed.     

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.     

RF Impedance of Power Lines and Line Impedance Stabilization Networks in Conducted Interference Measurements

Impedance measurements were made of 60-Hz commercial ac power sources throughout the LF-HF frequency spectrum and compared to the impedance presented by a typical 5-?H line impedance stabilization network. The results are presented in graphical and tabular form.     

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.     

RF Impedance of United States and European Power Lines

Impedance measurements were made of 86 commercial 50-Hz AC power distribution systems throughout the LF-HF (0.02-30 MHz) spectrum in six European countries. The impedances are those presented to devices/appliances connected to the ac power source. The European results are presented in graphic and tabular form and are compared to impedances of U.S. power lines.