Screening (or shielding) is one basic way of achieving electromagnetic compatibility (EMC). However, a confusingly large number of methods and concepts is available to test for the screening quality of cables and related components, and for defining their quality. This technical report gives a brief introduction to basic concepts and terms trying to reveal the common features of apparently different test methods. It should assist in correct interpretation of test data, and in the better understanding of screening (or shielding) and related specifications and standards.<\/p>\n
| PDF Pages<\/th>\n | PDF Title<\/th>\n<\/tr>\n | ||||||
|---|---|---|---|---|---|---|---|
| 4<\/td>\n | CONTENTS <\/td>\n<\/tr>\n | ||||||
| 7<\/td>\n | FOREWORD <\/td>\n<\/tr>\n | ||||||
| 9<\/td>\n | 1 Scope 2 Normative references <\/td>\n<\/tr>\n | ||||||
| 10<\/td>\n | 3 Electromagnetic phenomena Figures Figure 1 \u2013 Total electromagnetic field (Et, Ht) <\/td>\n<\/tr>\n | ||||||
| 11<\/td>\n | Figure 2 \u2013 Defining and measuring screening parameters \u2013 A triaxial set-up <\/td>\n<\/tr>\n | ||||||
| 12<\/td>\n | 4 The intrinsic screening parameters of short cables 4.1 General 4.2 Surface transfer impedance, ZT 4.3 Capacitive coupling admittance, YC <\/td>\n<\/tr>\n | ||||||
| 13<\/td>\n | Figure 3 \u2013 Equivalent circuit for the testing of ZT Figure 4 \u2013 Equivalent circuit for the testing of Yc\u00a0=\u00a0j\u03c9CT <\/td>\n<\/tr>\n | ||||||
| 14<\/td>\n | 4.4 Injecting with arbitrary cross-sections 4.5 Reciprocity and symmetry 4.6 Arbitrary load conditions 5 Long cables \u2013 coupled transmission lines Figure 5 \u2013 Electrical quantities in a set-up that is matched at both ends <\/td>\n<\/tr>\n | ||||||
| 17<\/td>\n | Tables Table 1 \u2013 The coupling transfer function T (coupling function)a <\/td>\n<\/tr>\n | ||||||
| 18<\/td>\n | Figure 6 \u2013 The summing function S{L\u00b7f} for near and far end coupling <\/td>\n<\/tr>\n | ||||||
| 19<\/td>\n | Figure 7 \u2013 Transfer impedance of a typical single braid screen Figure 8 \u2013 The effect of the summing function-coupling transfer function of a typical single braid screen cable <\/td>\n<\/tr>\n | ||||||
| 20<\/td>\n | Figure 9 \u2013 Calculated coupling transfer functions Tn and Tf for a single braid \u2013 ZF\u00a0=\u00a00 Figure 10 \u2013 Calculated coupling transfer functions Tn and Tf for a single braid \u2013 Im(ZT) is positive and ZF = +0,5 x Im (ZT) at high frequencies <\/td>\n<\/tr>\n | ||||||
| 21<\/td>\n | Figure 11 \u2013 Calculated coupling transfer functions Tn and Tf for a single braid \u2013 Im(ZT) is negative and ZF = \u20130,5 x Im(ZT) at high frequencies <\/td>\n<\/tr>\n | ||||||
| 22<\/td>\n | 6 Transfer impedance of a braided wire outer conductor or screen Figure 12 \u2013 L\u00b7S: the complete length dependent factor in the coupling function T <\/td>\n<\/tr>\n | ||||||
| 23<\/td>\n | Figure 13 \u2013 Transfer impedance of typical cables <\/td>\n<\/tr>\n | ||||||
| 24<\/td>\n | Figure 14 \u2013 Magnetic coupling in the braid Complete flux Figure 15 \u2013 Magnetic coupling in the braid Left-hand lay contribution Figure 16 \u2013 Magnetic coupling in the braid Right-hand lay contribution <\/td>\n<\/tr>\n | ||||||
| 25<\/td>\n | Figure 17 \u2013 Complex plane, ZT = Re ZT + j Im ZT , frequency f as parameter Figure 18 \u2013 Magnitude (amplitude), | ZT (f) | <\/td>\n<\/tr>\n | ||||||
| 26<\/td>\n | Figure 19 \u2013 Typical ZT (time) step response of an overbraided and underbraided single braided outer conductor of a coaxial cable <\/td>\n<\/tr>\n | ||||||
| 27<\/td>\n | Figure 20 \u2013 ZT equivalent circuits of a braided wire screen <\/td>\n<\/tr>\n | ||||||
| 28<\/td>\n | 7 Test possibilities 7.1 General 7.2 Measuring the transfer impedance of coaxial cables 7.3 Measuring the transfer impedance of cable assemblies <\/td>\n<\/tr>\n | ||||||
| 29<\/td>\n | 7.4 Measuring the transfer impedance of connectors 7.5 Calculated maximum screening level <\/td>\n<\/tr>\n | ||||||
| 30<\/td>\n | Figure 21 \u2013 Comparison of signal levels in a generic test setup <\/td>\n<\/tr>\n | ||||||
| 32<\/td>\n | Table 2 \u2013 Screening effectiveness of cable test methods for surface transfer impedance ZT <\/td>\n<\/tr>\n | ||||||
| 34<\/td>\n | 8 Comparison of the frequency response of different triaxial test set-ups to measure the transfer impedance of cable screens 8.1 General 8.2 Physical basics Figure 22 \u2013 Triaxial set-up for the measurement of the transfer impedance ZT <\/td>\n<\/tr>\n | ||||||
| 35<\/td>\n | Figure 23 \u2013 Equivalent circuit of the triaxial set-up <\/td>\n<\/tr>\n | ||||||
| 36<\/td>\n | Table 3 \u2013 Load conditions of the different set-ups <\/td>\n<\/tr>\n | ||||||
| 37<\/td>\n | 8.3 Simulations <\/td>\n<\/tr>\n | ||||||
| 38<\/td>\n | Table 4 \u2013 Parameters of the different set-ups <\/td>\n<\/tr>\n | ||||||
| 39<\/td>\n | Figure 24 \u2013 Simulation of the frequency response for g Figure 25 \u2013 Simulation of the frequency response for g <\/td>\n<\/tr>\n | ||||||
| 40<\/td>\n | Figure 26 \u2013 Simulation of the frequency response for g Figure 27 \u2013 Simulation of the frequency response for g <\/td>\n<\/tr>\n | ||||||
| 41<\/td>\n | Figure 28 \u2013 Simulation of the 3\u00a0dB cut off wavelength (L\/\u03bb1) <\/td>\n<\/tr>\n | ||||||
| 42<\/td>\n | Figure 29 \u2013 Interpolation of the simulated 3\u00a0dB cut off wavelength (L\/\u03bb1) Table 5 \u2013 Cut-off frequency length product <\/td>\n<\/tr>\n | ||||||
| 43<\/td>\n | Figure 30 \u2013 3\u00a0dB cut-off frequency length product as a function of the dielectric permittivity of the inner circuit (cable) <\/td>\n<\/tr>\n | ||||||
| 44<\/td>\n | Figure 31 \u2013 Measurement result of the normalised voltage drop of a single braid screen in the triaxial set-up <\/td>\n<\/tr>\n | ||||||
| 45<\/td>\n | Figure 32 \u2013 Measurement result of the normalised voltage drop of a single braid screen in the triaxial set-up <\/td>\n<\/tr>\n | ||||||
| 46<\/td>\n | Figure 33 \u2013 Triaxial set-up (measuring tube), double short circuited method Table 6 \u2013 Typical values for the factor v, for an inner tube diameter of 40\u00a0mm and a generator output impedance of 50\u00a0\u03a9 <\/td>\n<\/tr>\n | ||||||
| 47<\/td>\n | Figure 34 \u2013 Simulation of the frequency response for g Figure 35 \u2013 Simulation of the frequency response for g <\/td>\n<\/tr>\n | ||||||
| 48<\/td>\n | Figure 36 \u2013 Simulation of the frequency response for g Figure 37 \u2013 Simulation of the frequency response for g <\/td>\n<\/tr>\n | ||||||
| 49<\/td>\n | Figure 38 \u2013 Interpolation of the simulated 3\u00a0dB cut off wavelength (L\/\u03bb1) Table 7 \u2013 Cut-off frequency length product <\/td>\n<\/tr>\n | ||||||
| 50<\/td>\n | Figure 39 \u2013 3\u00a0dB cut-off frequency length product as a function of the dielectric permittivity of the inner circuit (cable) <\/td>\n<\/tr>\n | ||||||
| 51<\/td>\n | Figure 40 \u2013 Simulation of the frequency response for g Table 8 \u2013 Material combinations and the factor n <\/td>\n<\/tr>\n | ||||||
| 52<\/td>\n | Figure 41 \u2013 Interpolation of the simulated 3\u00a0dB cut off wavelength (L\/\u03bb1) Figure 42 \u2013 3\u00a0dB cut-off frequency length product as a function of the dielectric permittivity of the inner circuit (cable) Table 9 \u2013 Cut-off frequency length product <\/td>\n<\/tr>\n | ||||||
| 53<\/td>\n | 8.4 Conclusion Table 10 \u2013 Cut-off frequency length product for some typical cables in the different set-ups <\/td>\n<\/tr>\n | ||||||
| 54<\/td>\n | 9 Background of the shielded screening attenuation test method (IEC 62153 4 4) 9.1 General 9.2 Objectives Figure 43 \u2013 Definition of transfer impedance Figure 44 \u2013 Definition of coupling admittance <\/td>\n<\/tr>\n | ||||||
| 55<\/td>\n | 9.3 Theory of the triaxial measuring method Figure 45 \u2013 Triaxial measuring set-up for screening attenuation <\/td>\n<\/tr>\n | ||||||
| 56<\/td>\n | Figure 46 \u2013 Equivalent circuit of the triaxial measuring set-up <\/td>\n<\/tr>\n | ||||||
| 57<\/td>\n | Figure 47 \u2013 Calculated voltage ratio for a typical braided cable screen <\/td>\n<\/tr>\n | ||||||
| 58<\/td>\n | Figure 48 \u2013 Calculated periodic functions for \u03b5r1 = 2,3 and \u03b5r2 = 1,1 <\/td>\n<\/tr>\n | ||||||
| 59<\/td>\n | Figure 49 \u2013 Calculated voltage ratio-typical braided cable screen <\/td>\n<\/tr>\n | ||||||
| 60<\/td>\n | 9.4 Screening attenuation Figure 50 \u2013 Equivalent circuit for an electrical short part of the length \u0394l and negligible capacitive coupling <\/td>\n<\/tr>\n | ||||||
| 61<\/td>\n | 9.5 Normalised screening attenuation <\/td>\n<\/tr>\n | ||||||
| 62<\/td>\n | 9.6 Measured results Table 11 \u2013 \u0394a in\u00a0dB for typical cable dielectrics <\/td>\n<\/tr>\n | ||||||
| 63<\/td>\n | Figure 51 \u2013 as of single braid screen, cable type RG 58, L = 2 m Figure 52 \u2013 as of single braid screen, cable type RG 58, L = 0,5 m <\/td>\n<\/tr>\n | ||||||
| 64<\/td>\n | 9.7 Comparison with absorbing clamp method Figure 53 \u2013 as of cable type HF 75 0,7\/4,8 02YCY Figure 54 \u2013 as of cable type HF 75 1,0\/4,8 02YCY Figure 55 \u2013 as of double braid screen, cable type RG 223 <\/td>\n<\/tr>\n | ||||||
| 65<\/td>\n | 9.8 Practical design of the test set-up Table 12 \u2013 Comparison of results of some coaxial cables <\/td>\n<\/tr>\n | ||||||
| 66<\/td>\n | 9.9 Influence of mismatches Figure 56 \u2013 Schematic for the measurement of the screening attenuation as Figure 57 \u2013 Short circuit between tube and cable screen of the CUT <\/td>\n<\/tr>\n | ||||||
| 67<\/td>\n | Figure 58 \u2013 Triaxial set-up, impedance mismatches <\/td>\n<\/tr>\n | ||||||
| 68<\/td>\n | Figure 59 \u2013 Calculated voltage ratio including multiple reflections caused by the screening case Figure 60 \u2013 Calculated voltage ratio including multiple reflections caused by the screening case <\/td>\n<\/tr>\n | ||||||
| 69<\/td>\n | Annex A (normative) List of symbols <\/td>\n<\/tr>\n | ||||||
| 72<\/td>\n | Bibliography <\/td>\n<\/tr>\n<\/table>\n","protected":false},"excerpt":{"rendered":" Metallic communication cable test methods – Electromagnetic compatibility (EMC). Introduction to electromagnetic (EMC) screening measurements<\/b><\/p>\n |