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1、 IEC/TR 62153-4-1 Edition 1.0 2007-11 TECHNICAL REPORT Metallic communication cable test methods Part 4-1: Electromagnetic compatibility (EMC) Introduction to electromagnetic (EMC) screening measurements IEC/TR 62153-4-1:2007(E) Copyright International Electrotechnical Commission Provided by IHS und
2、er license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without license from IHS -,-,- THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2007 IEC, Geneva, Switzerland All rights reserved. Unless otherwise sp
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10、HS under license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without license from IHS -,-,- IEC/TR 62153-4-1 Edition 1.0 2007-11 TECHNICAL REPORT Metallic communication cable test methods Part 4-1: Electrom
11、agnetic compatibility (EMC) Introduction to electromagnetic (EMC) screening measurements INTERNATIONAL ELECTROTECHNICAL COMMISSION XA ICS 33.100; 33.120.10 PRICE CODE ISBN 2-8318-9364-X Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1
12、111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without license from IHS -,-,- 2 TR 62153-4-1 IEC:2007(E) CONTENTS FOREWORD.5 INTRODUCTION.7 1 Scope.8 2 Normative references8 3 List of symbols9 4 Electromagnetic phenomena.10 5 Intrinsic scree
13、ning parameters of short cables.12 5.1 Surface transfer impedance, ZT.12 5.2 Capacitive coupling admittance, Yc12 5.3 Injecting with arbitrary cross-sections.14 5.4 Reciprocity and symmetry14 5.5 Arbitrary load conditions 14 6 Long cables Coupled transmission lines.14 7 Transfer impedance of a braid
14、ed-wire outer conductor or screen.20 8 Test possibilities.26 8.1 Measuring the transfer impedance of coaxial cables.26 8.2 Measuring the transfer impedance of cable assemblies27 8.3 Measuring the transfer impedance of connectors .27 8.4 Calculated maximum screening level .27 9 Comparison of frequenc
15、y response of different triaxial test set-ups to measure transfer impedance of cable screens.32 9.1 Introductory remark .32 9.2 Physical basics32 9.3 Simulations35 9.4 Conclusion 49 Bibliography50 Additional reading .51 Figure 1 Incident (i), scattered (s) and resulting total electromagnetic fields
16、(Et, Ht) with induced surface current- and charge- densities J (A/m) and (C/m2) .11 Figure 2 Defining and measuring screening parameters Triaxial set-up 11 Figure 3a Equivalent circuit for the definition and possible testing of Z 13 Figure 3b Equivalent circuit for the definition and possible testin
17、g of Yc = j CT13 Figure 3c Definition of electrical quantities in a set-up that is matched at all ends .13 Figure 3 Defining and measuring screen parameters Equivalent circuits.13 Figure 4 Summing function flS for near (n) and far (f) end coupling .17 Figure 5a Transfer impedance of a typical single
18、 braid screen 18 Figure 5b Coupling transfer function for the same cable with negligible ZF(ZF Z2 (audio circuits). Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo r
19、eproduction or networking permitted without license from IHS -,-,- TR 62153-4-1 IEC:2007(E) 13 V E1 + Injection cylinder Shield Center conductor (1) l Sn above near end cut-off, yielding a directive effect. Key c )(fl cut-off point Figure 4 Summing function flS for near (n) and far (f) end coupling
20、Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without license from IHS -,-,- 18 TR 62153-4-1 IEC:2007(E) log ZT log f f1 20 dB
21、/dec. IEC 2158/07 ()/mm20MHz 10 1T =fZ Figure 5a Transfer impedance of a typical single braid screen ZT Env (Tf) log ZT log f fr fcnfcf Tn Tf l 2 1 Z12 Env (Tn) IEC 2159/07 Figure 5b Coupling transfer function for the same cable with negligible ZF(ZF fc. EXAMPLE: 1 r1 = (set-up), 22 r2 .= (cable), M
22、Hz 200 MHz, 40 m 1 CfCn =ffl Figure 5 The effect of the summing function Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without
23、 license from IHS -,-,- TR 62153-4-1 IEC:2007(E) 19 1105 1106 1107 1108 1109 11010 -80 -60 -40 TnztdBk TfztdBk fk T dB Tf Tn f Hz IEC 2160/07 Figure 6a Calculated coupling transfer functions Tn and Tf for a single braided when ZF = 0 In calculations the used parameters are: ZT (d.c.) =15 m/m and ZT
24、(10 MHz) = 20 m/m increasing 20 dB/decade (see Figure 5a), cable length 1 m, and velocities of the outer and inner line: v1 = 200 Mm/s and v2 = 280 Mm/s corresponding a velocity difference of 40 %. 1105 1106 1107 1108 1109 11010 -80 -60 -40 TndBk TfdBk TnztdBk TfztdBk fk T dB Tf Tn f Hz IEC 2161/07
25、Figure 6b As Figure 6a but Im(ZT) is positive and ZF = +0,5*Im (ZT) at high frequencies: Tn is 3,5 dB higher and Tf 6 dB lower than in reference Figure 6a because Tn ZF + ZT = 1,5*ZT and Tf ZF ZT = 0,5*ZT. 1105 1106 1107 1108 11010 1109 -80 -60 -40 TndBk TfdBk TnztdBk TfztdBk fk T dB Tf Tn f Hz IEC
26、2162/07 Figure 6c As Figure 6a but Im(ZT) is negative and ZF = 0,5*Im(ZT) at high frequencies: Tf is 3,5 dB higher and Tn 6 dB lower than in reference Figure 6a because Tf ZF ZT = 1,5* ZT and Tn ZF + ZT = 0,5* ZT NOTE 1 Tn for near-end, Tf for far-end and dB means that Tn,f are calculated in dB ( 20
27、 lg | Tn,f | ). NOTE 2 Tn dB: near-end when() TF 21ZZ=/ and Tnzt dB: near-end when ZF = 0. NOTE 3 Tf dB: far-end when () TF 21ZZ=/ and Tfzt dB: far-end when ZF = 0. Figure 6 The effects of the ZT and ZF to the coupling transfer functions Tn and Tf In Figure 6a, ZF = 0. Copyright International Electr
28、otechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without license from IHS -,-,- 20 TR 62153-4-1 IEC:2007(E) In Figure 6b and Figure 6c, ZF is significant () TF
29、 21ZZ=/). In Figure 6b ZT is positive and Figure 6c negative at high frequencies. log l S log l Env (l Sf) n f f = const. Env (l Sn) IEC 2163/07 NOTE 4 For l lc, the maximum value of T is attained, i.e. the maximum coupling (or the screening attenuation) is not dependent on l. NOTE 5 lcf strongly de
30、pends on r1. Figure 7 l S: complete length dependent factor in the coupling function T (see Table 1) 7 Transfer impedance of a braided-wire outer conductor or screen Typical transfer impedances of cables with braided-wire screens are shown in Figure 8. The constant ZT value at the low-frequency end
31、is equal to the DC resistance of the screen, the 20 dB/decade rise at the high-frequency end is due to the inductive coupling through the screen and the dip at the middle frequencies is caused by eddy currents or skin effect of the braid. Some braided cables may behave anomalously, having less than
32、a 20 dB/decade rise at high frequencies. By using an extrapolation of 20 dB/decade, this remains in most cases on the conservative side. This extrapolation can be used up to several GHz. An electrically short piece of braided coaxial cable (2) is considered to be placed in a triaxial arrangement as
33、in Figure 2. It is assumed that the outer circuit (1) is the disturbing one. As stated a braided cable has a transfer impedance ZT that increases proportionally to frequency at high frequencies, because of the leakage of the magnetic field through holes in the braid. The total flux of the magnetic f
34、ield induced by the disturbing current I1 is 1. A part of it, 12 leaks directly through the holes and includes a disturbing voltage U2 in the inner circuit. However, a part 12 of 1 flows in the braid and complicates the mechanism of the total magnetic leakage by the following additional phenomenon:
35、the braiding wires alternate between the outer and inner layer. It means that the inner and outer braid wires are likewise ingredients of both the inner (1) and outer (2) circuit of Figure 9a. Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Empl
36、oyees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without license from IHS -,-,- TR 62153-4-1 IEC:2007(E) 21 20 dB/dec.sb sbodb sba ss log f fr ZT Log scale IEC 2164/07 Key fr typically 1 . 10 MHz sb single braid sbo single braid optimiz
37、ed sba single braid anomalous db double braid s superscreen Figure 8 Transfer impedance of typical cables I1 Flux lines Braid Centre conductor U“2 (1) (2) “12 I1 1 IEC 2165/07 Figure 9a Complete flux “12 U“th (1) (2) IEC 2166/07 Figure 9b Left-hand lay contribution (1) (2) “12 U“rh IEC 2167/07 Figur
38、e 9c Right-hand lay contribution Figure 9 Magnetic coupling in the braid Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without
39、 license from IHS -,-,- 22 TR 62153-4-1 IEC:2007(E) Therefore it is necessary and unavoidable that 12 is partly also in the inner circuit, Figure 9b. Both the right hand (rh) and left hand (lh) lay of the braiding wires bring into the inner circuit (2) an equal disturbing voltage U2 induced by 12 /
40、2. The voltages are in parallel: Urh = Ulh = U2 = j12 (21) This phenomenon is similar to the “magnetic part“ of the coupling through a homogeneous screen. The two induced disturbing voltages oppose each other. +30 +20 +10 -10 -20 -30 -40 -50 -60 -70 -30 -20 -10+20+30 0 4 2 1 0,4 0,2 0,4 0,1 0,4 12 4
41、 8 14 1 2 4 m m Im Z T Re f/ MHz f/ MHz f/ MHz Underbraided Optimized Overbraided m m ZT IEC 2168/07 Figure 10a Complex plane, ZT = Re ZT + j Im ZT, frequency f as parameter Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, U
42、ser=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without license from IHS -,-,- TR 62153-4-1 IEC:2007(E) 23 Overbraided Underbraided Optimized m m ZT 1 000 100 10 1 0,1 110100 f (MHz) fr IEC 2169/07 Figure 10b Magnitude (amplitude), | ZT (f) | Figure 10 M
43、easured transfer impedance ZT (d.c. resistance ZT (d.c.) set to the value of 10 m /m Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permi
44、tted without license from IHS -,-,- 24 TR 62153-4-1 IEC:2007(E) IEC 2170/07 Figure 11a Overbraided cable IEC 2171/07 Figure 11b Underbraided cable Key Top trace: Injection step current (100 mA/div) Time base: 50 ns/div Amplifier gain: 30 dB, therefore Zt (time) = 12,5 m/m/div Lower trace: height of
45、spike corresponds to: - Figure 11a Zt(3 MHz) = 4,7 12,5 m/m = 59 m/m - Figure 11b Zt(3 MHz) = +4,7 12,5 m/m = +50 m/m Figure 11 Typical ZT (time) step response of an overbraided and underbraided single braided outer conductor of a coaxial cable Braid optimization is based on these important physical
46、 facts. Both leakage phenomena can be described by mutual inductances: 1 12 12 jI M = (22) 1 12 12 j2 1 I M = (2) Clearly it is possible to make braided-wire screens where either M12 or M12 are dominant or where they cancel each other, Therefore, underbraided, overbraided or optimized braids may Cop
47、yright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:34:49 MSTNo reproduction or networking permitted without license from IHS -,-,- TR 62153-4-1 IEC:2007(E) 25 be considered. Figure 10a shows me