IEC TR 61917:1998 pdf download – Cables, cable assemblies and connectors -lntroduction to electromagnetic(EMC) screening measurements

IEC TR 61917:1998 pdf download – Cables, cable assemblies and connectors -lntroduction to electromagnetic(EMC) screening measurements.
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.
2 Reference documents
IEC 60096-1:1986. Radio-frequency cables — Part 1: General requirements and measuring methods
Amendment 2 (1993)
lC 60096-2:1961, Radio-frequency cables — Part 2: Relevant cable specifications Amendment 1(1990)
IEC 60096-4-1:1990. Radio-frequency cables — Part 4: Specification for superscreened cables
— Section 1: General requirements and test methods
IEC 60169-1:1987, Radio- Ire quency connectors — Part I: General requirements and measuring methods
IEC 60169-1-3:1988. Radio frequency connectors — Part 1: General requirements and measuring methods — Section 3: Electrical tests and measuring procedures — Screening effectiveness
lEG 61196-1:1995. Radio.frequency cables – Parr 1: Generic specification — General, definitions, requirements arid test methods
IEC 61726:1995, Cable assemblies, cables, connectors and passive microwave components — Screening attenuation measurement by the reverberation chamber method
3 ElectromagnetIc phenomena
It Is assumed that If an electromagnetic field Is Incident on a screened cable, there Is only weak coupling between the external field and that inside, and that the cable diameter is very small compared with both the cable length and the wavelength of the incident field. The superposition of the external incident field and the field scattered by the cable yields the total electromagnetic field (E1, 14 in figure 1). The total field at the screen’s surface may be considered as the source of the coupling: electric field penetrates through apertures by electric or capacitive coupling: also magnetic fields penetrate through apertures by inductive or magnetic coupling.
Additionally, the Induced current In the screen results In conductive ow resistive coupling.
4.3 Injecting with arbitrary cross-sections
A coaxial outer circuit has been assumed so far in this report, but it is not essential because of the Invariance of ZT and ZF Using a wire in place of the outer cylinder, the injection circuit becomes two-wire with the return via the screen of the cable under test. Obviously the charge and current distribution become non-uniform, but the results are equivalent to coaxial injection. especially if Iwo injection lines are used opposite to each other, and may be justified for worst- case testing. Note that the lEO line injection lest uses a wire.
4.4 ReciprocIty and symmetry
Assuming linear shield materials, the measured ZT and ZF values will not change when interchanging injection 1) and measuring (2) circuits. Each of the two conductors of the two line circuit can be Interchanged, but in practice the set’up will have to take into account possible ground loops and coupling to the environment.
4.5 ArbItrary load conditions
When the circuit ends of figure 3a and figure 3b are not ideally short or open circuit, Z1 and ZF will act simultaneously. The superposition is noticeable in the low frequency coupling of the matched circuits (figure 3c and table 1).
5 Long cables — coupled transmIssIon lInes
The coupling over the wtiole length of the cable is obtained by summing up (integrating) the infinitesimal coupling contributions along the cable while observing the correct phase. It Is expedient to make the following assumptions and conventions.