Some observations on bulk cable current injection test method

Conductive susceptibility test by bulk cable current injection designated as CS114 by MIL.STD 461D is being recommended as an EMI test applicable to all electrical cables interfacing with the EUT enclosures. The basic concept of CS114 is to stimulate currents which will be developed on platform cabling from electromagnetic fields generated by antenna transmissions. An advantage of bulk current injection is that low RF power can induce currents in wire bundles that would require high radiated power to induce the same currents. However, the two different excitations might produce different current distributions, because, radiated excitation includes sources distributed over the length of the line while in injection, the source is a single discrete source. In view of the differences between these two excitations, the susceptibility aspects of a rocket power module (DC/DC converter) were examined for radiated excitation and current injection. The nature of current, induced on the cable bunches of the converter which were unshielded cables, was observed for radiated excitation and for current injection. The details of test setup, measurements and results are presented. To get more insight into the nature of the current induced by these two different excitations, general tests have been conducted on coaxial, twisted pair and twisted shielded pair cables of finite length and terminated with 50 ohm impedance. The cables are subjected to radiation and current injection and the currents induced on the cables in respective cases were measured using current probes and EMI meter