Circuit model of transient cross-coupling
Using a signal generator and an oscilloscope, measurements were made of the differential-mode current and the common-mode current in a twin-conductor cable installed on a test rig, over a range of frequencies which included half-wave resonances. Test data was used to assign component values to a Triple-T circuit model of the assembly. This model was then transformed into a transient coupling model. The signal generator was reset to generate square waves, and photographs were taken of the waveforms of the input voltage and the common-mode current. A close correlation was achieved between these waveforms and those of the transient coupling model. This demonstrates that the technique of circuit modelling and bench testing is reliable and accurate, in both the frequency domain and the time domain. The technique allows potential hazards due to transient interference to be analysed, tested, and quantified during the design process. Electromagnetic interference can be analysed without recourse to the mathematics of full-field modelling. It is also shown that, from the point of view of Electromagnetic Compatibility, the concepts of the single-point ground and the equipotential ground are both misleading and counter-productive.
