Circuit Modelling for Electromagnetic Compatibility






Circuit Modelling for Electromagnetic Compatibility



Circuit model of transient cross coupling


Plain language title
Simulating the effect of transient interference due to currents in adjacent conductors.


What’s it about?

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 transformed into a transient coupling model. The signal generator was set to generate square waves and photographs taken of the waveforms of the input voltage and the common-mode current. 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. The technique allows potential hazards due to transient interference to be analysed, tested, and quantified during the design process. It is shown that the concept of the single-point ground is profoundly misleading.


Why is it important?

By combining time-step analysis with the concept of moving charges, this model can be used to simulate the magnetostatic, electrostatic, and electromagnetic effects due to currents and voltages in adjacent conductors. Since it is a circuit model, it can be analysed by any electrical engineer. The Mathcad worksheets used to carry out the calculations can be downloaded and used to simulate the performance of any signal link or any power link.



The ability to analyse the mechanisms involved in the propagation of interference using circuit models brings with it a much better understanding of those mechanisms. This brings with it the further ability to create designs which meet EMC requirements.


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