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.