Column: EMC
The importance of RF current monitoring probes in troubleshooting EMI
By Dr Min Zhang, EMC consultant at Mach One Design, and design engineers at REO UK A
current probe plays an essential role in EMC engineering by allowing users to measure RF current on cable structures,
distinguish common- and differential- mode current on cable structures and troubleshoot ESD issues. It can also be used to predict radiated far-field performance of cable structures and troubleshoot structural resonances that could lead to both emission and immunity problems.
In theory Essentially, a current probe is a type of current transformer, but it differs from Hall-effect current probes and Rogowski coils, which work differently. As the name suggests, an RF current probe is not effective at lower frequencies down to DC, unlike a Hall-effect current probe. However, the great benefit of an RF current probe is its ability to accurately measure current up to 1GHz. Current probe performance depends on
two main factors: on one hand, the coupling mechanism between the probe and the cable needs to be a mutual inductance. At the same time, a current probe is designed to work only with magnetic field coupling, meaning minimal electric field coupling is desirable. Manufacturing an RF current probe
is a complex procedure, which is why a commercial-grade current probe is oſten expensive. But, thanks to some manufacturers’ efforts to reduce the cost, high-quality clamp-on current probes are now available for under $1,000.
Applications Case 1 Figure 1 shows our first case study, where an RF current probe is clamped onto the mains cable of an active clamp flyback converter that uses GaN devices. Here
10 June 2023
www.electronicsworld.com
Figure 1: Using an RF current probe to predict far-field emissions
Figure 2: Using an RF-current and near-field probes to troubleshoot conducted emissions
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