How to measure current in tight PCB layouts?

Branched Rogowski Sensor for Precise Current Measurement through PCB

The innovative design of the branched Rogowski coil enables accurate current measurement through PCB, offering a bandwidth of up to 30 MHz and a di/dt capability of 100 kA/μs. This is an ideal solution for densely packed power electronics systems.

Based on the well-established series of ultra-miniature Rogowski probes CWTUM from PEM, the new variants – CWTUM-F and CWTUMHF-F – have been designed to meet the growing demands of current measurement in mechanically and height-constrained spaces. High-density component layouts require a new design approach.

Thanks to the innovative “branched” geometry, the probes allow real, non-invasive current measurement in hard-to-reach PCB points, while maintaining high frequency response and noise immunity. This is especially useful when measuring fast current changes in modern converter topologies.

Innovative Geometry of the Branched Coil

The key element is a unique fork-shaped design that allows bypassing embedded and hard-to-access PCB conductors. The slim coil profile minimizes proximity to other conductors, enabling measurements in very narrow gaps and away from noise sources.

Unlike traditional Rogowski probes, the “branched” variants feature a slim clip-together clamping mechanism, with dimensions of only 7.5 mm × 6 mm, allowing access where conventional probes cannot reach.

Comparison of Models: CWTUM-F vs CWTUMHF-F

The new series includes two variants tailored to different performance requirements:

CWTUM-F

• Coil thickness: 1.3 mm
• Bandwidth (-3 dB): 15 MHz

CWTUMHF-F

• Coil thickness: 1.7 mm
• Bandwidth (-3 dB): 30 MHz
• Enhanced noise immunity thanks to electrostatic shielding

The slight increase in coil thickness in the HF variant is offset by a significant improvement in noise suppression and accuracy of high-frequency measurements.

High-Frequency Current Measurements and Noise Immunity

The CWTUMHF-F variant uses PEM’s patented electrostatic shielding, which minimizes the impact of parasitic capacitance and interference caused by fast voltage transitions. This is critical when measuring current in systems with fast edge rates or significant signal ringing, such as in wideband motor drives and power converters.

Electrical Parameters and Applications

Both coil variants are characterized by:

• Current range: 60 A – 12 kA (peak)
• Maximum di/dt capability: 100 kA/μs
• Wide dynamic range, suitable for measuring small signals and large pulses

Thanks to these parameters, the probes are suitable for applications such as:

• Current profiling in switch-mode power supplies
• Ripple current measurement in capacitors
• Transient diagnostics of inverters and power stages
• Monitoring motor drive performance under fast switching

Choice of the right variant

• CWTUM-F – economical solution for moderate switching environments, e.g. industrial drives, low-noise converters, and test setups in space-constrained areas.
• CWTUMHF-F – high-performance variant for research laboratories, broadband systems, and precise measurements in harsh interference conditions, ensuring faithful reproduction of fast current waveforms and switching artifacts.

Source:

Bodo´s Power Systems bodospower.com