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RF Current Monitoring Probes

An RF current monitoring probe is a valuable tool in the world of electromagnetic compatibility (EMC) engineering.

1. Purpose:

o Measuring High-Frequency Common-Mode (CM) Currents: These probes are specifically designed to measure high-frequency common-mode currents flowing on wires or cables.

o Troubleshooting EMC Issues: By using these probes, engineers can identify and troubleshoot issues related to poorly terminated (bonded or filtered) cable shields. These shields are often the primary cause of radiated emissions failures during EMC compliance testing.

o Predicting Test Chamber Performance: Engineers can predict, with a good degree of accuracy, whether a given cable current will pass or fail in the measurement chamber. This helps save time during testing and ensures efficient fixes.

2. How They Work:

o The RF current probe is an “inserted-primary” type of radio frequency current transformer.

o When clamped over the conductor or cable in which current is to be measured, the conductor becomes the primary winding.

o The probe acts as a broadband high-frequency transformer, allowing measurement of high-frequency currents in cables without physically disturbing the circuit.

o The clamp-on feature enables easy placement around any conductor or cable.

3. Common-Mode Currents:

o CM currents are generated due to finite impedance in system grounding, including circuit board signal/power return planes.

o Simultaneous digital switching causes “ground bounce,” leading to CM currents throughout the system.

o These CM currents propagate through common cabling or circuit traces and between circuits or sub-systems.

4. Application:

o Engineers use RF current probes to measure CM currents on cables passing through their aperture.

o These probes cover a wide frequency range, typically from 20 Hz up to 500 MHz.

o They come in different aperture sizes (e.g., 1.25" and 2.6") to accommodate various cable diameters.

In summary, RF current monitoring probes play a crucial role in diagnosing and addressing EMC-related challenges, ensuring compliance with electromagnetic compatibility standards.

Standard RF Current Monitoring Probes

Tekbox RF current monitoring probes cover frequencies up to 1 GHz. The fixed aperture series is particularly cost-effective. In situations where the cable harness cannot be easily disconnected to feed it through the aperture, Tekbox provides the TBCP2 series snap-on probes.

To calculate the current flowing through the wires passing the probe aperture, subtract the trans-impedance value documented in [dB] from the probe's output voltage.

RF Surface Current Monitoring Probes

RF surface current monitoring probes are used in applications where RF currents flowing on surfaces such as PC ground planes or traces, metal planes or wires need to be measured.

Coaxial RF Current Monitoring Probes

Coaxial RF current monitoring probes are used to measure RF currents in coaxial cables. They can be used as general purpose coupling devices to measure RF power or as loop antenna transducers.

RF Pulse Current Monitoring Probes

RF pulse current monitoring probes are typically used for surge or RF pulse current monitoring applications in the time domain.

Bulk Current Injection Probes

Bulk Current Injection probes are used to inject RF current into cables of electrical equipment to test their susceptibility to radiated electromagnetic energy. Tekbox BCI probes can be clamped around wire bundles up to 27mm in diameter. They are designed to meet the requirements of IC 61000-4-6 (domestic and industrial products) and ISO 11452-4 (automotive products).