What is Bulk Current Injection (BCI) Probes? 

A Bulk Current Injection (BCI) probe is an electrical device used in Conducted immunity testing. It is used to inductively inject RF current into the power lines and/or signal cables of the device under test (DUT) to assess the DUT's immunity to these injected RF-conducted disturbances. This testing procedure is known as Bulk Current Injection (BCI) testing. 

Figure: Bulk Current Injection (BCI) probe 

The purpose of the conducted immunity test is to inject RF test signals into the DUT’s cables/lines to simulate external conducted disturbances and evaluate the DUT's performance under these conditions. In the BCI test, the BCI probe injects RF current or test signals into the lines and cables of the DUT without requiring a direct connection (i.e., utilizing inductively coupling). If the DUT operates satisfactorily under the test conditions, it is considered to pass the immunity test and comply with relevant EMC immunity test standards; otherwise, the DUT is considered as failing the test and does not comply with the test standards.  BCI probe plays a key role in this test. 

The immunity test ensures that the DUT operates reliably without experiencing malfunctions in its intended practical environment, where RF-conducted disturbances may occur. 

Construction and Working Principle of a BCI Probe: 

Figure shows the bulk Current Injection (BCI) test setup. The test setup consists of a DUT, a signal generator, a power amplifier, a BCI probe, a measuring clamp, a suppression device, a spectrum analyzer/RF power meter, and other auxiliary equipment. The BCI probe construction consists of split-core ferrites with windings around the core, enclosed by a rugged circular outer shield with a 50 Ω coaxial input port. This design allows for easy placement of power lines or signal leads into the probe. A calibration fixture (not shown) is used to position the current probe around the conductor or cable.  

Figure: Bulk current Injection (BCI) test setup and probe construction 

The BCI probe functions as a toroidal transformer. When placed around a power line or signal lead to inject current, the probe acts as the multi-turn primary winding, while the power line or signal lead acts as the single-turn secondary winding. When an RF signal generator injects an RF test signal into the probe (via a power amplifier), there is a current flow through the primary winding, creating a magnetic field. This magnetic field induces RF currents into the secondary winding (the DUT’s cable/lines) through transformer action.

Additionally, a current measurement probe or monitoring probe is placed or positioned near the DUT to measure the injected current level with the help of a spectrum analyzer or RF power meter. This setup enables the BCI probe to inject a controlled level of RF stress level to the DUT without direct connection to the power line/cables.  

Applications: 

The Bulk Current Injection (BCI) probes are available in various frequency ranges, such as 10 kHz to 400 MHz, 500 MHz to 1 GHz, and 10 kHz to 1 GHz, to meet different standard requirements. They come with different maximum input power ranges and inner/outer diameters. These probes are utilized by various test standards such as IEC 61000-4-6 (commercial), MIL-STD 461 (Military), RTCA/DO-160 (aeronautics), and ISO 11452-4 & SAE J1113-4 (Automotive) to perform BCI testing for electrical and electronic devices with varying test levels and frequencies, as per test standard requirements.  

Key specification details of BCI probe: 

Frequency: The operating frequency range of the BCI probe, for example, 10 kHz to 400 MHz. 

Current: The current rating of the probe, expressed in amperes (A). 

Inner Diameter: The probe's inner diameter, typically expressed in millimeters (mm). 

Outer Diameter: The probe's outer diameter, typically expressed in millimeters (mm). 

Max Input Power: The maximum input power that the BCI probe can handle. 

EMC Standards: The EMC standards that the probe supports. 

Weight: The probe's weight, usually expressed in kilograms (Kg). 

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