Conducted susceptibility and immunity are essentially two important aspects of EMC Testing. Conducted susceptibility refers to the ability of electronic equipment to withstand electromagnetic interference that is coupled through the power or signal lines whereas Conducted Immunity, on the other hand, refers to the ability of electronic equipment to resist external electromagnetic interference that is coupled through the power or signal lines. The sources considered for conducted susceptibility testing includes those which are in the range of the device whereas, for conducted immunity, the sources are purely external.

Fig: Conducted Susceptibility Test Set-up

Generally, conducted susceptibility tests are intended to evaluate device response to low-mid frequency noise on the conductors. Conducted susceptibility test signals are injected at a pre-determined point on the conductors. The injected signal may be a voltage or a current. If the device operates acceptably as the signal is applied and swept over the specified frequency range, the device is considered to have passed.

Conducted susceptibility testing applies specific types of interference, such as surges, spikes, and bursts, to the power and signal lines of the device to assess its ability to withstand the effects. On the other hand, conducted immunity testing subjects the device's power and signal lines to a range of electromagnetic interference types, including high-frequency noise, to determine whether it can resist the effects of interference.

Conducted susceptibility and immunity testing is crucial to ensuring the proper function and safety of the electronic equipment. Without proper testing, electronic devices may malfunction, leading to potential safety hazards, lost productivity, and costly repairs. Moreover, regulations and standards such as MIL-STD-461, IEC 61000, and FCC Part 15 mandate that electronic devices undergo conducted susceptibility and immunity testing to ensure compliance with safety and performance standards. These tests help manufacturers to identify potential weaknesses in their products' design and to make necessary modifications to improve their resilience to interference. These tests also provide confidence that the device will function correctly in its intended environment, ensuring the safety of its users and others.

Standards that address conducted susceptibility:

MIL-STD-461: This is a U.S. military standard that specifies the requirements for the control of electromagnetic interference emissions and susceptibility in military equipment. Part 4 of this standard specifically addresses conducted susceptibility.

CISPR 25: This is an international standard that applies to the electromagnetic compatibility of vehicles, boats, and internal combustion engines. Section 5 of this standard specifies the requirements for conducted susceptibility.

IEC 61000-4-6: This is an international standard that specifies the requirements for immunity testing of equipment to conduct disturbances. It provides procedures and requirements for testing equipment under both laboratory and field conditions.

FCC Part 15: This is a U.S. Federal Communications Commission standard that regulates the emissions of radio frequency devices. Part 15 specifically addresses conducted emissions and susceptibility.

EN 50121: This is a European standard that applies to the railway environment. It specifies the requirements for the electromagnetic compatibility of railway systems and equipment, including requirements for conducted susceptibility.

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