What is Conducted Susceptibility?

Conducted Susceptibility is concerned with the ability of an electronic circuit, a piece of equipment, or a subsystem or system to operate acceptably when subjected to radio frequency voltage or current on interconnecting conductors.  Conducted Susceptibility is also known as conducted immunity, particularly in European Union nomenclature.

In real-world applications radio frequency noise is induced on electrical conductors from a variety of sources through a variety of coupling mechanisms.  Load switching, electromagnetic fields, and con conducted emissions from equipment sharing the conductors are examples.  Generally, conducted susceptibility tests are intended to evaluate device response to low-mid frequency noise on the conductors, while radiated susceptibility tests are intended to test the response to mid-high frequency noise.  Radiated susceptibility is discussed in the next section.

Conducted susceptibility test signals are injected at a predetermined point on the conductors and may be injected between two or more conductors or in series with one or more conductors.  The injected signal may be voltage or a current.  Usually the maximum current for an injected voltage, or the maximum voltage for an injected current, is also specified to account for circumstances where the impedance of the circuit under investigation has very low impedance or very high impedance, respectively.

If the device under investigation is found to be susceptible to the applied signal, the amplitude at which the device exhibits susceptible behavior is called the susceptibility threshold.  Thus, for injected signals levels below the susceptibility threshold the device operates acceptably, and at levels above the susceptibility threshold the device does not operate acceptably.  The criteria for establishing what constitutes "operating acceptably" are a function of the device and its intended use.  Susceptibility threshold for a given device typically varies as a function of frequency.

Conducted Susceptibility tests are performed on a device to determine whether the device is susceptible to RF signals levels having specified amplitude over a specified frequency range.  If the device operates acceptably as the signal is applied and swept over the specified frequency range the device is considered to have passed.  If not, it has failed.  In many cases a device that is adversely affected by the applied signal will return to normal operation when the signal is removed.

CS Analyst allows device circuits to be modeled so that induced current and voltage amplitudes at each circuit component can be calculated at each frequency specified.  It is incumbent upon the user to determine what level of induced current or voltage in the circuits may be problematic for the circuit.

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Conducted Susceptibility Limits