EMC Question of the Week: May 7, 2018
What noise source are Electrical Fast Transient (EFT) tests designed to simulate?
- electrostatic discharge
- lightning
- nuclear electromagnetic pulse
- switched inductive loads
Answer
The correct answer is "d." When the flow of electric current in an inductive load is suddenly interrupted (e.g. by opening a switch), a large voltage is developed across the point of the interruption (v = L di/dt). This voltage transient can cause arcing resulting in additional voltage and current transients in the circuit. This transient noise can then be transferred to other nearby circuits through electric and magnetic field coupling.
EFT test waveforms typically apply transients in bursts lasting several milliseconds, with each transient having transition times on the order of nanoseconds. The transients are coupled to the circuits under test through a capacitance using a coupling network or capacitive coupling clamp.
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