EMI/EMC Academy ~30 min Interactive

Immunity Pre-Compliance & Debug

Emissions are half of EMC; the product also has to keep working when the world pushes back. This module covers quick, safe bench checks that approximate ESD, EFT/burst, surge and radiated immunity — and how to harden a design that trips.

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Learning objectives. Recall the four common immunity tests and their standards; run safe, approximate bench pre-checks; reproduce field failures; recall the performance criteria (A/B/C); and harden with TVS/varistors, filtering and firmware recovery.
Test Standard Stress Deep dive
ESD IEC 61000-4-2 ±kV contact/air discharge ESD course
EFT / Burst IEC 61000-4-4 Fast repetitive transients on power/IO —
Surge IEC 61000-4-5 High-energy 1.2/50 µs surge Surge course
Radiated immunity IEC 61000-4-3 3–10 V/m RF field —

Conducted immunity (IEC 61000-4-6) injects RF onto cables and is the immunity counterpart to conducted emissions. Note the symmetry: the same coupling paths that let noise out (Modules 5–8) let interference in, so most emission fixes also improve immunity.

You can approximate immunity stresses cheaply — but respect the energy involved. ESD: an ESD simulator gun is ideal; if unavailable, a proper ESD pre-compliance kit beats improvised sparks. Radiated immunity: a small hand-probe/antenna driven by a signal generator + amplifier can find susceptible frequencies (relative, not calibrated). EFT: a bench burst generator couples onto power/IO via a capacitive clamp.

Safety first. Surge and EFT involve high voltage/energy — use proper generators, coupling/decoupling networks, isolation and PPE, exactly as in the Surge test-setup module. Do not improvise high-energy surge tests on the bench.
Reproduce the field failure first. If a customer sees resets when a motor switches nearby, that's an EFT/burst clue. Instrument the failing signal (scope on reset, power, key IO) so you can see the upset and prove the fix with the delta method.

Pick the observed failure and get the likely stress and first hardening steps.

Immunity results are graded by performance criteria: A = normal operation during the test; B = temporary degradation that self-recovers; C = requires operator intervention (e.g., power cycle). Know which criterion your product must meet — a watchdog that auto-recovers can turn a failing "C" into an acceptable "B".

Key takeaways. Immunity uses the same coupling paths as emissions, so bench pre-checks and the delta method still apply — safely. Harden with TVS/varistors, filtering, bonding and firmware recovery. Next, we assemble everything into one debug methodology.
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