Immunity vs. emissions — simply explained.

EMC has two directions: what does my device emit — and how robust is it against interference from outside? Once you keep the two apart, you understand test reports and countermeasures much better.

Emissions

Describes the electromagnetic interference a device emits — conducted (via cables) or radiated (through the air). The goal: don't disturb other devices. Typical causes are clock signals, switching edges and poorly routed return currents.

Immunity

Describes how robust a device is against interference from outside. Testing includes, among others:

ESD — electrostatic discharge (the “spark”).
Burst — fast transient interference (e.g. from switching operations).
Surge — high-energy transient overvoltages (e.g. from lightning/mains).

Why the two belong together

Countermeasures often affect both sides: a good grounding and shielding concept reduces emissions and increases immunity. That is exactly why we look at the system as a whole.

In brief

Which is more important — immunity or emissions?

Both are required for conformity. Which side is critical depends on the product, environment and standard — often the application decides (e.g. a medical or railway environment).

Can a single measure improve both?

Yes. A well-thought-out grounding concept and clean shield termination usually improve emissions and immunity at the same time.