= Electromagnetic compatibility
<Electromagnetic compatibility> is the ability of electrical equipment to operate as intended in its electromagnetic environment without causing unacceptable disturbance to other equipment. Emission and immunity are complementary questions: how strongly does a device disturb its surroundings, and how well does it tolerate disturbances arriving from them?
Interference requires a source, a coupling path and a susceptible receiver. A switching power converter may couple a disturbance into a sensor through shared supply impedance, capacitive coupling or radiated fields. In an illustrative circuit, a $0.2$ A switching-current change through a shared $0.1\,\Omega$ return impedance produces a $20$ mV reference shift, potentially much larger than the sensor signal. A balanced connection and finite <common-mode rejection ratio> help only to the extent that the disturbance remains common to the two inputs.
A useful test compares the sensor output with the converter switched on and off, then deliberately changes the coupling path or applies a calibrated disturbance. Antenna patterns, cable routing, grounding and frequency all enter the inference; passing one test configuration does not imply immunity to every disturbance.<Antenna Models for Electromagnetic Compatibility Analyses by C. W. Wang and T. Keech>[Executive summary, antenna parameters and electromagnetic-interference analyses]{ref}
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