How are EMS immunity test results determined?

During EMC testing, the frequently monitored conducted and radiated emissions tests generate measurement data to clearly show whether interference exceeds limits. However, the often overlooked EMS (Electromagnetic Susceptibility) immunity test also has limits. These limits are mostly based on the performance of the Equipment Under Test (EUT) after applying specified electromagnetic interference, and are evaluated in conjunction with performance criteria specified in relevant standards (such as the IEC 61000-4 series, product standard series, etc.). The following are the mainstream determination methods:



Performance Criterion Classification


The basic standards for EMS immunity testing typically classify performance criteria into the following categories:


Category A (Pass): During and after the test, the equipment functions normally, with no performance degradation or abnormalities, and conforms to design specifications.


Category B (Conditional Pass): During the test, a temporary reduction or loss of function or performance occurs, but it recovers automatically without manual intervention. Whether it passes depends on whether the product standard or test outline allows for such effects.


Class C (Failure): Abnormal function occurs during the test, requiring manual reset, restart, or operational intervention to recover.


Class D (Failure): Equipment is damaged or permanently loses function, and cannot be recovered.


Note: Product standards have basically simplified the criteria to three levels: A, B, and C. Class C includes situations requiring manual intervention or complete failure.


The above four levels are merely general descriptions of various basic standards. While the general meaning is similar, details must be based on the standard descriptions to clearly define the EMC product standard (basic, general, or product-specific) that the product should follow. For example, for lighting products, the main observation is changes in light intensity; for screen display products, the main observation is changes in image and whether there is a functional deficiency; for audio products, the main observation is the reproduction of the pitch, loudness, and sound type of musical sounds.

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