How can the EMC limits of power equipment such as electrical power measurement switches (PMS) meet the standards?

As electrical equipment, PMS (Power Measurement System) must meet both general standards (such as GB/T 9254) and applicable product-specific standards (such as GB/T 17215 "Electrical Measuring Equipment" series) in terms of EMC limits. The compliance strategy is to allow sufficient margin during design. For conducted emissions (CE), in the 150kHz-30MHz frequency band, Class A or Class B limits must be met (Class A is typically used in industrial environments). In terms of design, this is achieved by using input filtering (common-mode inductor CMZ1211-501T + X/Y capacitors) and board-level filtering to control measured values below the limits by 6dB.

For radiated emissions (RE), in the 30MHz-1GHz frequency band, the corresponding limits must also be met, depending on the enclosure shielding, internal PCB layout, and cabling. Regarding immunity, it must meet the severity levels specified in the GB/T 17626 series, such as surge level 4 and EFT level 4, achieved through graded protection and circuit hardening. Pre-compliance testing is crucial during the product development phase. It uses near-field probes, spectrum analyzers, and other equipment to conduct preliminary testing and identify and rectify any non-compliance issues early on. Finally, formal testing is conducted in a third-party laboratory to obtain a compliance report.