How to meet the emission immunity standards for I/O modules?

To ensure I/O modules meet radiated interference immunity standards, their resistance to electromagnetic fields in space needs to be enhanced. First, the module should have a fully shielded metal housing, with conductive gaskets at all cover joints to ensure electrical continuity, and waveguide plates used for ventilation holes. The housing provides the first line of defense. Second, all incoming and outgoing cables are the main pathways for interference coupling, therefore shielded cables must be used, with the shielding layer terminating 360 degrees to the housing at the entry point. For cables that cannot be shielded, common-mode chokes and filter capacitors should be installed at the ports. At the PCB level, local shielding can be used in critical circuit areas.

Optimize the PCB layout, reduce the area of high-frequency signal loops, and ground the clock signal. Use optocouplers or digital isolators that are insensitive to radiated interference for internal and external signal isolation. On the software side, add watchdog timers and exception recovery mechanisms to programs susceptible to interference-induced malfunctions. During testing, conduct tests in an anechoic chamber according to IEC 61000-4-3 standards, using field strength probes to monitor the field strength at key points inside the module, identify weak points, and strengthen shielding or filtering accordingly. Multiple iterations are usually required to achieve a higher field strength level.