How to connect the shielded ground of the I/O module?

Properly connecting the shielding ground of the I/O module is crucial for maximizing shielding effectiveness. The cable shielding should be connected to the chassis ground at the entry point into the module housing, using a metal connector housing or a dedicated shielding clip with a 360-degree low-impedance connection. Never twist the shielding layer into a "pig's tail" connection, as this introduces parasitic inductance and severely degrades high-frequency shielding. For partial shielding covers on the PCB, their grounding should be connected to the internal ground plane via a uniformly distributed array of vias around the perimeter, with the via spacing less than 1/20th of the wavelength of the highest frequency of interest.

If the shielding cover contains analog circuitry, it should be connected to the analog ground plane. The shielding layer of the isolation transformer or optocoupler inside the module should be connected to the static ground between the primary and secondary circuit grounds. In multi-level shielding systems, the grounding potential of the shielding layers should decrease sequentially from the inside out. After connection, shielding effectiveness testing is required, such as measuring attenuation at specific frequencies using an injection probe and receiving antenna. Simultaneously, ensure that the shielding connection does not accidentally introduce new ground loops.