How to properly connect the I/O module chassis ground

Properly connecting the I/O module chassis ground is crucial for both safety and EMC. The chassis ground should be reliably connected to the safety protective ground using low-impedance metal contacts, such as conductive foam, metal springs, or direct screw fixation, with a contact resistance of less than 10 milliohms. Whether the circuit ground on the PCB is connected to the chassis ground depends on the system grounding strategy. In floating ground systems, the circuit ground and chassis ground are connected through a high-voltage capacitor, such as a 1nF/2kV Y capacitor, providing a discharge path for high-frequency noise while maintaining DC isolation.

In single-point grounding systems, the circuit ground is connected to the chassis ground at a single point at the power input via a resistor or ferrite bead. Openings on the chassis, such as vents or interface openings, should be less than 1/20th of the wavelength of the highest interference frequency, or waveguide ventilation panels should be used. All cables entering and exiting the chassis should have their shielding connected to the chassis via a 360-degree overlap at the entry point. The chassis itself should maintain electrical continuity, with low overlap impedance between different parts. After connection, grounding continuity testing and radiated emission testing should be performed to verify the effectiveness of the connection.