How to ensure EMC when collecting data via dry contact of a concentrator?

The dry contact data acquisition of the concentrator (such as circuit breaker status) is susceptible to interference from induced overvoltage and contact bounce. Ensuring EMC requires a combination of external protection and built-in processing. For input dry contacts, an RC snubber network (0.1μF + 100Ω) is connected in parallel across the contact, followed by a current-limiting resistor (10kΩ) in series before entering an optocoupler (such as TLP181). The optocoupler provides isolation and level conversion. For output dry contacts (relay output), an RC snubber network (0.1μF + 100Ω) or an MOV (7D390K) is connected in parallel across the relay contact, and a freewheeling diode is connected in reverse parallel across the coil. All dry contact signal lines use shielded twisted-pair cable, with the shielding layer connected to the chassis ground at a single point at the concentrator end. In the PCB layout, the dry contact circuitry is centrally located and isolated from the digital circuitry using a ground plane. Software performs debouncing processing on the input (e.g., a 10ms delay). This design meets the requirements of IEC 61000-4-4 EFT Level 4 and IEC 61000-4-5 Surge Level 3.