How to suppress interference in the control signal of the PMS (Power Measurement System) switch?

The switch control signals received by the PMS (such as remote closing/opening commands) are usually dry contacts or 24V level, which are susceptible to interference and malfunctions during long-distance transmission. Anti-interference design needs to start with input protection, filtering, and logic fault tolerance. For dry contact inputs, an RC circuit (e.g., 0.1μF + 10kΩ) is connected in parallel across the contact to absorb jitter, and a current-limiting resistor (e.g., 10kΩ) is connected in series before connecting to an optocoupler (e.g., TLP181), which provides electrical isolation.

For 24V level inputs, a TVS diode (e.g., SMBJ24CA) is used for protection, followed by RC low-pass filtering (e.g., 1kΩ + 0.1μF) before being shaped by a Schmitt trigger (e.g., 74HC14) and then sent to the MCU. All input circuits should be located away from noise sources and connected using shielded wires, with the shield grounded at one end. In terms of software, a digital filtering algorithm is used, such as requiring multiple consecutive samplings to confirm the status before execution, and a minimum pulse width recognition is set (e.g., 20ms). Through a combination of hardware and software, the switch control input can withstand IEC 61000-4-4 EFT level 4 (4kV) interference, with a false operating rate of less than 10^-6.