How to suppress interference at the concentrator's data acquisition interface?

The concentrator's acquisition interfaces (such as pulse inputs and status dry contacts) are susceptible to external induced overvoltage and jitter interference. Suppression requires protection, filtering, and isolation. For pulse inputs (such as meter pulses), a TVS diode SMBJ6.5CA is connected in parallel at the input for transient suppression, followed by a 100Ω resistor in series and then an RC low-pass filter (1kΩ + 1nF) before entering the Schmitt trigger for shaping. For dry contact status inputs, an RC absorber (0.1μF + 10kΩ) is connected in parallel across the contact and isolated by an optocoupler (such as TLP181) before being sent to the MCU. All acquisition interface cables use shielded cables, with the shield grounded at a single point at the concentrator. In terms of PCB layout, the acquisition interface circuits are centrally located and isolated from the digital circuits using a ground plane. In terms of software, an anti-jitter algorithm is added when counting pulses. Through comprehensive suppression, the acquisition interface can withstand IEC 61000-4-4 EFT 4kV interference and acquire data without errors.