How to solve the noise problem when the PMS (Power Measurement System) switch is opening and closing?

During the opening and closing of the PMS switch, the bouncing and arcing of the mechanical contacts generate electromagnetic noise with an extremely wide bandwidth (tens of Hz to hundreds of MHz). This not only affects its own control circuit but may also conduct through the lines to interfere with the power grid. Solving this problem requires a combination of hardware and software solutions: multi-stage filtering and absorption in hardware, and debouncing and logic fault tolerance in software. Connecting a composite absorption circuit consisting of a metal oxide varistor (MOV) and an RC circuit in series across the switch contacts, such as a 7D390K varistor (V1mA=39V) in parallel with a 100nF capacitor and a 10Ω resistor, can effectively absorb arc energy and suppress voltage spikes. Installing a CMZ1211-501T common-mode inductor (500μH) on the switch control power line, along with a Y2 safety capacitor (2.2nF), filters the chassis. Adding a PBZ1608A-102Z0T ferrite bead to the output side of the switch driver optocoupler on the PCB. At the software level, a 10-20ms delay debouncing program is implemented after detecting a change in switch state to avoid misjudgment. This process reduces conducted interference from switch actions by more than 25dBμV, meeting the Level 4 requirement of GB/T 17626.4 Electrical Fast Transient/Bulk Immunity, and the false alarm rate during the switch's lifespan is less than 10^-5.