plc digital input output modulePLC

We know that the plc digital input output module in order to prevent interference generated by external circuit (such as voltage spikes, noise interference, etc.) caused by non-work PLC's even a damage to components, the general digital input module side are used optocoupler to cut off the internal circuit and the external circuit electrically PLC, to ensure the normal operation of the PLC. And in the input line has a RC filter circuit to prevent false signals due to the input jitter or pulse caused by external interference