How to suppress interference from long cables in I/O modules?

Suppressing interference introduced by long cables in I/O modules requires a comprehensive approach using multiple technologies. First, select an interface standard suitable for long-distance transmission, such as a 4-20mA current loop or RS-485 differential bus, which inherently possess strong anti-interference capabilities. For cable selection, shielded twisted-pair cables must be used; the shielding layer provides electric field shielding, and the twisting pairs cancel out magnetic field interference. Install matching resistors at both ends of the cable, such as the 120Ω terminating resistor for RS-485, to eliminate reflections. At the I/O module interface, implement multi-level protection circuitry, such as gas discharge tubes absorbing lightning strike energy, varistors suppressing medium-energy surges, and TVS diodes clamping fast transients. For common-mode interference, install common-mode chokes at the ports, such as the CML series. If the cable is particularly long, repeaters or signal conditioners can be installed at appropriate locations in the middle. During cabling, long cables should be kept away from strong interference sources and run through metal conduits or metal cable trays. For analog signals, signal isolators can be used to convert field signals into isolated signals before sending them to the module. Regularly check the condition of cables and connectors to ensure continuous shielding and proper grounding.