How to control interference at the I/O module DO output?

The key to controlling interference in the digital output channels of I/O modules lies in managing the high-frequency harmonics and voltage spikes generated by switching transients. For relay or transistor outputs, a freewheeling circuit must be connected in parallel across the inductive load, such as using fast recovery diodes RS2AB or ES3AC, to absorb the back electromotive force generated by the coil when turned off, preventing high-voltage breakdown. Simultaneously, output cables should use twisted-pair or shielded cables to reduce radiated emissions. A filter network consisting of ferrite beads and capacitors can be added to the output port; for example, a PBZ1608A-102Z0T ferrite bead paired with an X2 safety capacitor can effectively suppress noise conducted to the power line. In situations with severe high-frequency interference, ferrite cores can be used on the output lines to enhance high-frequency attenuation. At the PCB design level, the power supply of the DO driver circuit should be locally isolated using ferrite beads or small inductors, and the high-current return path should be short and wide to avoid loop antenna effects. Furthermore, optocouplers or magnetic couplings can be used for isolation between the output terminals and internal circuits; for example, high-speed optocouplers can be used for level conversion and noise isolation, blocking the conduction path of ground noise.