In today's industrial automation systems, programmable logic controllers (PLCs) play a central role. They connect measuring instruments and actuators that are linked via conventional wiring to the process. However, a PLC is not completely decoupled from the industrial environment, meaning that voltage spikes and inrush currents can indeed affect its functionality. To adjust the applied voltage and/or current, and to provide the PLC with suitable galvanic isolation, the appropriate interface should be installed for each input/output point, which regulates both the voltage and current levels while also providing isolation protection. Such interfaces are offered by ABB's relay and optocoupler series. They allow for a wide range of voltage (from 5 to 250 V) and current (from 0.01 to 8 A) adjustments, as well as high isolation between input and output of 2 to 4 kV. For high switching frequencies with low switching loads, transistor, MOS-FET, or triac outputs can be optionally selected.