In today's industrial automation systems, programmable logic controllers (PLCs) play a central role. They connect measuring instruments and actuators linked via conventional wiring to the process. However, a PLC is not completely decoupled from the industrial environment, so voltage spikes and transient currents can indeed affect its functionality. To adjust the applied voltage and/or current, as well as 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 and offers isolation protection. Such interfaces are provided by ABB's relay and optocoupler series. They allow for a wide range of voltage adjustment (from 5 to 250 V) and current adjustment (from 0.01 to 8 A), 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 selected as options.