Programmable logic controllers (PLCs) play a central role in today's industrial automation systems. They connect measuring instruments and actuators connected via conventional cabling to the process. However, a PLC is not completely decoupled from the industrial environment, so overvoltage peaks and transient currents can certainly affect its functionality. In order 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 both regulates the voltage and current level and offers isolation protection. The relay and optocoupler series from ABB offer such interfaces. They allow a wide range of adjustment of the voltage (from 5 to 250 V) and current (from 0.01 to 8 A) as well as a high level of isolation between input and output of 2 to 4 kV. Transistor, MOS-FET or triac outputs can be selected for high switching frequencies with low switching loads.