In today's industrial automation systems, programmable logic controllers (PLCs) play a central role. They connect measuring instruments and actuators connected to the process via conventional wiring. However, a PLC is not completely decoupled from the industrial environment, so that over-voltage peaks and transition currents can affect its functionality. In order to adapt the applied voltage and/or current and to provide the PLC with a suitable galvanic isolation, the appropriate interface should be installed for each starting point, which regulates the voltage and current level as well as offers a separation protection. Such interfaces are offered by ABB's relay and optocoupler series. They allow a wide adjustment of the voltage (from 5 to 250 V) and current (from 0.01 to 8 A) as well as a high insulation between input and output from 2 to 4 kV. Transistor, MOS-FET or Triac outputs can be selected for high switching frequencies at low switching loads.This text is machine translated.