As an interface they link the electronic controlling, e.g. PLC (programmable logic controller), PC or field bus systems, to the sensor/actuator level. Here, they take on various functions: switching of AC or DC loads with different resistive, inductive and capacitive parts, switching voltages from a few mV up to 250 V, switching currents from a few mA up to 16 A, amplification of weak control signals, electrical isolation of control and load circuits, and signal multiplying. In contrast to electronic switching devices, interface relays don’t use additional internal predective circuits and thus are overload proof against short time variations like current or voltage peaks.