These devices are single channel switching amplifiers with intrinsically safe input circuits. They are used to isolate and transfer discrete signals from a hazardous location to a non-hazardous location. Inputs are typically NAMUR sensors or dry contacts, although devices providing a variable resistance conforming to DIN 19234 may be used – e.g. variable resistors, thermistors, etc. Three programming switches on the front cover of each device enable selection of the output mode, and separate activation of wire-break and short-circuit monitoring.