Interface unit for digital signal input stages - has two interface elements in each unit with Zener diode connections providing protection against ground fault

摘要

Digital input stages (DE1, DE2) are provided to handle the outputs of signal generators (G1, G2) of a type used in automation or control systems. The signals are received by interface circuits (AS1-AS4), each of which has resistors (R1-R4) and a semiconductor, e.g. a Zener diode (ZD). Outputs are transmitted to electrically isolating couplings (PT1-4). Each of the input stages has a pair of interface stages with coupled inputs to a ground line (M). If a ground connection breaks the signal flows to the other stage. ADVANTAGE - Provides protection against ground line fault.