Active device for reading state of high voltage dry control switches in logical input interface circuit of e.g. automation system, has measuring unit to compare predetermined ranges, respectively defining states of control switches

摘要

The device has an electrical circuit (45) for connecting inputs of an operational amplifier (27), respectively with midpoints of primary resistors (33, 34) and secondary resistors (32, 35). A supply unit supplies power to the amplifier. The circuit connects an output of the amplifier with a fraction part (38) of a primary winding of transformers (24). A measuring unit (46) measures oscillation frequency of the transformers. The measuring unit compares predetermined ranges, respectively defining states of control switches (21).