Circuit for cross-monitoring of multi-core control lines in intrinsically safe circuits with half-cycle control

摘要

In intrinsically safe installations which operate using half-cycle technology in order to guarantee accident-proofing, and in which the central control unit is controlled by a plurality of command transmitters, supplied from a common power supply, via multi-core lines, hazardous operating situations occur when cores of different circuits are short-circuited as a result of an external mechanical influence on the line. This is prevented by the following safety circuit: in each case two optocouplers (4-5, 6-7), which are connected in reverse parallel are connected in series with the contact in front of and behind each command transmitter (1) with a changeover contact and diode (2, 3) connected in reverse parallel (positive half-cycle = on, negative half-cycle = off) so that the corresponding phototransisters and EXOR gates (8, 9) connected to their emitters are selected in every switch position, with the consequence that a quiescent current for a relay (13), whose tripping initiates a switching-off process in the controller, is connected via an AND-linking (10) of the EXOR gates and a transistor amplifier (12). This circuit guarantees that no inadvertent self-starting takes place in the event of line defects of any type or, however, that already running drives are stopped. IMAGE