Importance

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Abstract

A safety switching arrangement for the switching on and off of the power supply (11) of two actors (12a, 12b) for example relays, which, in dependence on the switching on of the current, and in dependence on a sensor switching signal (13a, 13b) jointly set a working apparatus (22) in operation, the safety switching arrangement comprising two main switches (14a, 14b) arranged between the power supply (11) and each preferably earthed actor (12a, 12b). In each case a controllable normally closed auxiliary switch (16a, 16b) is arranged between the sensor signal input (15a, 15b) and the main switches (14a, 14b) and, with the main switch (14a, 14b) closed by the application of a sensor closing signal, is briefly opened by a test generator (45) to provide a test pause via a first control input (19a, 19b) at regular time intervals offset timewise to the other respective auxiliary switch (16b, 16a) so that, in each case, the brief opening of the associated main switch (14a, 14b) brought about--in the troublefree state of the associated switch (14a, 14b)--is not sufficient as a result of the inertia of the actors (12a, 12b) to set the attached working apparatus (22) out of operation. A test circuit (18a, 18b; 21a, 21b, 24a, 24b; 27a, 27b; 36a, 36b) is provided which examines during the test pause whether the main switch (14a, 14b) associated with the respective auxiliary switch (16a, 16b) is also open. On non-opening of a main switch (14a, 14b) during the test pause, the other respective auxiliary switch (16b, 16a) is set into the open state and is permanently maintained in this state.

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First Claim