Safety switching module

摘要

A safety switching module ( 10 ) including at least two switch units connected in series and a switch control unit ( 20 ) for each switch unit ( 18 ). Each switch control unit ( 20 ) has a switch control input ( 38,40 ) to receive a shut down to open the respective switch unit ( 18 ). A switch monitoring means ( 46 ) is provided for each switch unit ( 18 ) to monitor whether the respective switch unit ( 18 ) is open or closed and is connected to the respective switch control unit ( 20 ) such that the switch control unit ( 20 ) can determine that a fault condition exists if the respective switch unit ( 18 ) has not opened on receiving the shut down signal. An operation control input ( 60 ) is provided on at least one of the switch control units ( 20 ) connectable to an operation controller ( 62 ) for controlling operation of the load. Each of the switch control units ( 20 ) is in communication with each other switch control units ( 20 ) to determine if fault conditions exist in any of the switch units ( 18 ). The switch control unit ( 20 ) connected to the operation controller ( 62 ) is arranged to open and close the respective switch unit ( 18 ) in response to signals received from the operation controller ( 62 ) unless any of the switch control units ( 20 ) have a fault condition or a have received the shut down