Patent ID: 7933104

Claim:
In safety control system for failsafe disconnection of an electrical load in an automated installation in accordance with the status of signaling devices comprising at least first and second signaling switches configured to monitor at least one fault condition associated with the automated installation, and at least one safety switching device responsive to at least one of said signaling devices for producing an output switching signal for disconnection of the load, the safety switching device comprising: a first and a second connecting terminal for connection to a remote first signaling switch, a third and a fourth connecting terminal for connection to a remote second signaling switch, a first and a second switching element configured to produce a redundant output switching signal for disconnection of the load, and a control circuit configured to control the first and second switching elements, wherein the first connecting terminal is supplied with a first steady-state potential, wherein the third connecting terminal is supplied with a second steady-state potential, which is different from the first steady-state potential, wherein the second connecting terminal is coupled to the first switching element forming a first circuit such that the first switching element receives the first steady-state potential via the first signaling switch, wherein the fourth connecting terminal is coupled to the second switching element forming a second circuit such that the second switching element receives the second steady-state potential via the second signaling switch, and wherein the control circuit comprises a first solid-state switching device having conductive and non-conductive states and connected to at least one of said first and second circuits to control the flow of current therethrough, and a controller having a first input connected to at least one of said second and fourth connecting terminals and a first output connected to said first solid-state switching device, and further wherein said controller is configured to determine the potential at said at least one of said second and fourth connecting terminals and control the conductive state of said first solid-state switching device in accordance with said determined potential.