Safety switching apparatus with fail-safe inputs

Security switching device (10) for failsafe shutdown of an industrial plant (12), with a first and at least a second input (30, 30 '). The first input (30) receives a first input signal (38) having a first input circuit (32) and the second input (30 ') takes a second input signal (38') having a second input circuit (32 ') on. The first and the second input circuit (32, 32 ') are in a first (I) and with a second circuit (II) which are electrically isolated from each other. In the first circuit (I), a first signal input circuit (40), a first threshold value element (44) and a first coupling element (42) of the first input circuit (32) and a second signal input circuit (40 '), a second threshold element (44') and arranged a second coupling element (42 ') of the second input circuit (32'). The first circuit (I) further comprises a first test device (46) having a third coupling element (48), wherein the first test device (46) is adapted to a current path from the first and second threshold value element (44, 44 ') (to a ground terminal interrupting 68). In the second circuit (II) are a second test device (52) and a first Ausleiteschaltkreis (54) of the first input (30) and a third test device (52 ') and a second Ausleiteschaltkreis (54') of the second input, wherein the first , second and third coupling element (42, 42 ', 48) the first and the second circuit (I, II) to each other.