A safety switching apparatus for safe disconnection of a load in an
automated installation has at least one input for receiving an analog
input signal. It further has an A/D converter which converts the analog
input signal to a digital signal. An evaluation and control unit controls
at least one output switching element as a function of the digital
signal. An analog signal combiner is designed to superimpose an analog
test signal on the analog input signal in order to form an analog
combination signal. The analog combination signal is supplied to the A/D
converter. The operation of the safety switching apparatus can then be
monitored for faults by means of the analog test signal.