Abstract: A logic safety system is disclosed having four redundant channels with each channel constituted by a logic circuit for controlling the triggering of a protective action, a logic alarm circuit connected to the control circuit and a logic inhibition circuit which makes it impossible to simultaneously inhibit several alarm circuits. Any attempt at inhibiting the alarm circuit of a second channel while an alarm circuit of a first channel is already inhibited will result in the automatic appearance of a protective action control signal at the output of the second channel regardless of the signal received at the input of the alarm circuit of the second channel.

Abstract: The switching device delivers an electrical output signal having a mean amplitude which changes progressively from the amplitude of a first signal to that of a second signal. One control signal produced by a logical unit is applied to each control input of a switching unit for closing or opening the switches of the switching unit. The control signal is given a first logical level during a first period and a second logical level during a second period. During an intermediate "switching" period the signal is given alternately the first logical level and the second logical level with a predetermined frequency. The time-duration of the half-waves of the first logical level thus decreases progressively when passing from the first period to the second period.