Abstract: The present invention relates to a redundant process control system including at least one control unit (PLC1) which produces an output signal (S1) resulting from a control function being applied to a set of input signals (E1). In addition, the system includes at least one test member (TES1) that is different from said control unit, which test member produces a test signal resulting from said control function being applied to said set of input signals (E1) and generates an alarm (AL1) whenever there is a difference between said test signal and the corresponding output signal (S1).