parallel connected amplifiers responsive to the signal to activate corresponding switching circuits and audio visual indicators application_number US 12432580 A description the invention may advantageously be described within the context of a rotational overspeed monitoring and protection system for a steam turbine for example in fig1 a toothed wheel or spur gear 10 is attached to the rotating shaft not specifically shown of a turbine rotor and is rotatable therewith at the same speed for redundancy two or more here three magnetic sensors 11 are coupled to the toothed wheel 10 to independently sense the speed of rotation an output signal from each magnetic sensor 11 is fed to a corresponding frequency to voltage converter 12 the output of which is an electrical signal whose magnitude is proportional to the turbine speed this output signal is then compared to a reference signal in a voltage comparator 13 the reference signal is preset to correspond to a speed at which corrective action must be taken for example an overspeed condition of 113 of turbine operating speed when the turbine speed reaches this preset speed voltage comparators 13 will sense the overspeed and independently provide signals indicating that the overspeed limit has been exceeded these signals in turn are applied as actuation signals to control logic network 17 the control logic network 17 includes a group of switching devices activated by the overspeed limit signals and which are configured in a network so that at least two out of three overspeed limit signals must be received before control action can follow details of the control logic network are more fully described below again within the context of turbine speed control as an example.