Patent ID: 7355828

Claim:
A turbine speed monitor module comprising: a sensor for generating a sensor signal in dependence upon rotational speed of a turbine a module arranged to receive said sensor signal and arranged in operation to generate a trip signal in dependence thereupon; and a trip output switch arranged to receive said trip signal and to generate a signal to cause said turbine to shut down in dependence upon said trip signal; wherein said module is arranged to generate a plurality of trip signals and said trip output switch comprises: a plurality of armature clamped relays each relay being driven by an associated trip signal, wherein a first armature of a pair is connected to a first armature of another pair and a second armature of said pair is connected to a second armature of said another pair and said first armatures form a first electrical path only when both first armatures are open or when both first armatures are closed and said second armatures provide a second electrical path when either or both second armatures are open or closed such that the second electrical path is discontinuous when either first armature is stuck in an open or closed position causing either second armature to remain floating between an open and closed position.