Stochastic dominance : an approach to decision-making under risk

An allowed speed signal received from an off-vehicle source and an actual speed signal generated on-board are each converted from their original form to a signal having a relatively high frequency proportional to the represented speed. Each conversion is dual channel to produce two outputs, for the same signal, which are compared in digital cycle checking apparatus for identical frequencies to assure the validity of the frequency conversion and thus the speed signals. One frequency signal from each pair is compared in another digital cycle checking apparatus to determine if an over or under train speed condition exists. Each cycle checking means periodically simulates an improper comparison, after which the correct condition must be detected to provide a continued output. Thus the validity of the cycle check operations is assured. Each of the frequency pairs must check equal and a train underspeed condition detected to produce the complete set of output signals which allow train movement to continue.