Fremgangsmåde, sikkerhedsstyreenhed og elevatorsystem til verificering af hastighedsdata for en elevatorstol for overhastighedsovervågning for elevatorstolen

The invention relates to a method for verifying speed data of an elevator car for overspeed monitoring of the elevator car. The method comprising obtaining at least one continuous speed data of the elevator car at two channels; obtaining a zone speed data of the elevator car within at least one zone of an elevator shaft at two channels, generating a two-channel verified speed information by comparing the said at least one continuous speed data to the zone speed data at least at one channel; generating a control signal, if the comparison indicates a mismatch at least at one channel; and if the comparison indicates a match at each of the at least one channel in which the comparison is provided; the method further comprising comparing the verified speed information at each channel between each other; and generating the control signal, if the reciprocal comparison indicates a mismatch. The invention also relates to a safety control unit and an elevator system performing at least partly the method.