Safety related position and speed detection

In this paper a concept is presented to develop a sensor arrangement in accordance with different standards to determine position and speed information for a safety Programmable Logic Controller (PLC). Different environments require a various selection of available sensors. Possible failures in design, production and maintenance have to be considered. Further failures of any other kind have to be assumed and detected in the system immediately. A single failure must not lead to a drop out of safety. Components, physical mode of operation, environmental interactions, concept of data transmission and the architecture of the system have to be designed in such a way that no fault occurs with a common cause failure. The requirement is to detect an initiating deropement of a funicular. Crosswind and misaligned traverses cause lateral forces. These forces generate a hazard of deropement. In case an initiating deropement is detected, counteractions will be triggered, for example reducing the operation speed or a final stop. The present state of the art is a combination of cable grabbers with deropement switches. This technology reduces the effect of a deropement, but not the deropement itself. Another solution works with safety related proximity switches, which check the position of the rope on the roller. In case of thunderstorms the rope works as a lightning conductor. These currents destroy many of these proximity switches, because they are close to the rope (Fig. 1). A more insensible solution is shown in Fig.2. Round stand ropes and splices provoke many unintentional activations. A new advanced concept is created. In changing the support point of the rope on the roller, the speed of the single roller is changing too. Comparing the speed of the rollers, a dislocation of the moving rope is detectable.