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Simple is safer

How cross-traffic enhances safety in your machine

Since openSAFETY only specifies the application layer, the performance and reaction times of a safe network that implements this safety protocol depends on the data transfer protocol that is used. Data transfer protocols differ in terms of available bandwidth, the cycle times that can be achieved, and functional features, such as e.g. hot-plugging capability or cross-traffic for data communication on the safe network. Though the reaction time of a safety solution is also determined by the cycle periods in absolute terms, cross-traffic is one capability that will decisively enhance the performance of a safety-oriented system. An original feature of the Ethernet standard, cross-traffic denotes the ability of nodes on a network to communicate directly with each other, with no need for a detour via a Master. In safety-oriented networks, cross-traffic not only enables installations in which safety controllers need not be placed in the center: by allowing for straight and direct communication in hazardous situations, cross-traffic capability also benefits reaction times. Since the emergency stopping distance of an axis (see illustration above) increases with the square of the fault response time and negative acceleration, quadrupling the signal transfer time will result in a 16-fold extension of the emergency stopping distance.

 

Fault response time for safe operational stop: even minimal extensions of reaction time may fatally increase the emergency stopping distance.