An alternative approach is using the AS-Interface Safety at Work. These safety input devices are simply connected to safety-rated, addressable input modules. Alternatively, dedicated safe-rated devices with integrated AS-Interface chips can be connected directly to the network, resulting in the greatest possible time saving and the cleanest possible layout.

Irrespective of how the safety input devices are connected to the network, the network is now used to transmit their state to the programmable Safety-Monitor, which replaces the safety relay in old, hardwired installation. From here on out, the logic behavior is defined in the software and specifying the necessary functionality is accomplished simply by combining “input blocks” with “logic-functions.” Diagnostics is easy and powerful and can be performed by any PLC connected to the network (either via a gateway or by means scanner cards connected to the PLC backplane. A typical setup uses e-stops and door interlock switches supporting zoned safety on a simple, two-conductor cable run.

AS-Interface Safety at Work reduces the amount of wiring by up to 90%, while adding significant flexibility. It prevents unsafe startups on hard-wired systems. The problem of deactivating the electron beam while the pneumatic system keeps running is easily solved using this safety networking technology.

This article was written by Helge Hornis, PhD, Manager of the Intelligent Systems Group of Pepperl+Fuchs Inc. (Twinsburg, OH). For more information, please contact Mr. Hornis at 330-486-0001, or visit

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