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  1. SICK Sensor Intelligence
16 December 2013

Cost-Efficient Cascading of Safe Switches and Sensors

Introducing the unique decentralised integration design of Flexi Loop, SICK meets the demand for cost-saving cascading of safe switches and sensors within a machine as well as for extensive diagnostic options, while maintaining performance level PL e.

In the context of a Flexi Soft control solution, Flexi Loop allows integrating and individually diagnosing up to eight sensor cascades with up to 32 dual-channel safety switches and safety sensors in a cost-efficient way.

This is technically and economically interesting with respect to machines and plants featuring a great number of doors, protective flaps, covers, emergency stop buttons, as well as machine openings protected by electro-sensitive devices. Their cascading by means of Flexi Loop is extremely cost-efficient because the entire ‘loop’ requires only one safe switching input and one can use unshielded five-core standard cables with standard M12 connector technology.

Flexi Loop nodes with integration and diagnostic function

For series connection and integration into different extension modules of the Flexi Soft safety controller, connection nodes are available both for electromechanical safety switches as well as for safety sensors featuring OSSD (output signal switching device) output switching elements. The Flexi Loop node contains the safe switch-off signal of the entire cascade as well as diagnostic data of each individual subscriber. In addition, the connected sensors are supplied with 24V via Flexi Loop.

Per node, there is one standard input as well as one standard output that can take on function switches, door locking, or the actuation of an indicator light. The distance between two nodes may be up to 30m, which means a ‘loop’ in fully expanded configuration may be up to 960m long. The transmitted diagnostic data of each switch/sensor contain the switch-off information, ‘Who was switching?’, as well as, in case of malfunction, the cause of the error, ‘Why did the switching take place?’.

In this way, easy integration into the machine diagnosis is possible. Accordingly, maintenance and repair work can be completed quickly and purposefully – minimising the duration and thus the costs related to the machine downtime.

Using Flexi Loop makes series connections safer and faster

One of great innovations of Flexi Loop is that series connections become safer. In case of conventional wiring, it is not possible to determine various errors because subsequent errors are ‘masked’ by the series connection. Flexi Loop prevents this by monitoring every single sensor.

Whereas from the perspective of safety technology, conventional wiring with several sensors results in a decrease of the performance level to PL d or PL c, the switch and sensor cascading with Flexi Loop meets the requirements of PL e in accordance with DIN EN ISO 13849-1 at any time, provided the appropriate devices are used. Moreover, the speed of the overall system increases, since in contrast to discrete wiring, the response time of Flexi Loop at 60ms is independent of the number of connected sensors and switches.

SICK sensor technology equipped for plug-and-play

Flexi Loop is open to the safety-capable switches and sensors of all manufacturers, a fact that helps maintain the procurement independence of the machine builder and the end customer alike. The easiest way, however, via plug-and-play, is using the switches from SICK: With M12 connectors and the suitable pin assignment, they are prepared from the start for Flexi Loop.

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