Variations of safety

The topic of safety is subject to tight standards. And that's good. Not everyone should define for themselves what is sufficient to avoid personal injury and property damage and what isn't. Nevertheless, safety concepts are always individual. Adaptations can be undertaken within the standard criteria as long as the overall concept still meets the safety criteria.

TWK has been active in the field of safety sensors for many years and is the market leader in a number of areas. And we respond to the requirements of our customers, who are unable to use anything 'off the peg'. For instance, we have developed a safety rotary encoder with CANopen interface that has a special transmission protocol (SIL2/PLd). In this case, the usual SRDOs (Safety Relevant Data Object) with the respective transmission conditions could not be used by the customer; instead, a modified standard protocol was required (PDO: Process Data Object). Besides the required position data, this PDO additionally contains an 8-bit sequence number which is decremented by 1 with each newly determined, i.e. 'real', position value. These two data are additionally used to generate a 24-bit CRC and also transfer it in the same PDO. The reading control system now expects the PDO from the rotary encoder in a fixed time frame, and the two measures ensure that this involves current position data which are additionally validated by a CRC. This variation of a safety rotary encoder enables the provision of a certifiable solution for this task.