Integration of safe control technology within the automation environment

Cycle times are becoming ever shorter, while productivity and the demands on plant and machine control systems are increasing. In addition to the technical control requirements, the need for information regarding process and machine data is constantly growing. As a result, communication technologies from the office world are increasingly making their mark on control technology. One consequence of this trend, for example, is the growth of Ethernet-based bus systems in automation technology, right down to field and process level.

Until now safety technology has been characterized more or less as a “monitoring function” and has been incorporated as such into the automation chain. The process control system dominates and defines the actual process stages. As a “monitoring instrument”, the safety control system either agrees or disagrees with the decisions of the process control system.

Monitoring is limited to safety-relevant control functions, as is the enable. Process outputs without a safety requirement are unaffected. A distinct benefit of such a procedure is the fact that the tasks, and therefore the responsibilities, are clearly separated. A separate system is responsible for the design and monitoring of the safety technology; another separate control system manages the machine and the process. This way it is possible to guarantee the absence of feedback: Changes made primarily in the standard control system will not adversely affect the safety control system. This is an essential safety requirement of a safety system.

The division of duties also has a number of positive aspects: firstly it increases overall performance, because each unit simply concentrates on the matters for which it has been designed and configured. Productivity increases do not just impact positively on the output of the plant or machine: they can also be beneficial in terms of handling, if faster reaction times enable safety distances to be minimized, for example. Separation can also be used to transfer responsibility for the individual systems to different individuals. That helps both sides, because everyone can concentrate on the task in hand.

“Enable” operating principle, with safety relay or safety control system.