Like other manufacturing sectors, the food industry must comply with the Occupation Health and Safety regulations of the state or territory. The demands to increase production and minimise downtime often means machines need to work faster for longer. The increase in speed can mean increase in risk to operators. Modern safety systems can help ensure safety while reducing downtime.
Traditional approaches to safety architectures separate the control and monitoring of safety functions from the rest of the application. For specific applications such as presses or cranes, safety control systems are often certified together as system solutions. Discrete automation users often employ safety controllers and sometimes safety buses in parallel with PLCs. Relevant control or diagnostic information from the safety controller to the main controller can be exchanged by means of a network link, but the two controllers operate independently.
This philosophy of separate solutions is changing. Technology developments have made it possible for a single controller to now handle both tasks, which has tremendous implications for cost savings in engineering and maintenance. Siemens’ challenge was to offer controllers capable of handling both the monitoring and control of safety and non-safety functions with a single CPU.
This single-CPU approach to safety controllers has tremendous advantages over solutions employing a separate safety PLC. Besides the obvious cost savings in hardware alone, fail-safe CPUs allow the user to program all safety functions using the same familiar engineering tools, which can substantially reduce engineering costs. Safety functions are programmed by means of the “S7 Distributed Safety” library of commands that includes TÜV-certified function blocks for functions such as emergency off, two hand control, muting, gate monitoring and others.
The rest of the standard application can be programmed in the CPU as before without affecting the safety functions, which can be password protected separately. Fail-safe controllers are certified to meet the safety requirements of international safety standards, typically category 3 or 4 for EN 954 or SIL 2 or 3 for IEC 61508.
The food industry can benefit from this approach. Often the controllers in the industry need to be housed inside stainless steel boxes. By reducing the number of components in the cabinet a significant reduction in cabinet size can be achieved. The high level of diagnostics available in integrated systems means fast precise localisation of faults ensuring a speedy return to production.
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