Integrated safety delivers on all fronts

by

Heiko Luckhaupt, Category Marketing Manager – Automation and Control, RS Components

 

Safety is an essential facet of any modern manufacturing environment. All major automation suppliers are now delivering the capability to integrate safety into manufacturing and process infrastructures, embedding the safety functionality onto the control system in order to deliver the best possible performance for the end users.

It was not all that long ago that safety was much lower down the pecking order when it came to machine and plant design. Often considered a bolt on or afterthought, many safety solutions relied upon cumbersome additional wiring and controllers that could often interfere with the control infrastructure driving production equipment.

It was not that people did not want to deploy safety, or indeed offer it as a feature, rather that it often added complexity and totally disparate networks and components to what could already be a complicated control solution.

Thankfully this is now a thing of the past as many manufacturers are taking a holistic view of safety and considering it as part of the solution rather than an additional burden. Indeed, the bolt-on mentality has now been confined to history as contemporary safety solutions can now sit happily side by side with their automation peers. They can also seamlessly interact with them over common networks, or at least in a manner that no longer impinges on the day-to-day operations of machines or lines.

The reason for this migration has been the development of more robust automation protocols and, more importantly, the way that they can deal with safety issues and consider them as part of the normal operating environment. Much of this has been driven by the realisation that safety solutions are now perceived as a way of saving money rather than an unwanted additional cost on top of the typical CapEx. In a nutshell, the balancing act of cost-versus-hindrance has now been replaced by one that considers the cost of a safety-related issue and the affect that it can have on the whole line or plant. One only has to consider the massive punitive charges levied by the automotive industry relating to late supply, for the cost-of-hardware issue to pale into insignificance compared to the potential costs that a significant line-downtime event can accrue.

Another major driving force in the safety arena has been the implementation and subsequent evolution of the Machinery Safety Directive, especially with the introduction of the new functional safety standards BS EN 62061 and BS EN ISO 13849-1.

These standards are designed to promote a focus on the necessary functions, the idea being that it can help reduce the individual risks on a machine, giving engineers an idea of what performance is required for each function, rather than simply relying on particular components. Each safety function is defined as either a Safety Integrity Level (SIL) 1,2 or 3 (BS EN 62061) or a Performance Level (PL) a, b, c, d or e (BS EN ISO 13849-1). In both instances, the architecture of the control circuit, which delivers the safety function, is a factor, but unlike BS EN 954-1 (which they replace) these new standards require consideration of the reliability of the selected components.

The beauty of this approach is that if individual components or circuits are ‘safe’ then the machine as a whole can be considered ‘safe’, but the overall functional combination of automation products and components must also be considered. Most leading suppliers can deliver standards-related safety data with regard to their components; data which typically includes figures such as MTTFd (mean time to dangerous failure) and PFHD (probability of failure on hourly demand).

If these figures, and others, are supplied by the automation vendors, machine builders will often turn to software solutions such as SISTEMA to assess and define the overall safety of their machine solutions. SISTEMA is a software tool, recommended by most major vendors, for the implementation of EN ISO 13849-1. Its use greatly simplifies the implementation of the standard. SISTEMA stands for "Safety Integrity Software Tool for the Evaluation of Machine Applications" It was developed by the BGIA in Germany and is free for use and simply requires the input of various types of functional safety data for an overall assessment to be made. The Data can be input manually or automatically by using a manufacturer’s SISTEMA Data Library.

It is the evolution of the control and communication infrastructures that have led to the development of integrated safety solutions, coupled with silicone advances that have enabled the controllers to handle safety functionality in a manner applicable to the most recent legislation. Most leading automation vendors utilise network solutions based around variants of Ethernet, and since its introduction forty years ago it has established itself as a very robust protocol which has undergone numerous iterations up to its current level, which is capable of delivering the speeds necessary for motion control and safety systems. Even those protocols not based on Ethernet have a large enough established user base that option modules can be available for plugging hardware into existing networks, with all the necessary speed and determinism needed for successful functionality.

Standalone safety solutions still exist and are still in demand for a great many applications. For simpler machines and applications that do not warrant a dedicated safety-capable PLC, simple safety controllers and relay-based systems are perfectly adequate and perform a very useful role. But in line with other developments in the safety and silicone arenas, the simple controllers are also much more amenable to integration into larger control infrastructures or, indeed, smaller PLCs or dedicated controllers, once again thanks to advances in communication software and hardware.

Thanks to all these technological advances and greater pushes from legislation, designers and engineers are now much more comfortable in designing, building and deploying safety systems, and what is more they are now appearing much earlier in the design process, in recognition of the vital role that safety plays in the overall functionality of the machine or line. Designers can now be confident that integrated safety features will no longer impinge on the operation of the machine and can indeed be used to an advantage, through the use of features such as safe-off functions on variable speed drives, where individual automation components can be brought to a safe level, rather than stopping the entire machine. This way remedial action can be undertaken much quicker and the resulting downtime kept to an absolute minimum.

There are those more ‘traditional engineers’ who are reticent towards integrated safety solutions, but the sheer weight of positive opinion and anecdotal evidence that integrated systems work just as effectively as standalone solutions is beginning to sway even the most ardent detractors. With industries such as oil and gas and petrochemical embracing completely integrated process control, safety, HVAC and fire control suites, it is only a matter of time before the concept of total integration becomes commonplace. Industries with greater risks to personnel have adopted the most contemporary solutions and are thriving from the reduction in design, development, installation, maintenance and management these systems can deliver.