08 March 2010
This new idea in safety technology uses what looks like standard safety I/O modules distributed across a wide area. But, there's a big difference: for one thing, there's no safety bus such as Profisafe or Interbus Safety connecting them. And for another, there isn't any safety PLC to control their operation.
What is going on here, and how is the safety being co-ordinated? Can this system really be considered "safe"?
For many years, the functional safety of machines and systems was ensured solely through the use of safety relays. There simply wasn't any other way to do it. Even large-scale systems were connected in parallel this way, using safety relay technology.
Thanks to the availability of safe controllers and safe networks, however, large machines are now equipped the more appropriate, and much more sophisticated components and systems.
The two approaches
There are now two established approaches for implementing safety technology.
The first involves the use of remote safety controllers (i.e., they are not connected to the standard machine controller and network) that feature their own, separately installed safe network. Compared to traditional safety relays, this approach dramatically increases the flexibility of the safety application since it allows a large number of widely distributed safety signals to be sent and received over the safe network.
And thanks to flexible programming, the safety functions can be optimally adapted to specific applications.
The costs for functional safety increase disproportionately, however, which is why the remote safety controller and the additional safe network with the relevant infrastructure components make economic utilisation difficult.
Figure 1: Topology of a safety-oriented application. A standard PLC accepts a signal from a safe input module, lower left, and sends its output to a standard intelligent safe output module, lower right.
In the second and more economical approach, the safe controller, which is integrated into the standard controller, uses the existing network to communicate with the safe devices. In practice, this approach has proven to be the better option in terms of technical and economic efficiency.
Since the existing networks and infrastructure can be used, the installation and connection work needed to integrate functional safety into the machine or system is significantly reduced. This approach is therefore ideally suited for distributed applications with a medium to high number of safe I/Os.
Special safety equipment no longer necessary
Various market studies show that less than 50 safe I/Os are built into most of the applications for machine and plant engineering. Based on these findings, the use of a safe controller makes economic sense only in situations where special factors apply, such as a machine or plant that covers an extensive area.
Many users are therefore looking for a solution that combines the flexibility of a safe controller and the associated safe I/Os distributed in the network and the intuitive operation of the safety relay. This is where SafetyBridge Technology presents itself as a simple and low-cost solution.
SafetyBridge functions independently of the network and installed controller. The existing automation network and the standard controller only serve as a means to transport the safety-relevant data packets that are exchanged between the safe input and safe output modules.
The safe inputs and outputs, which can be distributed anywhere in the network, do not require a parent safety controller or a separate safe bus system. As a result, users do not have to choose a safe network such as Interbus Safety or Profisafe and associated safety controllers, but can continue using their own communication system.
The complicated task of connecting the safety signals in parallel is no longer necessary since those signals are sent or received wherever they are generated or needed. This provides users with an as yet unheard of degree of flexibility in the area of bus-based safety applications (Figure 1).
Comprehensive diagnostic information
Phoenix Contact has incorporated SafetyBridge Technology into the tried and tested Inline installation system. No special safety-relevant guidelines need to be followed when installing the SafetyBridge modules.
Figure 2: SafetyBridge technology can be used to implement safety-oriented applications at a low cost independently from the network and standard controller.
In fact, once distributed in the network, the safety modules can be operated anywhere in the I/O station.
Innovative technology eliminates the need for a special bus coupler since the safety logic is processed directly in the intelligent safety output module. By using the extensive parameterisation options, the eight input and output channels can be flexibly adapted to the needs of any application.
The transfer of data from the safety input and output modules is securely handled by a special protocol. The standard controller must therefore only copy non-safety I/O data between the input and output modules in both directions without the need to actually understand the safety protocol. Like the existing network, it is not responsible for safety-relevant tasks.
The standard controller can access the input and output signals of the SafetyBridge module at any time. The standard application program can thus respond to an emergency stop request directly and then graphically show the user where the safety-related event occurred.
The standard controller can also access the diagnostic messages from the individual safety I/O modules, such as short circuits or cross circuits. This means that downtimes can be reduced without additional programming or connection work.
No programming skills required
The safety mechanisms used in the SafetyBridge system rely on technologies that have proven to be effective over the years and are used by Interbus Safety and Profisafe, for example.
This means that applications up to PL e and SIL 3 can be implemented if the right parameters are specified.
The Safeconf software offers a convenient way to configure the safety input and output channels and generate the safety logic. This tool, which requires no programming experience whatsoever, can be used to quickly implement safe applications since ready-made function blocks are available for almost any application. The safety applications distributed in the network can therefore be designed using SafetyBridge Technology at a low cost and independently of the network and standard controller (Figure 2).
Figure 3: As part of a special service concept, users receive comprehensive support ranging from initial consultation, training seminars and workshops, concept development and installation through to commissioning and after-sales service.
Safety no longer separate
Functional safety should no longer be viewed as a separate issue. Users can gain major competitive advantages by thoroughly integrating it into the automation solution of a machine or plant. Extensive diagnostic options reduce installation costs and downtimes and hence increase availability and productivity.
The intelligent use of safety technology provides machine and plant manufacturers with a real competitive advantage that can prove decisive in a market where the speed with which a company can act is more important than its size.
Author: Dipl.-Ing. Lutz Rahlves, Phoenix Contact Electronics GmbH, Bad Pyrmont, Germany
Sidebar: Seeing the challenge of safety technology as an opportunity
Many machine and system manufacturers consider functional safety to be a burden since it means dealing with standards, guidelines and additional work that, at first glance, offer no advantages.
Yet in the end, it's all about ensuring the safety of operating personnel. We live in a society that no longer tolerates high risks for people and the environment. One such example is the evolution of the automobile, which nowadays comes with standard features such as seatbelts, airbags and frequently other support systems as well.
Advanced solutions such as SafetyBridge Technology help dispel some of the reservations companies may have against safety technology. Easy integration into standard technology, network compatibility and high flexibility in addition to integrated diagnostics and intuitive operation create important competitive advantages. Combined with the comprehensive service package offered by many providers of safety products and systems, the challenge of "safety technology" can be transformed into an opportunity (Figure 3).
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