Modular and Flexible, Decentralized PSSuniversal I/O Platform for Safety and Control Technology Fits in Perfectly
Pilz Automation Safety L.P. Posted 07/07/2008
But rather than wishing to save directly on safety, more consideration should be given to opportunities for greater productivity, increased user benefits and new functionalities.
This starts with the design process, whereby safety functions are included right from the very first requirement manual.In the design process it is important to consider safety-related and control technology in equal measure.In practice this process is almost always habitual.
Electronic safety systems, for example, are designed to be self-monitoring as a prerequisite for complying with the relevant safety level, thus providing an additional benefit.They provide the user with detailed, universal fault diagnostics, almost as a by-product.Machine builders benefit from a short engineering phase and end users from a long service life plus high plant availability.
Intelligent combination of safety and standard
When these user requirements are considered, combined systems such as the decentralized modular I/O platform PSSuniversal have the advantage.First, they stand out due to an intelligent combination of safety and standard control functions. Second, they meet the specific requirements of standards and safety, such as extremely short reaction times, for example.
Even when the level of automation rises, the risk potential to plant and machinery must not be allowed to increase.Safety technology must approach this challenge with the cost-effective implementation of intelligent system solutions.
The PSSuniversal system consists of three key components.The head module primarily undertakes all the communication and processing functions.Base modules are connected to the head modules and are used for installing electronic modules and for connecting the I/O signals.Up to 64 “components,” each consisting of a base module and an electronic module, may be operated per head module.All electronic modules have a plug-in connection, so that the plant can be restarted as quickly as possible after expansion or after individual components have been swapped.This is done without the need to remove and then reconnect the periphery cabling.Cabling errors can therefore be avoided from the outset.
The system with all its signals is established automatically.For the user this means that no cross-wiring is required for 24V, 0V, functional earth or test pulse wiring for failsafe inputs.The necessary periphery signals are arranged on the respective module according to function.External terminal blocks are therefore completely unnecessary.Base modules have the choice between screw and cage clamp terminals.
The flexible supply concept ensures that any potentially isolated supply circuits can be used for the periphery.The use of additional supply modules enables the entire system to be divided into any number of supply groups, so that the system can be adapted to suit the most varied of supply concepts.Alternatively, a block switching module also may be incorporated into such a supply point; this can safely shut down the supply voltage to downstream standard output modules.
The electronic modules represent a scalable I/O interface.A wide range of standard and safety modules means that all automation functions can be covered.
Electronic modules for standard or safety I/Os can be arranged at will, so they can be split and adapted to all sub-sections of a plant or machine for an optimum configuration.Each module is standalone, so there is no need for additional external terminals or cross-wiring.The benefit lies in better clarity and inherent fault prevention.
Flexible and scalable
In accordance with Pilz's strategy to provide open systems, the I/O platform supports various communication routes from the very start.At field bus level these are Profibus-DP, DeviceNET and CANopen.They are available on their own or in combination with the safe bus system SafetyBUS p.At another level, head modules are available with local processing, while Ethernet communication interfaces are in development.The system is therefore geared for the future, protecting investment.Customer requirements for different technologies or manufacturers can be accommodated merely by changing the head module. It's even possible to transfer to different communication media and protocols at any time.With local pre-processing it is possible to implement additional commissioning and availability concepts.
Electronic modules are available for digital I/Os in both the standard and safety section, whether semiconductor or relay-based, and for the widest range of safety levels.
Pilz also supplies a software tool to support the user in selecting products and putting the system together.The “PSSuniversal Assistant” provides a graphical representation of the respective configuration, at the same time checking all the internal limitations such as currents or mechanical / electrical dimensions.The result is a complete configuration, which serves as a basis for the logistics process, the control cabinet design or subsequent programming.Data only needs to be generated once.
Discussions with users show that the mixed, flexible design of standard and safety functions is one of the central factors leading to acceptance of the PSSuniversal I/O platform.
Clear savings could be demonstrated even in the planning phase of user projects.This is primarily a result of the fact that all forms of cross-wiring are eliminated and that the number of components employed from different manufacturers can be reduced.Work arising from installation, programming and servicing can also be drastically reduced.By simplifying the interfaces, the complexity of the overall architecture is also reduced.Despite the mixed design of the standard and safety functions, the proven principles of operation without feedback were deemed to be vitally important for the PSSuniversal system design.On the PSSuniversal, standard and safety functions are mixed in physical terms, but are clearly separate in terms of logic.
Logic connection at I/O level
PSSuniversal brings safety technology's enable principle from control level to field level.The functional interaction of both the ST (standard) and FS (failsafe) control sections is transferred to wherever it is possible to achieve the greatest possible performance enhancements for the overall system.The “local enable principle” draws its information equally from both control sections and switches the safety-related outputs in the field directly.Comparisons of measurements taken under real conditions have shown that this can reduce actual response times by more than 60 percent.
As the control systems stay the same and only functional components are transferred, users benefit from the fact that they can continue to use their existing control and communication systems without modification.The open communications structure means that the system is immediately serviceable in any existing plant.So performance can be enhanced without having to change the system.
Safety-related approval for the system
First of all it's necessary to meet safety technology's objective – to protect man, machine and the environment.The technology status is laid down in the standards, among other documents, and as this undergoes change, so too the current position of the standards changes.An innovative new system must therefore take into account current and future requirements at national and international level.So PSSuniversal meets the requirements of Cat. 4 in accordance with EN 954-1 and its successor standard, ISO EN 13849-1, with performance level “e.”The I/O platform is designed to enable systems to be built in accordance with SIL 3 of IEC 61508 and to cover the requirements of the sector standard IEC 62061-1.In addition to a wide range of C standards (application-specific standards), the requirements of ul/Cul and NFPA are also met, for example.
By considering all the relevant international norms and standards, there is nothing to stop the system being used in applications worldwide.
Further expansion with analogue I/O modules
Even if “the real world” is analogue, processing in industrial automation systems is digital.In future, the PSSuniversal will have a wide range of analogue I/O interfaces, enabling analogue process signals from temperature sensors or level indicators, for example, to be read in to the control process.The main requirements of the key interfaces were drawn up in close co-operation with pilot customers.In the second expansion stage, the PSSuniversal will focus on the area of standard I/Os for analogue current and voltage signals, whereby incremental rotary encoders and SSI formats can also be supported.
PSSuniversal builds the platform for all further functional expansions:from I/O level through to complete pre-processing for standard and safety functions or connection to new Ethernet-based communication systems.Based on the functionalities and features described, the system meets the market requirement for an overall, open control concept that is geared for the future.
Armin Glaser is a product manager at Pilz GmbH & Co. KG.
About Pilz Automation Safety L.P.
Pilz Automation Safety L.P., U.S. subsidiary of German Pilz GmbH, Europe’s largest and most-respected maker of safety automation equipment, offers leading-edge safe automation solutions and control products.
Products include sensor technology, electrical monitoring relays, automation solutions with motion control, safety relays, programmable safety and control systems and an operating and monitoring range. Safe bus systems are also available for industrial networking. Pilz was the first to develop: the Emergency Safety Relay, the PNOZ product line, now the industry standard; all-electric safety relay, PNOZe1p: 16-amp safety relay, PNOZ power; a safe open-field bus system SafetyBUS p; and one of the first Programmable Logic Controllers (PLCs); and SafetyEYE, the world’s first safe camera system for control and monitoring in 3-D.
Pilz also provides a comprehensive range of consulting, engineering and training services. Accredited consultants are available for worldwide services for risk assessment, safety concept, safety design, CE services and safety sign-off. Applying lean manufacturing AND safety principles, Pilz LEANsafe™ methods increases productivity and safety.