High-speed trains such as the ICE, the TGV or the Shinkansen connect major cities - those coming from outside use appropriate feeder lines. In fieldbus technology, 'AS-i Safety Gateways', among others, take on this function: they collect the data from safety-related components in the periphery of a system and transport it in the function of a 'bus station' to networks and control worlds of different manufacturers. Complex automation solutions can thus be organized and implemented decentrally - and therefore more transparently, flexibly, efficiently, controllably and significantly more cost-effectively.

A major advantage of such an approach: In contrast to their direct integration into a network, the number of participants at the gateway does not lead to a potential loss of performance, for example in terms of response times. The reason: in the case of the AS-i safety gateways from Bihl+Wiedemann, whose portfolio includes integration solutions for Profibus, Profinet, Ethernet/IP, Sercos, Ethercat, Powerlink, Modbus, CC-Link or CANopen, the devices include two AS-i masters for two AS-i circuits. This means that up to 62 two-channel safe inputs are available - in addition to the three that are already directly integrated into the devices. Performance can be increased even further via the 'Safe Link' safe coupling, with which the solution can theoretically be expanded by up to 2000 safe inputs and outputs. For the higher-level network, however, the gateway only represents a single slave, regardless of the number of participants in the field, which does not affect the communicative stability of the fieldbus.

The 'direct line' to all common control systems

By integrating safe fieldbus communication into the gateways, safety-related sensors and actuators therefore have a 'direct line' to common automation systems. This applies not only to the I/O signals or the safe analog values that are also available (e.g. 4 to 20 mA, 0 to 10 V, PT100 or thermocouples), but also to the provision of extensive status and diagnostic information. The automatically generated diagnostic protocols of the devices include an evaluation of the configuration, the display of fieldbus parameters such as current, voltage, symmetry or earth fault as well as simple execution and interpretation of the data. In contrast, such diagnostics in central fieldbus concepts with directly connected sensors and actuators require a certain amount of additional effort for large numbers of participants, for example in the form of expensive measurement tools.

However, this is just one of many cost aspects that demonstrate the economic efficiency of AS-i Safety Gateways and the concepts that can be realized with them. One of the do-minating advantages is the significantly lower installation and wiring costs. If, for example, the data from 31 safety sensors is to be collected, the conventional periphery of a fail-safe control system requires four wires per sensor - i.e. 124 wires from the switchgear to the field.

With AS-i Safety at Work as a safe installation technology, the yellow flat cable is sufficient for this. What's more, the electrical connection is made using piercing technology - so there is no need for an expensive plug configuration for each participant. The power supply is also provided via the AS-i cable and does not need to be connected separately.

Using 'AS-i Safety Gateways', a universal safety concept for all control types can be realized on the basis of a modular system, which also includes Safe Motion applications.

© Bihl+Wiedemann

If safety technology is integrated directly into the control system, the number of participants in the fieldbus and the volume of data that the control system has to process increase 1:1. In addition, the performance of the network also suffers above a certain communication load - response times in particular are a critical issue here. Above a certain number of participants, all of this means that a control system not only has to be expanded to include the safety feature, but the next largest control system model must also be provided. Sample calculations show that the surcharge for safety alone is around 18% for individual control systems. And when switching to the next controller size, the additional costs for safety can quickly amount to more than 90 %.

The use of AS-i Safety Gateways is therefore much more efficient economically. Further cost benefits can be achieved during commissioning. Intuitive software solutions, such as Asimon360 from Bihl+Wiedemann, with their integrated hardware catalog, make configuration and parameterization much easier. This software provides the user with the various output circuits with the corresponding input options for logical linking. Complex programming in the control system, as required for direct fieldbus connection, is no longer necessary. Programming thus becomes parameterization, which again significantly reduces complexity.

Experience has shown that AS-i Safety Gateways result in immediate cost savings of over 50% in terms of installation, cabling and commissioning. If the safety-related scope is to be expanded at a later date, for example with additional sensors, switches or control devices, such expansions are possible without additional fieldbus couplers - and therefore without additional costs.

This is where another important (cost) aspect comes into play that speaks for AS-i Safety at Work: the granularity with which safety solutions can be implemented. A lot of safe input and output data is not always collected at a single point. Frequently, only one sensor or a few sensors with a small number of I/Os need to be connected at several points. Using active distributors with an integrated AS-i chip from Bihl+Wiedemann, this can be realized just as easily and economically as the integration of special sensors that do not have an integrated fieldbus interface.

Flexible in terms of granularity and expandability

In addition to the cost aspect, the subsequent expandability is also proof of the flexibility offered by the control-independent integration of safety technology. In other words, the actual safety technology can be configured independently of the subsequent integration. Complete, machine-related safety concepts can be developed, which then only require the appropriate 'safety gateway' for implementation. This means that only the fieldbus interface needs to be adapted to the higher-level control system. In addition, such safety concepts can be divided up, granulated more finely and later combined on a module-by-module basis. The safety technology functions can be simulated and optimized in advance in the gateways - during integration, only a fully functional slave is then connected to the fieldbus later on.

With active distributors, a wide variety of sensors, buttons or switches can be integrated easily and without great effort. The user can choose exactly the right device for the respective application from a wide range of options.

© Bihl+Wiedemann

Ultimately, the use of AS-i Safety Gateways is also a plea for decentralized safety technology - because they make complexity transparent and therefore manageable. With a centralized system structure, an appropriately dimensioned, fail-safe controller directly controls the entire safety technology. Safety-related logics and functions as well as status and diagnostic data are located in one place. If this organization is still clear and stringent for small to medium-sized applications, clarity is lost with increasing system size and complexity of the task.

With a decentralized structure, on the other hand, the entire safety technology can be subdivided into easily manageable sub-areas. The parameterization and commissioning of the safety technology in particular is much easier because it is clearer. Last but not least, the complexity becomes manageable - especially as settings and functional logic can be clearly understood during operation of the system or during a safety inspection.

Author: Johanna Schüßler works in product management at Wihl+Wiedemann, Mannheim