Central concept: A large fail-safe control unit controls the entire safety technology of the system.

© Bihl+Wiedemann

A simple calculation shows that this combination also offers enormous savings potential: to collect the data from 31 safety sensors, for example (maximum number of safe inputs on an AS-i circuit), the conventional peripherals of a fail-safe control system would require at least four times as many wires - i.e. 124 - from the switchgear to the field. With AS-i Safety at Work, the typical yellow cable alone is sufficient for the same application. For the implementation of such solutions in centrally organized safety concepts with different fail-safe control systems, appropriate products have been available for many years, such as the AS-i Safety Gateways to Profisafe via Profinet or Profibus from Bihl+Wiedemann. These devices can be integrated into the higher-level network as easily as a 'normal' slave and provide extensive diagnostic and status information to the fail-safe control system, in the case of Profisafe, for example, to the F-CPU from Siemens. This means that all relevant data reflecting the current status of the entire system is available in the safe command center at all times.

Decentralized concept: Safe Link in conjunction with the new 'AS-i Safety Profisafe Gateways' now also enables the decentralized networking of systems with safe drives and F-CPUs and those without safe drives and F-CPUs.

© Bihl+Wiedemann

With the 'AS-i Safety Gateways' commonly used to date, it is possible to connect up to two AS-i circuits per gateway to the fail-safe control system. However, Bihl+Wiedemann felt that this was not enough with a view to the future. "As we know from many discussions with users, the trend is clearly moving towards increasingly complex and branched systems," says company boss Jochen Bihl. "We have derived a clear development mandate from this: We need an 'AS-i Safety Gateway' that is capable of linking the safety technology of as many system parts as possible - even if different fieldbuses are used in these segments."

The Mannheim-based company already had the technology for this: Safe Link was developed a few years ago precisely for this purpose: to efficiently connect several safe AS-i networks and integrate them into complex applications in which different fieldbuses can be used.

Safe Link allows up to 31 gateways with integrated safety monitors and basic safety monitors with Ethernet interfaces to be linked together. Communication is based on so-called multicasts. This means that one safety monitor 'speaks' and everyone 'listens'. Up to 1922 slaves can thus communicate directly with each other across all connected AS-i networks, completely independently of the overall technological concept of the system. You have direct access to the input and output data of all the machines involved.

AS-i gateway to the F-CPU with Safe Link

If Profisafe is used in all parts of the system, the safe connection could in principle also be established via the F-CPU; however, Safe Link is the far simpler alternative for several reasons. For example, project planning is carried out with just a few mouse clicks. And thanks to the "everyone hears everyone" principle, the output data of a subscriber with Safe Link only needs to be created once and can then be used directly by all other connected subscribers.

The new AS-i Safety Gateway Profisafe via Profinet with Safe Link (BWU3367): It can be used to implement applications up to SIL3, PLe.

© Bihl+Wiedemann

With this in mind, it made sense for the developers to integrate the existing technology into the AS-i Safety Gateways for fail-safe control systems. "It doesn't sound that complicated at first," says Jochen Bihl. "In reality, however, it was a lot of hard work to pack both - i.e. the requirements for perfect interaction with the F-CPU and the capabilities for safe coupling with other AS-i networks - into one and the same device." In concrete terms, this means that not two, but three safety protocols had to be integrated into one gateway: AS-i Safety, Safe Link and Profisafe.

Such a solution was implemented for the first time with the AS-i Safety Gateway to CIP Safety via Sercos, which was presented last fall. The device itself combines two AS-i masters for two AS-i circuits and can be expanded by almost 2000 inputs and outputs via Safe Link. It also enters completely new spheres for AS-Interface: With its help, drives can be safely controlled and monitored via CIP Safety - directly and without an additional safety PLC.
Now comes the next development step: the new AS-i Safety Gateway for Profisafe via Profinet with Safe Link (BWU3367). It has two AS-i masters, three two-channel safe inputs and six independent safe outputs and can also be extended by almost 2000 safe inputs and outputs via Safe Link. With this solution, systems with safe drives can now also be flexibly networked with Profisafe and operated with a decentralized concept. This means that each part of the system has its own small or medium-sized controller, and in many cases the safety program is processed completely in the AS-i gateway. The individual segments are coupled very simply via Safe Link.

Author: Thomas Rönitzsch is responsible for corporate communications at Bihl+Wiedemann.