"AS-Interface with safety function is of interest in many applications because this bus system is extremely easy to handle at the lowest field level both for standard automation and for safety-related applications," says Dipl.-Ing. Andreas Ade, proprietor of the company AAC Ade Automation Consulting GmbH. As an automation specialist and Siemens Solution Partner, this company in Landau, Germany, has taken on the conversion of a plant for processing glass panels at Saint-Gobain Solar in Mannheim. Ingolf Ripberger, BU Director Solar Transformation Europe at Saint-Gobain Solar, confirms: "Within a retrofit project we upgraded the glass processing plant so that it is now state-of-the-art. In doing so, we were on the look-out for a safety solution that did not involve time-consuming installation work."

The plant comprises approximately ten work stages, with the different function modules interlinked via the Profinet bus system. To achieve full production levels as quickly as possible, it had to be possible to install the safety engineering quickly. The second, decisive aspect was the desired flexibility of the safety engineering in order to allow implementation of safety-related plant modifications without undue effort. Both were possible with ASIsafe.

"From our perspective as plant operators, ASIsafe offers just the features we need," says Ingolf Ripberger. "Because the bus system is easy to handle and is so flexible that we are able to expand new safety scenarios as and when these should become necessary." An ASI cable like this can be 100 meters in length, and it can be extended to 600 meters using repeaters and extension plugs. Thus, up to 31 fail-safe ASI devices can be processed on the typically yellow, trapezoidal cable. Depending on the header module of the Simatic ET 200SP, up to 29 ASIsafe networks per station can be set up. "Flexibility, performance capacity, and easy handling speak for themselves - and not just in the case of this retrofit project," says Andreas Ade.

BUS-BASED SAFETY ENGINEERING VERSUS CONVENTIONAL CABLING

Andreas Ade reports: "It all started at the turning station of the cut panels of glass. This station contains more than a dozen emergency-stop devices." The risk assessment carried out by Andreas Ade indicated that Safety Class SIL2 in accordance with EN 62061 has to be achieved for the protection of employees and plant. The existing safety commanding devices were single-channel only, with one signaling contact. The ASIsafe version was the obvious choice because it was possible to equip the enclosed signaling devices later on with a second channel (NC contact) and an ASIsafe element. "And ASIsafe also has the advantage that safety-related detection/shutdown and diagnostics can be combined in one," explains Andreas Ade. 

A window of half a day was estimated for integrating the safety functions into the production plant, something that would not have been possible with conventionally wired safety technology from the viewpoint of the automation specialist Ade. "With ASIsafe, it was no problem," he says. The CM AS‑i master was used in combination with the F‑CM ASi‑i‑Safety fail-safe expansion module for the Simatic ET 200SP distributed I/O from Siemens.A combination like this results in a particularly compact AS‑i F‑Link. "This solution is extremely compact and for that reason fitted outstandingly well into the new control box on site," says Bernd Geider, owner of the company Bernd Geider Elektrotechnik who provided the control panels for this project, either modified or new.

SIMPLIFIED ENGINEERING THANKS TO INTEGRATED SAFETY FUNCTIONS

Individual shutdown scenarios can be programmed for the ASIsafe safety solution, and adapted if required. Instead of several different programs, Step7 from Siemens is sufficient here for the standard automation, supplemented by Safety Integrated. Alternatively, the TIA Portal Engineering Framework can be used. This has more to offer with regard to handling and performance scope, in terms of configuring the AS‑i network topology comparable with Profinet and Profibus, as well as drive functions.

"The ability to implement everything on one platform is indeed a great benefit for automation engineers," emphasizes Andreas Ade. The benefits offered by the Totally Integrated Automation (TIA) system philosophy were evident at many points during the retrofit project in Mannheim. To take just one example: Communication for all devices or modules takes place via wireless-based Profinet (WLAN) to save time and installation work. "We were thus able to do without installing many additional cable links, and in this way, we saved a considerable amount of time and costs," says Ingolf Ripberger.

FAIL-SAFE WLAN CUTS INSTALLATION WORK

The controller topology is based on a Simatic S7‑317F‑2 PN/DP fail-safe controller from Siemens accommodated in the newly assembled control panel of the plant. Connected to this via an RJ45 interface is a Scalance W761‑1 Wireless LAN Access Point with a data rate of 150 Mbps. This transparent solution for the control panel provides the machine controls of the individual devices with the necessary information.

In six control panel sections, the necessary WLAN clients were added and wired via Profinet to the Simatic ET 200S distributed I/O system with IM 151‑3 PN High Feature header module. In this way, a Profinet network was created that can do without the typical green cable outside the control panels. This configuration provided the option of implementing the safety engineering on a bus basis at points at which ASIsafe is not yet used.

Ingolf Ripberger stated: "Part of the task was to integrate the safety systems of individual sections into a common safety concept to meet the requirements of the supervisory bodies." As the WLAN solution via a VPN connection can process not only Profinet, but also Profisafe, the wireless solution was also the obvious choice for the safety functions. For this purpose, the Simatic ET 200S stations were additionally equipped with fail-safe modules that ensure safety via conventional safety relays and parallel wiring, or are connected directly to the fail-safe Sinamics G120 frequency inverters. Bernd Geider adds: "If it should become evident during operation of the plant that further safety measures are necessary, we can integrate these via Profisafe, or we can loop the yellow ASIsafe cable through the plant."

SYSTEM PHILOSOPHY AND PLUG AND PLAY FOR MODERN SAFETY SOLUTIONS

Thus, a solution has been found that provides a transparent and flexible configuration for both the control engineering and the safety engineering. The chosen safety concept on the basis of ASIsafe and Profisafe proved to be technically and economically viable, above all for installations comprising different sub-machines.

In conjunction with fail-safe WLAN communication via VPN tunnel, it was possible to make substantial savings on installation work, with a positive effect on implementation time and costs. If data traffic via the wireless connection should break down, the plant immediately assumes a safe state, in other words, it shuts down completely.

For Andreas Ade, whose main area of competence is in the glass industry and pipe bending machinery, the retrofit project for glass panel processing presented two "firsts": ASIsafe and WLAN Safety - in combination. His final verdict is clear: "A holistic view of automation and safety engineering has many benefits - the greatest being flexibility and time savings thanks to plug and play."

Application overview