In 2000 we saw for the first time a major development in the philosophies of Automation and Safety control systems. This saw two separate networking worlds being created - the AS-Interface Safety at Work profile (or ASiSafe) and ProfiSafe, the functional safety profile of PROFIBUS. Here, for the first time, standard control and safety control could be combined in one network, albeit in separate domains. We can now introduce the next step forward with networked safety technology. This takes the form of a gateway between the two protocols, not only for the standard control but also for the safe data as well. This is a major move forward for both domains by developing a fully integrated approach to safety control across separate networks and protocols.
Profibus and ASi have always been the perfect partners when developing automation and control solutions. In many cases the backbone of many ASi systems is the Profibus protocol because of its unique features, including data capacity and distance. The limitations of ASi, while they may have changed with the launch of new ASi V3.0 specification, still see it firmly associated with the Sensor Actuator level of the control world. It has been designed for low level interaction between the installer/maintenance operatives and distributed control. With such features imbedded into the ASi protocol the use of it for safety in the operating cell was been an easy transition. For simple to medium complex systems ASi and ASiSafe are real alternatives to traditional Hard Wired control and safety systems.
ASiSafe
Since its launch in 2000 there have been about 50,000 ASi Safe monitors and approx 250,000 safe nodes sold world wide. In the UK, we have been at the forefront of its success, seeing its second installation after launch, at a regional airport on a baggage handling system. Since then we have seen the system being used on diverse systems, such as conveyors, brick manufacturing lines, welding systems, transport, Fun/Theme parks, and even training systems for Fire Fighters.
The ASiSafe system itself is centred around the Safety Monitor. This unit, programmable via standard software, is really an intelligent Safety Relay, its action being controlled and monitored over the ASi network. It is available in either a Basic or Enhanced format, the selection of which is determined by the user depending on the functionality required. There are either single or duel channel units available, again the selection being dependent on the overall control required. Each channel is capable of complying with Cat 4 of EN954-1 or SIL 3 of IEC 61508. For example, using a two channel monitor you could develop a two zone safety system with common interaction, depending on how the software is developed and utilised.
One of the system?s major plus points is that you do not require a Fail Safe PLC for correct safety operation. The safety control is all done through the ASi Safe Monitor via the password-protected software. Multiple monitors can be connected to the same system enabling the user to configure sometimes quite complex multi Safe Zone control applications.
Its limitations are the limitations of the standard ASi system. These include network length, and that we can only have 31 safe addresses on one network. A further limitation is that we currently have no safe outputs, which means that we cannot achieve a Stop Cat 2 function as required for some systems. This suggests that interaction with higher level Safety networks is very desirable. To be able to transmit safe data to other areas of the plant or control area and generate a Safe control function really does move the boundaries forward with regards to implementation and system design.
F-Link
The F-Link unit is a standard DP/ASi gateway but with the additional functionality of also transferring Safe data from the ASiSafe components to the ProfiSafe system via standard data traffic between the two systems. For the first time we have the capability to generate safe control across networks without having to hard wire this interaction. F-Link allows for real automation integrated solutions where global e-stops are required, or where faster responses are needed to improve stop functions. Real cell interaction can be constructed using the standard topologies of ASi and PROFIBUS without any compromise to the overall control philosophy or design.
For the first time this will allow safety data to be transferred between production cells to bring better coordinated functional safety across wider plant areas. Using innovative design this will allow more sophisticated safety engineering systems covering multiple plant areas.
Soon we will see the introduction of ASi Safe outputs too. Combined with the F-Link unit this will then allow for total integration between two networks for both safe inputs and outputs. Cell and plant control will then become much easier to configure while still maintaining the overall safety integrity of the system.
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