Remote IO - For Functional safety in the Explosive area!
Automation technology is an important part of the economy, as it is only the ability for automatic communication within networks, devices, installations and machines that makes mass production possible. Here, the system of fieldbuses has established itself in particular. This is because the use of such technological applications has the advantage of saving time and money. Furthermore, such components help to increase safety in systems. After all, as is particularly the case with conventional technologies, the transmission of signals is realized via so-called discrete signal lines. However, the problem arises as there is a lack of so-called SIL devices that have compatibility with a fieldbus. One possible alternative for avoiding this availability problem is the use of Remote IO technology. The reason for this is that this application has also been shown as suitable for use in explosive areas and as such, it can cover various applications.
The Problematic Basis for Remote IO
The task to be performed by Remote IO is a serious matter, as the basis on which this technology has to work is problematic. This is because with the aid of corresponding technology, the process of industrial communication is a process that is already characterized by the fact that there are risks and possible safety gaps. In addition to the conventional functioning of an installation, i.e. the execution of tasks without problems and in accordance with a specified order, it is also important to avoid hazards for humans who are in the vicinity of this type of process technology. Furthermore, environmental pollution also must be avoided as far as possible in order to achieve technology that is truly efficient. Up until now the procedure in the field of automation technology provides for the use of dedicated safety circuits, i.e. circuits having only one function. However, these point-to-point connections mostly are considered as out-of-date, as modern technologies are more convenient, more flexible and more efficient. For a long period now, such modern methods have included Remote IO, as it has been able to stand its ground when handling demanding applications and has significant range compared to conventional fieldbus networks within the field of explosion protection.
Remote IO also has the advantage that it already has the required components for SIL-2 installation, while the classic fieldbus systems have the disadvantage of lacking hardware. Accordingly, this is considerably more cost-intensive than the alternative of remote technology. The importance of the task that the Remote IO performs is not easy to recognize at a glance. Accordingly, the SIF protocol was conceived for the Foundation FB, i.e. the fieldbus specification of the Fieldbus Foundation. This stands for “Safety Instrumental Function” and in 2007, this established the basis for a series of inter-operability tests. The protocol for the SIL-3 applications came out one year later. Both systems bring standards along with them. Here, the data are transmitted via a process and a safety device by means of the same line of a bus network. These specifications implement various characteristics that are relevant for the recognition and correction of faults. Communication on a safety-critical standard is only then possible. In addition, it can only then be asserted as reliable. As such, these systems deliver secure data packets to the time stamps, to the instructions of response timers and for routine testing of the integrity. The difficulty that Remote IO brought to such an indispensable role in automation technology is evident at a second glance, where the lack of fieldbus devices becomes apparent. Namely, for both specifications there are hardly any devices that would support a fieldbus.
Accordingly, there are only a few manufacturers which offer SIL technology that would satisfy this criterion. And if such a device were to be available, there still would be the problem of its lack of suitability for areas at risk of explosion. Accordingly, at the Fieldbus Foundation, the SIF specification still is in an early state where the prototype still is being tested. Even with the Profisafe technology, there are only two control systems so far. Through this, there is stronger demand for the development of sensors and actuators that, on the one hand, have already proven themselves in operation and are SIl-2-certified. In addition to the secured protocol stack, they should also provide the respective interfaces. This paves the way for the success of Remote IO.
The Alternative Solution Remote IO
A way out of this difficulty, which is not only founded in theory but is also able to prove itself as feasible in practice, is the technology of Remote IO. This makes it possible to act inside the area at risk of explosion by communicating using PROFIBUS DP and PROFISAFE. This way, SIL devices can be connected to a control system by means of a (4 to 20) mA signal that can provide the necessary safety standards. Here, the connection is made via a fast bus line which serves the conventional flow of the process. For this application, there are sufficient devices that are suited to the SIL-2. However in order to create communication within the PROFIBUS network in which both types of connection can run over one and the same line, a special safety analog input module is needed which the Remote IO provides. Normally, this PROFISAFE slave assembly is composed of eight channels, which can then be installed within the Remote IO station. If the configuration is correct, use is even possible in circuits with hard signals.