The replacement of older control systems and the associated updating of the I/O level are issues currently facing many process automation engineers. With the right migration concept and the portfolio required for this, users can retrofit their plants without any major mechanical effort. Frank Rohn, VP sales process automation,Turck is interviewed here by Dr. Ulla Reutner from P&A Magazine.
When it comes to replacing outdated control systems what are the main critical factors involved?
Apart from the choice of control system supplier, the most important issue for many users is choosing the right technology for connecting the field devices. Shall I use the fieldbus technology, remote I/Os or interface or system I/O solutions? We can recognise a clear trend here: More and more users are becoming interested in system or remote I/O solutions on account of their performance. We can identify a significantly faster growth than in fieldbus technology.
What in your view are the arguments against the use of fieldbus solutions?
Besides the use of special transmitters, fieldbus technology also requires specially trained maintenance personnel with fieldbus know-how. With I/O solutions, it is only necessary to measure 4-20 mA. Furthermore, with the right I/O systems, you can also use Hart and implement efficient asset management. You have almost the same functionality as with the fieldbus, but have no problems when incorporating new field devices. With I/O systems you can send hundreds of signals to the control system via one connection. With a fieldbus, a maximum of ten signals per segment is possible. A new segment must then be sent to the system. This can only be achieved with a complex topology. Parallel wiring is often also required since the fieldbus technology does not allow for simple signal types.
What is the difference between system I/O and remote I/O?
With conventional remote I/O technology, point-to-bus, you reach the installation via Profibus in order to access the remote I/O to which the signals of the field devices are sent. By system I/O we understand it to be positioning I/O systems, including the Ex isolation, directly in the control cabinet and connecting them with control, systems. Here we replace the control systems own I/O level and, if necessary, the separate Ex isolation.
What is the reaction of the control system manufacturers to this concept?
The control system manufacturers also benefit from our approach since they have lost some projects with their own I/O cards, as the overall solution simply became too expensive, too large or too slow. They became more competitive when they used excom as the I/O level.
And how can the user benefit by this solution?
A system I/O solution is not only more attractive than the I/O levels of control systems in terms of price. The user also saves space and can always use the same cards with the excom system, regardless of which control system is connected and whether excom is used as a system or remote I/O. This means simple engineering, also with standard 4-20 mA technology. The system is easy to expand and can bring Hart signals right up to the control system. You then also have a diagnostics function for the transmitters already located in the field. The high speed backplane bus enables us to achieve very good cycle times.
You promise a very clever migration concept. What do you mean by this?
Firstly, excom is offered as a universal I/O solution that can be used both in the non-Ex area as well as in zones 2 and 1. The user can thus deploy the same system in the field as remote I/O or in the control cabinet directly at the control system. This all-round complete system has everything: racks, power supply units, standard I/O modules – with or without intrinsic safety – identical engineering, and last but not least all approvals, including for use on ships. In migration projects there are also two more points to be considered: The solution is compact in the 48 cm format so that old technology can be replaced without any major mechanical effort required.
What do you mean by major mechanical effort?
Where previously around 150 control system I/Os could be installed in one cabinet; now up to 720 are allowed. As these racks are based on the 48 cm format, the user can simply remove his own I/O cards in 48 cm racks and mount the excom stations. This saves three or four cabinets and enables both the I/O card of the control system and also the I/O level to be installed in one cabinet. This has been successful in many branches in the process industry – from the pharmaceutical sector right through to the oil and gas industry. There are now over 10 000 excom stations in operation worldwide in completely different application
fields, connected to all sorts of different control systems. Naturally many customers also fit this solution in new installations but
the major business currently involves migration. The BL20 I/O system can also be an interesting alternative to excom here if the features of intrinsic safety and continuous availability with redundant systems are not so important in a process plant.
As BL20 comes from the field of factory automation, does the system also meet the requirements of process automation?
BL20 was originally developed for manufacturing automation. However, unlike others in this sector, we have further developed this solution with our process technology know-how and now offer a Hart card, for example, or the possibility of hot plugging, i.e. removable or pluggable modules. This enables a card to be replaced quickly without any effort. Last but not least, BL20 ensures optimum integration in control systems since we also use a DTM – exactly as with excom.
Contact Brandon Topham, RET Automation, Tel 011 453-2468, firstname.lastname@example.org