Distributed Control Systems were developed in the mid-70's, representing the existing computing concepts at the time: in proprietary systems that integrate hardware, software and services from one vendor provided a solution. As in the administrative systems, this architecture represents a solution for y'80 años'70, but lacks the flexibility required for the '90s. Thus, the DCS have several proprietary networks at different levels, allowing the interplay of old and new technologies from a single source, although with some problems. For example, many of these systems have included UNIX-based workstations, but they can not be ported to this platform existing applications. From the point of view of integration of equipment from different vendors, it is only possible through the use of gateways, which allow limited communication between different protocols. Thus, coexist in a single plant DCS networks, networks of PLCs, control networks unilazo, etc.
Figure 2.7 - Distributed Control System
Another aspect that DCS could not be updated is in the processing of information, such as administration or use of objects related databases. Finally, their own internal hinder the carrying of applications from other systems.
In summary, the control systems in general owe the revolution who are suffering administrative systems, but are in the process of paying off that debt. In 1987 Foxboro introduced its Intelligent Automation I / A, as the first Open Industrial System (Open Industrial System, OIS). This concept was recognized as a necessity for both suppliers and consultants. Even though the market has not defined the name of this new generation of systems (OIS, OCS or DCS Open are some possibilities), it is clear that change is underway.
Basically, we can define an OIS as a control and information system. As such, it retains many of the concepts of the DCS (functional distribution of processors, communication networks that interrelate, etc..), And adds concepts associated with open systems (relational databases, intensive use of standards, management objects, interoperability, portability, etc.)..
X Window technology a combination of tooth technology GUI / Server
The basic architecture of a control system shows what types of devices is composed, and what the interrelated communications networks. To a large extent, the architecture of an OIS is similar to that of a DCS in regard to the functional distribution of tasks on multiple devices, and the interrelation of these devices via communications networks.
A DCS typically involves the existence of several coexisting networks: networks of controllers of previous technologies, most modern networks, PLC networks are separated or integrated through gateways, and in some cases, integration into the computer network through another gateway . If co-exist within a plant control systems from different vendors, each of them will have these networks independently. Their integration is unusual, and involves the use of gateways with high cost and limited supply.
In the OIS, the lower level allows intercommunication between other transmitters, controllers, PLCs, barcode reader, etc.. The network is called fieldbus (fieldbus), and connects with the real time processor through increased capacity. Some of these simply act as bridges, others are control processors running control strategies beyond the capacity of the field devices.
The real-time network communicates with each other application processors, operating stations, multi-loop control processors, PLC larger, and so on. The main feature of this network is that it allows management to ensure real time data on a redundant bus ¿.
Finally, some of the processors communicate simultaneously with real-time network and network administration. The degree of interoperability offered by OIS in this case reaches its peak. The enterprise-wide information flows freely between the administrative system and control system, allowing each user to access freely and easily to the information you need. Access to information in either environment is done in the same way. The main difference between the administrative network for the real time is its transactional and non-redundant and therefore can not guarantee data management with high availability and real-time.
The speed limitations imposed by the administrative network to transmit real-time information quickly and safely disappear as soon as new technologies with greater bandwidth. Currently available networks provide a bandwidth of some megabaud (eg, Ethernet at 10 Mbps). Some emerging technologies such as ATM (Asynchronous Transfer Mode) will increase the bandwidth to values of several gigabaudios. With this bandwidth, we predict that real-time networks and transactional be merged into a single network, which we call network.
All these networks are strongly based on standards, some of which already exist: administrative networks, TCP / IP, DECnet and 'Novell over Ethernet are common words.
Industrial network levels
The situation is slightly more difficult in the case of real-time network. In principle, can be based on IEEE 802.3, 802.4, 802.5, etc.. However, today there are no clear trends regarding the standard that would cover the remaining levels of the ISO / OSI model, while satisfying the following requirements: redundancy, failed cable recognition, recognition of their reinstatement, transfer of real time data from equipment from different vendors in a transparent (interpretation): etc.
More confusing is the status of fieldbus case in which attempts have been locked normalización1 mutually SP50, Profibus, FIP, ISP, World FIP, etc.
Figure 2.9 Fusing the two networks to computer system
