In general, the control problem can be divided into three domains: the regulatory control (PID, feedforward, etc..), Sequential (typical beat control: open a valve, wait 3 minutes, turn on a pump, etc..) And logical (eg, interlocks implemented with ladder logic, time to be executed in the order of milliseconds). Historically, regulatory control was control of the DCS, and PLC logic Both offer sequential control capability, in different ways.
Today, this boundary is fuzzy, because the PLC offers some sequential and regulatory control, although the application is not always easy to develop. Similarly, the DCS incorporated logical capacity, but generally very limited in scan time (0.1 sec, 0.5 sec and 1 sec even against the 10 ms. Typical of a PLC)
This trend is the result of pressure from users to have a single system that meets the needs of the three domains. This is because the interconnection of equipment from different suppliers demand additional resources and equipment engineering and application development platform for this venture is difficult. Because of the limitations we have described in the preceding paragraph, the equipment offered by suppliers do not fully meet demand, and lead in general to the need for DCS, PLC, sequence of events, and other equipment, with an arduous task of connectivity and configuration for their integration, with results that do not always cover the user's expectations.
Converge plant where regulatory control, sequential and logical
By contrast, an OIS integrates the three domains in a transparent control (Figi 2.10). The existence of different control processors that cover one or more of the domains of integrated control in real-time network facilitates the development of applications that integrate the three domains of control. For example, you can have on the same processor multifunction network carrying out regulatory control, and logical sequences, and other specialized logic control (such as a PLC), both exchanging information among themselves with minimal effort for. integration .. Additionally, these processors may be from different suppliers, giving more flexibility to! L user in the selection of equipment that fits your needs
Figure 2.10 Integration of the three domains of control
Below is the structure of an OIS as OPC (OLE for Process Automation):
Figure 2.11 Structure of an OIS
Industrial communication networks, allow us to know everything about an industrial process by fundamentals as measured by instruments installed in the field, allowing management to know how your company.
Yet another key aspect is that it allows the plant to large distance. To be able to control and integrate each of the field instruments must have a standard to enable them to communicate.
