How does a DCS work - Distributed Control System - PLC

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Over the years, industry as a wholehas undergone countless changes, especially when it comes to the technologies that are used. Automation is one of them, in fact, it has improved production and security processes. In this video we will talk about DCS. What are they and how are they used? The DCS is a system that coordinates and managesan entire plant with many different processes. Stated in this way, someone could ask what is the difference between the DCS and the PLC, which is already used in many sectors. The PLC, unlike the DCS, isgreat to manage single processes, usually employedfor repetitive controls; they are used for single batchprocessingor high-speed processes. They are very simpleand cheap to build, besides, with their design they can be configured and customized according to users’ needs easily. The operations speed managed bythe PLC is almost always very fast, an operator monitors the process through a SCADA screen.A DCS instead is used for continuous and complex controls, they have a control display that is very similar to the SCADA’s, and this is the heart of the system. Moreover, a DCS possesses a default number of functions that can be customized. The procession times are slower than the PLC’s ones and the operator interacts with the control system through a display. The proper scenery for a DCS is certainly a big plant or factory, with many processes and applications. For smallplants, the PLC usage is more preferable.Now let’s focus on the DCS and its components 1.Let’s imagine a level-basedsystem, as a hierarchical pyramid. Aclassical plant starts with a control center, commonly called an operator station; Fora DCS the operator stations are the heart of the system. Here is where the operator can observe all the operations that the plant performs, he can view warningsand alerts, he can monitor the production, and more.2.In the next level we findservers, storage computers, and design stations. The two parts usually communicate through an ethernet line. The servers store the processorsdata and they are responsible for the communication between the computers of the control center and the plant processors. Storagecomputers are used to store historical plant data, such as projects and technical specifications. The design stations are used to create the projects on which the processes are performed, such as the hardware configurations and graphics that the operator will see on the display; this is the station that will uploadthe projects to the various processors of the system.3. Next,we find the level of supervision and command; here an operator, through a man-machine interface, has the control and supervision of the area. Generally, this level is composed of a SCADA which transmits to the operator a series of process information coming from the area. 4. At the next level are the controllers and PLCs, which supervise and operate the individual processes. The controllers are also responsible for sending the data to the servers, which in turn will provide the images to the displays in the control center for monitoring.5. The next level is that of implementation, also called field. The communication between the processors and the components is very variable, it depends on the type of object that is performingthe operation. The components on this level are devices such as transmitters, switches, valves, motors and they communicate withthe highest level through electrical signals, emitted by the various devices in use. Let's try now to make a practical example:
-Let’s see an example ofa gas flow control valvein the 5th level, which is the field. -In the 4th level, the oneof the controllers, there’s a flowmeter, which acquires the data and send them to the operator.-In the 3rdlevel, the operator decides to regulate the flow rate, therefore he issues the command trough the interface-The 2nd level stores the data for similar future operations, later variousalgorithms can be created in order to identify this kind of operation.-In the 1st level the operator of the control center monitors the process and its execution.DCScan definitely takeautomation technologyto the next level with less margin oferror and with more efficiency.