Three key points of FCS

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There are three key points regarding FCS: (1) The core of an FCS system is the bus protocol, that is, the bus standard. For a given type of bus, once its bus protocol is determined, the relevant key technologies and associated devices are also determined. In terms of the basic principles of their bus protocols, all types of buses are similar, as they are all based on the concept of enabling bidirectional serial digital communication. However, for various reasons, the bus protocols of different types of buses vary greatly. 　　 To enable fieldbuses to meet interoperability requirements and become true open systems, international IEC standards specify that the user layer of the fieldbus communication protocol model must have a device description function. To achieve interoperability, each fieldbus device is described using a device description DD. DD can be considered a driver for the device, containing all the necessary parameter descriptions and the operational steps required by the master station. Since DD includes all the information required to describe device communication and is independent of the master station, it enables true interoperability among field devices. 　　 　　The actual situation is not consistent with what was mentioned above; the answer is no. The currently adopted international standards for fieldbuses include 8 types, whereas the original IEO international standard was just one of those 8 types, holding an equal status to the other 7 types of buses. For the other 7 buses, regardless of their market share, each bus protocol comes with its own set of software and hardware support. They are capable of forming systems and products, whereas the original IEC fieldbus international standard was nothing more than a framework without any software or hardware support. Therefore, achieving mutual compatibility and interoperability among these buses is almost impossible at the current stage. 　　 　　From the above, can we draw the conclusion that the interoperability of open fieldbus control systems, for a specific type of fieldbus, means that as long as the bus protocols of that type of fieldbus are followed, the products are open and interoperable. In other words, regardless of the manufacturer of the products, and as long as none of them are produced by that fieldbus company, as long as they comply with the bus protocol of that bus, the products can be interconnected to form a bus network, offering interoperability. 　　 (2) The foundation of the FCS system is digital intelligent field devices. Digital intelligent field devices serve as the hardware backbone of the FCS system and constitute its foundation; the reason for this is simple: the FCS system relies on a two-way digital communication protocol over field bus signals between automatic control devices and field devices. If the field devices do not follow a unified bus protocol, that is, the relevant communication standards, and lack digital communication capabilities, then so-called two-way digital communication is nothing but empty talk, and such systems cannot be called field bus control systems. Furthermore, a key feature of fieldbuses is the ability to enhance control functions at the field level. If the field devices are not multi-functional and intelligent products, then the advantages of field bus control systems no longer exist; benefits such as simplified systems, easier design, and improved maintenance are also illusory. 　　 (3) The essence of the FCS system is on-site information processing. For a control system, whether DCS or fieldbus is used, the amount of information that needs to be processed is at least the same. In fact, by using fieldbuses, more information can be obtained from the field. The amount of information in the fieldbus system has not decreased; in fact, it has increased, while the cables used for transmitting this information have **decreased**. This requires, on the one hand, **improving the capacity of cables to transmit information, and on the other hand, processing large amounts of information on-site to reduce the back-and-forth of information between the field site and the control room.** It can be said that the essence of fieldbuses is the localization of information processing. 　　 Reducing information back-and-forth is an important principle in network design and system configuration. Reducing information back-and-forth often brings the benefit of improving system response time. Therefore, when designing a network, nodes with high amounts of information exchange among them should be placed in the same branch as a priority. 　　 Reducing information back-and-forth and reducing the cables in a system can sometimes be contradictory to each other. At this point, the principle of saving investment should still guide the choices. If the response time of the selected system permits, a cable-saving solution should be chosen. If the response time of the selected system is tight, it is sufficient to reduce the amount of information transmitted slightly; in that case, a solution that reduces information transmission should be chosen. 　　 Today, some field instruments equipped with field buses come built with many functional blocks. Although the performance of these functional blocks may vary slightly across different products, it is an objective fact that there are numerous functional blocks with similar capabilities on a single network branch. Which function block from the field instrument to select is a problem that needs to be resolved in system configuration. 　　 The principle behind addressing this issue is to minimize the back-and-forth of information on the bus. Generally, it is possible to choose the function block on the instrument that provides the most information related to that function.