GESADA-1 PCB control board

Description

GESADA-1 PCB control board

GESADA-1 PCB control board

Differences between the three major control systems
We already know that FCS has evolved from DCS and PLC. FCS not only possesses the characteristics of DCS and PLC, but also takes a revolutionary step forward. At present, both the new DCS and the new PLC have a trend of approaching each other. The new DCS has strong sequential control function; And the new type of PLC is not bad at handling closed-loop control, and both can form a large network. The application range of DCS and PLC has a significant overlap. The next section will only compare DCS with FCS. In the previous chapters, the differences between DCS and FCS have actually been addressed. The following will describe the architecture, investment, design, usage, and other aspects.

Difference points DCS
The key to DCS systems is communication. It can also be said that the data highway is the backbone of the distributed control system DCS. Due to its task of providing a communication network between all components of the system, the design of the data highway itself determines the overall flexibility and security. The media for the data highway can be a twisted pair, coaxial cable, or fiber optic cable.
Through the design parameters of the data highway, it is basically possible to understand the relative advantages and weaknesses of a specific DCS system.

(1) How much I/O information can the system process. (2) How much control loop information can the system handle related to control. (3) How many users and devices (CRT, control station, etc.) can be accommodated. (4) How is the integrity of transmitted data thoroughly checked. (5) What is the maximum allowable length of the data highway. (6) How many branches can the data highway support. (7) Can the data highway support hardware produced by other manufacturers (programmable controllers, computers, data recording devices, etc.).
To ensure the integrity of communication, most DCS manufacturers can provide redundant data highways.

To ensure the security of the system, complex communication protocols and error detection techniques were used. The so-called communication protocol is a set of rules that ensure that the transmitted data is received and understood as the same as the transmitted data.

Currently, two types of communication methods are commonly used in DCS systems, namely synchronous and asynchronous. Synchronous communication relies on a clock signal to regulate data transmission and reception, while asynchronous networks use a reporting system without a clock.

The key points of FCS are three
(1) The core of the FCS system is the bus protocol, which has been described in the previous chapters of the bus standard. As long as the bus protocol of a type of bus is determined, the relevant key technologies and equipment are also determined. In terms of the basic principles of its bus protocol, all types of buses are the same, based on solving the problem of bidirectional serial digital communication transmission. However, due to various reasons, there are significant differences in bus protocols among various types of buses.
In order to meet the interoperability requirements of the fieldbus and make it a truly open system, the user layer of the IEC international standard fieldbus communication protocol model is explicitly specified to have device description function. To achieve interoperability, each fieldbus device is described using device description DD. DD can be considered as a driver of the device, which includes all necessary parameter descriptions and operational steps required for the main station. Due to the fact that DD includes all the information required to describe device communication and is independent of the main station, it enables true interoperability of on-site devices.
Is the actual situation consistent with the above? The answer is negative. The current international standard for fieldbus includes 8 types, while the original IEO international standard is only one of the 8 types, and its status is equal to the other 7 types of buses. The other 7 types of buses, regardless of their market share, each bus protocol has a set of software and hardware support. They can form systems and products, while the original IEC fieldbus international standard is an empty shelf with neither software nor hardware support. Therefore, achieving mutual compatibility and interoperability among these buses is almost impossible in terms of current state.
From the above, can we draw an image of the interoperability of open fieldbus control systems? For a specific type of fieldbus, as long as it follows the bus protocol of that type of fieldbus, it is open to its products and has interoperability. In other words, no matter what manufacturer’s product, no one is a product of the fieldbus company. As long as the bus protocol of the bus is followed, the products are open and have interoperability, and can form a bus network.

(2) The foundation of the FCS system is digital intelligent field devices
The digital intelligent field device is the hardware support and foundation of the FCS system, and the principle is simple. The FCS system executes the bidirectional digital communication field bus signaling system between the automatic control device and the field device. If the on-site device does not follow a unified bus protocol, that is, relevant communication protocols, and does not have digital communication functions, then the so-called bidirectional digital communication is just empty talk and cannot be called a fieldbus control system. Furthermore, a major feature of fieldbus is the need to add primary control functions on site. If the on-site device is not a multifunctional and intelligent product, the characteristics of the fieldbus control system will no longer exist, and the advantages of simplifying the system, facilitating design, and facilitating maintenance are also virtual.

(3) The essence of FCS systems is the fieldization of information processing
For a control system, whether using DCS or fieldbus, the amount of information that the system needs to process is at least the same. In fact, with the use of fieldbus, more information can be obtained from the field. The amount of information in the fieldbus system has not decreased or even increased, while the cables used to transmit information have greatly decreased. This requires greatly improving the ability of cables to transmit information on the one hand, and allowing a large amount of information to be processed on-site to reduce information round-trip between the site and the control room on the other hand. It can be said that the essence of fieldbus is the fieldization of information processing.

Reducing information round-trip is an important principle in network design and system configuration. Reducing information round-trip often brings the benefit of improving system response time. Therefore, in network design, priority should be given to placing nodes with high exchange of information between each other in the same branch.

Reducing information round-trip and reducing system cables can sometimes contradict each other. At this point, we should still make choices based on the principle of saving investment. If the response time of the selected system allows, a cable saving solution should be chosen. If the response time of the selected system is relatively tight, a slight reduction in information transmission is sufficient, then a plan to reduce information transmission should be chosen.

Nowadays, some field instruments with fieldbus are equipped with many functional blocks themselves. Although different products may have slight differences in the performance of the same functional block, it is objective to have many identical functional blocks on a network branch. Which function block to choose from on site instruments is a problem that the system configuration needs to solve.
The principle to consider this issue is to minimize the round-trip of information on the bus as much as possible. It is generally possible to select the function block on the instrument panel that outputs the most information related to this function.

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