From a conceptual, PLC, DCS is not a logical level concept, which can be seen from the name: PLC is named after functionality, DCS is named by architecture. PLC can make a DCS! Of course, performance differences or reality, but should be concrete to see products and needs. From an application perspective, simply distinguish between PLC, DCS, often walk into the misunderstanding. Knowledgers and later:
2003-9-12 9:03:00
DCS Control System and PLC Control Difference 1. DCS is a "decentralized control system", while PLC is only a (programmable controller) control "device", both of which is the difference between "system" and "devices". The system can realize the function and coordination of any device, and the PLC device only implements the functionality provided in this unit. 2. In terms of network, the DCS network is the central nervous of the entire system, and the system network in the MACS system of the company is used by the company's MACS system. Double redundant 100Mbps industrial Ethernet, adopted international standard protocol TCP / IP. It is a safe and reliable dual redundant high-speed communication network, and the expansion of the system is better. The PLC is based on the individual works, and its network form is in communication with other PLC or the host machine. Basically, the single network structure, the network protocol is often inconsistent with the international standard. On the network security, the PLC has no good protection. We use power, CPU, network dual redundancy. 3. DCS overall considerations, operator stations have engineers station function, and after running the schedule between the station and the station is a close relationship, any station, Any function, any controlled device is a mutual chain control, coordinated control; and a system that is connected to each other with PLC, the connection between the station and the station (PLC and PLC) is a loose connection method, it is There is no function of coordinated control. 4. DCS has a large amount of scalability interface, an external system or extension system, which is convenient, and the entire system of the PLC is completed, it is difficult to increase or reduce the operator station. of. 5. DCS Security: To ensure the security of the DCS control, DCS uses a dual redundant control unit. When the important control unit fails, there will be related redundant units in real time to switch to the work unit, Guaranteed the safety and reliability of the entire system. The system of the PLC is basically no redundant concept, but will not talk about the redundant control strategy. Especially when a PLC unit fails, it has to be stopped throughout the system to replace maintenance and need to be reprogrammed. Therefore, the DCS system is higher than its security reliability. 6. System software, updating a variety of process control schemes is a most basic function of DCS. After a certain program changes, the engineer only needs to be compiled after the engineering station, executes the following command. Yes, the following process is automatically completed by the system without affecting the original control scheme. System various control software and algorithms can increase process requirements control object control accuracy. For the system constituted by the PLC, the workload is extremely large, first of all, it is necessary to determine which PLC is to edit, then use the corresponding compiler to compile, and then use a dedicated machine (reader) One-to-one transfer the program to this PLC, during system debugging, a large number of debugging time and debugging costs, and extremely not conducive to future maintenance. The difference in control accuracy is far away. This determines why it is in a large and medium-sized control project (more than 500 points), which is basically no system that is connected by the PLC. 7. Module: All I / O modules of the DCS system have CPUs, which can achieve quality judgment and scalar transform for acquisition and output signals, fault-to-pull, random replacement. The PLC module is just a simple electrical conversion unit, there is no smart chip, and the corresponding unit is all paralyzed after the fault. We have to talk from the origins of PLC and DCS: the development of PLC Based on the on-site control requirements of manufacturing, the DCS development is based on continuous process control and monitoring of chemical industry. From the control requirements classification, the control system can be divided into: sequential control (Basic function of PLC), process control (DCS), position control (CNC), transmission control (speed or synchronization), but from the perspective of development, this Several partial control methods are gradually fused.
If you don't have to say different, I think there are the following points: 1. Object-oriented different: PLC is facing the general work control field, with strong versatility. DCS prefers process control for chemical industry. 2, DCS emphasizes the accuracy of continuous process control, achieving complex control of PID, feedforward, cascading, multi-level, blur, adaptive, generally PLC only has a PID function, and the control accuracy is not as high as DCS. 3, the DCS system has a powerful SCAND package with formula, and has developed an expert software (chemical process parameter configuration and control algorithm) for different lines, which is convenient than PLC. Finally, the modern PLC has been able to complete the most of DCS, and can do redundant or hot standby, and modules can also be charged. Select PLC or DCS key to see what you faced. The economy, reliable, and convenient is the most important.
