6. From the scale of application objects:
PLC is generally used in small automatic control places, such as the control of equipment or the control and interlocking of a small amount of analog quantity, while the large-scale applications are generally DCS.

Of course, this concept is not accurate, but it is very intuitive. We are used to calling a system larger than 600 points a DCS, and a scale smaller than this is called a PLC.

Having said so many differences between PLC and DCS, we should realize that PLC and DCS are in fact moving closer to each other in their development to this day. Strictly speaking,
The current PLC and DCS can no longer be cut across the board, and the concept between them has been blurred in many cases. Now, let’s discuss the similarity (like)
Place.
1. In terms of function:
PLC already has the control function of analog quantity, and some PLC systems have even quite powerful analog quantity processing capability, such as Siemens S7-400, ABB control board Control Logix and Schneider Quantum system. And DCS also has quite strong logic processing capabilities.

2. From the system structure:
The basic structure of PLC and DCS is the same. PLC has developed to today and has been fully transplanted to computer system control. Traditional programmers have long been
Be eliminated. PLCs for small applications generally use touch screens, and PLCs for large-scale applications use computer systems in an all-round way. Like DCS, the controller and IO station use
Use field bus (usually based on RS485 or RS232 asynchronous serial communication protocol bus mode), if there is no expansion between the controller and the computer
Requirement, that is to say, when only one computer is used, this bus communication will also be accepted. But if more than one computer is used, the system structure
Just like DCS, the host computer platform uses the Ethernet structure. This is one of the reasons why the concept of DCS is blurred after the large-scale PLC.

3. The development direction of PLC and DCS:
Miniaturized PLC will develop towards a more professional use perspective, such as more targeted functions, more targeted application environment, and so on. Large

The boundary between PLC and DCS gradually fades until it is completely integrated.
DCS will continue to develop in the direction of FCS. In addition to the more decentralized control system, the core of FCS is instrumentation. FCS abroad
The application has been developed to the instrument level. What the control system needs to deal with is only signal acquisition and provision of man-machine interface and logic control. The control of the entire analog quantity is divided into
Distributed to the field instruments, there is no need for a traditional cable connection between the instrument and the control system, and the field bus is used to connect the entire instrument system. (Currently, there is Yokogawa in the country
FCS is used in the CNOOC and Shell petrochemical project, and the instrument level uses intelligent instruments such as EJX, etc., which have the world's most advanced control level)
How to treat DCS and PLC correctly?
We should not emphasize the pros and cons between PLC and DCS, they should define a new term "control products." Provided to users is the most suitable
The user's control system. The vast majority of users will not use DCS because they want to use a set of DCS. Control products must be positioned to meet the user’s process
Based on requirements. Most of the users who even propose to use DCS or PLC have never touched automatic control products or have some special requirements. Overemphasize this
It will only fall into a dispute of tongues.

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