Main differences between DCS and PLC

The differences are as follows:

1. Different names

DCS: Distributed control systems.

PLC: Programmable Logic Controller is just a control "device".

2. Different emphasis

DCS is more focused on the process control field (such as chemical, smelting, pharmaceutical, etc.), mainly monitoring and regulating control of some field parameters.

PLC focuses on logic control (machining). Of course, the current PLC can also deal with process control problems well, but there is no DCS specialty.

3. Analog quantity is different

If the analog quantity is more than 100 points, DCS is generally used

If the analog quantity is within 100 points, PLC is generally used.

4. Different network forms

DCS network is the central nerve of the whole system, and the international standard protocol TCP/IP is usually adopted by DCS system. It is a safe and reliable dual-redundant high-speed communication network, and the system has better expansibility and openness.

Because PLC basically works for a single small system, when communicating with other PLCs or upper computers, the network form adopted is basically a single network structure, and the network protocol is often inconsistent with international standards.

5. Failure is different

All I/O modules of the DCS system are equipped with CPU, which can realize the quality judgment and scalar transformation of the collected and output signals, and can be unplugged and replaced randomly in case of fault. The PLC module is only a simple electrical conversion unit, without intelligent chips. After the failure, the corresponding units are all paralyzed.

Extended data

Programmable logic controller is a digital operation electronic system specially designed for application in industrial environment. It uses a kind of programmable memory to store instructions for logic operation, sequence control, timing, counting, arithmetic operation and other operations inside, and controls various types of mechanical equipment or production processes through digital or analog input and output.

Distributed control system is a new generation of instrument control system based on microprocessors and adopting the design principles of decentralized control functions, centralized display operation, taking into account division, autonomy and comprehensive coordination. Distributed control system is referred to as DCS, which can also be translated as "distributed control system" or "distributed computer control system". It adopts the basic design idea of decentralized control, centralized operation and management, and adopts the structural form of multi-level and cooperative autonomy. Its main feature is its centralized management and decentralized control. At present, DCS is widely used in power, metallurgy, petrochemical and other industries.