RELANCE 0-57406-E 电机驱动器

DCS整体考虑方案，操作员站都具备工程师站功能，站与站之间在运行方案程序下装后是一种紧密联合的关系，任何站、任何功能、任何被控装置间都是相互连锁控制，协调控制；而单用PLC互相连接构成的系统，其站与站（西门子PLC与西门子PLC）之间的联系则是一种松散连接方式，是做不出协调控制的功能。

4、DCS在整个设计上就留有大量的可扩展性接口，外接系统或扩展系统都十分方便，西门子PLC所搭接的整个系统完成后，想随意的增加或减少操作员站都是很难实现的。

5、DCS安全性：为保证DCS控制的设备的安全可靠，DCS采用了双冗余的控制单元，当重要控制单元出现故障时，都会有相关的冗余单元实时无扰的切换为工作单元，保证整个系统的安全可靠。而西门子PLC所搭接的系统基本没有冗余的概念，就更谈不上冗余控制策略。特别是当其某个西门子PLC单元发生故障时，不得不将整个系统停下来，才能进行更换维护并需重新编程。所以DCS系统要比其安全可靠性上高一个等级。

PLC是一种产品，由它可以构成SCADA、DCS。DCS是过程控制发展起来的，PLC是继电器—逻辑控制系统发展起来的，PLC是设备，DCS、SCADA是系统。

DCS与西门子PLC的区别要点： 1、DCS是一种“分散式控制系统”，而西门子PLC(可编程控制器) 只是一种控制“装置”，两者是“系统”与“装置”的区别。系统可以实现任何装置的功能与协调，西门子PLC装置只实现本单元所具备的功能。

2、在网络方面，DCS网络是整个系统的中枢神经，它是安全可靠双冗余的高速通讯网络，系统的拓展性与开放性更好。而西门子PLC因为基本上都为个体工作，其在与别的西门子PLC或上位机进行通讯时，所采用的网络形式基本都是单网结构，网络协议也经常与国际标准不符。在网络安全上，西门子PLC没有很好的保护措施。我们采用电源，CPU，网络双冗余。

SCADA system, also known as distributed data acquisition and monitoring system, is a small and medium-sized measurement and control system. It combines the two major advantages of strong on-site measurement and control function of PLC system and network communication ability of DCS system, with high cost-effectiveness.

SCADA and DCS are concepts, while PLC is a product, and the three are not comparable.

PLC is a product that can form SCADA and DCS. DCS has evolved from process control, PLC has evolved from relay logic control systems, PLC is equipment, and DCS and SCADA are systems.

Siemens PLC, which can be programmed as a controller, is suitable for measurement and control in industrial sites. It has strong on-site measurement and control functions, stable performance, high reliability, mature technology, wide use, and reasonable price.

DCS system, also known as distributed control system, belongs to the international advanced level of large-scale control system in the 1990s. It is suitable for industrial sites with multiple measurement and control points, high measurement and control accuracy, and fast measurement and control speed. Its characteristics are decentralized control and centralized monitoring, with network communication capabilities, strong measurement and control functions, reliable operation, easy expansion, convenient configuration, and easy operation and maintenance. However, the system is expensive.

the perspective of computers and networks, they are unified, and the main difference lies in the application requirements. DCS often requires advanced control algorithms. For example, in the refining industry, PLC requires high processing speed because it is often used in interlocking and even in fault safety systems; SCADA also has some special requirements, such as vibration monitoring, flow calculation, peak and valley regulation, etc. SCADA is the dispatch management layer, DCS is the plant management layer, and PLC is the on-site equipment layer.