RELANCE 0-57408-B 配套驱动控制模块
看看现在呢？ 老牌的PLC厂商均涉及DCS应用领域，如西门子，其系统不过是PLC加网络加软件加增强的控制器。DCS厂商如霍尼维尔等其系统也融入了PLC，以增强其逻辑控制功能。
要注意一点： 西门子PLC是一种控制器；
DCS是一种体系结构是由控制器+IO采集+网络+软件等组成的系统；
SCADA系统是另一个概念，有另一种应用需求所呈现的系统。顾名思义它是：分布式的数据采集监控系统，它的由来和应用的产生于前两者不同，它主要是用于数据采集，如电力的监控系统、输油管线的监控系统，它的特点是控制点分散，一个系统可能覆盖方圆数千公里[如北美的油气管道监控系统]；通信结构复杂，不是一般控制系统所能比拟的[从光纤到无线甚至卫星通讯]。它的基本单元是RTU。
其实DCS和SCADA是概念，应该理解为一种体系结构。 PLC、DCS是由早期不同的产品形态和应用场合逐步完善演化而来。可以说PLC有制造业的继电器演化发展而来。DCS是由过程控制的仪表发展演化而来。各自产品有其自己的使用场合和特点，随着技术的进步、行业的相互渗透和竞争的激烈。PLC和DCS这两种产品都在发展自己优势的同时向对方的渗透。
应该知道西门子PLC的逻辑控制功能很强大，而回路控制则是不值一提的[可以看一看型号稍微老一点的PLC，而DCS系统正好相反。这是由于两种系统的内部处理机制的不同。
Siemens PLCs are also divided into large, medium, small, and micro PLCs. Micro PLCs are only sold for a few hundred to 2000 yuan, with a relatively small number of points. Large PLCs can carry thousands of points, and their computing power is similar to DCS, but they have weaker capabilities for multi machine networking. Now both technology platforms are similar, but the focus is different.
In fact, DCS and SCADA are concepts and should be understood as an architecture. PLC and DCS have gradually evolved from different early product forms and application scenarios. It can be said that PLC evolved from the relay industry in manufacturing. DCS evolved from the development of process control instruments.
Module: All I/O modules in the DCS system are equipped with CPUs, which can be used to judge the quality of collected and output signals and perform scalar transformations. They can also be plugged and unplugged due to faults and replaced randomly. The PLC module is just a simple electrical conversion unit without intelligent chips, and all corresponding units will be paralyzed after a malfunction.
8. Nowadays, the high-end Siemens PLC and DCS have similar functions, and DCS has strong capabilities for network and distributed database scheduled scanning. At the same time, it is proficient in processing calculations and analog signals.
The download process is automatically completed by the system and does not affect the operation of the original control scheme. Various control software and algorithms in the system can improve the control accuracy of process requirements for controlled objects. For systems composed of PLCs, the workload is extremely large. First, it is necessary to determine which PLC to edit and update, then use the corresponding compiler to compile the program, and finally use a dedicated machine (reader) to transmit the program one-on-one to this Siemens PLC. During system debugging, it greatly increases debugging time and costs, and is extremely detrimental to future maintenance. There is a significant difference in control accuracy. This determines why in large and medium-sized control projects (above 500 points), systems connected entirely by Siemens PLCs are rarely used.