RELANCE 0-57408-B 配套驅(qū)動控制模塊
看看現(xiàn)在呢？ 老牌的PLC廠商均涉及DCS應(yīng)用領(lǐng)域，如西門子，其系統(tǒng)不過是PLC加網(wǎng)絡(luò)加軟件加增強的控制器。DCS廠商如霍尼維爾等其系統(tǒng)也融入了PLC，以增強其邏輯控制功能。
要注意一點： 西門子PLC是一種控制器；
DCS是一種體系結(jié)構(gòu)是由控制器+IO采集+網(wǎng)絡(luò)+軟件等組成的系統(tǒng)；
SCADA系統(tǒng)是另一個概念，有另一種應(yīng)用需求所呈現(xiàn)的系統(tǒng)。顧名思義它是：分布式的數(shù)據(jù)采集監(jiān)控系統(tǒng)，它的由來和應(yīng)用的產(chǎn)生于前兩者不同，它主要是用于數(shù)據(jù)采集，如電力的監(jiān)控系統(tǒng)、輸油管線的監(jiān)控系統(tǒng)，它的特點是控制點分散，一個系統(tǒng)可能覆蓋方圓數(shù)千公里[如北美的油氣管道監(jiān)控系統(tǒng)]；通信結(jié)構(gòu)復(fù)雜，不是一般控制系統(tǒng)所能比擬的[從光纖到無線甚至衛(wèi)星通訊]。它的基本單元是RTU。
其實DCS和SCADA是概念，應(yīng)該理解為一種體系結(jié)構(gòu)。 PLC、DCS是由早期不同的產(chǎn)品形態(tài)和應(yīng)用場合逐步完善演化而來?？梢哉fPLC有制造業(yè)的繼電器演化發(fā)展而來。DCS是由過程控制的儀表發(fā)展演化而來。各自產(chǎn)品有其自己的使用場合和特點，隨著技術(shù)的進步、行業(yè)的相互滲透和競爭的激烈。PLC和DCS這兩種產(chǎn)品都在發(fā)展自己優(yōu)勢的同時向?qū)Ψ降臐B透。
應(yīng)該知道西門子PLC的邏輯控制功能很強大，而回路控制則是不值一提的[可以看一看型號稍微老一點的PLC，而DCS系統(tǒng)正好相反。這是由于兩種系統(tǒng)的內(nèi)部處理機制的不同。
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.