What is the advantage of DCS over PLC?

Answer 1

SCADA is an abbreviation for Supervisory Control and Data Acquisition .

DCS stands for Distributed Control System.

Normally, a SCADA system will get the data from a RTU (remote terminal unit). A RTU runs independently, except for some control from the central supervisory system such as fire fighting, emergency shut-down (i.e water & oil pipelines). The communication path will be through a GSM, wireless technology, etc...

For a DCS system, it controls the process as a stand-alone system. It has the control loops built into it's own controller. The communication path will be through something like a LAN high-speed Ethernet, or other communications network. DCS is a single unit, or a group of local units

I think that my clarification helps a little bit on the subjects of DCS and SCADA.

Thanks

Answer 2

The traditional system, monitoring processes across multiple sites, involved the collection of data to a single location. This is what SCADA does, primarily the "DA" portion of SCADA, i.e. data acquisition. Some control was usually present but not a significant amount. The modern DCS, or distributed control system, could be described by taking each word of the acronym out and explaining it.

First, 'Distributed' implies that the functions are all distributed. These functions refer to the data collection, processing, controlling outputs, alarming, collecting historical data, etc. In a typical DCS system, you will find physical boxes that handle each of the above functions (well, almost). There is additionally an implication about geographical distribution, or that the functions can be distributed in different physical locations. This is a benefit in that prevents failure in one part of the system from affecting another part.

The word 'Control' implies the ability of the system to close the loop between an input measurement and a manipulated handle in the process. This means that the DCS shall have the capability for basic and advanced control algorithms.

The word 'System' implies that all of the above is connected as one contiguous system i.e. in simple words, one comprehensive system with systems and physical parts spread over potentially a wide area carrying out monitoring and control functions. A control system may have one or more PLCs (programmable Logic Controllers). The PLC is a term applied in different ways. In large process facilities, there is a requirement that there be two systems--one for control while another for safeguarding. The plant-wide safeguarding portion is typically done by a safety-certified PLC. However, smaller PLCs could be used in smaller single loop control and safeguarding applications as well.

PKumar68 May08

Answer 3

PLC'S is just a controller where as DCS is a controller + MIMO(multiple input multiple output)