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These days there is no real difference between PLC and DCS systems.
Of course there are differences between manufacturers equipment but most modern systems are capable of doing the work of emulating relay logic (PLC) and analogue control (DCS) with intelligence, integration and SCADA capabilities all available if needed.
Some systems may have more resilience, redundancy, be more capable in certain areas or maybe just more visually dynamic. Each manufacturer will have a reason why they say their system is better. Often it just comes down to cost per point or a client specification requiring a specific system over another.
Vote me up please if you like :)
DCS VS PLC
1. Single vendor Mutiple
2. Small Area /LAN Large Area/WAN
3. Many I/O Less I/O
4. Use for Monitoring Used for Controlling
When we come to PLC, it is best for batch processing or machine control, it takes lesser time and good control. But when we are talking about DCS, it is better in process control especially in non-stop/contrinuous processing.
The world is becoming small, DCS offers more varieties than PLC, and today PLC and DCS combining and automation is growing. In past PLC was not helpful when we face any trouble, it have to shutdown to change the program. But DCS produce intime change in program, means during the process, we can change the program according to our needs without stopping the process.
DCS is mostly used for huge plant with a lots of I/O ( more than 10 thousand ) and it is reasonable for this kind of application , but for smaller application with less I/O PLC can works well with lower price , in some how we can say PLCs, PCs , other devices in network can be parts of DCS configuration
DCS has a main control, PLCs are connected also in the network. While PLCs are the controllers through Stand-alone Platform.
DCS is a wide network control system (SCADA/BMS) which has a main control, PLCs are connected also in the network. While PLCs are the controllers through BACNET or in Stand-alone Platform.
PLC is kind of opposite DCS, I/O processsing using one module, DCS I/O module and processing is different module. DCS is more powerfull than PLC because is design for large plant and can be connected to PLC (Remote)
PLC-The system has processor and I/o's and some functional units like basic modules, communication modules and so on. uses a scada for visualization. generally the scada does not use a central database.
DCS-is often used in the big plants where the redundancy level needed is more and the analog input used are high.
PLC and DCS both are accurate and relaiable systems, the difference is not the accururacy but the requirements and objectives.like
The PLC is controlling a machine, while the DCS is controlling the plant.
The actuall question should be, how to select the right system.
The seven questions are designed to make one think about company's operating philosophy and application requirements, taking into account the point of view of all the major stakeholders in your plant (engineering, operations, maintenance, etc.).
1. What are you manufacturing, and how?
2. What is the value of the product being manufactured and the cost of downtime?
3. What do you view as the "heart" of the system?
4. What does the operator need to be successful?
5. What system performance is required?
6. What degree of customization is required?
7. What are your engineering expectations?
Here i share a link, hope to be useful .
https://w3.siemens.com/mcms/process-control-systems/SiteCollectionDocuments/efiles/pcs7/support/marktstudien/PLC_or_DCS.pdf
Scanning time of PLC is quicker than DCS but DCS is good for process control industries for large I/O's and reduntancy.
Pesently advanced PLC s offering complete DCS type contollers by SFC, STL etc. Ex AB plc Control logix can be used as DCS.
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