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DCS is more accurate and wide area operational control as compare to PLC
Tariq Fayaz has already added detail answer
DCS is more accurate as tasks in DCS are divided.
It is not the matter of accuracy when slectiong PLC or DCS for a plant. Suppose the number of inputs and outputs are less. So a single PLC can controll all the outputs with respect to the input change within a short cycle time(ms).
Suppose the number of Inputs and Outputs are very high. So the program will be also big and the cycle time will be also high. The number of inputs outputs may be high than the maximum capacity of a single PLC. So at that time we can use DCS systems. DCS system include many PLCs. Each PLC is used for 1 part of the plant and these PLCs are communicated for transferring their inputs and outputs status. A DCS is nothing but combination of many PLCs.
In Energy plants, PLC is a subsystem of the DCS in some occasions when the situation calls for it. DCS is the master because of its capability of providing a single source of hardware support and service. PLCs are stand alone and perform a particular task, where a DSC is a network of PLCs/RTUs that communicate in some fashion to accomplish a particular task. PLC handles only sequential process; where DCS can handle both continue process and loop controls.
dcs is advanced control system and which more accurate
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
DCS control system, "Man to machine communication" is easy.
PLC is stand alone sequential control.
Both are accurate.
