A distributed control system (DCS) is a control system for a plant or industrial process that is made up of sensors, controllers, and computers distributed throughout the process and connected by a network. The DCS acts as the central brain that receives real-time data from sensors, uses control logic to make automated decisions, and sends instructions to controllers. This allows one DCS to control and automate an entire plant by coordinating adjustments across multiple interconnected processes more efficiently than individual controllers. DCS systems are commonly used in large manufacturing plants like oil refineries to improve safety, quality, reliability and efficiency of complex continuous production processes.
3. The DCS is a system of sensors, controllers, and associated computers that are distributed
throughout a plant. Each of these components serves a different function, such as data
acquisition, process control, data storage, and graphical display.
The plant's local area network – also known as a control network – connects these
individual elements to a centralized computer. The DCS, as the plant's "central brain,"
makes automated decisions based on production trends that it sees in real-time throughout
the plant.
For example, a power plant's DCS may automatically increase the capacity of multiple
turbines to meet changing demand for electricity during hot summer days, and then
decrease it as outdoor temperatures cool overnight and demand decreases. Whereas a PLC
can only change a single unit operation, a DCS can change all of a plant's interacting unit
operations.
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4. In recent years, the use of smart devices and field buses has increased the
prominence of distributed control systems (DCS) in large and complex
industrial processes, as opposed to the previous centralized control system.
This distribution of control system architecture throughout the plant has
resulted in more efficient ways to improve control reliability, process quality,
and plant efficiency.
Nowadays, distributed control systems can be found in a wide range of
industrial fields, including chemical plants, oil and gas industries, food
processing plants, nuclear power plants, water management systems,
automobile industries, and so on.
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5. How DCS is used?
While DCSs are used in many process control industries to supervise complex
production processes, they are most commonly found in large, continuous
manufacturing plants such as those in the petrochemical industry.
These and other manufacturers can efficiently coordinate adjustments in a
top-down fashion using a centralized network of computers with the help of a
DCS. DCS instructions are distributed throughout a plant and fed to individual
controllers. When properly configured, the DCS can improve safety while also
increasing production efficiency.
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6. Working and operations of DCS system –
DCS works as follows: sensors sense process information and send it to local
I/O modules, to which actuators are also connected to control process
parameters. The information or data from these remote modules is collected
and transmitted to the process control unit via field bus. When smart field
devices are used, the sensed data is sent directly to the process control unit
via the field bus.
The collected data is then processed, analyzed, and output results are
generated based on the control logic implemented in the controller. The
outcomes or control actions are then transmitted to the actuator devices via
the field bus. As previously stated, DCS configuration, commissioning, and
control logic implementation takes place at the engineering station. At
operation stations, the operator can view and send control actions manually.
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7. Architecture of DCS –
DCS has three main characteristics, as the name suggests. The first is the division
of various control functions into relatively small sets of semiautonomous
subsystems that are linked by a high-speed communication bus. These functions
include data acquisition, data presentation, process control, process supervision,
information reporting, and information storage and retrieval.
The second feature of DCS is the automation of manufacturing processes through
the integration of advanced control strategies. The third characteristic is the
ability to organize things as a system. DCS organizes the entire control structure as
a single automation system in which various subsystems are unified through a
proper command structure and information flow.
These characteristics of DCS can be seen in the architecture displayed in the
diagram below. A DCS's basic components include an engineering workstation, an
operating station or HMI, a process control unit or local control unit, smart
devices, and a communication system.
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