Process Control SystemShort overview

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Distribute Control System (DCS)

• A distributed control system (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or more controllers. The entire system of controllers is connected by networks for communication and monitoring. DCS is a very broad term used in a variety of industries, to monitor and control distributed equipment.

http://solve.nitk.ac.in/dmdocuments/electrical/DCS_write_up.pdf

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CONTROL ROOMOperation, Maintenance, Reporting

Firewall

Remote Connections

OFFICEReporting, Enterprise Integration

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DCS architecture

AUTOMATION ROOMControls, Optimization, Connectivity

Engineering and Maintenance, Asset Management, DNA Historian

Distributed

FIELD FIELD

FIELD FIELD

Wireless solutions for operation and maintenance

One platform for all control applications • Integrates major field buses and field asset management

Centralized

Safety instrumented system

Star or ring topology redundant Ethernet network

Name based communication

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Functionality

• A DCS typically uses custom designed processors as controllers and uses both proprietary interconnections and communications protocol for communication. Input and output modules form component parts of the DCS. The processor receives information from input modules and sends information to output modules. The input modules receive information from input instruments in the process (or field) and transmit instructions to the output instruments in the field. Computer buses or electrical buses connect the processor and modules through multiplexer or demultiplexers. Buses also connect the distributed controllers with the central controller and finally to the Human–machine interface (HMI) or control consoles.

http://solve.nitk.ac.in/dmdocuments/electrical/DCS_write_up.pdf

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Sensors

• There is a huge amount of sensors that use different physical principles to measure process parameters. Sensing element is placed directly to the process (pipe, tank, boiler etc.). Sensor is equipped with convertor, that converts measurement to electrical form. From DCS point of view they can be split on two categories –binary and analog.

• Analog sensors provide analog interpretation of physical parameter in electrical form. The most widely used analog signal in industry is 4…20 mA.

• Binary sensors do the same in binary form (0/1). The most widely used binary signal in industry is 0/24 VDC.

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Input Cards

• Sensors’ signals are measured in DCS input cards (analog AI or binary DI). Input card converts signal to digital form and forwards them to input/output bus controller.

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Analog sensor

Analog input card channelField

Field

Binary input card channel

Binary sensor

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I/O card rack

• I/O cards are usually combined in groups. Each group is connected to I/O bus controller through internal bus. I/O bus controller communicates with Process Control Station through the network.

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ACN I/O units M80 seriesI/O Power SupplyIPSP

I/O Bus ControllerIBC I/O Units

Mounting Board for I/Os (MB)- MB for 2 or 8 I/O units- MB’s can be connected together

Max. 32 I/O units per IBC

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ACN I/O Ethernet field bus, non redundant

• ACN I/O Ethernet field bus twisted pair 100 Mbit/s- max. 3 Ethernet field buses / ACN

• Unmanaged Ethernet switch in I/O cabinet

I/OIBCIPSP

I/OMBS

I/OIBCIPSP

I/OMBS

I/OIBCIPSP

I/OMBS

I/OIBCIPSP

I/OMBS

I/O cabinetPCS

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Automation applications

• Automation application is created using one of the programming languages defined by IEC 61131 standard:

- Ladder diagram (LD), graphical- Function block diagram (FBD), graphical- Structured text (ST), textual- Instruction list (IL), textual- Sequential function chart (SFC), has elements to organize programs for

sequential and parallel control processing.

• Automation applications performs inputs processing, communication with HMI and calculation of outputs according to control algorithm.

• Automation applications are executed on PCS (controller or industrial PC).

• Following example shows use of function blocks in programs.

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Graphical application configurationEfficient engineering and maintenance

Metso DNA Engineering Function Block CADdiagram parts are as follows: 1. Area for configuration function blocks and

connections2. Administration part of function block diagram

(document names, revisions etc) 3. Administration part of control diagram

(process controller, execution cycle, order)4. External input I/O connection (e.g. physical

I/O)5. External output I/O connection (e.g. physical

I/O)6. Connection from other module, which can be

in the same or some other process controller or in the other subsystem (e.g. remote setpoint, interlocking, calculated value)

7. Function block for the configuration of the control application

8. Connection between I/O and function blocks or between function blocks

9. Names and tag of the loop

10. Configuration for loop windows11. Alarm and event configurations of the loop12. Cross reference list (list of other loops where

this loop information is used)13. Synchronize marks (@) for updating

information from runtime environment to engineering environment

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Operator interface

• Human-machine interface is done using operator displays.• Operator displays (process pictures) show running process in

schematic form indicating process parameters.• Operating environment communicates with control applications all

the time to update parameters in real time.• Operator can interact with the process by giving commands through

operator displays.• Operating environment runs in industrial or common PC.

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History of control rooms and user interfaces1970’s Today

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Operator’s desktop

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Design clear view to the processMetso DNA Operate Picture Designer

• Metso DNA Operate Picture Designer

- WYSIWYG (what you see is what you get) picture design tool)

- Extensive library of three dimensional devices, tanks, pipelines and other process components.

- Part of the engineering toolset

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Output cards

• When outputs are calculated by automation application they are sent to output cards through the same I/O bus controllers.

• Output card converts digital signal to electrical one.• Same 4…20 mA are mainly used for analog signals and 0/24 VDC

for binary.• Output card channels are connected directly to low-voltage

actuators.• For connection to high-voltage actuators intermediate relays or

convertors are used.

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Output cards

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Analog actuator

ON/OFF actuator

Rea

ly

ON/OFF actuator

High voltage

Bin

ary

outp

ut

ORAnalog output card channel

Binary output card channel

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Actuators

• Actuators use low voltage control signal to affect some more powerful environment (high voltage, pneumatic, hydraulic).

• Final result is some mechanical action (opened valve, running pump, moving hydraulic cylinder etc.)

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