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1. Distributed control systems (dcs) المحاضرة الثالثة أ.م.د. عمار ابراهيم مجيد منظومات السيطرة الموزعة

2. CONTROL SYSTEM A  control system  manages, commands, directs or regulates the behaviour of other devices or  systems , then the control system is a system that  senses ,  switches , or  regulates  another system. INTRODUCTION OPEN LOOP SYSTEM One type of  control system  in which the output has no influence or effect on the  control  action of the input signal is called an  Open - loop system. Examples Traffic Light Controller, Electric Washing Machine ,clothes dryer, … etc.

3. CLOSE LOOP CONTROL SYSTEM An automatic control system in which an operation, process, or mechanism is regulated by feedback Example- Missile Launching System, Human Respiratory System, Autopilot System etc.

4. TYPES OF CONTROL ANALOG CONTROL SYSTEM Examples- Volume Control of Radio, Room Temperature Control With Thermostat etc. Signal Conversion I/P Transmitter 1 to 5V DC Operational Amplifier 4-20 mA DC Final Control Element Set Point

5. DIGITAL CONTROL SYSTEM Examples- PLC, DCS, SCADA, Embedded System etc.

6. Centralized Processing Unit CPU PV2 PV3 PV1 PV4 PVn MV1 MV2 MV3 MV4 MVn SV1 SV2 SV3 SV4 SVn Drawbacks of Centralized Control System (CCS): If the CPU fails the entire plant gets affected. Redundancy concept is not available.

7. Distributed Control System is a control system for a process or plant, where control elements are distributed throughout the system. Each process element or machine or group of machines is controlled by a dedicated controller. DCS consists of a large number of local controllers in various sections of plant control area and are connected via a high speed communication. Example scenarios where a DCS might be used: Chemical Plants Petrochemical (Oil) And Refineries Papermaking Cement production Boiler Controls And Power Plant Systems Nuclear Power Plants Environmental Control Systems Water Management Systems Distributed CONTROL SYSTEM (DCS)

8. DCS A rchitecture

9. DCS A rchitecture DCS System –  Level 0 This level contains the field devices such as flow and temperature sensors, and final control elements, such as control valves. DCS System –  Level 1 This level contains the marshalling cabinets where the field termination takes place. Also houses the intrinsic safety barriers, relays, Terminal blocks, Isolators etc. from here the signal travels from the Junction boxes wherein the signals are paired and received from the appropriate sections in the field area.

10. DCS A rchitecture DCS System – Level 2 This level contains the system cabinet which is designed to accommodate power supply , controller and I/O cards . The field signals will be digitally processed by the I/o cards and sent to the controller for further digital processing. This part will be located in the top most part of the cabinet and will be brain of the automatic system. DCS System – Level 3 This level consists of visual display unit or computer , is the operator interface. It is production control level, which directly control the process. Plant operational schematics are displayed. Alarm and interlock cause and effect diagrams are displayed in different pages.

11. Engineering Station (ES) Operating station (OS) Automation Station (AS) Plant Bus/Terminal Bus Field devices Basic COMPONENTS OF DCS

12. It is the supervisory controller over the entire distributed control system. It can be a PC or any other computer that has dedicated engineering software. This engineering station offers powerful configuration tools that allow the user to perform engineering functions such as creating new projects, creating various input and output logics, modifying sequential and continuous control logic, configuring various distributed devices, preparing documentation for each input/output device … etc. Engineering Station

13. Engineering Station Some Tasks of Engineering Station: To build graphics using the graphic builder program. The configure control loops/monitoring loops. To assign I/ Os to various I/O modules during generation of application software. To configure shutdown logic/sequence logic. To write/edit user written program in higher level languages. To download the generated application software to various system nodes. To generate “self documentation” i.e. it should be possible to store the generated information on a CD as well as to enable user to take a printout of the system configuration. To emulate generated control loops/scheme/graphics, etc. before it is downloaded to any control processor or operator stations. The graphic and database equalization of all the operator station shall be performed from engineering station with a single command.

14. Operator Station The operator stations are used for monitoring all system operations and for effecting control actions and parameter adjustments. There are normally multiple operator stations, as illustrated in figure below, each of which contains all of the process graphic displays and historical trend displays for the system.

15. Some of the operations performed through the operator stations are listed below; Logging on and off the system using passwords and user names. Invoking process displays to view the operations throughout the system. Effecting control modes for various equipment in the system; for example, Manual and Automatic modes, placing equipment in or out of service. Changing set-point parameters, with appropriate security allowance. Effecting manual control actions for equipment, such as start/stop and open/close. Viewing historical trend displays and transferring data to other files for exporting. Viewing the current alarm summary to identify alarm conditions requiring attention. Viewing the alarm/event summary to view the chronological series of events. Operator Station

16. SYSTEM Cabinet In system cabinet, all electronic modules will be installed like processor cards (CPU), input modules, output modules, serial communication cards, power supply modules, rack to rack inter-communication modules, fieldbus cards, profibus cards, modbus cards. Main types of input modules are analog input (AI) cards, digital input (DI) cards. The number of IO channels will vary depends on the user selection of these cards like 8 channel, 12 channel, 16 channel & 32 channel.

17. Marshalling Cabinet Marshalling cabinets shall be used to terminate all field cables as well as for grouping of various signals from the field devices properly tagged. Sometimes different marshalling cabinets can be allocated based on type of signals like analog input/output signals, digital inputs, digital output and relays.

18. The automation station is a controller or hardware for performing the logical task like PLC but here it will work as master control. It registers and processes process variables from the connected central and distributed I/O and outputs control commands to the process. It supplies the operator station with the data for visualization. It registers actions on the operator station and forwards them to the process. Automation Station (AS)

19. It can be placed near to field devices (sensors and actuators) or certain location where these field devices are connected via communication link. It receives the instructions from the engineering station like set points and other parameters and directly controls field devices. It can sense and control both analog and digital inputs/outputs by analog and digital I/O modules. These modules are extendable according to the number of inputs and outputs. It collects the information from discrete field devices and sends this information to operating and engineering stations. Distributed I/ O s or Remote I/ O s

20. Field bus is communication bus from field device to device coupler which are installed in field area or potentially wide area. Plant bus is communication bus from device coupler to Automation station or operating station for supervisory and monitoring level. For field bus Profibus PA, DP, HART, AS-I, Modbus. These protocols are used. In Plant bus Profinet, Industrial Ethernet, TCP/IP or RS 232 , RS 485 are used. Field Bus and Plant bus/Terminal Bus

21. Field devices control local operations such as opening and closing valves, breakers, collecting data from sensor systems and monitoring the local environment for alarm conditions. Examples- Transmitter, Electrical Drives, … etc. Field DEVICES

22. dcs v/s plc DCS’s are designed to control processes. DCS are made available to the user in a way that only configuration in form of a Functional Block has to be carried out. Scan time of the DCS is comparatively higher. A DCS has inherently multiple processor capability thus Engineer has to put in less efforts for intercommunication of the processors. A DCS takes much longer to process data, so it’s not the right solution when response times are critical. In fact, safety systems require a separate controller. Highly redundant. PLC is in discrete control of manufacturing processes. In PLC complete programming has to be implemented using any one of the different languages available in the system. Scan time of the PLC is lower. This is possible now in PLC but more efforts have to be put in. Response times of 1/10 of a second make the PLC an ideal controller for near real time actions such as a safety shutdown or firing control. Redundancy is not possible at greater levels.

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