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System Architecture
Basic Architecture of DCS
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SYSTEM ELEMENTS
DCS system element
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Basic element of DCS are
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Field control station
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Intermediate station
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Central computer station
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Monitoring and control facilities element
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Data communication link
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Field control station
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Filed control unit
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Lowest level of DCS
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It consist a few ( 1 or 8 or 32 ) measuring points or control loop
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The primary function of field control unit is to
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Collect and pre process analog and digital signals
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Monitor and log the alarming message
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Perform open loop and close loop control functions
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BUS oriented Internal structure of MICON P-200 (VDO)
Back up data
transfer
RAM (10K)
Microprocessor
PROM (24K)
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Vertical Data
Transfer
Lateral Data
Transfer
Analog
Output (AO)
Digital
Output (DO)
Internal BUS
Display and
Command
Analog
Inputs (AI)
Digital Inputs
(DI)
Internal structure of filed station
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Filed control unit- I/O Devices
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Its consists the process interface , a separate serial bus so that input output
communication capacity of the station increase
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The second bus used for interconnection between neighboring station.
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Analog input:
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Input current: 0-20ma, 4-20ma
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Input voltage: 0-5v,1-5v,0-10v
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Thermo elements: 0-25mv, 0-50mv, -10 to +10 v
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Resolution: 8-12 bits
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Filed control unit- I/O Devices
Analog outputs:
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output voltage: 0-5v,1-5v,0-10v
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output current: 4-20ma, 0-20ma
Binary input :
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Input current: 0/10ma, 0/100ma, 0/200ma
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Input voltage: 0/24V
Binary output :
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output current: 0/10ma, 0/100ma, 0/200ma
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output voltage: 0/24V
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Filed control unit- I/O Devices
 Total number of analog input and output per field station is 4, 8, 16, 48 or 64.
 RS-3 and TDC 3000 DCS system :- 128
 MOD 300, AS 215 DCS system :- 256
 AS 220, As 230, ASEA master :- 1024
 BINARY input output per station:
 WDPF,CENTUM ,ASEA MASTER, NETWORK 90: 512
 AS 230 : 4096
 TIMER , COUNTER , MOTOR CONTROL, STEPPER , POSTION , PULSE CONTROL
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Filed control unit- Communication
Interface
 TDC 3000- RS232
 P 4000, RS-3 and WDPF – RS422
 A 500, PROCONTROL 1 – RS 485
 Network 90 , PLS 80- IEEE 488
 A 500- Bit bus
 ASEA Master , PLS 80, MICON- MODBUS
 ASEA master , MOD 300- MAP/Ethernet
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Intermediate stations
 The intermediate functional system units which are placed in between the lowest and the
highest hierarchical levels are known as group or supervisory stations.
 The stations are the autonomous systems elements with the restricted domain of
influence to a group of field stations, pertaining to a closed, well defined, and relatively
autonomous part of the plant.
 The most common functions of the intermediate stations are
 State observation of the process variables
 Calculation of reference values for control loops at “ lowest ‟ level (SV & PV)
 Tracking of order processing and material and energy balances
 Efficiency analysis and Reporting
 Data exchange with “higher” level stations (central station)
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Intermediate stations
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Central Computer Station
 Central computer station enables centralized plant monitoring, direct operation on plant
instrumentation, and offers important program generation and system diagnostics
services.
 The stations connected to other system through the system bus which can initiate the
necessary data transfers.
 Central computer station also called process operator console
 Its consist the display unit for plant monitoring and keypad for plant control
 Functions of the central computer control can be classified as
 Plant oriented
 General application
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Central Computer Station
 Plant oriented
 Process display and control
 Data collection and retrieval
 Inter level communications
 System diagnosis
 General application
 Program generation and test
 Scientific and commercial calculations
 System simulations
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Monitoring and Command Facilities
 Screen Partition
 Message area
 Overview area
 Main display area
 Operator’s instruction area
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Hierarchical Structure of Monitoring
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Overview Area
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Bar Representation
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Group Display
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Control Loop Display
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YOKOGAVA Centum CS 3000
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Human Interface Station (HIS)
 The HIS is mainly used for operation and monitoring – it displays process variables, control
parameters, and alarms necessary for users to quickly grasp the operating status of the
plant.
 It also incorporates open interfaces so that supervisory computers can access trend data,
messages, and process data.
 Console Type HIS
 This is a new console type human interface station, at which a general purpose PC is installed.
 There are two types of console type HISs:
 Enclosed display style: usual style appearance
 Open display style: selectable configurations
 Desktop Type HIS
 This HIS uses a general purpose PC
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Enclosed display style
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Open display style
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Field Control Station (FCS)
 FCS for FIO
 This FCS uses the Fieldnetwork I/O (FIO) modules, which are compact and consist of various
lineup such as the connector types and so forth.
 According to the application capacity, there are the standard model and the enhanced model.
 Compact FCS for FIO
 This is a compact FCS with I/O modules integrated into the Field Control Unit.
 FCS for RIO
 This FCS uses the Remote I/O (RIO) modules, which have many installation bases and M4 screw
terminals to connect signal cables.
 According to the application capacity, there are the standard model and the enhanced model.
 Compact FCS for RIO
 This controller is usually installed near the equipment or process it controls, and is ideal for
communicating with subsystems.
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Compact FCS for FIO
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Engineering PC (ENG)
 This is the PC with engineering functions used to perform CENTUM CS 3000
system generation and maintenance management.
 It can be the same type of general-purpose PC as the HIS, and can even be the
same PC as the HIS.
 By having HIS operation and monitoring functions on the same PC, you can use
the test (control station emulation) functions to provide an efficient and easy-touse engineering environment.
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Other Major Components
 Bus Converter (BCV)
 This links the V net system bus to another CENTUM CS 3000 domain or to an existing CENTUM or
µXL system.
 Communications Gateway Unit (CGW)
 This links the V net control system bus to an Ethernet bus (to a supervisory computer system or
general purpose personal computer).
 By CGW wide area communication function, you can also link two CENTUM CS 3000 V nets in
different places using a dedicated telephone line.
 Migrated Field Control Station (RFCS2)
 You can leave the I/O cards and field wiring of a CENTUM-XL or CENTUM V system “as is”, and
replace the CPU nest with an KFCS, which can be connected to the V net just like a CENTUM CS
3000 system FCS.
 SI bus is used as a (dual-redundant) bus connecting existing FCS I/O units to new FCS CPU.
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Other Major Components
 Advanced Process Control Station (APCS)
 The Advanced Process Control Station (APCS) is a personal computer (PC)
connected to the V net and applied to advanced process control and
efficiency improvement.
 Generic Subsystem Gateway Package (GSGW)
 GSGW is a PC connected to V net. It uses OPC servers for subsystems,
facilitating subsystem data acquisition and setting without creating specific
communications programs.
 Exaopc
 This provides OPC Server functions to enable applications in a supervisory PC
to access CENTUM CS 3000 data. It provides a link between control layer and
business data processing layer.
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Other Major Components
 Business Information PCs and Supervisory Computers
 These can run MES and ERP integrated business management software. They can access
the DCS via Exaopc or CGW.
 Safety Instrumented System (ProSafe-RS)
 ProSafe-RS is a dedicated system to prevent probability and spread of accidents when it is
used as an interlock device, emergency shutdown system and fire and gas protection.
 Safety Engineering PC (SENG)
 This is a component equipped with engineering, test and maintenance functions to
generate system and manage maintenance for safety control station (SCS).
 Safety Control Station (SCS)
 This is a safety controller that executes logics for systems including interlock, emergency
shutdown and fire and gas protection.
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Other Major Components
 V net
 The V net real-time control system bus links stations such as FCS, HIS, BCV
and CGW. Dual-redundant V net support is standard.
 Ethernet
 Ethernet is used to link HIS, ENG and supervisory systems. It is also used for
transferring data files to supervisory computers, and for HIS data equalization.
 Fieldbus
 The FOUNDATION Fieldbus is a multidrop digital communications bus for field
instruments, and
is expected to replace the conventional 4 to 20 mA analog
interface
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When the V net is extended, Field
Control Stations distributed around a
large plant can be
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monitored from HIS in a central control
room. Bus repeaters and optical repeater
pairs can be
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mixed, up to four sets in total, to extend
the V net up to 20 km.
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References
 Reference : Distributed computer control for industrial
automation by Popovic & Bhatkar.
 http://www.yokogawa.com/dcs/products/cs/overview/dc
s-cs-0101en.htm
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