Logical Function Blocks available in DCS  Generally in DCS Functional Block Diagram (FBD) is used for programming and Sequential Flow Charts (SFC) is preferred for batch control applications. Functional Block Diagram (FBD) This language basically is a graphical language wherein the users are allowed to program elements in the form of blocks. The blocks then can be wired together like electrical circuits. It describes a function between input and output variables. It is a graphical method of programming DCS. Functional algorithms and control strategies for a particular plant can be implemented by FBD. The control modules are treated as unique entity in DCS system. Each function block contains specific algorithm such as AI, AO, DI, DO, PID and the parameters required for the algorithm. Function blocks ranges from simple input conversion block to a complex control strategy. Generally available Function blocks are Input/ Output (I/O) Math Logical Timer/ Counter Analog Control Advanced cont

Difference between PLC and DCS PLC  PLCs are can respond to a change within one tenth of a second DCS DCS are slower than PLCs. Typical respond time of DCS is 30ms PLC  A PLC is capable of handling few hundred IOs. It can handle tens of them. DCS A DCS can handle thousands of IOs. It can handle hundreds or even thousands of analogs IOs and PID functions PLC  PLC can programmed be programmed based on our application DCS DCS comes with built in control functions that need to be configured based on the application PLC  PLCs can be made redundant with additional hardware which makes them expensive than DCS  DCS Redundancy is a default feature of distributed control systems. PLC  PLCs have a simple and flexible architecture. A PLC system consists of controllers., IO modules, HMIs and an engineering software.  DCS DCS system are less flexible. They come with controllers, IO systems, database servers, engineering and operating servers. PLC  PLCs are best suited for dedicated applications that

  Generic Features of DCS Currently, most large-scale process plants such as oil refineries, petrochemical complexes, and various other processing plants are controlled by microcomputer-based DCS (distributed control systems). these systems generally include the following features Cathode ray tube (CRT)-based operator consoles and keyboards, which are used by plant operators or engineers to monitor and control the process Controllers, multifunction control modules, and programmable logic controllers (PLCs), which provide the basic control computation or operation  A communication network, which is used to transfer the information between control modules and operator consoles across the node on the network  I/O (Input/Output) modules, which are used to convert the field instrumentation signals from analog to digital and digital to analog form for controller modules and console displays Fieldbus communication links, which are used for communication between remote I/O devices and control

  Distributed Control System (DCS)  What is a Distributed Control System ? A distributed control system, also known as DSC, is a computer control system for a process plant, typically with multiple control loops, in which autonomous controllers are distributed throughout the system. A distributed control system integrates the PLC and the process controller of the process line into a coordinated, interactive system. Distributed Control System (DSC) Architecture Block Diagram Level 0 : Field Level This layer includes the basic field devices like sensors, transmitters etc. Field level components are directly linked to the process. Level 1 : Direct Process Control This level handles various functions as Data Acquisition Data Check Plant Monitoring Open and Closed loop Control Reporting Level 2 : Plant Supervisory Control This level handles various functions as Plant Performance Monitoring Plant Coordination Optimal Process Control Adaptive Control Failure Detections Level 3 : Production Sc