Difference Between Plc And Dcs r4852

DIFFRENCE BETWEEN DCS AND PLC You must automate a process, but you can't decide between a DCS and aPLC. Are these systems really all that different? The answers depend ona slew of other questions.Turn the clock back 10-15 years: The programmable logic controller (PLC) is king of machine control while the distributed control system. (DCS) dominates recesscontrol. If you manufacture plastic widgets, You speak PLC. If you producechemicals, you speak DCS.Today, the two technologies share kingdoms as thefunctional lines between them continue to blur. We now use each where the other used to Rule. However, PLCs still dominate high-speed machine control, and DCSsPrevail in complex continuous processes. The early DCS looked dramaticallydifferent from the early PLC. Initially, the DCS performed the control functions of theanalog Instruments it replaced, and its interface mimicked their Displays. DCSs then gained sequence logic capabilities to control batch Processesas well as continuous ones. DCSs performed hundreds of analog Measurementsand controlled dozens of analog outputs, using Multi-variable Proportional IntegralDerivative (PID) control. With the Same 8-bit microprocessor technology that gaverise to the DCS, PLCs Began replacing conventional relay/solid-state logic inmachine Control. PLCs dealt with input/output (I/O) and started/stoppedMotors by performing Boolean logic calculations. The big change in DCS over thepast 20 years is its move fromProprietary hardware to the personal computer (PC) and standard LANTechnologies. With each advance in PC power, DCSs have moved up inPower. PCs gave us speedy, responsive, multi-media, windowed, Operatorprocessinterfaces (OPI). Relational databases and spreadsheet Software enhances theability of DCSs to store and manipulate data. Artificial intelligence (AI) technologygives us "smart" alarming. Today's DCS architecturally looks much like the DCS of 20 years ago, But tomorrow's DCS may control through networked "smart" devices-with No I/O hardware of its own. Most DCSs offer redundant controllers, networks,and I/Os. Most give you "built-in" redundancy and diagnostic features, with no needfor -written logic.DCSs allow centralized configuration from the operator or engineering Console in the control room. You can change programming offline, and without restarting the system for the change to be effective.DCSs allowintercontroller communications. You can do data exchange in Most DCS systemsad hoc (no need for predefined data point lists). You Access data by tag name,regardless of hardware or location.DCSs use multi-tasking operating systems, soyou can and run Applications aside from the real-time control functionsand still do Fractional-second control. DCSs now come in "micro" systems, toPrice-compete with PLCs-but with full DCS features and capabilities.The typicalDCS has integrated diagnostics and standard display Templates that automaticallyextend/update when your database changes. This database is central to the system-you don't have different Databases sitting in the controllers.DCSs have -friendly configuration tools, including structuredEnglish, control block libraries, SFC (sequential function chart), andEven RLL (relay ladder logic)

As you know PLC as to its name Programmable Logic Controller. Its main purpose is to replace the relay logic controls which is "On" or "Off". And DCS "Distributed Control Systems" its emphasis is Fast analog handling because of communications through Bus systems, networking and etc. 1. A PLC is cost-effective up to a certain I/O count, and so is the DCS. But the difference is in their starting points: the PLC is cost-effective from 0 to a few thousand I/O points; the DCS becomes costeffective starting from a few thousand points and beyond. 2. A PLC becomes a subsystem of the DCS in rare occasions when the situation calls for it, i.e., purchase of huge package systems with engineering schedules incompatible with the DCS schedule (I/O lists cannot be submitted on time before the DCS hardware freeze date). Note that this package system is a process system using continuous control, not discrete. Based on this, a PLC can never be larger than a DCS in of I/O count. 3. In large plants the DCS is king because most owners want a single source of hardware and service, and this mentality naturally denies the PLC a foothold. Package vendors are no longer required to provide PLC for their system. Everything is connected to the DCS. -WAG

PLC is a programmable Logic controller which is used mainly for interlocking different equipments. DCS is Distributed Control Systems which is used to control very big plants by using simple GUI

screens.PLCs are interfaced with DCS for interlocking. SCADA is Supervisory Control and Data Aquisition which is used to control and Monitor small number of Equipments in a field.SCADA systems are typically used to perform data collection and control at the supervisory level. Some systems are called SCADA despite only performing data acquisition and not control.The supervisory control system is a system that is placed on top of a real-time control system to control a process that is external to the SCADA system (i.e. a computer, by itself, is not a SCADA system even though it controls its own power consumption and cooling). This implies that the system is not critical to control the process in real time, as there is a separate or integrated real-time automated control system that can respond quickly enough to compensate for process changes within the time constants of the process. The process can be industrial, infrastructure or facility based as described below: PLC is programmable logic controller. Its inputs are the open or closed position of a switch.(It coulde a a manual switch, a relay , a limit/proximity switch etc). Its outputs are the presence(usually 24V dc) or the absence (0V)of a voltage. A program is written which relates the inputs to the outputs. ()The output can activate motors solenoid valves etc. The program could be reasonably complicated. Earlier its task was done by electromagnetic relays with a lot of messy wiring. SCADA is Supervisory Control and Data Acquisition which is more complicated and involves one or more PCs constantly monitoring a system providing information to the operator who can take control action wherever it is not automatic. DCS is digital control systems normally used to automate control of large process plants.