DCS (1)

Dharmsinh Desai University, Nadiad Faculty of Technology

Instrumentation and Control Engg. Dept. Process Control and Automation Systems (PCAS) Lab

UG Level Course: Instrumentation Systems (IC 604) Laboratory Experiment-14: Distributed Control System (DCS)

Page 1 of 14 Prepared by: Prof. Jignesh G. Bhatt

AIM: Distributed Control System (DCS) OVERVIEW: The latest development in the evolution of the process control came with the development of the concept of Direct Digital Control (DDC), wherein the function of the analog instrumentation was incorporated in the computer and the analog controllers were thereby eliminated. The motivation was to reduce the control system cost and increase design flexibility for newer processes that were more complex by their inherent nature. This new design concept initially met with mixed reviews, primarily because the computers – especially the software, which had become extremely complicated – were not sufficiently reliable, and in most cases, when the computer went down, so did the process, with flashing lights and sirens of alarm annunciation. However, as mini and micro computers began to replace the old process control computers, it became economically feasible to provide redundancy in the form of dual computers (i.e. duplication of hardware). This was frequently done at various hierarchical levels of computer based process control systems. Then, a major advancement came in 1976, when Honeywell announced that the first Distributed Control System (DCS), named the TDC 2000. The hallmark of the system was reliability based redundancy – redundancy in micro-process based controllers, redundancy in communications and redundancy in operator interface. In a DCS, the data acquisition and control functions are performed by a number of distributed microprocessor-based units, situated near to the devices being controlled or, the instrument from which data is being gathered. DCS have evolved into providing very sophisticated analog (e.g. loop) control capability. A closely integrated set of operator interfaces (or Human Machine Interfaces – HMIs) is provided to allow for easy system configurations and operator control. The data highway is normally capable of high speeds – typically 1 Mbps up to 10 Mbps as shown in Fig. 1 given below:

Figure-1: Distributed Control System (DCS)





DCS v/s SCADA: The goals of Distributed Control System (DCS) and Supervisory Control And Data Acquisition (SCADA) System are quite different. A DCS is a process-oriented system and it treats the control of the process, (the chemical plant, refinery or whatever) as its main task, and it presents data to operators as part of its job. On the other hand, a SCADA system is data gathering oriented; and the control centre and operators are its focus. Interestingly enough, the remote equipment is merely there to collect the data – though it may also do some very complex process control. A DCS operator station is intimately connected with its input/output signals (I/O) through local wiring, communication buses (e.g. Field Bus, networks), etc. When the DCS operator wants to see information, he/she usually makes a request directly to the field I/O and gets a response. Field events can directly interrupt the system and advise the operator. A SCADA system must continue to operate when field communications have failed. The ‘quality’ of data shown to the operator is an important facet of SCADA system operation. SCADA systems often provide special ‘event’ processing mechanisms to handle conditions that occur between data acquisition periods. There are many other differences, but they tend to involve a lot of detail. The underlying points are:

(1) A SCADA system needs to transfer secure data and control signals over a potentially slow, unreliable communications medium, and needs to maintain a database of ‘last known good values’ for prompt operator display. It frequently needs to do event processing and data quality validation. Redundancy is usually handled in a distributed manner.

(2) A DCS is always connected to its data source, so it does not need to maintain a database of ‘current values’. Redundancy is usually handled by parallel equipment, no by diffusion of information around a distributed database.

Over a span of 35 years, the Distributed Control System (DCS) has been undergoing continuous change and development. This change is due to the rapid development of electronics and information technology and higher consumer expectations. This industrial development has in fact helped the DCS systems to be not only flexible but also become more user-friendly. At present, customers expect the systems to be modular and expandable, capable of handling both continuous and batch applications, should have an open network structure and also a very high level of reliability and convenience in maintenance. Communication of DCS systems with either ERP or Internet is now almost mandatory. The Forbes Marshall MICROCON DCS system is tailor made and designed keeping in mind the said requirements of today's control system user. These multifunction features make the system ideal for applications in a variety of industries such as chemical, pharmaceutical, food and beverage, power, petrochemical, metallurgical, cement, glass, paper and pulp, water supply and treatment, sugar, distillery and many more.





SYSTEM ARCHITECTURE:

The system has been designed to have a completely modular and expandable architecture and also to handle both continuous and batch applications simultaneously. In order to cater to area wise system requirements, the system has the remote I/O configuration as a standard feature and is also capable of supporting various field bus standards so as to satisfy future demands for expansion. The I/O modules of the system communicate to the main controller on PROFIBUS-DP and the controller module has direct Ethernet connectivity. This DCS system has been designed with advanced technology to provide a high level of reliability and also can provide various levels of redundancy as per user demand. The engineering and operator stations of the system work on Microsoft Windows based packages and the engineering software is designed as per IEC 61131-3 Standard to provide advanced function blocks, ladder logics, sequential function charts, structured texts as well as computing formulae as the programming tools for configuration requirements.

Figure-2: The Microcon System Architecture





DCS TRAINER:

Figure-3: DCS Trainer

SALIENT FEATURES: • All process parameters can be controlled simultaneously. • The DCS Trainer is extremely flexible, yet comprehensive. One can connect all test rigs to the Trainer for a comprehensive graphics based control and testing. Trainer for DCS or PLC • The system can combine the features of DCS & PLC in this trainer by running through the various experiments. The experiments have a theory to go through prior to executing the practical. The industrial process mimics will appraise the student to get the industrial feel. It can simulate an industrial environment • Output from the DCS Trainer includes both, graphical representation of the test rigs as well as actual industrial process graphics. • Switch with ease between both to obtain an immense industrial experience. Test rigs can be used either with the system or separately





• The DCS trainer is available separately for those who already own test rigs. Optionally test rigs are available with the Trainer to meet individual needs. Start comprehensive training even with one rig • Even if all rigs are not available, the DCS Trainer’s sophisticated software takes over the task of simulating the actual field values for the balance inputs by feeding manually. Efficient data handling • Data logging is efficient and advanced. Data from configured tags is logged every second and can be viewed for trends, or printed on reports. The alarm management is handled effectively by the software. Report generation-a wide variety • The DCS Trainer comes with a variety of pre‐configured reports built in. Choose from these Standard Reports or define your own parameters for custom reporting. Both, Trend reports and Status reports are available, such as shift reports, daily reports or experiment reports. Range configurable as per users’ requirements • The input ranges can be configured on the software as per the need of the user. Every channel of the analog inputs can be connected to various types of signals from the field, such as 4‐20mA or 0‐20mA. SPECIFICATIONS:

Supply voltage: 230VAC,50Hz Analog input: 12 Analog output: 8 Digital input: 4 Digital output: 8 Type of Analog inputs: 4-20ma, 0-20ma Type of Digital inputs: potential free(with 24VDC interrogation voltage) Type of Digital outputs: potential free, 24VDC, 110/230 VAC Keyboard: Standard keyboard Operator/Engineering station: IBM compatible PC based workstation with configuration: P III @ 500 MHz (and above)

64 MB / 128 MB RAM 20 GB Hard Disc, 1 x 3.5� Floppy drive,

Keyboard, Mouse, SVGA colour monitor, 2 serial, 1 Parallel Port, Windows 9X/2000/ NT / XP

Software: Programming language 61131-3 compliant with Function block Ladder logic, Sequential charts Structured text, continuous function chart

HMI: Open system software with SQL & ODBC connectivity. Panel: Free standing panel 800×800×1200 mm





FLOW AND LEVEL PROCESS RIG:

The level/flow process trainer is a single loop system allowing the study of the principles of process control, using liquid level and flow rates as the measured process variables. The system is a completely self contained, low pressure flowing water circuit supported on a bench top mounted panel, making it suitable for individual student work or for group demonstration. It comprises a dual compartment process tank, linked to a sump tank by manual and solenoid operated valves. Water is pumped through the system, via a van able area now meter and motorised control valve. Level is measured in the process tank. Flow is measured through an optical pulse flow meter. FEATURES: • Use water as the process medium. • It is controlled using industry standard 4-20mA signals. • Control of the system being affected by a linearized profiled seat, electrically-actuated gate valve. • The rig has three tanks which are constructed of welded polycarbonate. • The three tanks are: a sump tank and a 3L and 2L dual compartment Process Tank. • The level and flow rig is fitted with a submersible 10 L/min 12V dc pump. • Level is measured using either a Float Switch or a Float Sensor. Flow is measured using a 0 to 4.5 L/min Pulse Flow Sensor.

Figure-4: Flow and Level Process Rig





• Flow can be observed using a 0.4 to 4.4 L/min Variable Area Flow meter. • The system incorporates different orifice solenoid valves allowing step change of supply & drain rates. • Contains selection of level and flow sensors & indicators • Flow controlled by linear motorised control valve • On/Off and proportional control • P, PI and full PID control with auto tune facility •Modern push fittings ELLIPSE HMI DEVELOPMENT PLATFORM: It is a supervisory, control and data acquisition based on windows. The organizer gives you a clean and organized view of all the application, helping edition and configuration of all the objects involved in a system through a hierarchical options tree. Ellipse window has 4 brand-new tools. ELIPSE WATCHER: •SCADA software for system monitoring including digital image acquisition, storage and transmission in real time. Supports a variety of file formats, including MPEG. Allows you to create an image database searching by period or event and also image transmission in real time for remote stations using TCP/IP or dial-up connection. ELIPSE WEB: •Supervisory and control system through the Internet. Using a commercial browser (Internet Explorer, Netscape, etc.) you can connect to a remote supervisory station, receiving data in real time.

Figure-5: Ellipse HMI development platform





ELIPSE POWER: •Allows connection with IED’s (Intelligent Electronic Device) and RTU’s (Remote Terminal Units) using any communication protocol, including IEC 870-5/DNP 3.0. Uses a local time base, allowing SOE (Sequence of Events) with 1ms precision and oscillography, wave form transferring and visualization in local stations or tale supervisory systems. ELIPSE LAB: •System for laboratory test applications, allowing graph registers and oscillograph substitution, ATE’s construction and creation of virtual instruments. Has GPIB communication (including IEEE-488.2), RS-232/422/485 and a driver development kit for any instrument. CODESYS PROGRAMMING ENVIRONMENT: • CoDeSys is a complete development environment for your PLC. (CoDeSys stands for Controlled Development System). • CoDeSys puts a simple approach to the powerful IEC language at the disposal of the PLC programmer. Use of the editors and debugging functions is based upon the proven development program environments of advanced programming languages (such as Visual C++). •Project Components •POU (Program Organization Unit) •Function •Program •Resources •Libraries •Data types •Visualization

Figure 6: CoDeSys Programming Environment





COMMUNICATION NETWORKS: Operational Level: Data communication of the operational level of the system is known as System Network (S-Net). It is a redundant real time industrial Ethernet with star, loop or bus topology structure. It follows IEEE 802.3 and IEEE 802.3u standards with adaptable communication speeds of 10 to 100 Mbps. For long distance communication, optical fibre options are also available. Control Level: The data communication of control level known as Control Network (C-Net). It is a PROFIBUS-DP industrial field bus allowing the controller modules to communication with the IO modules and field devices. It is completely based on IEC61158 International Standards and works on master-slave topology with communication speeds of 12 Mbps. A PROFIBUS-DP link can be connected to maximum 126 nodes (0-125) with a variety of communication media like twisted pair, optical fibre or combination of both. This communication can be carried through a distance of 1.2 km to 10 km by selection of proper medium. ENGINEERING STATIONS: The Engineering Station is designed to operate on Microsoft Windows based operating system and mainly carries out functions related to system configuration, data base management, control arithmetic, logic and sequence. It also facilitates on-line monitoring and management functions. The configuration software is designed as per IEC61131-3 Standard and allows the user to choose advanced function blocks, ladder logics, sequential function charts, structured texts as well as computing formulas as the programming tools for the configuration requirements. The unique feature of the engineering software is that it allows the user to use all these languages simultaneously even in the same loop. The entire software has graphical representation and hence the engineer does not need to know any computer language. Some of the system configuration tools include data base configuration tools, control scheme configuration tools, graphic configuration tools and report configuration tools. An extensive library of function blocks is provided for the user to pick up the readymade blocks and use them to create his own strategy. Function Block Diagrams:

Figure-7: Function Block Diagrams





Function Block Diagrams is a graphical function block language enabling the basic function blocks, links inputs and outputs, calculations and control. The language describes the call sequence of all function blocks and parameters required by corresponding module calculations. Ladder Logics:

Ladder Logics is a continuous executing language used for basic logic controls consisting of contacts, coils, connections, timers and counters. This is an ideal tool for discrete logic control, motor control interlocks, random checks and simple sequence controls. Sequential Function Charts:

Figure-8: Ladder Logics

Figure-9: Sequential Flow Charts





Sequential Function Charts is again a graphical language which can be used as the connection between continuous control or logic control and input output monitoring parameters to describe and control the sequence of operations of various process events, also by applying various status controls for each event. It consists of a series of steps and transitions where each step may include a group of actions affecting the process. It also supports concurrent sequence and diversified qualified characters. OPERATOR STATION: The operator station of the system consists of highly reliable PC workstations with monitoring software operating in a Windows environment. The software performs operator control functions, plant monitoring and display functions, logging functions, SOE recording, performance calculations and optimization functions, historical data storage and retrieval functions. The software provides overview displays, group displays, dynamic graphics and mimic displays, individual tag point data displays, bar graph displays, trend displays, X-Y plots, alarm management and event displays and reports. The system can print logs / reports automatically at prescribed time intervals or on demand or by the occurrence of predefined events. In addition to the standard logs, the operator can create new logs, modify existing logs and reassign them among the printers online. The Sequence of Event Recording (SOE) function refers to the system recording the sequence of event at a high timing resolution. An SOE record usually consists of an event source that leads to the event sequence record and a number of binary value status changing events, while an event source can be a number of external interrupted binary values. The system is also capable of performing online real time performance calculations such as analyze boiler and turbine working conditions and identify actions required to optimize operations. The performance calculations include calculations of flows, enthalpies, efficiencies, heat rates, saturation temperatures etc. The prime objective of plant performance calculations is to provide the plant operator, with controllable losses in a tabular form, including deviations in heat rate and efficiencies, on a continuous basis, to determine the optimized operating conditions. Engineering Flow Charts:

Figure-10: Engineering Flow Charts





All the measuring points monitored by the control system can be displayed using graphical icons/symbols including digit, current values, ranges and upper and lower limits. The software supports multilevel display structure and the graphics can also be called in various modes such as Manual mode, Movable Window Display, Automatic Pop-up Display, Hot Point Call and Keyboard Call. Sequential Function Charts:

The sequential function charts feature in Microcon system provides an easy tool for operators to operate the entire batch sequence in their own language / terminologies. Various recipes, manual interventions can be acknowledged, logged and downloaded, which makes the tool extremely user friendly. The operator only requires knowing his process and needs not have any specific computer skills. Reports:

Figure-11: Sequential Function Charts

Figure-12: Reports





The Microcon report package, which is an integral part of the operator software, provides a variety of reports, such as daily reports, shift-wise reports, monthly reports, batch reports etc. In addition to this, user definable reports can be generated from the system. Additional features can be provided for batch costing, SQC techniques, Supply Chain Management etc. The entire report structure of Microcon is MS Excel based and hence can be very easily exported either by e-mails / integration to MIS / ERP system. Trend Displays: Microcon provides a variety of trend displays, a useful tool for analysis, in terms of real time and historical trending. The X-Y trend graphs can be used for analyzing relationship of various parameters with each other and can also be used as an effective tool not only for process development but also for fine tune up of various process parameters. Alarms:

Figure-13: Trend Displays

Figure-14: Alarms





The alarm functions in Microcon software help and reminds the operator to take corrective actions in case of abnormal status of process / equipment failures. Alarms can be prioritized depending on the nature of the alarm and can be displayed / logged based on the priorities, status and events. The special Microcon SOE module provides time stamping of sequence of events at 1 msec. time interval. The time stamping is done on the digital input module itself. Remote monitoring: Microcon also offers wide choices of communications through Internet for long distance monitoring using broadband GPRS, GSM, radio frequency or V-Sat mode as per the user’s choice. This feature allows Senior Executives to monitor the plant performances remotely and can also be used for remote site monitoring / control for multiple or remote area site locations. The system can also have GPS clock synchronization features for time synchronization between various operator stations and other third party devices.

Figure-15: Remote Monitoring

DCS (1)

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