TRAINING REPORT ON
Distributed Control System
UNDERTAKEN AT
Larsen & Toubro, India
SUBMMITED BY:DHANRAJ 1
ELECTRONICS AND COMMUNICATION (ECE) SCET, BUCHOLI ROAD, MAHENDER GARH
ACKNOWLEDMENT "Give me the tools, and I will give you the work" These words are the motto of an engineer. I am proud to say that my training in LARSON & TURBO shall be a valuable tool in keeping my engineering skills on the right track. This confidence has come with the invaluable guidance and support of the senior persons of the company who have been highly inspiring, for which I shall remain indebted to them. I am thankful to Mr. Parveen Sharma For providing me opportunity to undergo training in such an esteemed company. I also take this opportunity to express my sincere and deepest sense of grat gratit itud ude e towa toward rds s all all the the staf stafff memb member ers s of the the ESE ESE depa depart rtme ment nt.. I specially thank for having shared with me all their experiences and gave their full support to complete my training.
I also would like to thank everybody involved directly or indirectly in helping me completing my training in L&T
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In order to print this document from Scribd, you'll ELECTRONICS AND COMMUNICATION (ECE) first need toSCET, downloadBUCHOLI it. ROAD, MAHENDER GARH Cancel Download And Print ACKNOWLEDMENT
"Give me the tools, and I will give you the work" These words are the motto of an engineer. I am proud to say that my training in LARSON & TURBO shall be a valuable tool in keeping my engineering skills on the right track. This confidence has come with the invaluable guidance and support of the senior persons of the company who have been highly inspiring, for which I shall remain indebted to them. I am thankful to Mr. Parveen Sharma For providing me opportunity to undergo training in such an esteemed company. I also take this opportunity to express my sincere and deepest sense of grat gratit itud ude e towa toward rds s all all the the staf stafff memb member ers s of the the ESE ESE depa depart rtme ment nt.. I specially thank for having shared with me all their experiences and gave their full support to complete my training.
I also would like to thank everybody involved directly or indirectly in helping me completing my training in L&T
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TABLE OF CONTENTS -: Cancel
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•
Introduction to L&T
•
DCS
•
PROTOCOLS USED IN DCS
•
PLC
•
RELAYS
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INTRODUCTION TO Larsen & Toubro Cancel
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Larsen & Toubro Limited (L&T) is a technology, engineering, construction and manufacturing company. It is one of the largest and most respected companies in India's private sector. Seven decades of a strong, customer-focused customer-focused approach and the continuous quest for world-class quality have enabled it to attain and sustain leadership in all its major major lines of business. L&T has an international international presence, with a global spread of offices. A thrust on international business has seen overseas earnings grow significantly. It continues to grow its overseas manufacturing footprint, with facilities in China and the Gulf region. The company's businesses businesses are supported by a wide marketing and distribution network, and have established a reputation for strong customer support. L&T believes that progress must be achieved in harmony with the environment. A commitment to community welfare and environmental protection are an integral part of the corporate vision.
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Engineering Services Cancel
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L&T Engineering Services / Consulting group is staffed with a well-focused and vibrant work force of over 1200 professionals having cross-industry experience. Using cutting-edge technology, L&T provides end-to-end engineering solutions to various verticals including oil & gas, refinery, petrochemicals, fertilizers, chemicals, power etc. L&T Engineering is supported by specialized engineering groups namely FEED Group (Front End Engineering & Design), Technology & Innovation Center (TIC) and Research & Development Department (R&D). The FEED group provides the basic engineering and process engineering support. L&T also has joint v enture engineering companies namely : L&T - Chiyoda Limited (LTC) for hydrocarbon process plants and L&T - Sargent & Lundy Limited (LTSL) for power plants, both located at Baroda, and L&T Valdel, based at Bangalore, which specializes in engineering for off-shore / on-shore platforms, pipelines etc. Our offerings include : • • • • • • • • • • • • • • • • • • • • • • • • • •
Technology Evaluation and Feasibility Study. Preparation of Pre-FEED/FEED (Front End Engineering and Design) Package Steady State & Dynamic Simulation Computational Fluid Dynamic Studies Advanced Process Control & Optimization Materials Science & Corrosion Engineering Detail Engineering Plant & Piping Engineering Machinery & Equipment Engineering Civil & Structural Engineering Electrical Engineering Control & Instrumentation Engineering Preparation of Specifications and Drawings Preparation of Material Take Off Procurement Assistance Project Management Project Planning and Monitoring Pre-commissioning and commissioning assistance Asset Management Value Proposition Rich Domain Knowledge Flexible Working / Operating Models More than 3000 person-years of experience Commitment to Quality Commitment to Schedule Strong Financial Background
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In order to print this document from Scribd, you'll Effective Knowledge Management System & Talent Retention first need toProcesses download it. Ability to adapt to Customer and Methodologies Readily Available Infrastructure Excellent Project Management skills Download And Print Cancel Ability to Ramp up big team Data & Information Security
SERVICES PROVIDED Construction ECC – the Engineering Construction & Contracts Division of L&T is the major contributor in L&t's share market. Which is India’s largest construction organisation. L&T covers every discipline of construction – civil, mechanical, electrical and instrumentation. L&T has also expanded its focus to the Middle East, South East Asia, Russia, CIS, Mauritius, African and SAARC countries. L&T also has keen interest in the markets of Indian Ocean rim countries, Africa and Latin America.
Electrical and electronics L&T is an international manufacturer of a wide range of electrical and electronic products and systems. L&T also manufactures custom-engineered switchboards for industrial sectors like power, refineries, petrochemicals and cement. In the electronic segment, L&T offers a range of meters and provides control and automation systems for industries. Medical equipment and systems manufactured by L&T include advanced ultrasound scanners and patient monitoring systems.
Information technology Larsen & Toubro Infotech Limited, a 100 per cent subsidiary of the L&T, offers software solutions and services with a focus on Manufacturing, BFSI and Communications and Embedded Systems. It also provides services in the embedded intelligence and e Engineering space. no 1 in electrical switchboard manufacturing.
Machinery and industrial products L&T manufactures markets and provides service support for critical construction and mining machinery – surface miners, hydraulic excavators, aggregate crushers, loader backhoes and vibratory compactors; supplies a wide range of rubber processing machinery and injection moulding machines; and manufactures and markets Industrial valves and allied products and a range of sophisticated application-engineered welding alloys. 6
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ESE DEPARTMENT
Cancel Download Print L&T is the market leader for switchboards in India. ItAnd manufactures custom-built switchboards with conventional as well as intelligent protection, control and communication to meet the power distribution and motor control needs of key industries. It’s Power Control Centers (PCC) and Motor Control Centers (MCC) are installed at major and prestigious plants in India.
L&T manufactures maximum number of panels every year and has a steady market share. It associates with its customers at the project conceptualization stage and the association continues even after the project is commissioned. The range of custom-built switchboards comprises fully drawout PCCs and MCCs, distribution boards and control panels. Its PCC type TF is rated up to 6000A and houses L&T-made Air Circuit Breakers to take care of power distribution. The MCC type TQ is rated up to 5000A. L&T offers assistance in product selection, application engineering and detailed engineering, installation and commissioning, retrofitting and upgradation of switchboards, after-sales service and training. It also designs and manufactures enclosures in flat pack systems for switchboard assemblers world-wide. L&T offers retrofitting solutions for a wide range of LV & MV switchgear including IMCS. Marine Business has developed marinised switchgear, switchboards, distribution boards, starters and control systems for application onboard Naval Ships as well as commercial ships. Larsen & Toubro Limited is among the major manufacturers of low voltage switchgear in the World, with the scale, sophistication and range to meet global benchmarks. In addition to its leadership position in the Indian market established over a decade ago, L&T has a growing presence in international market. L&T switchgear conforms to international design standards, KEMA certification and CE markings, attest to quality and reliability. The company's continuous investment in upgrading capabilities has led to a technology base at par with the finest in electrical industry worldwide. State of art manufacturing facilities at Mumbai & Ahmednagar conform to the principles of lean manufacturing, six sigma and value engineering. Testing facilities include a 85 kA short circuit test station. Each of L&T's manufacturing facilities reflect the company's overriding concern for the environment.As a leader in the switchgear industry, L&T views its role as a complete solution provider for power distribution and control in the low tension segment. L&T has therefore set up full-fledged training centres at three locations around the country to propagate good electrical practices and offer advance professional skills in operation and maintenance of switchgear. Expert assistance in product selection and specification as well as effective post-sales service is offered through a wide network of service centres across the country.
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1. Distributed Control System (DCS) Cancel Download And Print A distributed control system (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or more controllers. The entire system of controllers is connected by networks for communication an d monitoring. DCS is a very broad term used in a variety of industries, to monitor and control distributed equipment. • • • • • • • • • •
Electrical power grids and electrical generation plants Environmental control systems Traffic signals radio signals Water management systems Oil refining plants Chemical plants Pharmaceutical manufacturing Sensor networks Dry cargo and bulk oil carrier ships
Distributed control systems (DCS) use decentralized elements or subsystems to control distributed processes or complete manufacturing systems. They do not require user intervention for routine operation, but may permit operator interaction via a supervisory control and data acquisition (SCADA) interface. Distributed control systems (DCS) consist of a remote control panel, communications medium, and central control panel. They use process-control software and an input/output (I/O) database. Some suppliers refer to their remote control panels as remote transmission units (RTU) or digital communication units (DCU). Regardless of their name, remote control panels contain terminal blocks, I/O modules, a processor, and a communications interface. The communications medium in a distributed control system (DCS) is a wired or wireless link which connects the remote control panel to central control panel, SCADA, or human machine interface (HMI). Specialized process-control software is used to read an I/O database with defined inputs and outputs. Selecting distributed control systems (DCS) requires an analysis of network protocols. Ethernet is a local area network (LAN) protocol that uses a bus or star typology and supports data transfer rates of 10 Mbps. To han dle simultaneous demands, Ethernet uses
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In order to print this document from Scribd, you'll carrier sense multiple access / collision detection (CSMA/CD) to monitor network traffic. first need to download it.protocol used for communications among Fieldbus is a bi-directional communications field instrumentation and control systems. Network protocols for distributed control systems (DCS) also include controller network bus control network Cancel areaDownload And(CANbus), Print (ControlNet), DeviceNet, INTERBUS (Phoenix Contact GmbH & Co), and PROFIBUS (PROFIBUS International). The process fieldbus (PROFIBUS®) is a popular, open communication standard used in factory automation, process automation, motion control, and safety applications.
Distributed control systems (DCS) differ in terms of complexity and applications. Smaller implementations may consist of a single programmable logic controller (PLC) connected to a computer in a remote office. Larger, more c omplex DCS installations are also PLC-based, but use special enclosures for subsystems that provide both I/O and communication. In terms of applications, some distributed control systems (DCS) are used in electrical power grids or electrical generation facilities. Others are used in environmental control systems, wastewater treatment plants, and sensor networks. Distributed control systems (DCS) for petroleum refineries and petrochemical plants are also common. Fully-distributed systems enable remote nodes to operate independently of the central control. These nodes can store all of the process data necessary to maintain operations in the even of a communications failure with a central facility.
Elements A DCS typically uses custom designed processors as controllers and uses both proprietary interconnections and communications protocol for communication. Input an d output modules form component parts of the DCS. The processor receives information from input modules and sends information to o utput modules. The input modules receive information from input instruments in the process (a.k.a. field) and transmit instructions to the output instruments in the field. Computer buses or electrical buses connect the processor and modules through multiplexer or demultiplexers. Buses also connect the distributed controllers with the central controller and finally to the Human-Machine Interface (HMI) or control consoles. See Process Automation System. Elements of a distributed control system may directly connect to physical equipment such as switches, pumps and valves or may work through an intermediate system such as a SCADA system.
Applications Distributed Control Systems (DCSs) are dedicated systems used to control manufacturing processes that are continuous or batch-oriented, such as oil refining, petrochemicals, central station power generation, pharmaceuticals, food & beverage manufacturing, cement production, steelmaking, and papermaking. DCSs are connected to sensors and
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In order to print this document from Scribd, you'll actuators and use setpoint control to control the flow of material through the plant. The first to download most common example is aneed setpoint controlit.loop consisting of a pressure sensor, controller, and control valve. Pressure or flow measurements are transmitted to the controller, usually through the Cancel aid of a signal conditioning Input/Output (I/O) device. Download And Print When the measured variable reaches a certain point, the controller instructs a valve or actuation device to open or close until the fluidic flow process reaches the d esired set point. Large oil refineries have many thousands of I/O points and employ very large DCSs. Processes are not limited to fluidic flow through pipes, however, and can also include things like paper machines and their associated variable speed drives and motor control centers, cement kilns, mining operations, ore processing facilities, and many others.
A typical DCS consists of functionally and/or geographically distributed digital controllers capable of executing from 1 to 256 or more regulatory control loops in one control box. The input/output devices (I/O) can be integral with the controller or located remotely via a field network. Today’s controllers have extensive computational capabilities and, in addition to proportional, integral, and derivative (PID) control, can generally perform logic and sequential control. DCSs may employ one or several workstations and can be configured at the workstation or by an off-line personal computer. Local communication is handled by a control network with transmission over twisted pair, coaxial, or fiber optic cable. A server and/or applications processor may be included in the system for extra computational, data collection, and reporting capability.
SYSTEM ARCHITECTURE General Control system architecture can range from simple local control to highly redundant distributed control.SCADA systems, by definition; apply to facilities that are large enough that a central control system is necessary. Reliability criteria for C4ISR facilities dictate the application of redundant or distributed central control systems.
Distributed control Distributed control system architecture (figure 3-3) offers the best features of both local control and centralized control. In a distributed control system, controllers are provided locally to systems or groups of equipment, but networked to one or more operator stations in a central location through a digital communication circuit. Control action for each system or subsystem takes place in the local controller, but the central operator station has complete visibility of the status of all systems and the input and output data in each c ontroller, as well as the ability to intervene in the control logic of the local controllers if necessary. a. There are a number of characteristics of distributed control architecture which enhance reliability:
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In runs orderare to print from Scribd, you'll disruption or (1) Input and output wiring shortthis anddocument less vulnerable to physical first need to download it. electromagnetic interference. (2) A catastrophic environmental failure in one area of the facility will not affect controllers or wiring located in another area. Cancel Download Print (3) Each local controller can function on its own upon lossAnd of communication with the central controller. b. There are also specific threats introduced by distributed control architecture that must be addressed in the design of the system: (1) Networks used for communication may become electronically compromised from outside the facility. (2) Interconnection of controllers in different locations can produce ground loop and surge voltage problems. (3) If the central controller is provided with the ability to directly drive the output of local controllers for purposes of operator intervention, software glitches in the central controller have the potential to affect multiple local controllers, compromising system redundancy. (4) Distributed control system architecture redundancy must mirror the redundancy designed into the mechanical and electrical systems of the facility. Where redundant mechanical or electrical systems are provided, they should be provided with dedicated controllers, such that failure of a single controller cannot affect more than one system. Equipment or systems that are common to multiple redundant subsystems or pathways, (such as generator paralleling switchgear) should be provided with redundant controllers.
Types of distributed control systems a. Plant distributed control system (DCS): While the term DCS applies in general to any system in which controllers are distributed rather than centralized, in the power generation and petrochemical process industries it has come to refer to a specific type of control system able to execute complex analog process control algorithms at high speed, as well as provide routine monitoring, reporting and data logging functions. In most applications, the input and output modules of the system are distributed throughout the facility, but the control processors themselves are centrally located in proximity to the control room. These systems typically use proprietary hardware, software and communication protocols, requiring that both replacement parts and technical support be obtained from the original vendor. b. Direct digital control (DDC): DDC systems are used in the commercial building heating, ventilation and air conditioning (HVAC) industry to monitor and maintain environmental conditions. They consist of local controllers connected to a network with a personal computer (PC) based central station which provides monitoring, reporting, data storage and programming capabilities. The controllers are optimized for economical HVAC system control, which generally does not require fast execution speeds. Their hardware and control software are proprietary, with either proprietary or open protocols used for network communication. c. Remote terminal unit (RTU) based SCADA: RTU-based systems are common in the electric, gas and water distribution industries where monitoring and control must take place across large geographical distances. The RTUs were developed primarily to provide monitoring and control capability at unattended
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In order tostations, print thispump document fromand Scribd, you'll sites such as substations, metering stations, water towers. They communicate first need to download it. with a central station over telephone lines, fiber-optics, radio or microwave transmission. Monitored sites tend to be relatively small, with the RTU typically used mainly for monitoring and only Cancelare proprietary, Download And Print limited control. Hardware and software with either proprietary or open protocols used for data transmission to the central station. d. Programmable logic controller (PLC) based systems: PLCs, which are described in greater detail in the next section, can be networked together to share data as well as provide centralized monitoring and control capability. Control systems consisting of networked PLCs are supplanting both the plant DCS and the RTU-based systems in many industries. They were developed for factory automation and have traditionally excelled at high speed discrete control, but have now been provided with analog control capability as well. Hardware for these systems is proprietary, but both control software and network communication protocols are open, allowing system configuration, programming and technical support for a particular manufacturer’s equipment to be obtained from many sources.
2. The DCS Protocol Three components comprise the DCS architecture: hardware servers (DHS), GUI clients, and the DCS server, DCSS. GUI clients and hardware servers communicate solely with DCSS, and DCSS operates the only listening sockets (i.e., network server) in the DCS system. Consequently, hardware servers are in a sense network clients of DCSS and are sometimes referred to as clients of DCSS in the DCS message protocol docu mentation. DCS hardware servers encapsulate low-level control of physical devices such as motors, shutters, detectors, and so on. Hardware servers simply connect to DCSS and do whatever DCSS tells them to do. DCS GUI clients such as BLU-ICE are the ultimate source of these instructions to the hardware servers. DCSS passes the requests from GUI clients down to the appropriate hardware servers, and broadcasts all replies from hardware servers back to all of the GUI clients, thus keeping all GUI clients in complete synchronization.
VARIOUS PROTOCOLS USED IN DCS ARE: • • •
Modbus Profibus IC 61850
MODBUS Data Link Layer 2.1 MODBUS Master / Slaves protocol principle The MODBUS Serial Line protocol is a Master-Slaves protocol. Only one master (at the same time) is connected to the bus, and one or several (247 maximum number) slaves nodes are also connected to the same serial bus. A MODBUS communication is always
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order to print this document from Scribd, you'll initiated by the master. In The slave nodes will never transmit data without receiving a first need to download it. will never communicate with each other. request from the master node. The slave nodes The master node initiates only one MODBUS transaction at the same time. Cancel Download And Print The master node issues a MODBUS request to the slave nodes in two modes:
* In unicast mode , the master addresses an individual slave. After receiving and processing the request, the slave returns a message (a 'reply') to the master In that mode, a MODBUS transaction consists of 2 messages: a request from the master, and a reply from the slave. Each slave must have an unique address (from 1 to 247) so that it can be addressed independently from other nodes.
*In broadcast mode , the master can send a request to all slaves. No response is returned to broadcast requests sent by the master. The broadcast requests are necessarily writing commands. All devices must accept the broadcast for writing function. The address 0 is reserved to identify a broadcast exchange.
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2.2 MODBUS addressing rules The MODBUS addressing space comprises 256 different add resses. 0 From 1 to 247 From 248 to 255 Broadcast address Slave individual addresses Reserved
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In order to print this document from Scribd, you'll The Address 0 is reserved as the broadcast address. All slave nodes must recognize the first need to download it. broadcast address. The MODBUS Master node has no specific address, only the slave nodes must have an address. This address must be unique on a MODBUS serial bus.
2.3 MODBUS frame description Cancel Download And Print
The MODBUS application protocol [1] defines a simple Protocol Data Unit (PDU) independent of the underlying communication layers:
Data
Function code
MODBUS PDU The mapping of MODBUS protocol on a specific bus or network introduces some additional fields on the Protocol Data Unit. The client that initiates a MODBUS transaction builds the MODBUS PDU, and then adds fields in order to build the appropriate communication PDU . Address field Function code Data CRC (or MODBUS SERIAL LINE PDU On MODBUS Serial Line, the Address field only contains the slave ad dress. As described in the previous section the valid slave nodes addresses are in the range of 0 – 247 decimal. The individual slave devices are assigned addresses in the range of 1 – 247. A master addresses a slave by placing the slave address in the address field of the message. When the slave returns its response, it places its own address in the response address field to let the master know which slave is responding. The function code indicates to the server what kind of action to perform. The function code can be followed by a data field that contains request and response parameters. Error checking field is the result of a "Redundancy Checking" calculation that is performed on the message contents. Two kinds of calculation methods are used depending on the transmission mode that is being used (RTU or ASCII).
2.4 Master / Slaves State Diagrams The MODBUS data link layer comprises two separate sub layers : • The Master / slave protocol • The transmission mode (RTU vs ASCII modes) The following sections describe the state diagrams of a master and a slave that are independent of transmission modes used. The RTU and ASCII transmission modes are specified in next chapters using two state diagrams. The reception and the sending of a frame are described. Syntax of state diagram: The following state diagrams are drawn in compliance with UML standard notations. The notation is briefly recalled below:
State_A
State_B
Trigger [guard condition] / action When a "trigger" event occurs in a system being in "State_A", system is going into "State_B", only if "guard condition" is true. An action "action" is then performed.
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2.4.1 Master State diagram The following drawing explains the Master behavior :
MASTER STATE DIAGRAM
Some explanations about the state diagram above: State "Idle" = no pending request. This is the initial state after power-up. A request can only be sent in "Idle" state. After sending a request, the Master leaves the "Idle" state, and cannot send a second request at the same time When a unicast request is sent to a slave, the master goes into "Waiting for reply" state, and a “Response Time-out” is started. It prevents the Master from staying indefinitely in "Waiting for reply" state. Value of the Response time-out is application dependant. When a reply is received, the Master checks the reply before starting the data processing. The checking may result in an error, for example a reply from an unexpected slave, or an error in the received frame. In case of a reply received from an unexpected slave, the Response time-out is kept running. In case of an error detected on the frame, a retry may be performed. If no reply is received, the Response time-out expires, and an error is generated. Then the Master goes into "Idle" state, enabling a retry of the request. The maximum number of retries depends on the master set-up. When a broadcast request is sent on the serial bus, no response is returned from the slaves. Nevertheless a delay is respected by the Master in order to allow any slave to
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In order to print this document from Scribd, you'll process the current request before sending a new one. This delay is called "Turnaround first need to download it. delay". Therefore the master goes into "Waiting Turnaround delay" state before going back in "idle" state and before being able to send another request. In unicast the Response time out must be set long enough for any slave to process the Cancel Download And Print request and return the response, in broadcast the Turnaround delay must be long enough for any slave to process only the request and be able to receive a new one. Therefore the Turnaround delay should be shorter than the Response time-out. Typically the Response time-out is from 1s to several second at 9600 bps; and the Turnaround delay is from 100 ms to 200ms. Frame error consists of : 1) Parity checking applied to each character; 2) Redundancy checking applied to the entire frame. See §2.6 " Error Checking Methods" for more explanations. The state diagram is intentionally very simple. It does not take into account access to the line, message framing, or retry following transmission error, etc … For more details about frame transmission, please refer to 2.5 paragraph, "The two serial Transmission Modes".
2.4.2 Slave State Diagram The following drawing explains the Slave behavior:
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SLAVE STATE DIAGRAM
Some explanations about the above state diagram: State "Idle" = no pending request. This is the initial state after power-up. When a request is received, the slave checks the packet before performing the action requested in the packet. Different errors may occur: format error in the request, invalid action, In case of error, a reply must be sent to the master. Once the required action has been completed, a unicast message requires that a reply must be formatted and sent to the master.
If the slave detects an error in the received frame, no respond is returned to the master. MODBUS diagnostics counters are defined and should be managed by any slave in order to provide diagnostic information. These counters can be get using the Diagnostic MODBUS function (see Appendix A, and the MODBUS application protocol specification [1])
2.5 The two serial Transmission Modes Two different serial transmission modes are defined: The RTU mode and the ASCII mode. It defines the bit contents of message fields transmitted serially on the line. It determines how information is packed into the message fields and decoded. The transmission mode (and serial port parameters) must be the same for all devices on a MODBUS Serial Line.
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In order to print this document from Scribd, you'll Although the ASCII mode is required in some specific applications, interoperability first between MODBUS devicesneed cantobedownload reachedit.only if each device has the same transmission mode: All devices must implement the RTU Mo de. The ASCII transmission mode is an option. Cancel Download And Print Devices should be set up by the users to the desired transmission mode, RTU or ASCII. Default setup must be the RTU mode.
2.5.1 RTU Transmission Mode When devices communicate on a MODBUS serial line using the RTU (Remote Terminal Unit) mode, each 8–bit byte in a message contains two 4–bit hexadecimal characters. The main advantage of this mode is that its greater character density allows better data throughput than ASCII mode for the same baud rate. Each message must be transmitted in a continuous stream of characters. The format for each byte (11 bits) in RTU mode is: Coding System: 8–bit binary Bits per Byte : 1 start bit 8 data bits, least significant bit sent first 1 bit for parity completion 1 stop bit Even parity is required , other modes (odd parity, no parity ) may also be used. In order to ensure a maximum compatibility with other products, it is recommended to support also No parity mode. The default parity mode must be even parity. Remark: the use of no parity requires 2 stop bits. How Characters are transmitted serially: Each character or byte is sent in this order (left to right): Least Significant Bit (LSB) . . . Most Significant Bit (MSB) Start
1 2 3 4 5 6 With parity checking (bit sequence in RTU mode)
7
8
Devices may accept by configuration either Even , Odd, or No Parity checking. If No Parity is implemented, an additional stop bit is transmitted to fill out the character frame to a full 11-bit asynchronous character : Start Stop
1 2 3 4 5 6 Stop Bit Sequence in RTU mode (specific case of No Parity)
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Frame Checking Field : Cyclical Redundancy Checking (CRC) Frame description:
Slave address 1 Byte
Function code 1 Byte
Data 0 upto 252 byte(s)
CRC 2 Bytes
RTU Message Frame The maximum size of a MODBUS RTU frame is 256 bytes.
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2.5.1.1 MODBUS Message RTU Framing Cancel Download And Print A MODBUS message is placed by the transmitting device into a frame that has a known beginning and ending point. This allows devices that receive a new frame to begin at the start of the message, and to know when the message is completed. Partial messages must be detected and errors must be set as a result. In RTU mode, message frames are separated by a silent interval of at least 3.5 character times. In the following sections, this time interval is called t3.5.
3 Physical Layers 3.1 Preamble A new MODBUS solution over serial line should implement an electrical interface in accordance with EIA/TIA-485 standard ( also Known as RS485 standard). This standard allows po int to point and multipoint systems, in a “two-wire configuration”. In addition, some Devices may implement a “Four-Wire” RS485-Interface. A device may also implement an RS232-Interface. In such a MODBUS system, a Master Device and one or several Slave Devices communicate on a passive serial line. On standard MODBUS system, all the devices are connected (in parallel) on a trunk cable constituted by 3 conductors. Two of those conductors (the “Two-Wire” configuration) form a balanced twisted pair, on which bi-directional data are transmitted, typically at the bit rate of 9600 bits per second. Each device may be connected (see figure 19): -either directly on the trunk cable, forming a daisy-chain, -either on a passive Tap with a derivation cable, -either on an active Tap with a specific cable. Screw Terminals, RJ45, or D-shell 9 connectors may be used on devices to connect cables (see the chapter “Mechanical Interfaces”). 3.2 Data Signaling Rates 9600 bps and 19.2 Kbps are required and 19.2 is the required default Other baud rates may optionally be implemented: 1200, 2400, 4800, 38400 bps, 56 Kbps, 115 Kbps … Every implemented baud rate must be respected better than 1% in transmission situation, and must accept an error of 2% in reception situation.
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In order to print this document from Scribd, you'll Openness and standardization guarantee the supply of PROFIBUS products from many first need to download it. different vendors as well as the availability of know-how and support from many different experts close to you. With more than 1 3,000,000 nodes installed there are significantly more PROFIBUSCancel nodes installed than ofAnd anyPrint other fieldbus. Work proceeds Download as about 400 engineers in 40 Working Groups continue to advance the state-of-the-art, adapting to the ever-changing automation landscape.
Welcome to PROFIBUS
PROFIBUS is the powerful, open and rugged bus system for process and field communication in cell networks with few stations and for data communication in accordance with IEC 61158/EN 50170. Automation devices such as PLCs, PCs, HMI devices, sensors o r actuators can communicate via this bus system. The IEC 61158/EN 50170 standard makes allowance at the same time for the future of your investments since existing plants can be expanded using components that conform to the standard. PROFIBUS is part of Totally Integrated Automation ® (TIA) , the uniform, integrated product and system range from Siemens for efficient automation of the entire production process – for all sectors of industry. Possible uses
PROFIBUS can be used, for example, for the following applications: •
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Factory automation Process automation Building automation
Different PROFIBUS versions are available for the various fields of application: •
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Process or field communication - PROFIBUS DP (for fast, cyclic data exchange with field devices) - PROFIBUS PA (for intrinsic safety applications in process a utomation Data communication - PROFIBUS FMS (for data communication between programmable co ntrollers and field devices
SIMATIC NET products are particularly suitable for use in industry. For implementing Profibus networks, SIMATIC NET offers the required network components and system interfaces for connecting S7 and PC/IPC. •
Network components PROFIBUS networks can be implemented quickly and easily using the network
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components from the SIMATIC NET ® product range. V arious cables and first need to download it. connections are available depending on application. In the case of copper cables, in particular, FastConnect stripping technology ensures fast and reliable cabling. Cancel Download And Print System connections SIMATIC S7 and PG/PC are connected via communications p rocessors - this relieves the CPU of communications tasks.
Other advantages •
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Investment protection through integration of PROFIBUS devices in Industrial Wireless LANs using IWLAN/ PB Link PN IO or in Industrial Ethernet - or PROFINET networks using IE/PB Link or IE/PB Link PN IO. High availability through ring redundancy with OLM. Fast assembly and startup on site with the help of the FastConnect wiring system. Continuous monitoring of network components through a simple and effective signaling concept. Configuration, commissioning, and troubleshooting can be carried out by any party. This results in freely selectable communication relationships that are very versatile, simple to implement, and easy to change.
PROFIBUS Automation Technology
PROFIBUS - your direct route to Automation Technology PROFIBUS, the market leader in automation technology, is applicable to every
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The success of PROFIBUS is unparalleled. About a million applications run using PROFIBUS. More than 2,500 products are available from internationally and locally recognized manufacturers. PROFIBUS is standardized in the international standards IEC 61158 and IEC 61784, and supported by more than 1,200 member companies of the PROFIBUS International user community. PROFIBUS for Process Automation
PROFIBUS is a standardized, open, digital communications system for all areas of application in manufacturing and process automation. The PROFIBUS protocol is based on the international standards EN 50170 and IEC 61158. This technology is suitable for replacement of discrete and analog signals. PROFIBUS for Process Automation meets the demands of the chemical industry for use in explosive areas, use in areas where both power and communication are available over the bus. Furthermore, standardized application profiles are available and Plug & Play instruments even in potentially explosive areas. PROFIBUS Technology and Application - System Description
It is recommended to connect the shield on both sides low inductively with the protective ground in order to achieve optimal electromagnetic compatibility. In case of separate potentials (e.g. refinery) the shield should be connected only at one side of the bus cable to the protective ground. Preferably the connection between shield and protective ground 24
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In order to print this document from Scribd, you'll is made via the metal cases and the screw top of D-sub connector. If this is not possible first need download the connection can be made via to pin 1 of theit.D-sub connector. It should be noticed that this is not the optimal solution. In such a case it is better to bare the cable shield at an appropriate point and to groundCancel with a cable as short And as possible Download Print to the metallic structure of the cabinet. This could be achieved with a ground bus bar in front of the bus connector.
This is the universal solution for the communication tasks a t the upper level (cell level) and the Field Level of the industrial communication hierarchy. In order to carry out the extensive communication tasks with acyclic or cyclic data transfers at medium speed, the Fieldbus Message Specification (FMS) services offer a wide range of functionality and flexibility. PROFIBUS-FMS is included into the European Fieldbus Standard EN 50170. This is the performance optimized version of PROFIBUS, specifically dedicated to timecritical communication between automation systems and distributed peripherals. It is suitable as a replacement for the costly parallel wiring of 24 V and 4(0) to 20 mA measurement signals. PROFIBUS-DP is included into the European Fieldbus Standard EN 50170. Every DP/PA device type has to have an individual Ident Number. This number is necessary, so that a DP-master is able to identify the types of the connected DP/PA devices without a significant protocol overhead. The master compares the Ident Number of every connected device with the Ident Number in the configuration database. User data transfer in the operation phase is only possible when the right DP-Slave is connected with the correct address. This ensures a very high protection against parameterization faults. The vendors must apply to the PPROFIBUS Support Center for an individual Ident Number for every DP/PA device type. PROFIBUS-PA is the solution for process automation, connecting automation systems and decentralised field devices. PROFIBUS-PA is based on PROFIBUS-DP (acc. to EN 50170) and permits a transparent communication from general purpose automation to process automation. The Profibus-PA profile defines the behaviour of the field devices and ensures full interoperability and interchangeability of the field devices from different manufacturers. Profibus-PA operates either with intrinsic safe transmission technology (acc. to IEC 1158-2) or standard transmission technology (acc. to RS485). PA fulfils the special requirements of the process automation industry e.g. chemical or petrochemical applications. •
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The transparent communication between process automation and general purpose automation is permitted by PROFIBUS-PA. PROFIBUS-PA permits powering of the stations and data transmission over the same two wires. PA can be used within areas with high explosion risk using intrinsic safe transmission technology according to IEC 1158-2. Intrinsic safe and non-intrinsic safe bus segments are separated by segment couplers.
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to print this document from Scribd, you'll The hamming distance In is order a messure for how secure a protocol is against misinterpretation first need to download it. of a packet with errors as a different legal packet. HD=4 tells us that at least 4 bits has to be wrong, and still match the checksum calculations in order to be mistaken as another valid packet. Cancel Download And Print
Termination of a bus line is done to prevent signal reflections on the PROFIBUS cable. Wrong or missing termination of the line results in lower efficiency due to transmission errors. Worst case is that the communication link is lost. In addition to traditional termination, the PROFIBUS termination also provides a defined idle level on the cable. Profiles are commitments about used non-mandantory services and bus p arameters for specific areas of applications. It helps to minimize the implementation efforts to implement PROFIBUS functionallty into appropriate field dev ices. Profiles are available for • • • • • • • •
Communication between PLCs (FMS) Sensor / Actor networks (FMS) Low voltage switch devices (FMS) PA field devices (PA) NC / RC control systems (DP) Encoder Devices (DP) Drives Technology (DP/FMS) Safety Applications (DP)
This is a very subjective issue, as the faced challenge is setting the importance of the different aspects leading to a choice. But - provided that the technical solution is satisfactory for the task, it all boils down to cost/benefit comparisons. • • • • • •
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PROFIBUS has the largest portfolio of products in the fieldbus world. Now close to 200 vendors of PROFIBUS products and services. It is supported by the largest user organisation in this industry. The demand for quality is driving the competitors to supply good products. The competition and volume keeps prices at highly competetive level. PROFIBUS technology is defined for several levels within the information flow in a company. Knowledge of one standard can be utilized on several levels. Wide application area including factory, process and building automation. Stable protocol with many protocol chips available today. Installed base > 2 Million devices Suitable for operation in intrinsically safe areas in process control Supported by many manufacturers of both master and slave device technology providing truly open approach and practical vendor independence. Platform independence, PC, PLC or VMEbus based co ntrollers. 244 byte telegram means that even large packets of data can be sent without segmentation.
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In order to print this document from Scribd, you'll > 100km distance achievable. first need to offers download PROFIBUS at 12 MBaud theit.fastest transmission speed available today for any fieldbus system. PROFIBUS is the clearCancel Fieldbus market leader in Europe Download And Print and the UK. (ref IMS, Benchmark Research Ltd., and Consultic fieldbus studies).
A class 1 master can communicate activly only with it's configured slaves and is able to communicate in a passive way with a class 2 master. The class 2 master is the 'supervisory' master. He can communicate with other class 1 masters, theire slaves and his own slaves for configuration, diagnostic and data/parameter exchange purpose The base of the specification of the PROFIBUS standard was a research project (19871990) with the following members: • • • • • • • • • • • •
ABB Phoenix Contact AEG Rheinmetall Bosch RMP Honeywell Sauter-Cumulus Kloeckner-Moeller Schleicher Landis & Gyr Siemens
and five German research institutes • • • • •
FZI Karlsruhe LRT IITB WZL LPR
There was also a minor sponsorship of the German government. The result of this project was the first Draft of the DIN 19245, the PROFIBUS standard, part 1 and 2. Part 3, PROFIBUS-DP was defiened 1993 by the following working group: • • • •
Mr. Emmerling, MicroSyst Mr. Dr. Endl, Softing Mr. Schmitz, Pepperl + Fuchs Mr. Schneider, MBB Gelma
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In order to print this document from Scribd, you'll Mr. Szabo, TMG i-tec first need to download it. Mr. Thiesmeier, Kloeckner-Moeller Mr. Tretter, Siemens Mr. Volz, Bosch Cancel Download And Print Dr. Weber, Siemens
Yes, 10 years is a long time .... hope this helps a little bit to remember! PROFIBUS has been designed to allow configurations where redundant cabling is possible and this takes account of wire breaks. Also node failures can be configured to be ignored or to trigger a stop in the master, in this case unaffected nodes can continue operation. When a failure is identified the master will immediately resend the telegram and you can configure the number of times a re-try is attempted. Information relating to the failure is generally available on a node, module within a node and a channel specific basis. Certification testing of devices through an authorised test laboratory ensures that failures conform to what is expected of them. In addition to a PLC and the devices to be controlled •
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a cable - Shielded Twisted Pair with terminating resistors or Fibre Optic with Optical Link Modules a GSD file for each device. (A simple ASCII text file containing device data like identification info, what transmission speeds are supported, data format, time required to respond etc.) a software configuration tool - Like Allen Bradley's Plug and Play software or the Siemens COM Profibus package. This configures the active stations and tells them what devices are present on the bus and how much data it needs to exchange with them etc.
is required. The PROFIBUS Standard does not specify an alternative to the 9 pin D-SUB connectors, but it is often necessary to have alternatives available. The test specification for DP-Slaves defines: Alternative connectors may be used. No special connector is defined. But if the device with these alternative connectors should be certified, it must have all the mandatory signals of the Profibus D-SUB connector available. Furthermore, you should take into consideration for high speed usage, that some additional components should be used in combination with the D-SUB connector, or any other one. These components (R, L, C) are specified into the Implementation Guideline for PROFIBUS-DP, and are explained in detail including sample circuit diagrams in the new
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The PROFIBUS standard defines two variations of the busPrint cable. However it is Cancel Download And recommended to use cable Type A in all new installations. Type A is especially recommended for high transmission speeds (>500 kBaud) and permits doubling of the network distance in comparison to Type B. Technical specification:
Impedance: 35 up to 165 Ohm at frequencies from 3 to 20 Mhz. Cable capacity: < 30 pF per meter. Core diameter: > 0,34 mm², corresponds to AWG 22. Cable type: twisted pair cable. 1x2 or 2x2 or 1x4 lines. Resistance: < 110 Ohm per km. Signal attenuation: max. 9 dB over total length of line section. Shielding: CU shielding braid or shielding braid and shielding foil Max. Bus length: 200 m at 1500 kbit/s, up to 1,2 km at 93,75 kbit/s. Extendable by repeaters. O Top v e r v i e w
PROFIBUS is the most universal fieldbus for plantwide use accross all sectors of the manufacturing and process industries. It is the fieldbus having world wide best economic success. Independent market studies confirm market leadership for PROFIBUS today and high growth rates for the future. Using PROFIBUS means to have great cost advantages and improved flexibility.
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order to print this document from Scribd, you'll First of all thereInare major cost savings in hardware and assembly. Here most first need to download important is you need less hardwareit.components as I/O, terminal blocks, and barriers. The installation becomes easier, quicker and chea per. Very impressive are theCancel cost savings in engineering and documentation, which Download And Print makes the configuration much easier (only one tool for all devices), which improves the asset management of an automation system and which facilitates the documentation of the of the production procedure(easy and up-to-date documentation) An important feature of PROFIBUS based automation is the greater manufacturing flexibility. This feature covers a lot aspects, of which the most important are: improved functionality increases plant productivity, improved availability and reduced down time and optimized use of limited resources and raw materials
One of the most important advantage of using fieldbusses in the automation is reduced installation efforts. E.g., the cost savings estimated in process automation if PROFIBUS is used instead of the conventional 4-20mA technology are sumed up to more than 40%. For the device development or implementation of the PROFIBUS protocol, a broad spectrum of standard components and development tools (PROFIBUS ASICs, PROFIBUS stacks, monitor and commissioning tools) as well as services are available that enable device manufacturers to realize cost-effective development. A corresponding overview is available in the product guide of the PROFIBUS User Organization. PROFIBUS Interface Modules are ideal for a low/medium number of dev ices. These credit card size modules implement the entire bus protocol. They are fitted on the master board of the device as an additional module. PROFIBUS Protocol Chips (Single Chips, Communication Chips, Protocol Chips) are recommendable for an individual implementation in the case of high numbers of devices. The implementation of single-chip ASICs is ideal for simple slaves ( I/O devices). All protocol functions are already integrated on the ASIC. No microprocessors or software are required. Only the bus interface driver, the quartz and the power electronics are required as external components. For intelligent slaves, parts of the PROFIBUS protocol are implemented on a protocol chip and the remaining protocol parts implemented as software on a microcontroller. In most of the ASICS available on the market all cyclic protocol parts have been implemented, which are responsible for transmission of time-critical data. For complex masters, the time-critical parts of the PROFIBUS protocol are also implemented on a protocol chip and the remaining protocol parts implemented as software on a microcontroller. Various ASICs of different suppliers are currently available for the implementation of complex master devices. They can be operated in combination with many common microprocessors. Modem Chips are available to realize the (low) power consumption, which is required when implementing a bus-powered field device with MBP transmission technology. Only a feed current of 10-15 mA over the bus cable is available for these devices, which must
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In order to print this document from Scribd, you'll supply the overall device, including the bus interface and the measuring electronics. first need tooperating download it. These modems take the required energy for the overall device from the MBP bus connection and make it available as feed voltage for the other electronic components of the device. At the same time, the digitalDownload signals of And the connected protocol chip are Cancel Print converted into the bus signal of the MBP connection modulated to the energy supply.
IEC 61850 based Substation Automation Systems
IEC 61850 Benefits Speed: 100 Mbps instead of few 10 kbps More data for a better operation & maintenance Peer-to-peer: No extra hardware Design of innovative automation schemes, late tuning Conditional report instead of polling Optimal performances IP (Internet Protocol) routing: Ubiquitous data access Capability to extend the system outside of the substation Client-server: Instead of master-slave Flexible designs easy to upgrade Pre-defined names: Single vocabulary between users Easier engineering between teams XML references: Formal interfaces Consistency between engineering tools Flexibility of Usage Free usage of functions on all levels, no assumptions or constraints are imposed by the standard on the substation architecture. If the architecture is a centralized RTU based architectures with one computational element and parallel wiring from the primary equipment or a fully distributed architecture with intelligent sensors and actuators connected via a process bus does not matter. All possible architectures are equally and well supported by the standard.
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Scope of Expansion
Extension rules governs how to extend the scope of the standard in order to support new applications All applications defined today for substation automation are included and supported in the standard. This is however not enough. The standard also have an object model and set of rules that makes it possible to extend the scope of the standard and include new applications in the future, all this without need for additions or changes to the standard itself
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Programmable logic controller (PLC) Cancel
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PLC & input/output arrangements A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.
History The PLC was invented in response to the needs of the American automotive manufacturing industry. Programmable logic controllers were initially adopted by the automotive industry where software revision replaced the re-wiring of hard-wired control panels when production models changed. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of relays, cam timers, and drum sequencers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and expensive, as electricians needed to individually rewire each and every relay. In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hard-wired relay systems. The winning proposal came from Bedford Associates of Bed ford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates' eighty-fourth project, was
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In order to print this document from Scribd, you'll the result. Bedford Associates started a new company dedicated to developing, first need to download it. product: Modicon, which stood for manufacturing, selling, and servicing this new MOdular DIgital CONtroller. One of the people who worked on that project was Dick Morley, who is considered to be the "father" of the PLC. Cancel Download And The PrintModicon brand was sold in 1977 to Gould Electronics, and later acquired by German Company AEG and then by French Schneider Electric, the current owner.
One of the very first 084 models built is now on display at Modicon's headquarters in North Andover, Massachusetts. It was presented to Modicon by GM, when the unit was retired after nearly twenty years of uninterrupted service. Modicon used the 84 moniker at the end of its product range until the 984 made its appearance. The automotive industry is still one of the largest users of.
Development Early PLCs were designed to replace relay logic systems. These PLCs were p rogrammed in "ladder logic", which strongly resembles a schematic diagram of relay logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used a form of instruction list programming, based on a stack-based logic solver. Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C. Another method is State Logic, a very high-level programming language designed to program PLCs based on state transition diagrams. Many early PLCs did not have accompanying programming terminals that were capable of graphical representation of the logic, and so the logic was instead represented as a series of logic expressions in some version of Boolean format, similar to Boolean algebra. As programming terminals evolved, it became more common for ladder logic to be used, for the aforementioned reasons. Newer formats such as State Logic and Function Block (which is similar to the way logic is depicted when using digital integrated logic circuits) exist, but they are still not as popular as ladder logic. A primary reason for this is that PLCs solve the logic in a predictable and repeating sequence, and ladder logic allows the programmer (the person writing the logic) to see any issues with the timing of the logic sequence more easily than would be possible in other formats.
Programming Early PLCs, up to the mid-1980s, were programmed using proprietary programming panels or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. The very oldest PLCs used non-volatile magnetic core memory.
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In order to print this document from Scribd, you'll More recently, PLCs are usually programmed using special application software written first needand to download it. between the desktop computer and the for use on desktop computers, connecting PLC such as via Ethernet RS-232 or RS-485 cabling. Such software allows entry and editing of the ladder-style logic, and then may provide additional Cancel Download And Print functionality to assist debugging and troubleshooting the software (for example, by highlighting portions of the logic to show current status during operation or via simulation). Finally, the software may allow uploading and downloading of the program between the computer and the PLC, for backup and restoration purposes. Alternately, specific devices known as programming boards are used to hard wire the logic into the controller by the use of a removable chip, such as an EEPROM, where the program is transferred to the programming board from the workstation via serial or other bus logic.
Functionality The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, a llow a general-purpose desktop computer to overlap some PLCs in certain applications. Regarding the practicality of these desktop computer based logic controllers, it is important to note that they have not been generally accepted in heavy industry because the desktop computers run on less stable operating systems than do PLCs, and becau se the desktop computer hardware is typically not designed to the same levels of tolerance to temperature, humidity, vibration, and longevity as the processors used in PLCs. In addition to the hardware limitations of desktop based logic, operating systems such as Windows do not lend themselves to deterministic logic execution, with the result that the logic may not always respond to changes in logic state or input status with the extreme consistency in timing as is expected from PLCs. Still, such desktop logic applications find use in less critical situations, such as laboratory automation and use in small facilities where the application is less demanding and critical, because they are generally much less expensive than PLCs. In more recent years, small products called PLRs (programmable logic relays), and also by similar names, have become more common and accepted. These are very much like PLCs, and are used in light industry where only a few points of I/O (i.e. a few signals coming in from the real world and a few going out) are involved, and low cost is desired. These small devices are typically made in a common physical size and shape by several manufacturers, and branded by the makers of larger PLCs to fill out their low end product range. Popular names include PICO Controller, NANO PLC, and other names implying very small controllers. Most of these have between 8 and 12 digital inputs, 4 and 8 digital outputs, and up to 2 analog inputs. Size is usually about 4" wide, 3" high, and 3" deep. Most such devices include a tiny postage stamp sized LCD screen for viewing simplified ladder logic (only a very small portion of the program being visible at a given time) and status of I/O points, and typically these screens are accompanied by a 4-way rocker push button plus four more separate push-buttons, similar to the k ey buttons on a VCR remote
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In order to print this document from Scribd, you'll control, and used to navigate and edit the logic. Most have a small plug for connecting first need to download it. so that programmers can use simple via RS-232 or RS-485 to a personal computer Windows applications for programming instead of being forced to use the tiny LCD and push-button set for this purpose. Unlike regular PLCsAnd thatPrint are usually modular and Cancel Download greatly expandable, the PLRs are usually not modular or expandable, but their price can be two orders of magnitude less than a PLC and they still offer robust design and deterministic execution of the logic.
PLC Topics Features
Control panel with PLC (grey elements in the c enter). The unit consists of separate elements, from left to right; power supply, controller, relay units for in- and output The main difference from other computers is that PLCs are armored for severe conditions (such as dust, moisture, heat, cold) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.
System scale
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order to print this document from Scribd, you'll A small PLC will have In a fixed number of connections built in for inputs and outputs. first need to download it. model has insufficient I/O. Typically, expansions are available if the base
Modular PLCs have a chassis (also rack) intoAnd which are placed modules with Cancelcalled aDownload Print different functions. The processor and selection of I/O modules is customised for the particular application. Several racks can be administered by a single processor, and may have thousands of inputs and outputs. A special high speed serial I/O link is used so that racks can be distributed away from the processor, reducing the wiring costs for large plants.
User interface See also: User interface See also: List of human-computer interaction topics PLCs may need to interact with people for the purpose of configuration, alarm reporting or everyday control. A Human-Machine Interface (HMI) is employed for this purpose. HMIs are also referred to as MMIs (Man Machine Interface) and GUIs (Graphical User Interface). A simple system may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. More complex systems use a programming and monitoring software installed on a computer, with the PLC connected via a communication interface.
Communications PLCs have built in communications ports, usually 9-pin RS-232, but optionally EIA-485 or Ethernet. Modbus, BACnet or DF1 is usually included as one of the communications protocols. Other options include various fieldbuses such as DeviceNet or Profibus. Other communications protocols that may be used are listed in the List of automation protocols. Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser. PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI devices such as keypads or PC-type workstations.
Programming
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Under the IEC 61131-3 standard, PLCs can be programmed using standards-based programming languages. A graphical programming notation called Sequential Function Charts is available on certain programmable controllers. Initially most PLCs utilized Ladder Logic Diagram Programming, a model which emulated electromechanical control panel devices (such as the contact and coils of relays) which PLCs replaced. This model remains common today. IEC 61131-3 currently defines five programming languages for programmable control systems: FBD (Function block diagram), LD (Ladder diagram), ST (Structured text, similar to the Pascal programming language), IL (Instruction list, similar to assembly language) and SFC (Sequential function chart). These techniques emphasize logical organization of operations. While the fundamental concepts of PLC programming are common to all manufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different models may not be directly compatible.
PLC compared with other control systems PLCs are well-adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods, customized control systems are economic due to the lower cost of the components, which can be optimally chosen instead of a "generic" solution, and where the non-recurring engineering charges are spread over thousands or millions of units. For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an electromechanical cam timer costing only a few dollars in production quantities. A microcontroller -based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies, input/output hardware and necessary testing and certification) can be spread over many
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