Studied by 6 peoplePROCTECH 4IC3
Elements of Industrial Automation Systems
Enterprise Level: • Other Support Systems (Energy, Operator & Machine-Condition Monitoring systems) (External) • Manufacturing Support Systems Factory Level: • Manufacturing Systems • Automation and Control Technologies • Material Handling Technologies • Manufacturing Processes & Assembly Operations • Safety Systems (External) • Buildings & Facilities (External) In-between: • Quality Control Systems
ISA Automation Systems Hierarchy
International Society of Automation (ISA) defined four hierarchical functions of automation systems in ISA-95 standard
ISA Automation Systems Hierarchy Levels
• Enterprise • Manufacturing • Supervision • Process Control • Group Controls • Unit Controls • Field
ISA Automation Systems Hierarchy - Enterprise
Set production goals, plan resources, coordinate different sites, manage orders (Through ERP - Enterprise Resource Planning)
ISA Automation Systems Hierarchy - Manufacturing
Manages execution, resources, workflow, quality supervision, production scheduling, maintenance. (Through MES -Manufacturing Execution System)
ISA Automation Systems Hierarchy - Supervision
Supervise the production and site, optimize, execute operations visualize plants, store process data, log operations, history (open loop; Through SCADA)
SCADA
Supervisory Control and Data Acquisition
SCADA - Supervisory Control
A control scheme whereby a computer or controller monitors and intermittently downloads programs, sets sub-goals, or adjusts control parameters of a lower-level automatic controller. Supervisory controllers are usually PCs - PCs can easily do supervisory control while doing the data acquisition.
SCADA - Data Acquisition
The process of collecting data from the system through some manual or automatic means for the purpose of producing reports for operating, supervisory, maintenance, or accounting disciplines.
SCADA
displays the current state of the process (visualization)
display the alarms and events (alarm log, logbook)
display the trends (historians) and analyze them
display handbooks, data sheets, inventory, expert system (documentation)
allows communication and data synchronization with other centers
ISA Automation Systems Hierarchy - Process Control
Can be defined further as Group Control and Unit Control
ISA Automation Systems Hierarchy - Group Control
Controls a well-defined part of the plant (closed loop, except for intervention of an operator)
ISA Automation Systems Hierarchy Group Control Includes
• Coordinate individual subgroups • Adjust set-points and parameters • Command several units as a whole
ISA Automation Systems Hierarchy - Group Control Includes
• Usually coordinates the activities of several unit controls • PLC based control is often hierarchical (supervisory) control • It can be also be peer-to-peer (from unit control to unit control, or a Distributed Control System (DCS))
Distributed Control System (DCS)
Distributed Control System refers to having one control unit/controller for multiple units, or units containing different PLCs/elements that interact with each other and provide information and system control.
Distributed Control System (DCS) Features
• Implemented using a controller • Often has multiple redundant communication and I/O modules • Often has multiple redundant controllers
PLC Based Distributed Control
• A design approach in which factory or machine control is divided into several sub-systems • Each managed independently by a unique programmable controller, yet all interconnected to form a single entity. • Individual subsystems may be interconnected via communications networks
ISA Automation Systems Hierarchy - Unit Control
Controls the regulation, monitoring and protection of parts of a group (closed loop except for maintenance)
ISA Automation Systems Hierarchy Unit Control Includes
• Measure: Sampling, scaling, processing, calibration • Control: regulation, set-points and parameters • Command: sequencing, protection and interlocking
ISA Automation Systems Hierarchy - Unit Control
Consists of compete machines that carries out specific tasks.
Process Control: Unit level - Programmable Logic Controller Advantages
• Easy to use and install • Inexpensive • Electricians can diagnose and upgrade • Flexible - Easy to expand installation
ISA Automation Systems Hierarchy - Field
Includes data acquisition (Sensors & Actors) and data transmission. There is no processing except measurement correction and any built-in protection.
ISA Automation Systems Hierarchy - Field
Is in direct interaction with the plant's hardware (Primary technology); Valves and regulators (Actuators), as well as transmitters (Sensors)
Explain the differences between the terms DCS, group control, and SCADA.
DCS - Is one controller for multiple units or units with different PLCs that coordinate with each other to provide system control
Group Control - Usually coordinates the activities of several unit controls
PLC based group control is often hierarchical (supervisory control)
It can be also be peer-to-peer (from unit-to-unit control; distributed control system)
SCADA is a high-level controller that supervises lower-level controllers; and collects data from the system for the purpose of producing reports for operations, maintenance, or accounting.
How do Industrial Networks support DCS, Group Control, and SCADA
The industrial network architecture is hierarchical regardless of whether it is based on classical or Ethernettechnology.
Fieldbuses connect the field level to the unit controllers.
Unit controllers are interconnected through the process network to create a group control system. The network also connects lower level controller to the supervisory controller.
The supervisory controller usually also collects control data, thus the process network connect the unit and group control system to the SCADA level
The MES can be connected to the plant network, or it can be outside of the plant and connected to the plant network through a gateway like the ERP.
This shows that the industrial network architecture serves to provide necessary isolation and interconnection among the various levels of automation. The network allows process data from and to the field level to be shared among units to create group control systems which are configured as DCS or supervisory controllers. Furthermore, the network allows the control and field level data to be collected and stored at the supervisory level, creating a SCADA system.
LAN (Local Area Network)
Localized communication path between computers, file-servers, PLCs, and other devices
WAN (Wide Area Network)
Use public telecommunication systems to link LANs together.
WAN (Wide Area Network)
It is best for connecting controllers located in different areas. The size Does not depend on number of controllers or size of the network.
Circuit Switching
Temporary continuous connection is made across the network between two different points
Packet Switching
Transfer of packets of data (can contain 1560 bytes MAX).
Packet Switching
It enables multiple devices to share a single communication channel
Two types of packet switching
Datagram
Virtual circuit
Datagram Packet Switching
Each packet is independently routed (UNRELIABLE service).
Virtual Circuit Packet Switching
Data packets follow a pre-established route thus providing a reliable service called Connection Oriented Service (COS)
ISO Open System Interconnection (OSI) Communication Reference Model
A conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to their underlying internal structure and technology.
The Goal of the OSI Model
Achieve interoperability of diverse communication systems.
ISO OSI Communication Reference Model Layers
Application
Presentation
Session
Transport
Network
Data Link
Physical
OSI Layer - Application
This layer is responsible for services that directly support user applications, such as software for file transfers, database access, and e-mail.
OSI Layer - Application
This is the layer at which communication partners are identified (Is there someone to talk to?), network capacity is assessed (Will the network let me talk to them right now?), and that creates a thing to send or opens the thing received.
OSI Layer - Application
This layer is not the application itself, it is the set of services an application should be able to make use of directly, although some applications may perform application layer functions.
OSI Layer - Presentation
This layer is usually part of an operating system (OS) and converts incoming and outgoing data from one presentation format to another.
OSI Layer - Presentation
This layer is responsible for converting protocols, translating data, encrypting data, changing or converting character sets, and expanding graphics commands.
OSI Layer - Presentation
This layer manages data compression to reduce the number of bits that need to be transmitted.
OSI Layer - Session
This layer sets up, coordinates and terminates conversations. Services include authentication and reconnection after an interruption.
OSI Layer - Session
This layer allows two applications on different electronic devices to open, use, and close a connection called a session.
OSI Layer - Session
This layer carries out name-recognition and other functions, such as security, that are needed to allow two applications to communicate over the network. It also synchronizes user tasks by placing checkpoints in the data stream.
OSI Layer - Session
This layer implements dialog control between communicating processes, such as regulating which side transmits, when, and for how long.
Data Transmission Modes
Simplex
Half-Duplex
Full-Duplex
Simplex Data Transmission
A data transmission system in which data can only be sent in one direction only.
Half-Duplex Data Transmission
A data transmission system in which data can be sent in both directions but only one at a time.
Full-Duplex Data Transmission
A data transmission system in which data can be sent in both directions at the same time.
OSI Layer - Transport
This layer is responsible for breaking data down into smaller pieces, providing an additional connection level beneath the session layer.
OSI Layer - Transport
This layer manages the packetization of data, then the delivery of the packets, including checking for errors in the data once it arrives.
OSI Layer - Transport
This layer ensures that packets are delivered error free, in sequence, and without losses or duplications.
OSI Layer - Transport
At the sending device, this layer repackages messages, dividing long messages into several packets and collecting small packets together in one package.
OSI Layer - Transport
At the receiving device, this layer opens the packets, reassembles the original messages, and, typically, sends an acknowledgment that the message was received.
OSI Layer - Transport
This layer provides flow control and error handling, and participates in solving problems concerned with the transmission and reception of packets.
OSI Layer - Transport
On the Internet, TCP and UDP provide these services for most applications.
OSI Layer - Network
This layer handles the addressing and routing of the data; sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level.
What does UDP use for its Transportation Layer?
Datagram Packet Switching
What does TCP use for its Transportation Layer?
Virtual Circuit Packet Switching
OSI Layer - Network
This layer is responsible for addressing messages and translating logical addresses and names into physical addresses.
OSI Layer - Network
This layer determines the route from the source to the destination. It determines which path the data should take based on network conditions, priority of service, and other factors.
OSI Layer - Network
This layer manages traffic problems on the network, such as switching and routing of packets and controlling the congestion of data. If the network adapter on the router cannot transmit a data chunk as large as the source computer sends, this layer on the router compensates by breaking the data into smaller units.
OSI Layer - Network
Examples of this layer include:
IP
BACnet
CLNP (Connectionless Networking Protocol)
EIGRP (Enhanced Interior Gateway Routing Protocol)
ICMP (Internet Control Message Protocol)
OSI Layer - Data Link
This layer sets up links across the physical network, putting packets into network frames. This layer has two sub-layers, the Logical Link Control Layer, and the Media Access Control Layer.
OSI Layer - Data Link
The layer sends data frames from the network layer to the physical layer; controlling the electrical impulses that enter and leave the network cable.
OSI Layer - Data Link
On the receiving end, this layer packages raw bits from the physical layer into data frames.
OSI Layer - Data Link
This layer is responsible for providing error-free transfer of frames from one device to another through the physical layer. This allows it to anticipate virtually error-free transmission over the network connection.
OSI Layer - Data Link
Usually, when this layer sends a frame, it waits for an acknowledgment from the recipient. The recipient layer detects any problems with the frame that might have occurred during transmission. Frames that were damaged during transmission or were not acknowledged are then re-sent.
Media Access Methods
Network standards used to determine the way in which computers in a network communicate, includes communication media and topology
Media Access Method Categories
Master-slave (client-server) method
Contention method
Token passing method
Hybrid method
Master-Slave (client-server) Method
The simplest Media Access Method
Master-Slave (client-server) Method
▪ Only the master initiates communication ▪ There must be only one master (talk-end) on the network, the rest are slaves.
Contention Method
Based on first come first served - Carrier Sense Multiple Access or Collision Detection (CSMA/CD). This method is a probabilistic system.
Token Passing Method
A Token is passed from node to node with predefined sequence. This method is Deterministic - a node can access the network for a max predetermined time.
Hybrid Method
A combination of the Token Passing and Master Slave methods.
Hybrid Method
A Token is passed from master to master with predefined sequence. The master with token can initiate communication with its slaves; hence the name Master-Slave Token Passing (MSTP).
Frame Error Checking - Cyclic Redundancy Check
A binary message is converted to a polynomial (from LSB to MSB) and then divided by another predefined polynomial called the key. The remainder from this division is the CRC.
Frame Error Checking - Parity Check
Append 0 or 1 to achieve even or odd parity (i.e. even or odd number of 1s). For Even parity, if number of 1s received is odd then and error has occurred.
Frame Error Checking - Checksums
Bytes in packets that constitute a message are added arithmetically. A checksum number is appended to the packet sequence so that the sum of data plus checksum is zero. When received, a local microprocessor may add the packet sequence along with the checksum. o If the sum is non-zero, an error has occurred. o If the sum is zero, it is highly unlikely (but not impossible) that any data has been corrupted during transmission.
OSI Layer - Physical
This layer conveys the bit stream through the network at the electrical, optical or radio level.
OSI Layer - Physical
This layer provides the hardware means of sending and receiving data on a carrier network. For LANs Ethernet is the main type in use.
OSI Layer - Physical
This layer transmits the unstructured, raw bit stream over a physical medium (such as the network cable). It is totally hardware-oriented and deals with all aspects of establishing and maintaining a physical link between communicating electronic devices.
OSI Layer - Physical
This layer also carries the signals that transmit data generated by each of the higher layers.
OSI Layer - Physical
This layer defines how the cables are attached to the NIC.
OSI Layer - Physical
The layer provides data encoding and bit synchronization, responsible for transmitting bits (zeros and ones) from one computer to another, ensuring that when a transmitting host sends a 1 bit, it is received as a 1 bit, not a 0 bit. Because different types of media physically transmit bits (light or electrical signals) differently, this layer also defines the duration of each impulse and how each bit is translated into the appropriate electrical or optical impulse for the network cable.
What is the problem with the OSI model in Industrial Networks? What is it's solution?
Carrying out all the tasks associated with the seven layers of the OSI model makes systems too slow and un-deterministic for most industrial applications. A Reduced OSI Model for Industrial Applications was then developed.
The Reduced OSI Model Layers
Application
Data Link
Physical
What is the result of the Reduced OSI Model?
Even with reduced OSI model, different industrial applications need different amount of emphasis on different OSI model layers. Many industrial protocols as a result aim at different applications.
A message is made up of the following two bytes 10001110 and 11011011. What is its checksum?
10010111
Legacy Industrial Networks
Historically, these kinds of industrial networks or network protocols have been developed by different companies and later became standards.
Why do manufacturers of industrial automation equipment continue to implement legacy (old) industrial networks?
Big automation companies support them. Industrial devices that use legacy network protocols tend to have a long useful life. Legacy industrial network protocols exhibit a high degree of determinism with low cycle times, typically less than 15 milliseconds.
What are most legacy networks designed for?
Data communication among sensors, actuators, remote I/O modules, and controllers. I/O data tends to be captured as short strings (small data) with many cases no more than 32 bytes per message, but vertical integration to plant level leads to need for communication protocol with capability to carry complex data.
Examples of Legacy Networks
Modbus serial and Modbus Plus
CANBUS and DeviceNet
Profibus-PA & Profibus-DP
MODBUS Protocol
This protocol was created by MODICON (now Schneider Electric) in 1979 to connect PLCs to programming tools. It is now widely used to establish master-slave communications between intelligent devices.
MODBUS Protocol
This protocol is independent of the physical layer. It can be implemented using RS (Recommended Standard) 232, RS422, RS485, fiber, radio, cellular, Ethernet etc.
MODBUS Protocol
This protocol is a lower midlevel network, usually used to integrate small controllers such as small PLCs and microcontrollers with large complex controls such as advance PLCs and DCS systems. Some flavors of it are used at the plant level of the IEC automation hierarchy.
MODBUS Protocol
This protocol/network can carry more data than AS-i network, therefore it can be used at the field level of the automation system where the amount of the data that need to be transferred is higher than at the sensor level.
MODBUS Protocol Features
o Topology: Bus with line terminations o Maximum distance: With RS485: 1000 m without repeater o Data rate: From 1,200 to 115 Kbits/s o Max. no. of devices: With RS485: 32, master included o Method of accessing the medium: Master slave o Transmission method: Messaging o Max. useful data size: 120 words o Transmission security: LRC or CRC, start and stop delimiters, parity bit and continuous stream
Note
Flashcard