Introduction to Fieldbus Technology

Transcription

1 EEET2105 Industrial Automation Introduction to Fieldbus Technology Dr. Alan Wong

2 EEET2105 PLC Profibus Foundation Fieldbus Industrial Data Communication

3 Fieldbus technology is LAN for instruments in process, manufacturing and building automation industries. Digital network in the base level of the hierarchy of a plant More than one standards available for communication between the field instruments, master controllers and existing computer networks.

4 Connecting Shop Floor to Computer Network System Plant Wide Network Departmental Computer System Control System/ LAN Automation and Display System Fieldbus Network Field Devices and Instrumentations

5 Example of Fieldbus System: Profibus ET 200S S7 300S

6 Automation Network using Foundation Fieldbus

7 Automation Network using Profibus

8 History of Fieldbus Digital communication in process and control industry started in the 80 s. Purpose :- to replace existing 4-20mA technology. Many different protocols were created by vendors with the purpose of monopolising the automation market. Problem arises due to this phenomenon and leads to non-interoperability between devices produced by different vendor. Worse still, the documentations on the operation of these protocols are not available to the public.

9 History (cont.) - Disadvantages Since there were only limited range of product from one vendor, it was common to mix and match equipment for one project because one vendor is never best at everything. However, each vendor has different protocol for their products and caused plants to have isolated islands of automation system that could not communication with each other. Example: DCS and PLC. These two devices are not sharing information due to incompatibility and therefore building a larger and more efficient network is almost impossible!

10 History(cont.) - Solution Temporary Solution :- Third Party device driver. However, each driver solves the problem for one combination of hardware and software. In many cases, the subsystem has to fall back on conventional analog system.

11 History(cont.) Another problem with a proprietary system had been the locked-in by manufacturers. Low set-up cost and extremely high replacement cost Furthermore, due to incompatibility, vendors were unable to compete with other suppliers. Incorporating several protocols in one device would also drive the cost of the product up. Up to the present moment, there is no one fieldbus standard to which all manufactures of automation and control devices conform to.

12 Direct Digital Control System Computer Terminal Control Room Field Devices Direct Digital Control (DDC) System

13 Distributed Control System Computer Terminal Controller Controller Controller Control Room Field Field Devices Distributed Control System (DCS)

14 Fieldbus System Computer Terminal Distributed Control System (DCS) Control Room Field Fieldbus Devices Fieldbus System

15 Fieldbus Technology 1. Digital replacement of 4-20mA 2. Control, alarm, trend, and other functions distribution to field devices 3. Interoperability and Multiple-Vendor System 4. Openness, where specifications available without licensing agreement.

16 Benefits of Fieldbus Technology

17 Benefits - More information Controller Controller I/O Subsystem Valves Drives Valves Drives Traditional 4-20mA one variable, one direction Fieldbus Multiple variables, bi-direction More than one variables can be sent to the master controller

18 Benefits Less Wiring Controller Controller I/O Subsystem IS IS IS Valves Drives Valves Drives Traditional 4-20mA One IS barrier and one wire for each device Fieldbus One IS Barrier and one wire for many devices Fieldbus allows many devices to share a single pair of comms. cable

19 Benefits Better Diagnostic Capability Controller Controller I/O Subsystem Valves Drives Valves Drives Traditional 4-20mA View stops at I/O Subsystem Fieldbus View extends into instrument More critical info. from fieldbus devices can help to reduce downtime and improve safety

20 Benefits Less System Hardware Controller Controller PID I/O Subsystem AI Valves Drives Valves Drives Traditional 4-20mA Fieldbus Fieldbus devices use standard function blocks to implement the control strategy. AI, AO, PID may be integrated into the fieldbus devices.

21 Classes of Fieldbus Fieldbus devices and network can be categorised into three network-oriented classes: Bit (sensors) Byte (device) Message (field)

22 Classes of Fieldbus

23 Classes of Fieldbus Bit Simple operations such as on/off, high/low Example : proximity sensor, contact closure, push buttons, and etc. Binary one and zero are used to represent the current state of the device. The network of such devices is called Sensor Bus **Example: ASI Bus Binary Message

24 Classes of Fieldbus Binary Binary oriented systems are used in much broader applications such as motor starters, barcode readers, VSD and etc. Larger information content, larger addressing capability This network of device is known as Device Bus Example: Device Net

25 Classes of Fieldbus Message Message oriented systems refers to systems containing over 16 bytes per message Examples: PCs, PLCs, Engineering workstation Capability to upload and download system configuration. Example of these systems: Profibus, Foundation Fieldbus

26 The Importance of OSI Layer in Fieldbus Technology

27 OSI Reference Model Faced with the proliferation of closed network systems, the Internatinal Organisation for Standardisation (ISO) defined a Reference Model for Communication between Open Systems in This has become known as the OSI model (ISO7498). The OSI model is essentially a data communication management structure which breaks data communication down into a manageable hierarchy of seven layers. Each layer has a defined purpose and interfaces with the layers above and below it. By laying down standards for each layer, it allowed the system designers to develop protocols for each layer independent of each other. The OSI reference model is not a protocol or set of rules for how a protocol should be written, but rather an overall framework in which to define protocols.

28 OSI 7 Layers Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

29 OSI 7 Layers Application (layer 7): the provision of network services to the user s application program Presentation (layer 6): Map the data representation into an external data format that will enable correct interpretation of the information on receipt Session (layer 5): Control of the communication between the users. This includes the groups together of messages and the coordination of data transfer between grouped layers. Transport (layer 4): The management of communication between two end systems Network (layer 3): Responsible for the control of the communications network. Functions include routing of data, network addressing, fragmentation of large packets, congestion and flow control.

30 OSI 7 Layers Data Link (layer 2): Responsible for sending a frame of data from one system to another. Attempts to ensure that errors in the receive bit stream are not passed up into the rest of the protocol stack Physical (layer 1): Defined the electrical and mechanical connections at the physical lavel or the communication channel itself. Functional responsibilities include modulation, multiplexing, and signal generation.

31 OSI Communication Channel The OSI Layer Transmitter Receiver Application Layer Application Layer Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Network Layer Network Layer Data Link Layer Data Link Layer Physical Layer Physical Layer

32 Example: Sending Message String Engineers are Cool! message Application AH message Presetation PH AH message Session SH PH AH message Transport TH SH PH AH message Network NH TH SH PH AH message Data Link DLH NH TH SH PH AH message DLH Physical PhH DLH NH TH SH PH AH message DLH PhH

33 Fact: Fieldbus - OSI Layer Profibus uses layer 1, 2 and 7 Foundation Fieldbus uses layer 1, 2 and 7

34 Other Protocols The objectives of this three lectures is to provide students with basic knowledge on different industrial communication standards used in industry. Although we only focus on two standard in this course, namely profibus and foundation fieldbus, there are many other standards available on the market today. These standards include: Devicenet Industrial Ethernet Lonworks CanBUS MODBus HART AS-I