Technical information foundation fieldbus

Technical information foundation fieldbus - Mạng Truyền Thông Foundation Fieldbus

Part 4 Communication FOUNDATION Fieldbus Technical Information 4 AI 110 AO 110 PID 110 Part 1: Fundamentals Part 2: Self-operated Regulators Part 3: Control Valves Part 4: Communication Part 5: Building Automation Part 6: Process Automation Should you have any further questions or suggestions, please do not hesitate to contact us: SAMSON AG Phone (+49 69) 4 00 94 67 V74 / Schulung Telefax (+49 69) 4 00 97 16 Weismüllerstraße 3 E-Mail: schulung@samson.de D-60314 Frankfurt Internet: http://www.samson.de Technical Information Foundation Fieldbus Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Historical development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 User organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Approval of devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Performance features . . . . . . . . . . . . . . . . . . . . . . . . . 8 Layered communications model . . . . . . . . . . . . . . . . . . . 10 Physical layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 H1 bus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 • EEx-i instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 High Speed Ethernet (HSE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Bridge to H1-HSE-Kopplung. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Communication stack . . . . . . . . . . . . . . . . . . . . . . . . 18 Link Active Scheduler – LAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Communication control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 • Scheduled data transmission. . . . . . . . . . . . . . . . . . . . . . . . . . . 19 • Unscheduled data transmission . . . . . . . . . . . . . . . . . . . . . . . . . 23 • Communication schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Application layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 • Fieldbus Access Sublayer (FAS). . . . . . . . . . . . . . . . . . . . . . . . . 26 • Fieldbus Message Specification (FMS) . . . . . . . . . . . . . . . . . . . . 27 User application. . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Block model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3 Part 4 ⋅ L454EN SAMSON AG ⋅ 00/05 CONTENTS Device descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 System management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 System configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Appendix A1: Additional literature . . . . . . . . . . . . . . . . . . . . . . . . . 38 4 Communication ⋅ FOUNDATION Fieldbus SAMSON AG ⋅ V74/ DKE CONTENTS Introduction The F OUNDATION fieldbus can be flexibly used in process automation appli- cations. The specification supports bus-powered field devices as well as al- lows application in hazardous areas. The Fieldbus FOUNDATION’s slogan ‘ . dedicated to a single international fieldbus’ expresses the organization’s claim to establishing an international, interoperable fieldbus standard. Fieldbus technology replaces the expensive, conventional 4 to 20 mA wiring in the field and enables bidirectional data transmission. The entire communi- cation between the devices and the automation system as well as the process control station takes place over the bus system, and all operating and device data are exclusively transmitted over the fieldbus (see also Lit./4/). The communication between control station, operating terminals and field devices simplifies the start-up and parameterization of all components. The communication functions allow diagnostic data, which are provided by up-to-date field devices, to be evaluated. The essential objectives in fieldbus technology are to reduce installation costs, save time and costs due to simplified planning as well as improve the operating reliability of the system due to additional performance features. Fieldbus systems are usually implemented in new plants or existing plants that must be extended. To convert an existing plant to fieldbus technology, the conventional wiring can either be modified into a bus line, or it must be replaced with a shielded bus cable, if required. Note: To ensure troublefree operation, the communication system must be designed and configured by experts. For this purpose, a variety of assistance as well as comprehensive documentation can be obtained. This Technical In- formation does not claim to replace this type of support, but aims at explain- ing the basic principle of operation of the FOUNDATION fieldbus as well as its special characteristics to users, who have an interest in this technology. It must also be noted that the FF specification is not yet completed at this stage – November 1999 – so that the facts presented here can be subject to future changes. 5 Part 4 ⋅ L454EN SAMSON AG ⋅ 00/05 fieldbus for process automation applications fieldbus technology saves time and reduces costs Historical development In 1992 an international group, the ISP – ‘Interoperable Systems Project’, was founded with the intention to create an internationally uniform fieldbus standard for use in hazardous environments. At the same time, the manufac- turers and users of the French FIP (Flux Information Processus; previously: Factory Instrumentation Protocol) established the international user organi- zation WorldFIP. Together with the FIP North America, they were a strong counterweight to the ISP consortium. In 1994, for technical, economic and political reasons, the ISP and the WorldFIP merged to form the Fieldbus FOUNDATION. The aim of the Fieldbus FOUNDATION was and is to create a single, international fieldbus standard for hazardous environments which will find widespread use as IEC standardized fieldbus. The same goal is pursued by the PROFIBUS user or- ganization with its PROFIBUS PA fieldbus. While the PROFIBUS PA has its roots and its largest user community in Europe, the FOUNDATION fieldbus manufacturers and users are concentrated in America and Asia. The Fieldbus FOUNDATION utilized some elements from the FIP for the specification of their FOUNDATION fieldbus (FF) as well as – similar to PROFIBUS PA – details from the ISP specification. This is why the physical bus design of both fieldbus systems is the same. Also, the device interface for ap- plication, which is based on function blocks, exhibits many common fea- tures. This is due to the fact that both systems have similar ambitions. However, when taking a closer look and comparing the system functions, it can be seen that there are also great differences (see also Lit. /6/). 6 Communication ⋅ FOUNDATION Fieldbus SAMSON AG ⋅ V74/ DKE Fieldbus F OUNDATION emerged from ISP and WorldFIP same bus design as PROFIBUS-PA User organization The Fieldbus FOUNDATION is an independent not-for-profit organization which aims at developing and maintaining an internationally uniform and successful fieldbus for automation tasks, the FOUNDATION fieldbus. Mem- bers include users and manufacturers of field devices and automation sys- tems. The Fieldbus FOUNDATION incorporates various workshops which are responsible, among others, for technical support, marketing and support of the members. Approval of devices The Fieldbus is an open bus standard which enables devices of different manufacturers to be integrated in one system and, if required, interchanged (interoperability). This is only feasible when all the devices exactly meet the specification. Devices approved by the Fieldbus FOUNDATION are a guar- antee for the user and the manufacturer that they comply with the specifica- tion. 7 Part 4 ⋅ L454EN SAMSON AG ⋅ 00/05 Fig. 1: Logo of Fieldbus FOUNDATION members approval confirms compliance with the specifications independent not-for- profit organization Performance features The F OUNDATION fieldbus provides a broad spectrum of services and func- tions compared to other fieldbus systems: 4 intrinsic safety for use in hazardous environments 4 bus-powered field devices 4 line or tree topology 4 multi-master capable communication 4 deterministic (predictable) dynamic behavior 4 distributed data transfer (DDT) 4 standardized block model for uniform device interfaces (interoperability, interchangeability’) 4 flexible extension options based on device descriptions The characteristic feature of distributed data transfer enables single field de- vices to execute automation tasks so that they are no longer ‘just’ sensors or actuators, but contain additional functions. For the description of a device’s function(s) and for the definition of a uniform access to the data, the F OUNDATION fieldbus contains predefined function blocks (see ‘User application’ on page 29). The function blocks implemented in a device provide information about the tasks the device can perform. Typi- cal functions provided by sensors include the following: ‘Analog Input’ or ‘Discrete Input’ (digital input). Control valves usually contain the following function blocks: ‘Analog Output’ or ‘Discrete Output’ (digital output). 8 Communication ⋅ FOUNDATION Fieldbus SAMSON AG ⋅ V74/ DKE important characteristics predefined function blocks sensors control valves The following blocks exist for process control tasks: ‘Proportional/Derivative’ (PD controller) or ‘Proportional/Integral/Derivative’ (PID controller). If a device contains such a function block, it can control a process variable in- dependently. The shift of automation tasks – from the automation level down to the field – results in the flexible, distributed processing of control tasks. This reduces the load on the central process control station which can even be replaced en- tirely in small-scale installations. Therefore, an entire control loop can be im- plemented as the smallest unit, consisting only of one sensor and one control valve with integrated process controller which communicate over the F OUNDATION fieldbus (see Fig. 2). The enhanced functionality of the devices leads to higher requirements to be met by the device hardware and comparably complex software implementa- tion and device interfaces. 9 Part 4 ⋅ L454EN SAMSON AG ⋅ 00/05 Fig. 2: Complete control loop based on the F OUNDATION fieldbus AI 101 PID 101 AO 101 H1 bus HSE flexible, decentralized process control control processes Layered communications model The F OUNDATION specification is based on the layered communications model and consists of three major functional elements (Fig. 3a): 4 Physical Layer 4 Communication “Stack” 4 User Application The User Application is made up of function blocks and the device descrip- tion. It is directly based on the Communication Stack. Depending on which blocks are implemented in a device, users can access a variety of services. System management utilizes the services and functions of the User Applica- tion and the application layer to execute its tasks (Figs. 3b and 3c). It ensures the proper cooperation between the individual bus components as well as 10 Communication ⋅ FOUNDATION Fieldbus SAMSON AG ⋅ V74/ DKE Fig. 3: Structure and description of the FF communication layers user application user application function block model device descrip- tion system m a n a g e m e n t application layer presentation layer session layer transport layer network layer data link layer physical layer physical layer physical layer communication stack F OUNDATION Fieldbus F OUNDATION Fieldbus data link layer fieldbus access sublayer (FAS) fieldbus message specification (FMS) 7 6 5 4 3 2 1 a) c) b) system management