Basics of Foundation Fieldbus

FOUNDATION FIELDBUS All digital serial two-way communication system –interconnects field equipment (sensors, actuators and controllers) – architecture for building inter operable distributed real time control systems. Multidrop wiring ( 32 devices on a single pair of wires (called a segment) Multivariable Instruments (Multiple variables from one field device ) Two-way communication New types of information Control in the field Interoperability :Device from different suppliers can be communicate with each other and perform their function in multi-vendor environments. (standardize communication protocol from Physical layer through Application Layer) Interchangeability: Device from different suppliers can be functionally interchanged by providing the same functionality for the same type of devices. (Standardize various function blocks) What user wants is to provide interoperability and the same basic functionality for the same type of devices and room for innovation by suppliers for additional unique functionality (Provide a common way to describe/understand suppliers specific features (DDL). Foundation fieldbus communications model The Physical Layer Data Link Layer and Application Layers The User Layer Physical Layer: Translating messages into Physical signals on the wire –and vice versa Physical Layer: Provides the common Electrical Interface for all foundation fieldbus devices. (H1 segments -Power supply 9-32 Volts DC Power and 15-20 mA of current per device – communication rate –31.25 kbaud –32 devices per segment; upto 240 devices total with repeaters. Data link and Application layers: Control transmission of data on the fieldbus. Standard way of packaging the data as well as managing the schedule for communication and function-block execution. User Layer: contains transducer block, resource block and function blocks that describe and execute –device capabilities such as control and diagnostics. Device descriptions enable the host system to interact with and understand these blocks without custom programming. Benefits of Fieldbus System can be built from devices manufactured by different vendors No single company controls the evolution of the standard Interoperability Reduced Cost Less wiring installation and maintenance cost because of multi-drop Better diagnostics through software Control distributed in the field More data available from the devices Diagnostic Data Multiple variables