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 )
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
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