Quick Overview of FOUNDATION Fieldbus


The Concept

FOUNDATION Fieldbus is an open standard for networking input, output, and process control devices that, when configured, can run independently of a computer system. Fieldbus can operate independently of a computer system because devices called Link Masters (such as the FP-3000) have processing capability and are capable of controlling the bus. There are also basic devices that cannot control the bus, but provide input, output, and/or additional functionality, such as PID or expression block execution.

You can have multiple Link Masters on the bus; however, only one Link Master can control the bus at a time. The device that is currently controlling the bus called the Link Active Scheduler (LAS). This device has the schedule for all the devices and sends commands to other devices, telling them when to broadcast data. The LAS also publishes time information and allocates time to devices to allow them to broadcast unscheduled messages, such as alarms.

The Connections

Only two lines connect devices on the bus. These lines can also be powered with a DC offset so that devices can draw power and get control information over the same lines. At most, you can connect 32 devices per segment of the bus. With a single port on an interface board, you can have a maximum of 5 segments if you use repeaters to connect the devices. In this case, the 5 segments (connected by four repeaters) are treated as one segment by the NI-FBUS Configurator, both for configuration and licensing purposes. The default software license allows for four segment (port) connections. See the publication “Wiring & Installation 31.25 kbit/s, Voltage Mode, Wire Medium” from the Fieldbus Foundation (http://www.fieldbus.org) for more information on the wiring specification. For a more readable document, see the Fieldbus webpage of Relcom, the company that provides the power hubs shipped by National Instruments with our Fieldbus interfaces (http://www.relcominc.com/fieldbus/).

National Instrument's Role

National Instruments provides both software and hardware for FOUNDATION Fieldbus.

National Instruments provides interface boards, for the ISA bus (AT-FBUS), PCI bus (PCI-FBUS), and PCMCIA (PCMCIA-FBUS). Each National Instruments interface board comes with the NI-FBUS Communications Manager software that the board uses to communicate over the bus.

National Instruments provides the NI-FBUS Configurator software you use to configure the segment and develop your control strategy. See the article "Why do I need Configuration Software?" for more information on its functionality.

National Instruments provides the FP-3000, a Fieldbus H1 device that, among other things, allows users to integrate legacy 4-20 mA devices into a FOUNDATION Fieldbus system. For more information, see the related link Functionality of the FP-3000 Network Module.

National Instruments provides roundcards for device development. Contact Fieldbus, Inc., our device development Value Added Reseller, for purchasing information.

See Also:
Functionality of the FP-3000 Network Module