Foundation Fieldbus (FF)

The number of field units and automation components with FF inter-faces is growing rapidly. Together with such fast new Ethernet technology such as the H2 Bus that combines the slow H1 buses, fieldbus foundation will help more and more applications to automate. This will increasingly make it an alternative to PROFIBUS-PA.

Advantages of fieldbus technology

Fieldbus technology is contiuously replacing 0/4...20mA technology. This results in functional advantages coupled with cost-cutting potential. The possible savings shown below for installation costs have been demonstrated time and time again during actual applications. Tests show a savings potential of approximately 25% for complete automation. Operating costs show similar savings.

Functional benefits include: High resolution of measured value, no loss of accuracy, highly reliable data transmission, higher dependability due to self-tests, multifunctional field units, maintenance support.

The number of field units and automation components with FF inter-faces is growing rapidly. Together with such fast new Ethernet technology such as the H2 Bus that combines the slow H1 buses, fieldbus foundation will help more and more applications to automate. This will increasingly make it an alternative to PROFIBUS-PA.

FOUNDATION Fieldbus (FF) is an entirely digital serial communication system that can transfer data in both directions, that is to say it func-tions bidirectionally. This fieldbus system can also be used as a Local Area Network (LAN) for field and automation devices in factory and process automation. The fieldbus is the basic network in the overall communication hierarchy of a system and covers vertical integration right up to total plant control.

In contrast to manufacturer-specific communication networks, FOUNDATION Fieldbus is neither controlled by a single company nor by a single country?s Standards Committee. Foundation Fieldbus technology is controlled solely by the Fieldbus Foundation, of which KROHNE was one of their early members. The Fieldbus Foundation is a non-profit organisation that consists of more than 120 manufacturers together with a number of users.

The technology of the Foudation Fieldbus

FOUNDATION Fieldbus can be divided into two parts. For the field level, including Ex-applications, an H1-Bus is utilised that is based upon the Physical Layer IEC 61158-2, also used in PROFIBUS-PA. Serving as ?collective track? of the relatively slow H1 buses is the super-fast High Speed Ethernet Fieldbus, whichwas defined in the Fieldbus Foundation. This allows entire ? even very large ? plants to be networked. With the H1 fieldbus solution in addition to the physical level 1 the data transfer protocol and the application levels are also defined. Network and system management is added to this. This System Management is used for the logical integration of field devices at the plant control level. The following functions are covered:

	Automatic allocation of the physical station address
	Automatic connection between outputs and inputs of the functional blocks
	Synchronisation of applications (control via several stations)
	Clock synchronisation
	Functional blocks and Device Discription Language

It is important that not only communication but also applications be defined. This requires functional blocks and a Device Description Language that is prescribed for each device. Functional blocks represent standardised applications.

With the aid of these blocks and the DDL, the interoperability (not the interchange-ability as with the PROFIBUS-PA-Profile V3.0) of the devices of various manufacturers is guaranteed.

A library containing over 20 functional blocks has been established that covers virtually all applications. The HART® Device Description Language has been utilised and a number of functions added. This describes not only device parameters but also all functional block parameters. Thus it is possible for the language to be used for a variety of FF devices as a manufacturer-independent operating tool.

The advantages of Foundation Fieldbus at a glance:

	Interoperability via Device Description
	Definition of a broad range of functional blocks
	Control function in field device possible
	100% deterministic regulations are possible via the Fieldbus
	Intensive conformity tests of communication software
	Interoperability test in test lab is obligatory
	Only certified devices may use the FF-label.