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Yokogawa Electric Corporation





An Introduction to Fieldbus Technology

FOUNDATION™ fieldbus - the path to the future

The Internet is having a major impact on information flows. Yesterday's hierarchical systems with vertical information flows are being replaced by systems that have a flatter structure and more diverse information flow patterns. In today's world, it is essential to construct networks that are integrated with the Internet and can make use of the information available on it.

More and more today, process instrumentation is being field networked. As both the quantity and quality of field information increase, new instrumentation technologies will surely develop. The following table summarizes the key differences between conventional systems and field networked systems.

  Field wiring Info.
Quantity of info. Info.
Control functionality Maintenance location Maintenance type
Conventional 4 to 20 mA system Point-to-point Uni-directional Single data value Measure-ment numerical value Centered on a control system Mainly in the field Corrective maintenance
Field network Multi-drop Bi-directional Multiple data values Various data types Optimally allotted to control system and/or field devices From a remote location Predictive maintenance

The field signals used in process instrumentation have been standardized so that control systems and field devices from a variety of suppliers can be interconnected using standard 4 to 20 mA analog signals. The FOUNDATION™ fieldbus standard developed by the Fieldbus Foundation™ constitutes the next level of standardization and it is designed to meet modern needs. In addition to having interconnectivity equivalent to that available using 4 to 20 mA analog signals in a conventional field network, FOUNDATION™ fieldbus allows multiple devices to be connected to a single FOUNDATION™ fieldbus, permits the interactive communication of various types of information, and enables the distribution in the field of intelligent functions including self-diagnostics and control functionality.

When FOUNDATION™ fieldbus was first proposed, more attention was given to its ability to convey multiple field signals over a single cable and the benefit this would have in reducing wiring costs. But now the focus is on its ability to transmit various types of information in addition to field signals and to distribute intelligence to distributed field devices. These features enable remote monitoring, real-time self-diagnostics, and proactive maintenance of field devices, as well as plant resource management using field communication. This will enable the costs of operating instrumentation systems to be greatly reduced.