FIELDBUS FOUNDATION RECOGNISES GROWING INTEREST IN 'CONTROL IN THE FIELD'
12 April 2005 - Fieldbus Foundation

Production plants installing a FOUNDATION fieldbus system can implement both batch and logic control at the field level. FOUNDATION technology enables primary PID and secondary PID (cascade) functions, as well as feed/forward and lead/lag, to reside in smart control valve positioners/controllers. This approach eliminates the need to load PID algorithms in host systems, and frees plant resources to handle more complex data management and operational analysis.

The FOUNDATION fieldbus network architecture allows control to be distributed to the field at the H1 (31.25 kbit/s) level, or in High Speed Ethernet linking devices, which integrate H1 fieldbus segments into a high-speed Ethernet backbone. The linking devices function as a 'bridge' between HSE and H1 channels, interconnecting field devices to each other and to other hosts, and are an essential component for integrating system communication with direct I/O access and advanced control applications.

Locating control functionality in HSE linking devices unifies the control structure across the control room and process sub-systems. Linking devices can be situated in close proximity to the process where points of communications converge. Distributing control to the H1 or HSE layers in the field also minimises the effects of any loss or failure of supervisory control. The loss of a single device only affects a fraction of the overall control capabilities.

According to the Fieldbus Foundation's director of technology development, David A. Glanzer, control in the field is an effective solution for today's increasingly complex and demanding process design requirements. He said, 'By moving control functionality to the field, and implementing distributed FOUNDATION fieldbus linking devices connected by the HSE communication protocol, end users can restore single-loop integrity to their process and achieve a control system that is easier to define, engineer, procure, test, install and maintain.

Glanzer added, 'As end users have gained more familiarity with the capabilities and reliability of the technology, we are seeing a trend of distributing control across field devices. The inherent flexibility of the function block structure provides users with a significant opportunity to enhance the complexity of their control strategy and improve its reliability.'

John Rezabek, lead controls engineer for BP's Lima, Ohio, BDO production plant, is a leading industry proponent of field-level control for process automation. Rezabek stated, 'With control on the wire, end users can achieve a truly distributed automation architecture and minimise the need for redundancy at the host level. They can also reduce the footprint of control cabinets. FOUNDATION fieldbus' precise error handling, signal status propagation, and configurable fault tolerance make control in the field extremely robust. We've had over 70 loops running in field devices since June 2000 with no process shutdowns due to device failure.'

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