A fieldbus presentation and demo to UK contractors

Interest is growing from EPCs in learning more about fieldbus systems: Nick Denbow reports on a well attended Reading event organised by the Fieldbus Foundation in the UK for these contractors.

With many end users now specifying fieldbus systems in the projects referred to contractors, these users are looking to contractors to provide expertise and input in the development of the project.

The Fieldbus Foundation UK Committee followed up this interest with a recent seminar at the Madejski conference centre in Reading, West of London.

While the location and the presentations were aimed at project managers and engineers in the local EPCs, the objective was to demonstrate what users can gain from fieldbus systems.

The growth in interest in fieldbus information and training at all levels from the EPCs was shown by the size of the audience: over 60 engineers had been sent along 6 or more contractors, and one or two major oil and gas users.

A show of hands indicated that around 70% had not previously worked on a fieldbus project to date, but they were keen to learn.

Travis Hesketh of Emerson Process Management stressed that while all new plant designs using Foundation Fieldbus do gain from the approximate 50% reduction in engineering drawings, plus the faster commissioning speed and accuracy, with less terminals, the major CAPEX benefits have been realised by offshore installations.

Here there is a real measureable benefit by taking advantage of the smaller system footprint and the lower system weight, from reduced cabling and cabinets.

However for the land based user, the real business benefits are now realised as in better OPEX performance, performance of the plant to get better efficiency and productivity by using the intelligence available via the instrumentation and the communications system.

Foundation fieldbus delivers meaningful intelligence information to operations and maintenance personnel, in time for them to react effectively to a poorly performing control loop or a maintenance request on a valve or transmitter.

Examples were presented of some of the intelligent information now available as standard from FF transmitters and valves, that can provide performance warnings before the plant operations are affected.

A warning of reduced pneumatic supply pressure at a control valve (resulting possibly from an air leak, which could be located by a maintenance visit); a dual-sensor temperature transmitter indicating that one probe had failed, but where the second sensor continued to provide valid measurement signals, keeping the plant going; and a pH transmitter that knows when the glass of the probe needs cleaning, and signals this as a developing maintenance requirement.

More interesting perhaps were the system monitoring tools that could identify control loops that display high variability, and list out all the loops where control had been switched to manual.

Andrew Tither from MTL reviewed the many different options now available for running fieldbus segments in hazardous areas, which include the FISCO options for Division 1 areas, and FNICO options for non-incendive Division 2 areas.

An explosion-proof approach allows the use of Exd field devices and Exe wiring for the junction boxes and field trunking, with other systems becoming available using field barriers at the end of Exe trunking.

Inevitably perhaps, the interest from the EPCs was in segment design, and the allocation of control, either for control in the field, or control back in the DCS.

Tony Alexander from Honeywell demonstrated the procedures used to build a control loop within a Foundation fieldbus segment, the need to load the DD files for each device, and how the devices should be allocated.

When setting up a control loop, another consideration has to be how often the loop control software runs, allocated between every 250msec and 16 secs.

Much of the EPC audience interest related to the allocation of devices and control functions to each segment, which looked like a major topic for its own specific seminar! Conventional design training brought out questions about segment calculators, which would allow the current and power limits in a segment to be summed in terms of the power available.

While many different segment calculators were available from the different manufacturers (all promised as a follow up on the conference summary CD), there is a significant variability in the current drawn by different devices: many devices are below 20mA, particularly if just acting as a simple transmitter, which can be as low as 11mA.

But similarly more modern complex transmitters are also low in current consumption.


There were several topics that seemed to reflect the interests of the audience of EPC engineers (and some BP delegates) that possibly surprised the suppliers, and vice versa, which it was interesting to observe.

The audience was really interested in the decision over whether to undertake control in the field (often said to produce fast response and tight control), or control in the DCS/main system (requiring communication back to the Host system).

Honeywell confirmed that refineries tend to want to keep control back in the DCS, which was the same answer as came from Yokogawa, based on experience with nuclear installations, where the situation of each programmable device has to be separately evaluated.

On the other hand the ABB experience was reported that in practice around 20% of loops were controlled in the field.

The idea of having some form of Foundation Fieldbus ‘design tips’ on how to approach a FF project, and how to avoid the quoted installation hassles such as earthing problems and too much communications activity around the network, was taken up by the audience: it would certainly be a valuable document to build into a segment design engineer’s manual! The topic of network implementation was quoted as covered in documentation from the Foundation, along with installation standards.

Individual suppliers of host systems were quoted to have their own documentation and tools, to provided the processes and procedures to assist with the new aspects of the technology, such as segment design.

The supplier topic that went down badly with the EPC audience was the potential to provide multi-variable outputs from a single sensor, for example using a flowmeter also as a measurement point to measure process temperature.

This just did not seem to fit into a conventional box, so might need a little more promotion.

The EPC question that went down badly with the FF suppliers was a wish to know “How many people had recently evaluated a Foundation fieldbus solution for their project and rejected it, and why!” After an intake of breath, the suppliers could not seem to remember any such event!.

CONCLUSION: A day enthusiastically received by the EPC audience, showing a demand for further such events, to enable the expertise and enthusiasm from the suppliers to be passed to the EPC design engineers, and built into their project proposals with confidence.

While each supplier undoubtedly arranges training courses for clients and their operations engineers, the contractors possibly need to have some across the board training from FF, to enable them to make their own choice of host system, undertake the proposal work in-house, and push more fieldbus systems into the normal routine of smaller development projects or add-on sections to existing plants.

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