Fieldbus now OUT IN THE FIELD

This month (on 19 March) the first Foundation fieldbus `technology familiarisation training course' in the UK takes place at Sira Test & Certification's centre in Chislehurst, Kent. Now to those with sufficient stamina to have followed the fieldbus debate in recent years, the temptation to ask `so?' might be irresistible. But Sira says its course - and the training and demonstration facility behind it - is `designed to move fieldbus technology from the technical arena to practical application'. And there are certainly encouraging signs that the fieldbus concept is now moving out of the committee rooms and into its rightful home on plant.

This is not to say that we yet have one internationally recognised standard for the digital networking of process control and instrumentation. But we are getting closer. The Fieldbus Foundation, remember, came into being only a couple of years ago when the then two main protagonists in the debate - the WorldFIP and ISP (Interoperable Systems Project) consortia of, primarily, vendors - buried the hatchet and started working together to develop a definitive fieldbus specification that, they hope, will eventually lead to an IEC international standard.

COLLABORATION, NOT CONFLICT

An indication of the degree of collaboration that now exists can be seen at Monsanto's Chocolate Bayou petrochemical complex near Houston, Texas. Initially the site of an ISP test programme (see PE April 1994, p38), this was home last year to a beta plant test of the Foundation fieldbus. The test - implemented with prototype fieldbus instruments on a condensate recovery system - `demonstrated and confirmed that fieldbus offers significant advantages in terms of installation and commissioning, especially when compared with traditional analogue systems,' according to the Foundation's manager of technical services Kurt Zech.

In Europe, however, it seems that even more co-operation may be needed if the Foundation fieldbus is to flourish. This follows the adoption last year by Cenelec of a European standard for fieldbuses, EN50170, which incorporates the three distinct national standards of France, Germany and Denmark - WorldFIP, Profibus and P-Net respectively. Although the UK, in the form of the British Standards Institution, argued against EN50170, the BSI has now submitted the Foundation specification as a `draft for development' to be incorporated into the European standard.

Meanwhile, both WorldFIP and Profibus - with between them hundreds of thousands of actual installed nodes across manufacturing industries - are starting to penetrate the process sector. According to John Beeston, WorldFIP's UK representative, many manufacturing sectors have been able to move faster towards the adoption of fieldbus technologies because they have less hazardous processes. Also they often have high speed machinery, which gives WorldFIP an edge because of its major strength in high speed (1Mbit/s and above) bus applications. Many of these applicatons have been in the continuous process arena, but mainly on activities such as power distribution, motor control and shutdown systems, rather than process control per se.

As Beeston explains, part of the essential solution for running intrinsically safe fieldbus devices in hazardous areas is the availability of low power chips. And this WorldFIP can now offer with MicroFIP, a low-cost component suitable for agent devices in the field and capable of operating in standalone mode. WorldFIP has also recently announced a HART gateway that provides a migration path to allow phased introduction of a WorldFIP high speed backbone into a plant with an installed base of HART-compatible instruments that operate over the conventional analogue 4-20mA systems.

While WorldFIP claims over 50 UK installations, across a range of industry sectors, Profibus is pointing to its first process orders for Profibus-PA, its low speed solution for intrinsically safe and other process applications. With deliveries that started towards the end of last year, some 20 separate process industry projects around Europe have specified Profibus-PA. For just four of these - at the Bitburger Brewery, Wacker Chemie and Shell Hamburg in Germany, and for ICI Billingham - the total value of PA-compatible instrumentation ordered is over $3.5million.

PROCESS ENHANCEMENTS

Profibus has also recently announced enhancements to its high speed bus - Profibus-DP for applications up to 12Mbits/s - that it says will benefit PA as well. The extended functions are mainly for intelligent field devices that require the transmission of parameters and alarm messages in parallel with the real-time I/O data transfer needed for closed loop control.

The consortia members of both Profibus and WorldFIP, itself a member of the Fieldbus Foundation, promise migration paths to the IEC standard when it finally appears from the committee rooms, but clearly neither they nor their process customers are prepared to wait. They now have the benefit of some real reference sites, but with the help of the Sira training and demonstration facility, the Foundation might not be too far behind. Certainly, with manufacturers such as ABB Kent Taylor, Fisher-Rosemount, Foxboro, Honeywell, MTL, Pepperl & Fuchs, Yokogawa and SMAR committed to using the facility, end-users can now learn about the potential benefits of fieldbus on neutral territory.