Practical Aspects of Profibus PA in Process

The UK Profibus organization sponsored a process industry specific training day at the end of November 06, with the title of the “Practical Aspects of Profibus PA”: Nick Denbow reports.

This seminar was hosted by Mark McCormick of Siemens in their impressive offices in Bracknell, to provide a Southern UK venue following the 2005 event in Manchester.

It focused on presenting the key practical issues arising from the use of digital fieldbus communications technologies in process applications, from system design and hazardous area considerations through to maintenance and fault-finding.

Mark Cargill, originally listed as from Purac, explained that Purac was now called EnPure, following an MBO of the business from AWG, the original Anglian Water.

Mark described the practical steps he has found needed, in order to plan and then succeed with a Profibus project: useful input since no-one in that day’s forty strong audience claimed to have previously achieved a success with a Profibus installation (But no-one had failed either).

The audience profile was from many industries, but the major representation was from the water industry, which was identified as having major Profibus potential by most of the speakers.

Perhaps surprisingly, Mark stressed the need for more advanced planning with a Profibus project (compared to a conventionally wired one): it was necessary to choose the equipment supplier for PLC and field devices carefully and early, preferably as a single supplier approach, and also important to insist on receiving the GSD files in advance: plus all devices should be requested pre-addressed.

This meant that a Profibus project has to start ‘far earlier’ than a conventional project, (measured to the start of site installation presumably) because the good groundwork will compress these later phases, including most importantly the provision of the as-built drawing package to cover the complete installation and wiring records.

However, for the installation phase, it is essential the field installer chosen has previous Profibus project experience, or has completed the certified training courses offered through the Profibus Group, because cabling errors (such as mixing up the use of Profibus DP and PA cables) are the major problem area resulting from an installer with poor awareness.

Tony Grassby from Endress + Hauser continued the discussion of the need for careful component and cable selection, but commented that in terms of equipment, most projects he has seen had been multi-vendor installations.

Tony covered the selection of hazardous and non-hazardous area DP/PA segment couplers and links, and lightning protection devices.

In addition, while all devices should be wired into a junction box on an individual spur, using glands or plugs and sockets, most system faults in his experience were in the field in the junction boxes.

An example of one company who investigated the capabilities of fieldbus cabling thoroughly was quoted as Imerys, (originally English China Clays) who in their area of Cornwall suffer from a lot of electrical storms.

Only after a year of successful on site testing of a trial network installation were they prepared to consider major Profibus PA installation projects, and now Imerys typically specify and request Profibus equipment.

A combined demonstration from all the lecturers with the equipment on display showed the software tools available for correcting and adjusting field instrumentation, firstly via the Siemens PCS7 PLC using the Siemens PDM Process Device Manager, then using the E+H FieldCare system, then using the 800XA system from ABB.

All the systems demonstrated the ease with which faulty devices can identified and replaced in the field, automatically being re-configured to fit the system requirements originally established.

It also showed how easily the process values can be reconfigured, and further operational data extracted.

All the different proprietary programmes can derive the data from the field devices, usually over Profibus, but also other data communication formats, like HART and FF and Ethernet and RS232 and Modbus, so the final programme and monitoring method used depends on the choice made for the site, rather than the equipment or the communications format it uses.

To have all these systems, plus also an Allen Bradley PLC all demonstrated alongside each other, within the Siemens HQ, caused some lifted eyebrows, even amongst the lecturers, but demonstrates the standardisation and interoperability of their Profibus communications systems! Andy Verwer of MMU also created and then showed how to analyse faults on the Profibus system, using protocol analysers and waveform visualisation using a softscope, to give a flavour of the possibilities when working with these systems once installed.

While I, perhaps a less technical one of the audience, found this difficult to follow, it certainly demonstrated an earlier comment that: “For Profibus systems you need a different fault finding approach: typically a fault, evident at one end of a bus will have its source at the opposite end”.

Gareth Johnston of ABB had the unenviable task of summarising what had been demonstrated, and looking ahead to seek suggestions for future events.

With a lot of different aspects crammed into a few hours of seminar time, the day did not give enough information to allow anyone to feel competent enough to engineer a project as a result! But the main message was evident, that there is a need to train and learn about these systems, and that such training is readily available through the Profibus Group, with upcoming events listed on their website, via http://www.profi-bus.co.uk.

Suppliers, Contractors, Installers and in user companies the Project Engineers are using Profibus systems to good effect, and are available to assist and advise on the necessary planning beforehand.

The next similar UK based Seminar and Process related event organized by the Profibus Group will be on March 9th, hosted by ABB at their Daresbury offices.

This will be followed by the regular annual two day International user conference and workshops in Warwickshire, from 26-27 June, see http://www.profibus.co.uk.

Registration forms for both events can be downloaded from http://www.uk.profibus.com, or are available on request to admin@uk.profibus.com .