The growth of fieldbus in the process industry

In this article Irwin Hodgkiss of Burkert Fluid Control Systems discusses the use of Fieldbus technology in process control applications, and the training equipment donated to UK based centres.

In this article Irwin Hodgkiss of Burkert Fluid Control Systems discusses the use of Fieldbus technology in process control applications, and the training equipment donated to UK based centres.

For years the control of process and machines was a labour intensive operation, requiring a large number of people to oversee even relatively simple tasks.

Whilst engineering ingenuity led to the development of simple electrical and mechanical devices that allowed much of the manual commitment to be dispensed with, as processes and machines became more sophisticated, so the amount of control required increased in proportion.

The advent of modern mass production techniques made it increasingly important for information to be available for use by production engineers and maintenance personnel to enable fault diagnosis and planned/predictive maintenance to take place.

Safety also became a major issue that significantly increased the amount of safety related controls in a system.

The introduction of PLC controllers and 4-20mA circuits and devices did much to alleviate pressure on control systems design and manpower commitments, but by now the costs involved in implementing process and machine control had risen out of all proportion.

The installed cost per device (or node) was increased by the amount of parallel wiring needed for its operation.

It became obvious to PLC and control manufacturers that they would benefit from being able to use the same technology for interconnecting devices that was being increasingly used by the emerging PC industry for networking PCs and peripheral devices together.

This technology used a pair of wires, loosely twisted together (and generally referred to as a 'twisted pair') to form a data 'Ring Main' onto which devices were attached.

These devices were fitted with microprocessors that enabled the data signals to be addressed to, and translated by, a compatible device and thus give an output in response.

The 'Ring Main' became known as a 'Bus' (short for 'Busbar' or 'power rail') and in a relatively short time became the focus of intensive development by all the major PLC manufacturers both in Europe and America.

Now referred to generically as the Fieldbus its advantages as a networked solution for process control installations are generally well known.

Savings on cabling and installation time can be significant, and, due to their inherent diagnostic capabilities, Fieldbus systems can reduce downtime, increase supervisory information and control and therefore maximise the effectiveness of a process.

For many process applications their ability to accommodate large numbers of different components over long distances, and process their data using a well organised protocol, means that, for example, a flow transmitter fitted at one end of a linear bus can communicate with a valve 500 metres away at the far end of a network.

Up to now, Fieldbus has been associated with major process automation projects, where the Fieldbus network is generally the standard chosen route.

Many engineers working on smaller projects are still using discreet I/O and PLC structures with hard wiring to control devices, and are only just beginning to appreciate the advantages of networked solutions.

The Fieldbus (Profibus, DeviceNet, Interbus, etc) is potentially an extremely powerful control system accommodating large numbers of 'nodes', which may include valves, transmitters, machines, motor inverters etc Smaller systems, such as AS-interface, can accommodate up to 62 devices (usually on/off devices) and its master controller, in turn, can be linked to a larger, higher level Fieldbus, where it is simply recognised as a single node.

There are various options for connecting to the Fieldbus so, where a networked control solution is being considered, it is important to carefully assess the scale and structure of the final layout in order to assign the appropriate system.

For example, an intelligent device with an embedded chipset - such as a flow transmitter or control valve - can be connected directly to the Fieldbus cable and is classed as a single device (or node).

A similar result can be achieved using a passive (non-intelligent) device wired to the Fieldbus system via an input module that forms part of an appropriate I/O assembly.

Fieldbus is extremely effective as a site-wide system for a single site.

However, it also has the capability of linking any number of sites in locations around the world and relaying the process data to a number of specified, remote monitoring sites.

As an example of this principle, an operator in the UK can scrutinise in detail the performance of a system in Australia - eg a bulk product holding tank level or a single production line component - from a desktop or laptop computer connected via a modem link.

The information can be displayed and recorded by using a SCADA system, thus giving visibility of the total process operation.

If comparable functionality was required from a conventionally wired system, its structure would be many times more complex and would be extremely costly to design and implement.

A Profibus fieldbus system was certainly the most cost-effective solution for Colgate Palmolive, one of the world's leading manufacturers of hygiene and healthcare products.

The company, which produces millions of tubes of toothpaste per week at its plant in Salford near Manchester - including famous brands such as Total and Ultrabrite - has recently installed a Profibus DP controlled dedicated ring main as part of a control system that delivers purified water to six toothpaste batch mixing vessels.

Each vessel produces between four tonnes of toothpaste per batch and five batches per eight-hour shift.

The water needs to be maintained at a constant 75C and a constant velocity to meet Colgate hygiene standards.

Burkert Profibus compatible modulating globe valves and zero dead leg (ZDL) diaphragm valves are fitted as part of the control system for the ring main, which includes six loops to deliver purified water to each of the batch mixing vessels as well as the main process vessel.

The modulating valves control the flow in each loop in order to maintain the velocity and volume of purified water in the system.

The ZDL diaphragm valves are used to shut off the flow to the loops and direct water into the process vessel.

Burkert has also supplied state-of-the-art components, technology and experience to support AS-I, Profibus PA and DP fieldbus systems that are a major part of an automation system design for United Milk PLC at Westbury in Wiltshire.

The project, which is claimed to be the largest milk processing Fieldbus installation in the UK and provides shopfloor-to-boardroom automation for this world class production facility, was won by GEA Tuchenhagen against strong international competition from a number of major process equipment suppliers.

The equipment supplied included AS-i cable plugs, mini top and diaphragm, general purpose and solenoid valves.

The importance of Fieldbus technology for the future of the process industry should not be underestimated, which is why companies like Burkert, who are members of the user groups set up to develop and promote the various protocols, are actively supporting the next generation of young process engineers: Burkert support has included the donation of a selection of Profibus and AS-i products to two of the UK's main training centres.

Manchester Metropolitan University, which is the UK Profibus Centre of Excellence, runs a number of courses including a Profibus Engineers Course, Profibus Installers Course and an AS-i Course.

The courses are recognised by the UK Profibus and AS-i User Groups.

Eight sets of training equipment have been donated, with products including AS-i cable plugs, angle seat process valves, temperature switches with integral AS-i control, on/off valves and a number of actuated valves.

Two courses being run by University of South Wales College Newport are training engineers to install Profibus and AS-i products and networks using a section of a virtual factory donated by Burkert.

The process demonstration unit was exhibited at the 2002 AS-iTec exhibition and built as a joint venture between Burkert, Tyco, IFM, Group Schneider and Woodhead Connectivity.

The virtual network included process control, automation, robotics and power handling.

It can be used as a stand-alone fieldbus network or as a single Profibus node.

As members of both Profibus and AS-i groups in the UK and Germany, Burkert believes it is important to support the universities to ensure that responsible and correct training is available to the engineers of the future.

This will enable engineers at every level of the process industry to benefit from the simplicity, reliability and diagnostic capability of the Fieldbus to increase production, reduce costs and improve their process management.

Back to top