Open networks or OPEN MINDS?

The development of control networks and fieldbus technologies has undoubtedly played a major part in the revolution in industrial control that started with the introduction of the PLC. The ability to transfer and exchange information via such networks has made possible a host of improvements in manufacturing and control. It is unfortunate, though, that the development of such powerful tools has frequently resulted in debate on `which is the perfect network', rather than `what is best in my situation'. The objective of seamless distributed control has all too often been put aside in favour of battle honours as vendors or individuals become standard bearers for a particular `ideal solution'.

The plethora of open standards on offer - Profibus, Fieldbus Foundation, LonWorks, CanOpen and the rest - plus the equally long list of proprietary protocols, should emphasise the need for diversity but again arguments of `bestness' encourage misconceptions and hamper the adoption of these important technologies. No one would be fooled by a car salesman who claimed that one particular model was the best choice for all situations, so anyone recommending a single fieldbus solution for all needs should be treated with equal scepticism.

In simple terms the role of the network should be as `glue' that holds the organisation together, exchanging information and enabling control. More and more manufacturing companies have swapped the mass of paper once needed for order processing, stock control, quality checks, delivery dates, etc, for some form of Manufacturing Resource Planning (MRP) system running on networked PCs.

A single network type for all areas would certainly be ideal but, in spite of the wide capabilities of Ethernet, this is not yet possible and most companies have separate islands of business information and automation.

So much for the big picture, you may say, but the reality is that I need to upgrade one particular part of the operation and need to decide on the network to use. How then to decide on the best network for me?

First requirements are an audit of your existing control system and an understanding of the nature of your operation. Then, with your ideal enterprise-wide solution in mind, you are in a strong position to implement your automation and control strategy on a modular basis, one step at a time.

It is a common misconception that fieldbus systems are only considered when major plant wide system upgrades are on the cards. In reality a simple low-level fieldbus solution can bring major advantages even at single machine level, but it is still important to keep your overall objectives in mind when selecting your network.

If you are integrating products from more than one manufacturer a single open network such as Profibus or Actuator Sensor Interface (AS-i) may be most suitable for your needs, but if all the control items are manufactured by one company there are definite advantages to using their own network solution. Proprietary systems are often criticised for tying you to one supplier but they can have major cost and maintenance advantages. They can provide the optimum balance between ease of installation and performance, as well as a one stop shop for support.

Bear in mind that there are pros and cons with any network solution and the manufacturer of your control system products should be able to offer a selection of proprietary and open system options and be able to discuss the benefits of each without prejudice.

Thinking back to the car salesman, avoid any suggestion that there is a single `best' solution. A company with only one system to offer is not likely to give objective advice. Ask yourself, are they offering an open system or an open mind? PE

Chris Hazlewood is Industrial Control Product Manager with Mitsubishi.