Unravelling today's networks tangle

With so many wireless standards and products available, the process engineer's task of selecting the right option to meet company requirements can be a major challenge. No-one wants to choose the Betamax of the wireless world, but equally no-one wants to miss out on a potential new solution that may solve today's problem.

Whilst the range of standards and products can at first seem bewildering they can mostly be categorised into three distinct types for the process engineer:

- Wide Area Network (WAN) - Products that can enable communications from a data centre or control room to large process works, typically many kilometres. Data rates in this type of network would need to be high enough to cope with frequent data updates and near-real-time control needs.

- Local Area Network (LAN) - Products for communications around a process works or its immediate vicinity, typically a few hundred metres. Data rates in this type of network need to be higher than for WANs to allow continuous updates and real-time control.

- Personal or Plant Area Network (PAN) - The Personal Area definition comes from the typical Bluetooth application of intercommunications of hand held device or peripheral communications. These types of applications typically require very high data rates but only over a very short range - a few tens of metres.

The Plant Area definition portrays the needs of the process engineer to connect very remote items of plant for monitoring and control needs. While still over a relatively short range, the data rates here may be lower than for Personal Area Networks. This allows for the use of products that operate at lower power consumption and need less maintenance.

There are many other options available, including low power radio, UHF radio, Power Line Carrier and a host of satellite solutions.

The key to creating a future-proof and flexible wireless process control network is to recognise that no one wireless standard can solve all needs. Since a multi-communications network is required this allows some room for flexibility, since the future of any standard is always going to be uncertain. For instance, despite only being available for a few years the GPRS network will be superseded by the UMTS network and all GPRS equipment will have to be upgraded.

In the figure across, the three network layers (WAN, LAN and PAN) radiate outwards from the data centre/control room. This method allows the process engineer to cost effectively connect more remote plant into the network for monitoring and control purposes.

WAN- and LAN-level equipment must cope with higher data rates and be permanently powered. In addition to the initial capital outlay, the cost of powering can be expensive and inappropriate for some remote sites. However using PAN equipment, such as Zigbee, the process engineer can install monitoring and control nodes that operate for many years on battery power.

The European Community explosives atmospheres (ATEX) directive defines the mandatory requirements for equipment that is to be installed in environments, such as oil & gas production and distribution, petrol stations and sewers. Those involved in the running of such environments must monitor and control processes and so need to ensure that monitoring and control devices comply with the ATEX requirements.

This mainly involves ensuring that the devices cannot generate sufficient energy to cause ignition of the explosive atmosphere that they are installed in. With wireless devices, this can be at odds with the requirement to transmit data as far and as quickly as possible.

The ability to provide wireless devices that transmit data as far as possible at reasonable data rates but still comply with ATEX requirements is limited to a few specialist providers but the demand for such products is significant and growing. Some providers design ATEX complaint products from scratch and others specialise in making standard products ATEX compliant.

Wireless monitoring and control installations often need to operate in the absence of mains power. Just as wireless communications allows lower cost installation in locations where traditional wired communications would be needed, alternatives to mains power reduce installation costs and increase availability of solutions.

Battery power is an obvious choice and indeed many products exist today that can run from a non-rechargeable battery pack for many years. However users are demanding more data, more often and the end result is either a larger battery pack or a shorter life, even bearing in mind the improvements in electronic design that have greatly reduced power consumption.

Users can also opt for solar, wind and even water to generate energy to recharge batteries thus increasing serviceable life. However, such options can be expensive and difficult to install and so tend to be less popular.

An exciting new developments is energy harvesting. Here a small device uses the vibration of machinery to generate sufficient energy to charge a small wireless transmitter for long enough to allow it to transfer its data. The potential for such a solution is huge, allowing users to monitor rotating machinery without the need for large devices that require regular battery changes.

Wireless communications offers users the ability to monitor and control remote sites. But if this increases the likelihood of an attack on that site, rendering it inoperable or allows criminals to obtain commercially sensitive material, then the viability of the solution will be called into question. Wireless networks are inherently insecure and care is needed if they are to be deployed for monitoring and controlling mission critical processes.

Manufacturers of modern wireless solutions recognise the limitations of the medium and most equipment uses standard security features, such as the Wireless Encryption Protocol used in WiFi equipment. If used correctly, and in conjunction with a comprehensive overall system security policy, wireless can be as secure as any other type of networking solution.