Firms planning to put wireless networks on the factory floor will have to deal with a range of issues.
Wireless technology has become very much part of our every day lives in the form of mobile phones and wireless Internet access. Just as Ethernet has been embraced and made inroads into the industrial networking market, wireless too has been adopted within a broad range of industrial applications. For example, oil and gas companies use wireless devices to monitor remote fields and pipelines.
However, wireless technology has not been widely adopted for in-plant applications and there are several reasons for this. The range of sensors and transmitters for acquiring data had been limited, and reliability was an issue. Technology had not addressed customer needs for industrial grade security, or for effective powering of field devices. Standards for wireless did not exist and neither did an overall architecture.
In addition, plant owners and operators could only acquire and install proprietary point to point solutions, and there was also no opportunity to expand to plant-wide systems.
Technological advances, including the development of mobile communication-based technologies, has changed all that, enabling process industry issues to be largely resolved. Wireless networks based on open standards connecting a broad range of measurement devices with control capability are now available making integration with digital automation systems and Asset Management predictive maintenance software seamless.
Wireless gives processing companies the opportunity to open up applications that they simply could not justify with wired technology. It enables access to remote devices at hard to reach unmanned sites and opens up blind spots in a facility where measurements are not taken as often as they should be. By adopting wireless, blind spots disappear and plant operators gain access to information previously unavailable. In an average process plant there can be literally hundreds of devices currently capturing both process and diagnostic information, but with no way to deliver them. Wireless offers the opportunity to eradicate many manual readings, which can increase operator productivity and improve operator safety by removing the need for them to enter hazardous areas.
If the desire is to gain access to additional process and maintenance information, then the obvious attractions of wireless are the major savings that can be made to achieve this when compared with installing the wired equivalent. For example, installing additional wired measurement points within hazardous areas, such as a refinery, can cost up to £25,000 and therefore can be cost prohibitive. By overcoming the physical/environmental barriers to expensive wiring, installed costs can be reduced by as much as 90 per cent.
Installation of new measurement points is also simplified - with wireless field networks you don't need to run cables to every device. The major attraction of the technology is that you don't have to deal with the complexity of all the wires.
Potential applications are extensive and include automating operator rounds, incremental measurement points, and measurements on rotating or moving plant equipment. For example, the opportunity now exists for wireless vibration sensors to give you a real-time indication of equipment reliability every day, not just once a quarter, or whenever the schedule dictates. Safety relief valve emissions can be monitored for more effective regulatory compliance and safety showers can be monitored 24/7 so help can be dispatched immediately. Of course, many of these applications are possible without wireless technologies, but wiring costs or technical limitations make them impractical.
Wireless technology is not a complete replacement for wires, at least not for a while, but by using the information received from incremental measurement points and dedicated maintenance devices within the control network, it is possible to gain a better insight into your plant. This leads to significant improvement in plant efficiency, reduced maintenance schedules and increased times between scheduled shut downs.
Self-organising mesh networks
There are various wireless technologies available for a range of industrial applications including GSM/GPRS, Bluetooth and WLAN (IEEE802.11 a/b/g/h), but not all are suitable for the harsh environments found at most process plants, including the inevitable 'canyons of metal' that are found everywhere and that can present the inevitable problems for wireless signals.
Following the extensive testing and customer feedback programmes, Emerson Process Management concluded that the self-organising mesh network was clearly the best technology for in-plant smart wireless solutions.
Self-organising networks use IEEE 802.15.4 radios with channel hopping as the physical layer and form the basis for the approved WirelessHART open standard. They are designed and tested to be tolerant to almost all interference and can co-exist with other wireless networks in your plant. The networks are also highly scaleable and capable of one-second scanning with low latency (latency is the delay in processing data).
As a self organising network expands, new devices connect automatically. If a new device is not within range of a gateway, its messages are passed through other devices until they reach their destination. This makes them easy to install. There is no need for an extensive site survey, and when each device is installed it is ready to go. If something disrupts communication between devices, the self-organising network recognises the problem and automatically re-routes communications along the next best path. This self-healing capability results in a data reliability level that is greater than 99 per cent.
Self-organising network technology also reduces the effort and infrastructure to set up a successful wireless network. One of the difficulties of setting up the traditional point-to-point wireless network is the requirement to do a site survey to be certain that every node in the system has a line-of-sight path. This is expensive and also tends to require up to three times as many infrastructure nodes as a self-organising network. Another advantage of self-organising networks is that they are dynamic. As new obstacles are encountered in a plant - such as scaffolding, new equipment, or moving vehicles - the networks can reorganise around them. All of this happens automatically, without any intervention by the user.
In 2006, Emerson introduced Smart Wireless solutions. Using the time synchronised mesh protocol (TSMP), IEEE 802.15.4 with channel hopping next generation self-organising network technology, the company extended and unplugged its PlantWeb digital plant architecture to connect intelligent field devices wirelessly. Smart Wireless incorporates wireless instruments that are fundamentally the same as those used elsewhere in the plant, including having the same process connections, which means that technicians are familiar with them.
Emerson addresses the issue of security by providing advanced, standards-based AES 128-bit encryption as well as identification, authentication and validation techniques, verification, key management, and direct sequence spread spectrum (DSSS) anti-jamming techniques.
Smart Wireless has been adopted by a broad range of end-users in various applications including wellhead and heat exchanger monitoring at StatoilHydro's Grane offshore platform, temperature and tank level measurement at PPG Industries, and providing continuous monitoring for detection of potentially hazardous rising temperatures in railway wagons at Croda Inc.
Plant wide network
The next logical step having collected more data is to make it more readily available. By using the information received from a broad range of available wireless devices within the control network and then introducing technologies such as Voice over Internet Protocol (VoIP), video and handheld tablets, it is now possible to make the data available over the plant wide network. This enables end-users to track people/assets, send alarms and provide historical/live data to mobile operators.
Emerson recently announced that it is collaborating with Cisco to offer open-standard solutions for wireless process and plant management applications that install easily and operate reliably in challenging industrial environments. By using tools normally found in the office environment, such as email or Internet, we can make operators more effective. This is achieved by integrating Cisco wireless access points throughout the plant.
For example, a maintenance operator who is already out in the plant is now able to receive valve diagnostic information directly to his handheld PC. Should there be a fault with the valve, he will know exactly what is wrong and how to fix it, thereby improving efficiency.
In addition, the safety of maintenance and operating staff is paramount and the introduction of wireless is enabling fieldworker communication and location tracking.
Stuart Robinson, manager, Manufacturing Vertical Sector, Cisco Systems (UK), explains: "Emerson will use the Cisco Unified Wireless Architecture to provide ubiquitous, highly secure wireless LAN coverage and integration within the plant's existing IT infrastructure; this integration eliminates the need for a complex wireless overlay network. Cisco's Wireless Control System will centralise the configuration and management of the plant's Wi-Fi network, reducing overall cost of ownership."
Wireless offers the ability to add additional measurement points to previously unreachable or unaffordable places throughout the process plant. This means greater access to information about the process and also the health of devices. Wireless mesh networking solves the problem of reliability within tough non wireless-friendly areas. Security issues have been addressed and in WirelessHART the process industry has an open standard to work with. By adding plant wide wireless networks it is now possible to improve the availability of this extra data to those that need it most.