Wireless technology has advanced so rapidly that strategic measurements and other data solutions can now be implemented that simply were not possible with wired communications. Hartmut Wallraf, Chief Technology Officer with Invensys Process Systems Europe, Middle East and Africa, outlines where the technology is now and what the future holds for it

As wireless communication begins to be more widely adopted by the world's process industries, companies must recognise the importance of planning in order to ensure appropriate levels of integration, robustness and security.

Wireless technology now makes it possible to incorporate new strategic measurements and other data within solutions that simply were either not practical or even possible to implement in a wired communications environment. This includes solutions for process optimisation, device management, real-time equipment condition monitoring, energy management, personnel tracking, asset tracking, security, and enterprise asset management that can all work in unison to address both industrial asset utilisation and availability.

The plant wireless environment

Many plants have existing applications that use either fibre or copper cables as the communication medium. There are some limitations to a wired infrastructure such as this, especially in the plant environment. Many new applications require upgraded cabling, and expansion to existing applications may require additional cabling.

Along with the cabling itself, there are many associated costs with this kind of infrastructure. In order to expand a cable plant, costly engineering studies need to be performed so that wiring locations and paths can be determined.

Depending on the age and condition of the existing environment, there may be some issues that need to be remediated with the addition of cabling. For example, asbestos may exist behind walls that are to house cabling. Also, trenching may be required to run new cabling. The plant environment inherently has some issues that need to be taken into consideration, such as excessive heat and magnetic fields.

To alleviate these concerns, wireless networking has been investigated in the plant environment. Wireless networks provide the connectivity required by the existing and new applications, but also allow for some additional benefits. Deploying a wireless network for a particular application allows access even in places where it is difficult to run cables. A wireless network can be designed to be self-healing and redundant so that single points of failure in the network are virtually eliminated. Roaming can be configured so that a mobile worker can traverse the entire plant and never lose connectivity to a centrally managed application.  

As in the case of wired networking deployments, an engineering study, or site survey will need to be performed in order to determine the most efficient placement of wireless networking devices, but these studies are usually considerably less expensive than those of the wired variety.

The advantages of wireless networking are many, and include the following:

*More mobile workforce and safety monitoring.
*More efficient and less expensive asset tracking.
*Eliminating wires leads to cost savings.
*New applications are easily deployed and result in bottom line improvements.

There are many wireless protocols and technologies to choose from. In order to take full advantage of the wireless network, a site survey is recommended to determine the best technologies to use and the placement of the related devices. A properly designed and deployed wireless network is fully expandable and has a very short ROI. The next few sections describe the existing wireless technologies.

Why Wi-Fi?

The catchall term ‘Wi-Fi’ refers to the protocols contained in the 802.11a, b, and g standards, which are wireless technologies typically deployed in the home, office, and plant environment. 

802.11b and 802.11g utilise the same wireless frequency range (2.4GHz), but offer different speeds. 802.11g is significantly faster, provides a data rate of 54 Mbps, while 802.11b provides 11 Mbps. From a distance perspective, wi-fi can be classified into indoor and fixed outdoor wireless. We can achieve distances up to 25kms with fixed outdoor wireless using either 2.4 or 5GHz frequency by choosing a high gain antenna (provided there is line of sight). In indoor applications it offers a distance up to 300 feet, however the interior building materials provide enough of a signal reduction to lower the distance to 100 to 150 feet between devices.

The major drawback for these protocols is that there are a number of other devices, such as cordless telephones and microwave ovens that also utilise the 2.4 GHz band.  That said, a properly conducted site survey will determine these points of contention and make sure that they are alleviated in the final design and deployment.

802.11a, on the other hand, utilizes the 5 GHz band and provides speeds up to 54 Mbps. The advantage of using this protocol is that there are so few devices utilising the 5 GHz band, interference or signal contention is virtually eliminated. Also, whereas 802.11b and 802.11g are compatible with each other, 802.11a is not compatible with either. So, once again there are few devices competing for this frequency.

This illustrates the interoperability of 802.11b and 802.11g, since the access points speak both and translate to either of the protocols, depending on the device connected to it. It also illustrates the use of 802.11a as the bridging technology between the access points.  Because of the lack of competition in the 5 GHz range, greater bridging distances can be achieved.

One of the concerns of administrators related to wireless networking is the issue of security. There are many security options to address these issues, including WEP, WPA, WPA2 and Radius Authentication. Encryption can be used to secure links so that the communications cannot be eavesdropped. Furthermore, access technologies can be implemented so that rogue users cannot connect to the network.

In addition to Wi-Fi networking, other application-specific wireless technologies can be deployed. These include wireless sensor networking (WSN) and radio frequency identification (RFID). The following sections illustrate these technologies.

WSN

Wireless sensor networking utilises a technology designed from the IEEE 802.15.4 standard. This standard depicts a self-sensing, self-healing network of devices that can report sensor information back to a centralised management station. These devices can be deployed in a number of topologies. However, the most efficient method is to deploy these devices in a mesh.

Each device can route traffic back to the gateway, so that even if one device is not directly connected to the gateway, it can still send its information back. Furthermore, the network is self-healing. In short, if one of the wireless sensor devices fails, the network will correct itself to bypass the faulty device.

RFID

RFID can be used for asset tracking, for personnel tracking, and for information storage.  The technology revolves around tags that are placed on devices and used for the purpose of tracking.

The RFID tag is scanned by a wireless device and information about the inventory can be uploaded to a data base and used to track the piece. This is an example of a passive RFID tag. On the contrary, an active RFID tag has a small power source and can provide more services, has the ability to store information in the tag itself, and provide a greater distance from which the tags can be read (60 metres indoor/200 metres outdoors).

Active RFID tags provide real time location services. This example is equipped with a battery that lasts over four years, is ATEX certified, intrinsically safe and features a call button for emergency services. This device is well suited for safety applications and asset tracking of expensive or critical equipment and products.

Conclusion

The challenges for developing and maintaining a wireless infrastructure in a plant are numerous. As noted above, WiFi can provide a high-speed wireless infrastructure to enable various plant applications. However, an emerging standard called WiMAX (Worldwide Interoperability for Microwave Access) provides greater performance across longer distances, and improved security and certainly looks to be the way forward.