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I n d u s t r i a l W i r e l e s s 30 Sensor networks: wireless mesh or wireless backbone? Automation plant operators should carefully consider their current and future needs before choosing an industrial wireless system. Some applications are well suited to a field device meshing network, while others are better served by an infrastructure meshing network. To gain the maximum benefit that meshing can offer, the selected system should support both topologies simultaneously and seamlessly in a single network. In the following article, Soroush Amidi explains the salient characteristics of each topology to help end users decide which one best serves their needs. THE PACE OF ADOPTION for industrial wireless by the very conservative automation and manufacturing industry testifies to the strength of wireless meshing technology. Every year, thousands of plants opt to use wireless devices, such as mobile handhelds running apps for maintenance and process monitoring, video collaboration cameras, asset location tags and wireless field instruments. This improves organisations’ operational and capital expenditure performances. The attractiveness of industrial wireless lies in its mobility, flexibility and lower cost. The use of wireless technology in the process industries is not new. Automation professionals began using wireless transmitters more than a decade ago to collect data from remote areas or equipments where the use of wired transmitters were not feasible, either because of physical or financial constraints. What is new, however, is the development of wireless meshing technology, which offers the reliability and robustness that was lacking in point-to-point wireless products used at the beginning of the 21st century. Today, a growing number of industrial end users are implementing wireless devices, including wireless transmitters. In fact, wireless transmitters are even being installed for process monitoring in areas where wired transmitters can be used. Why? Again, it is because of the reliability offered by the wireless meshing technology. When it comes to implementing a wireless meshing network, automation professionals are faced with choosing from several different topologies. They can implement a field device meshing topology where field devices, typically battery powered wireless field instruments or wired field instruments with wireless adapter, form a peer-to-peer meshing network. Alternatively, they can implement an infrastructure meshing topology where infrastructure nodes, i.e. line-powered industrial access points, form a peer-to-peer meshing network connecting wireless field devices, field instruments and/or Wi-Fi devices. Field device meshing topology Field device meshing enables a wireless peer-topeer network to form among wireless field instruments. This approach does not require any lined powered wireless infrastructure to be present. Communication packets can hop between transmitters to reach the final destination. Transmitters auto-discover neighbouring transmitters and establish a communication path with each other, thus forming a mesh network. Wireless sensor meshing or wireless sensors with high-speed backbone? Automation plant operators should carefully consider their current and future needs before choosing an industrial wireless system. PHOTO: HONEYWELL industrial ethernet book Wireless sender for ISA100.11a: It can operate with an update rate of 1s, but at the expense of battery life. Each transmitter acts as an independent router (i.e., the transmitter can send its own data as well as route data received from other transmitters). This allows for continuous connections and reconfiguration around broken or blocked paths by ‘hopping’ from transmitter to transmitter until the packet reaches the wireless sensor gateway. Infrastructure meshing topology In an infrastructure meshing network, field instruments do not act as routers. Instead, linepowered infrastructure nodes route the data. These infrastructure nodes auto-discover each other and establish a peer-to-peer network. This allows for continuous connections and reconfiguration around broken or blocked paths, again by ‘hopping’ from node to node. A Field Device Access Point hosts an ISA100.11a backbone router board (refer to ISA100.11a standards for backbone router definition) in an industrial enclosure. Data can be routed through other ISA100 field devices using the ISA100.11a standard or via a highspeed backbone router such as an IEEE 802.11 WLAN via the Ethernet port hosted on each node. Multinodes route data through other Multinodes using the IEEE 802.11 standard. They also host a backbone router board connected to a meshing access point board in the same industrial enclosure. They can route ISA100.11a data as well as Wi-Fi data. sponsored by Advantech PHOTO: HONEYWELL
Fig. 1. Field device meshing and infrastructure meshing: The OneWireless system supports field device meshing and infrastructure meshing topologies in either standalone mode, or in combination. The ISA100.11a standard So as to realise the maximum benefits offered by meshing, both field device and infrastructure meshing topologies need to be supported simultaneously and seamlessly in a single network. This is one of the core requirements of the ISA100.11a standard for wireless field instruments, which was developed by ISA100's 500-plus members representing the plant automation industry. This technology was designed for use in remote applications with low frequency update rates, as well as in control and critical monitoring applications with high frequency update rates. ISA100 members ensured that ISA100.11a transmitters could operate with both field device and infrastructure meshing topologies. Figure 1 illustrates how ISA100.11a field instruments operate in either field device meshing or infrastructure meshing mode. A comparison Table 1 (over page) shows the characteristics of a field device meshing topology versus that of an infrastructure meshing approach. Latency. The ISA100.11a standard is intended to optimise the battery life of wireless transmitters. When in field device meshing/routing mode, ISA100 field instruments wake up on a periodic basis to listen to other transmitters and route data based on reporting rates. This capability allows field instruments to save power and maximise their battery life, which effectively translates to lower latency. In a star meshing topology, routing infrastructure nodes listen and route data in real-time. This is possible since the devices are line-powered. Field instruments simply need to transmit their data to the routers. Network timeslot allocation is much easier in an infrastructure meshing topology. As just described, there is a significant difference in data latency between a field device meshing network and an infrastructure I n d u s t r i a l W i r e l e s s sponsored by Advantech industrial ethernet book 31
Page 1 and 2: sponsored by Special Issue ISSN 147
Page 3 and 4: GET CONNECTED… www.iebmedia.com
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Page 7 and 8: IEEE 802.11n: the next step for ind
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Page 11 and 12: Fig. 2. 802.11 relative rate and ra
Page 13 and 14: Lessons learned from IEEE802.11n En
Page 15 and 16: IEEE 802.11p MAC protocol for vehic
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Page 19 and 20: Explicit Messaging application: Wir
Page 21 and 22: Frequency hopping sequencing Freque
Page 23 and 24: Simulcast RF wireless networks aid
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Page 27 and 28: RFID technology Active RFID tags ha
Page 29: Extended WLAN is a single network A
Page 33 and 34: Internet Protocol for wireless conn
Page 35 and 36: For several reasons, including cost
Page 37 and 38: Flow-based compression techniques a
Page 39 and 40: 6LoWPAN node Router solicitation Ro
Page 41 and 42: This happened in the early days of
Page 43 and 44: Glossary • DSSS - Direct Sequence
Page 45 and 46: Fig. 6. IPv6 LoWPAN network example
Page 47 and 48: With Diversity Path Mesh (left) all
Page 49 and 50: Two case studies Wireless solves pr
Page 51 and 52: 60GHz Industrial Wireless: perfect
Page 53 and 54: Wireless avoids cable trouble on el

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