industrial wireless book special edition - Networking ...

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