Image Processing Reference
In-Depth Information
WSN
Radio
transceiver
Sensor
Power
source
CPU/memory
FIGURE .
Components of a WSN device. (From Aakvaag, N. and Frey, J.-E.,
ABB Rev
., , , . With
permission.)
27.2.1.2 Self-Organizing
The nodes self-organize their networks in an ad hoc manner, rather than having a preprogrammed
network topology. For example in wired network technologies, some designated nodes, usually with
custom hardware (routers, switches, hubs, and firewalls), perform the task of forwarding data to other
nodes in the network. In a WSN, typically each node is willing to forward data for other nodes,
resulting in a dynamic network configuration based on the network connectivity.
27.2.1.3 Self-Healing
WSNs have the ability to self-heal, i.e., if one node goes down, the network will find new ways to route
the data packets. This way, the network as a whole will survive even if individual nodes lose power
or are destroyed. his type of dynamic reorganization can also be triggered by other conditions than
node failure, such as maximum node power consumption and communication latency.
27.2.2 (Re)-Defining WSNs
Industrial applications differ from the definition above in a number of respects.
27.2.2.1 Cooperative Sensing Is Not Commonplace in Industrial Automation
First, and maybe most importantly, all sensors are crucial to the operation of the plant. his implies
that losing one node is not an option, even if the overall network stays operational. A faulty node
will have to be replaced. Increasing the availability by adding redundant sensors would be techni-
cally possible, but hardly feasible from a cost perspective. Although the cost of radio transceivers
is continuously dropping, the majority of the cost of industrial-grade WSN devices is not driven by
the cost of the transceiver alone. To this, you need to add the life cycle cost associated with installing
and maintaining a device throughout its lifetime (which is a factor of at least - times longer than
consumer products).
The notion of cooperative sensing prescribed by classical WSN is also not readily applicable to
today's automation control systems, which are rather input and output (I/O) centric. Measurement
points are not “dispersed” across the plant, but rather installed in very exact locations. he data are
collectedandfedbacktothecontrolsystem,whereitisprocessedandanalyzed.Addingameasure-
ment point is associated with manual engineering and application programming before it can be
utilized in the system.
