As conditions change or new obstacles are encountered in a plant—such as
temporary scaffolding, new equipment,
or a parked construction trailer—these
wireless networks simply reorganize. All
of this happens automatically, without
any involvement by the user. This capability provides redundant communication paths and better reliability than
direct, line-of-sight communications
between individual devices and their
gateways.
This self-organizing technology optimizes data reliability while minimizing
power consumption. It also reduces the
effort and infrastructure necessary to
set up a successful wireless network.
Traditional point-to-point wireless networks require costly and time-consuming site surveys to be certain that every
node in the system has a line-of-sight
path. Such a network can require up to
three times as many infrastructure
nodes as an efficient self-organizing network.
These self-organizing field networks
use IEEE 802.15.4 radio technology
with channel hopping as the physical
layer. They are designed and tested to be
tolerant to interference and can co-exist
with other wireless networks in a plant.
The networks are also highly scalable
with low latency.
The cornerstone of this system is the
wireless gateway, which can serve up to
100 wireless field devices on a single
network or on multiple networks. In the
future, remote operations controllers
will also operate as gateways. These
gateways pass on the field-generated
information to the control system where
appropriate alarms can be established
to notify operators of changes occurring
in any of the monitored devices. Diagnostic data are passed to asset management software to be processed and
made available for use by maintenance
personnel.
Wireless on Valves
Most operations have a large number of
“blind valves” that are either manual or
semi-automatic but provide no valve
position feedback, normally because of
cost or location. As such valves age,
their performance can degrade to sluggish, slow operation. The true position
of the valve may be questionable, and
operators have to start visiting certain
trouble-prone valves to verify their position. Where valve position monitoring
does not currently exist, wireless monitoring is a great way to start using this
technology with minimum risk.
There is also an excellent opportunity
to obtain previously unavailable performance information, sometimes called
“stranded diagnostics,” from many
valves, such as automated control
valves. Digital valve controllers generate useful diagnostic information, but
the data cannot be captured remotely
because the plant does not support a
digital architecture. If a valve is not
actually closed when it is supposed to
be, leaking steam or a process chemical
can cost thousands of dollars without
anyone knowing about it. A wireless
device could provide assurance of the
closed position, thus eliminating an
operator’s “blind spot.” At a minimum,
this would result in decreased response
times to developing problems—and it
could help prevent expensive losses.
The wireless infrastructure will be
largely incremental, allowing reexami-nation of previous automation decisions
for improved process operations and
safety. In both cases, valve health issues
can be discovered before they affect the
process.
Wireless monitoring of valves not
only makes sense but can be done today.
For those considering wireless, look
around at your valves and ask how you
can be more responsive when their performance starts to degrade. At the same
time, you can make better use of personnel by not having to send them out to
check valves as often, if the same valve
information can be obtained wirelessly.
And it’s being done—today. VM
KURTIS JENSEN is an Instruments Product Manager
at Emerson Process Management, representing
Fisher and Valve Automation Products. His responsibilities include control accessories and related
field instrumentation. Reach Jensen at kurtis.
jensen@emerson.com.
