Every device is connected to other
devices to form this mesh, which greatly
increases the number of paths of communication as well as eliminating the
requirement that a device be within a certain distance of the gateway. If one path
fails from something such as a temporary
construction project blocking a communication path, another path is automatically used without intervention. The
result is very high reliability that in many
aspects exceeds wired I/O.
For wired, a single set of wires runs
between the input and output channel in
the cabinet room to the conduit tray to the
transmitter or valve. On the other hand,
wireless is not subject to problems such as
a broken cable from a situation such as
when a fork lift runs into a cable tray.
SAFE OPERATIONS
Security is critical to data reliability.
Wireless network standards employ security measures similar to those used for IT
(information technology) systems.
Several important elements come into
play with wireless transmission security.
The first is encryption, which is a method
of using seemingly random symbols that
surround each transmission.
With wireless transmissions, encryption keys are adjustable to match security
requirements that are designed to change
before the transmission data can be intercepted. The IT systems can set how often
these encryption keys are changed. In
addition, each transmission must be
authenticated, meaning that the sending
and receiving devices must recognize
each other. If those devices do not recognize each other, the transmission is
ignored. The data is also verified by the
receiving device.
Specific authentication and verification rules are built into each transmitter
so no foreign devices can intercept a
transmission or send bogus information
to the receiving station.
Another advantage of wireless mesh
networks is channel-hopping, which pro-
tects against frequency jamming by inten-
tional or unintentional sources. If a chan-
nel or frequency does not work, the
devices automatically make use of 15 dif-
ferent frequencies without user interven-
tion. The wireless transmitters communi-
cate their data to a network access device,
also called a gateway. End users also may
choose to install redundant gateways to
eliminate the unlikely event that a partic-
ular gateway fails in critical applications.
Channel-hopping coupled with the multi-
path networks, as well as redundant gate-
ways, provide a solid infrastructure to
move forward safely and securely with
complete wireless operations, including
critical and control applications.
USING THE DATA
The first uses with the new wireless data
will be with interlock systems. In this
case, actions will not be taken unless a
piece of equipment is in the correct
state. Referring back to our earlier
example of a manual clean-out valve
where filling the reactor will not occur
unless the valve is closed—an interlock
system would not allow the process to
move to the next stage unless the valve
is closed. Today, such action is sometimes completed manually by sending
someone to the valve and verifying its
position before transitioning the
process. Along with requiring human
resources, this can slow down a process
while automation could improve
throughput and increase consistency by
reducing the possibility of transitioning
the process without actually checking
valve position.
New information can also be stored
in repositories where it is analyzed and
used to make improvements in processes. These improvements lead to greater
confidence in operations. An example of
this would be with forensics such as situations in which equipment state is needed to understand what happened just
before an incident or when faulty or out-of-specification product is produced.
Added information can reveal corrective
actions that can improve safety and
reduce accidents. An example is a valve
not completely closed on a chemical
reactor during a specific phase—when a
vacuum is pulled on the reactor, air
could be allowed into the vessel, which
could negatively affect the product.
Such improved data on processes his-
torically has been associated with high-
end control systems. However, it is possi-
ble to store information in generic SQL
(Structured Query Language) databases,
so that common office applications can
interface with the data easily and without
expensive control system software. More
frequently, data mining (database
queries) would result in greater aware-
ness of the state of processing equipment.
A WINNING SITUATION
Automated valves can be coordinated
with simple interlock controls, such as
PLCs (programmable logic controllers),
while PID (proportional integral derivative) control can be interfaced easily with
control systems. Gateways are generic in
design—they connect the wireless field
devices’ control systems and databases
and can communicate with many types of
equipment that use different communication languages. The result is easy integration with whatever control package is in
use. The automated valves and control
loops of the future will leverage open
standards such as WirelessHART so
designers can choose from a variety of
suppliers and replace devices without
replacing the entire network or control
system.
Wireless makes valve monitoring
more feasible and encourages more valve
automation. Because of this, many plant
operations are already embracing position monitoring and looking toward wireless valve automation and control in the
near future. Designers of control strategies will take advantage of wireless
valves to enable greater control as well as
greater process and equipment health
awareness, all of which results in greater
confidence in operations and processes.
Designers going forward will be well
equipped to go to management with new
wireless projects armed with a proven
track record. VM
KURTIS JENSEN is an instrument 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.
