2012 - PageSuite

aUTOMaTIONSOLUTIONS
Solar kits allow accurate monitoring and
control of processes or equiment without a
power infrastructure. Courtesy: B&B
Electronics
like local decision-making and controls, and
redundant backhaul paths.
Using sensors
to enhance systems
Recognize the limitations, then plan
for redundancy.
By Mike Fahrion
B&B Electronics
The network edge is continually expanding
into new applications and new
industries, and network-enabled sensors
are leading the way. Metcalfe’s
Law tells us that every time you add another
device to a network, whatever that device’s
function may be, you increase the value of
the network.
Sensors demonstrate that point every day.
Whether they’re measuring deformation errors
in a tire plant, geo-fencing an oil pipeline, or
monitoring well water quality for the U.S.
Geological Survey, sensors lower costs and
enhance productivity.
Each new application presents its own set of
new problems. Sensors must function in a wide
array of environments, and they must be able
to report their data. This article will describe
system design techniques that anticipate issues
like brownouts and equipment failure, and
prepare for them by employing solutions
The myth of 100% uptime
All data communications installations have
vulnerabilities. Fiber optic cable, for example,
the option with by far the greatest range and
bandwidth, is used by the telecommunications
companies to move data across entire
continents.
Uptime is excellent, but the system isn’t
perfect. The cables are either run through sewers,
where backhoes break them with annoying
regularity, or they’re strung along telephone
poles, where they’re knocked down by everything
from windstorms to sleepy truck drivers.
Indoor fiber optic connections have problems
of their own. Transceivers and receivers eventually
fail. Cables can be bent or broken by
anything from careless forklift drivers to the
cousins of the raccoons that get into power
substations and shut down the grid.
Copper cable adds additional weaknesses.
Any strong magnetic field can induce current
on a copper cable, which will lead to power
surges that can burn out sensors, integrated
circuits, and connectors. Industrial machinery
isn’t the only thing that can generate those
strong magnetic fields. For example, a 1989
solar flare famously produced a magnetic
storm that took out the power grid for all of
Quebec. Lightning strikes will also produce
damaging electrical events, as will the ground
loops that occur when connected devices have
different ground potentials.
Wireless connections are subject to failure,
too. Interference from other devices on
the same frequencies can lead to data loss.
And radio signals attenuate with the square
of distance. Merely doubling the range would
require a four-fold increase in power.
No system is perfect. And the harder you try
to achieve perfection, the faster your costs will
rise. It’s cheaper and easier to eliminate the
need for 100% uptime from the very beginning.
Rugged devices and isolation
While 100% uptime is a mirage, at least for
a price that any reasonable person would be
willing to pay, that doesn’t mean you shouldn’t
try to do your best. Industry-hardened network
devices that will stand up to off-the-desktop,
76 • November 2012 plant engineering www.plantengineering.com