Addressing SSTDR Technology
Security and alarm business makes sense of complexities
Security and alarm systems become more complex
every day as new services, features, technologies
and capabilities are added. This complexity
is powered by good old electricity, and without
a reliable and consistent source of power, the systems
are useless. All of the wiring configurations within
each system that carry data, video, signal and voice,
Cat-5, coax cable and Romex are the backbones that
transmit the information about the overall health of
Power over Ethernet, low-voltage sensor lines and
AC and DC voltages all flow over these different types
of conductors. If something goes wrong, you want to
know about it as soon as possible and figure out what
to do about it for the customer. But what happens
when an intermittent condition pops up and trips
alarms or sets off sensors? And then what happens
when a technician responds and shuts off the power
to check the circuits but finds nothing? How does a
system get checked for electrical faults while it is running,
without disturbing the service to the customer?
What if you could look into the electrical workings
of any cables such as security and alarm, CCTV coax,
data, electrical power, high-voltage utility cable and/
or aircraft cables while they are carrying voltage, video
or even high-speed data, and see active faults such
as intermittent shorts or arc faults? Well, now you
can. A new technology is making its way to market,
and the impact on all these things will be tremendous.
The new technology is an advanced form of
spread-spectrum time-domain reflectometry (SSTDR),
and it is being developed and commercialized
by two American companies for worldwide applications
of all types.
SST has been around for a long time. It was first
thought of during World War II for use in secure communications
from submarines. Qualcomm developed
a version of this concept to help cellphones connect
with each other over a noisy and uncertain wireless
environment. The reason someone in Hong Kong can
dial your cellphone and reach only you, not the other
7 billion people on earth, is mostly due to spreadspectrum
implementation. What has happened over
the wireless world is now coming to the wired world.
The advanced form of this technology promises to
revolutionize the TDR cable-testing market and make
it safer and easier to see exactly what is happening on
live, energized circuits on all types of equipment and
over all types of conditions.
A time-domain reflectometry (TDR) cable tester
uses a generated pulse that is shot down a cable
to seek out opens and shorts that exist in the cable.
The reflected pulse shows a delay in time that can be
translated into distance or location of the fault. Traditional
TDRs can work only when the cable they are
testing is off or unpowered. This is because the voltage
noise on the line interferes with the pulse, and the
reflection is lost in this noise. Advanced SSTDR fixes
this by skipping or “floating” around the noise by
generating multiple frequency pulses that cut through
all the interference and capture the reflected pulse to
show exactly where the fault occurs, when it occurred
and what its characteristics are. In addition, unlike
older TDR technology, SSTDR also can do dynamic
testing, which can monitor an energized cable system
while it is under load or stress and in use and wait for
a fault to occur.
This is handy for those faults that are intermittent
due to some outside influence, such as voltage surges
or outside signal interference, that changes the character
of the circuit. An example of this is a short in
a power cord attached to a piece of machinery that
shorts out only when a parts cart rolls over it, or an
aircraft that has some abraded insulation in its wiring
harnesses that is shorting for only nanoseconds during
takeoff or landing.
SSTDR technology was developed out of a need to
see what is happening on live circuits on a 24/7 basis.
Developed at Utah State University and University
of Utah physics labs, the technology got its major
impetus after the July 1996 crash of TWA Flight 800,
which blew up over the south shore of Long Island,
N.Y., killing all 230 people aboard. The cause of that
crash was later attributed to an abraded control cable
that went through the belly tank of the 747 aircraft.
The wiring was arcing against a strut intermittently,
for what could have been months, and the fuel in the
center tank exploded with a terrible result. This event
triggered development grants from DOT, FAA and
the military for ways to avoid or locate these types of
faults in aircraft wiring.
Fifteen years and 16 patents later, the advanced
form of SSTDR is now being commercialized into
handheld and portable test equipment as well as
applications where it can be embedded to act as a
watchdog for “events” on cabling systems inside data
system switches, monitoring equipment for security/
alarm systems or fire alert systems. By being able to
report live and immediately, SSTDR technology gives
a clear, real-time view of any electrical event that happens,
no matter how briefly and at what intervals.
In addition, the sensitivity of the technology offers
another interesting possibility. By using new capacitive
coupling techniques, a security/alarm technician
can clamp on the insulation of a pair of conductors
without touching bare wire or disconnecting anything
and monitor the lines continuously to detect, locate
and characterize an intermittent problem that could be
reported wirelessly to his or her cellphone. This remote
monitoring of electrical conditions within a security
system could pinpoint bad connections or failing cable
without having to take the entire system offline.
Where Will it be Used?
Advanced SSTDR technology will be used on the
new electromagnetic braking systems being designed
by major truck manufacturers. It is now being tested
by the Navy for inclusion in flight-line equipment on
carriers and shipboard systems fleet-wide. The smart
grid can now be smarter with SSTDR modules inside
of power switches, distribution points and even circuit
breakers at homes and businesses. Street lighting systems
can report light outages or cable theft attempts
instantly, mining equipment can be monitored underground
to mitigate explosions caused by electrical arcing
in equipment and cables, and security and alarm
systems will have a new tool that can keep customer
systems running and without interruptions.
Key monitoring switches, servers and sensors
might have this technology embedded inside their
control units so it could self-test 24 hours a day. The
applications for such a revolutionary and disruptive
technology are many and varied.
What it Means
The detection, location and characterization of intermittent
electrical faults on live energized conductors
can now be done easily, which will create safer electrical,
data and video systems in all industries and let service
organizations keep networks running smoothly. For security
and alarm system installers and servicing organizations,
it means finding intermittent faults faster and
determining the reason for the faults more accurately,
while making systems more reliable for the customer.
A new emerging technology such as SSTDR will
make a lasting and important contribution to the security
and alarm business both in the form of handheld
or portable testing equipment and with OEM
equipment that will have it built in as an important
safety feature for each and every cable run.
Advances such as this will help the complexity
of newer security enhancements being added to networks
work better and more reliably.
This article originally appeared in the June 2012 issue of Security Today.