Theory Of Operation - Optex Fiber SenSys Terrain Defender TD 100 Installation Manual

Theory of Operation

The basic concept behind E2EC is illustrated in Figure 2.
TD100 #1 TD100 #2
Lead-in
Lead-in
Cable
Cable
d1
d2
More
Sensor
In-Line In-Line
TX Cable
Cables in
Connections Connections
Networked
System
RX Cable
Figure 2. System E2EC
The leaky coaxial sensor cable is a standard coaxial cable with an aperture or a continuous slot
in the outer conductor to allow Radio Frequency (RF) energy to couple between the signal
traveling inside the cable to a surface wave traveling outside the cable but bound to the cable.
There are two transmitters and two receivers in each processor - one TX/RX pair looking left
and the second TX/RX pair looking right. The "Blue" trace in
Figure 2 shows the TX 1 from
TD100 #1 propagating down the cable to illuminate the intruder.
A portion of the energy is reflected along the RX cable to the receiver. This is referred to as "Out
and Back" flow of energy as the contra-directional coupling. The time delay between the onset
of the coded pulse and the receipt of the change due to the intruder determines the intruder's
location. The same process is repeated by TD100 #2 from the other end of the cables, "Green"
trace. E2EC requires that the intruder be detected at the same time and at the same location to
be declared as an alarm within one-meter accuracy.
As illustrated in Figure 3, the response measured in dB decays linearly due to cable attenuation.
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