Home' RTCA Documents for Review : DO-230H FRAC Contents 147
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Detection Capabilities – Walking, running, jumping, crawling, rolling
The detection zone exists in a narrow line-of-sight region between the main and second poles. The beam
width is 3.54 inches (8.99cm) with a transmitter beam divergence of 15 mrads and a receiver beam
divergence of 7.5 mrads.
System Limitations – Fog, heavy rain, smoke, and wind-blown particulates will attenuate the beam.
Tunneling, trenching, bridging, and climbing are problematic. Crawling under a detection zone or digging
lose ground to tunnel under it, proximity to tall buildings or structures that would allow for easy jumping
or bridging over, susceptible to animals and vegetation growth. If deep enough, snow depth will block the
lower beams, giving no detection if someone crawls across in the snow.
Snow build-up or drifting snow can block the lower beam elements and cause an alarm. In areas
with frequent snow build up optional bottom beam cut off feature is available to suppress the alarm
of the bottom beams until snow can be removed leaving the upper half of the sensors active for
Heavy fog can cause alarms depending on the zone length. In areas where this type of fog is
frequent, consideration should be given to reducing the operating zone length.
Winds do not directly affect the performance of a properly installed IPID sensor system. However,
wind induced movement of a natural or manmade object in or through the detection zone may cause
alarms. More frequent grounds keeping actions or possibly construction of animal fencing may also
Small seismic or mechanical disturbances of the pulsed infrared hardware, such as those produced
by vehicle traffic, wind and aircraft should not affect the sensors.
Acoustic noise and vibration are not known to adversely affect the sensors.
Foraging animals in the detection zone may cause nuisance alarms. Therefore, removal of food and
water sources in the area may he required. More frequent grounds keeping actions or possibly
construction of animal fencing may also be required.
Testing – Walk, run, jump, roll and crawl through the detection zone. The most common defeat of this
technology is vaulting over or crawling under where the ground surface is not solid.
The system should be capable of detecting an individual weighing a minimum of 35 kilograms (77
pounds) passing between the transmitters and receivers whether the individual is walking, running,
jumping, crawling, or rolling.
This means that the infrared beams should be placed and interlaced to form an infrared “wall”.
The systems should be able to operate as above with a factor of 20 (13dB) insertion loss from
atmospheric attenuation (e.g., fog) at a maximum range of 100 meters (328 feet).
Coaxial Cable Technology
General Characteristics – Sensors mounted on a fence detect motion. Vibration associated with intrusion
activities such as cutting or climbing are distinguished from normal vibrations.
Fence Protection Systems detect intruders by using a fence mounted sensor cable, which sends analog
signals to an electronic signal processor when the cable is physically disturbed. Any mechanical effect that
tends to deform the coaxial cable such as flexing, vibration, twisting, squeezing will produce a transfer of
charge between the coax conductors detectable as a difference in potential at the input to the signal
processor. The input signal is processed through a signature filter which generates a count when the count
exceeds a preset limit alarm is generated.
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