Introduction
FlexPS Product Guide
Page 69
Understanding FlexPS alarm detection
The FlexPS processor constantly evaluates the input signals from the sensor cables to
discriminate between Cut events, Climb events, and environmental activity. The characteristic
response of a Cut event is a sharp spike with a fast rising and fast falling edge. For a climb event,
the response includes the fast rising edge, which is followed by a series of peaks and valleys
caused by the continued presence and changing stresses on the fence. Environmental activity is
generally of longer duration, lower magnitude, and has more gradual increases and decreases.
illustrates typical response signals for cut, climb, and environmental activity.
The processor examines the signal magnitude of each sample in sequence, and compares these
magnitudes to preceding and subsequent samples. In this way, the processor increments the Cut
Count, or the Climb Time, based on typical expected results. When the processor interprets
activity to be the result of environmental stimulus, it removes the “Noise” value from the displayed
signal magnitude. As a result, the processor discriminates between Cut and Climb events, and
environmental activity. However, with all of the variables such as fence type and condition, attack
type and tools used during an attack, it is possible that the processor may report a Climb event as
a Cut event or vice versa. Regardless of how the processor interprets an actual event (as a cut or
a climb) the processor will record the event and report an intrusion alarm when the user-specified
detection parameters are satisfied.
Intruder detection
There are three intrusion attempt scenarios:
•
Cut scenario - An intruder attempts to cut through the fence fabric.
•
Climb scenario 1 (climb-over) - An intruder attempts to climb over the fence.
•
Climb scenario 2 (crawl-under) - An intruder attempts to crawl under the fence by lifting the
fence fabric.
An intrusion alarm resets automatically when the event is over or when the Alarm Hold Time
lapses. The Alarm Hold Time is a factory setting which is used to prevent subsequent alarms from
being declared for a single event. The Alarm Hold Time is 2 seconds, and cannot be adjusted.
Once the processor declares an alarm, another alarm will not be triggered for 2 seconds.
Cut detection
Cutting the fence fabric produces a high amplitude signal that exceeds the cut alarm Threshold.
Each time the cut Threshold is exceeded a Count (cut event) is recorded. When a specified
number of cuts occur within a preset time Window, the system generates a cut alarm. If the cut
Count is not exceeded within the time Window, the cut Count resets.
Figure 75: FlexPS detection response
Note
It is possible that strong gusting wind or the sudden onset of heavy
precipitation can be interpreted as intrusion activity.
Cut response
Climb response
Environmental response