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 4.1.2.3 Pressure-Sensitive Sensors. Also called pressure mats, this sensor
consists of switch(es) enclosed in a mat which are normally placed at
approaches to areas containing objects requiring special protection. Mats
vary in sensitivity from 5 pounds to 20 pounds per square foot and may be
cut to fit the area of application. Activation of the switch causes an
alarm signal to be transmitted via the connecting wires (which should be
concealed) to a control unit. The following application and installation
considerations apply to pressure-sensitive sensors.
a) Positioning is critical since these mats, normally only the
width of a stair runner, may be easily stepped over. They should be
concealed and positioned where someone approaching the protected object
would have to step, for example, just inside door openings, under stair
runners, or under a carpet immediately surrounding the protected object.
b) Plastic-encased versions should be specified to preclude
failure due to dampness or high humidity. Sealing connections in epoxy will
help avoid such failures.
c) These sensors can be extremely cost effective when purchased in
bulk rolls. Properly positioned, they offer good protection against an
unsophisticated intruder.
4.1.3 Floor, Wall, and Ceiling Protection. While most unsophisticated
intruders take the most obvious approach to attempt an intrusion, an
intruder who is knowledgeable of the presence, capabilities, and limitations
of IDS elements protecting portals may attempt to bypass this protection and
obtain entry through other parts of the building perimeter (floors, walls,
or ceilings). The sensors discussed in this section are specifically
designed to detect such forcible intrusion attempts.
4.1.3.1 Vibration Sensors. Also called "shock" sensors, these sensors
operate as described in "Vibration/Ultrasonic" and the same considerations
for application and installation apply. Other considerations are:
a) Figure 19 depicts the inner workings of one type of vibration
sensor. Others of equal quality may use one or more balls or other "mass"
devices balanced between contacts. When the electrical circuit is completed
(or broken), an alarm results.
b) The simplest vibration sensor is a mechanical contact switch
designed to actuate when the surface on which the sensor switch is mounted
starts to vibrate. This latter type is also subject to more nuisance alarms
13.02-40
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