enclosures.
Passive ultrasonic sound sensor emits no energy but simply
"listens"
for
ultrasonic
frequencies
produced
by
breaking
through
construction materials such as glass, wood, masonry, etc. The sensitivity
of this alarm can be adjusted.
Figure 4-1.
Photoelectric IDS.
(2) Characteristics.
(a) Advantages.
This device is economical and easily installed.
After an alarm is received, the amplifier may be adjusted to monitor sounds
coming from the protected area. This system also has high salvage value.
(b) Disadvantages.
This device can be used only in vault type
installations or other enclosed areas where a minimum of extraneous sound
exists.
This device is not satisfactory where high ambient noise levels
occur, especially traffic.
Also, this system cannot be used effectively
outdoors.
Neither can it be used indoors in areas where sensitive
classified discussions occur.
4-7
MP1002
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