Figure 8-23.Conductive foil on picture window.
Figure 8-24.Complete glass-door protection.
INDUSTRIAL COMPONENTS OF
Industrial security/fire-alarm systems are
essentially the same as those used for residential
applications. There are, however. a few additional
components that are used mostly in industry.
Vibration detectors are often used on industrial
buildings to detect vibrations caused by forced entry.
Such detectors have been used on a variety of
construction materials. such as hollow tile, plaster and
lath, brick, concrete. metal ceilings, and wood. Once
mounted in place, they may be adjusted with a setscrew
for the desired sensitivity.
Some factories maintain a security fence euipped
with fence-guard detectors. This type of dectector will
detect climbing, cutting, or any other penetration of the
fenced area. Most of these detectors operate on
standard closed-circuit controls as described
Fence-guard detectors use a vertical-motion
detector that is sensitive to movement created by
climbing or cutting the fence. Normal side motions,
such as wind or accidental bumping, do not affect the
detector and cause false alarms. The detectors are
normally mounted about midway up the fence and
every 10 feet (3 m) of fence length. Most of these
devices set off the alarm if they are tampered with or if
the wire is cut. They may be connected to a control
panel and the alarm will sound in the form of a bell or
horn, or it will silently dial the local law-enforcement
Another type of detector that is used is the outdoor
microwave detector. This detector is used for pro-
tecting large outdoor areas like car lots, construction
sites, and factory perimeters. In operation, a solid,
circular beam of microwave energy extends from a
transmitter to the receiver over a range of up to 1,500
feet (457 m) for some brands. Any movement inside of
this beam (fig. 8-30) will activate the alarm.
The continuous linear thermal sensor is a small-
diameter coaxial wire that is capable of sensing
temperature changes along its entire length. The sensor
is made up of a center conductor and an outer stainless
steel sheath. The center conductor is electrically
insulated from the outer sheath by a ceramic thermistor
material, as shown in figure 8-31.
Since the thermistor has a negative coefficient of
resistance, the electrical resistance between the center
wire and the outer sheath decreases exponentially, as
the surrounding temperature increases (fig. 8-32).
The changing resistance is monitored by one of
several control panels that then can actuate
extinguishing systems or any other electrically
Such sensors have a diameter of approximately
0.080 inch (0.2 cm) and, therefore, have a small mass
that permits them to sense changes in temperature
rapidly. They can sense temperatures from 70°F
(21°C) up to 1200°F (649°C) if the thermistor material
is properly selected.