Figure 8-25.Various components of a residential security/fire-alarm system.
Figure 8-26.Floor-mat detector.
Since electrical resistance is measured across two
wires (center and sheath), the sensor has the ability to
detect a high temperature on a short wire as well as a
lower temperature on a longer one.
The elements are mounted by clamps spaced along
their lengths and the detectors, being all solid state,
have only two electrical failure modes: open circuit
and short circuit. Both of these conditions can be
caused only by mechanical means and are minimized
by rigid mounting. Figure 8-33 shows the construction
and mounting details.
Figure 8-27.Ultrasonic motion detector.
Ultraviolet-Radiation Fire Detectors
Ultraviolet-radiation fire detectors combine large-
scale integration circuit techniques with an ultraviolet
detection assembly to form a simple, yet flexible, fire-