INSTRUCTIONS
Smoke Detector
for Classified Areas
U5005
3.1
©
Detector Electronics Corporation 2010
3/10
95-8452
APPLICATION
The Det-Tronics U5005 Smoke Detector is a sensitive
yet rugged, state-of-the-art protection device that is
designed for classified areas in hazardous industrial
and commercial locations. The detector is designed to
operate effectively with both slow smoldering and fast
burning fires. Typical applications that use the U5005
include:
Combustible storage facilities
•
Munitions manufacturing
•
Volatile chemical storage
•
Chemical processing plants
•
Petroleum refineries
•
Turbine enclosures.
•
DESCRIPTION
The photoelectric smoke detector uses a solid state
infrared emitting diode (IRED) and a light sensing
photovoltaic cell arranged in a labyrinth assembly. The
labyrinth permits free access to smoke but restricts
external light. Because of its critical function to the
operation of the detector, each IRED is selected with
extreme care and is subjected to rigorous pre-production
testing to ensure long-term reliability and performance.
During normal operation (no smoke), the detector
samples the air approximately every four seconds for a
period of less than one millisecond. The photo-voltaic
smoke cell, which is placed at an angle to the pulsed
invisible light source, is sensitive to the infrared light in
the specified frequency emitted by the IRED light source
and is designed to receive a signal only when the pulsed
IRED source is activated. See Figure 1.
When smoke enters the chamber, the light from the
IRED reflects off the smoke particles and reaches the
photovoltaic smoke cell. When the amount of light
reflected by smoke reaches the factory set threshold
level, the smoke alarm circuit is actuated.
The detector will respond to a slow smoldering fire when
smoke in the chamber reaches the pre-set sensitivity
setting,
typically 2.3%
.
If a fast burning fire should occur, including fires
in flammable liquids and other materials such as
plastics that generate black smoke, the abnormally
rapid movement of smoke into the detection chamber
is sensed by a special rate compensating circuit. An
increase in smoke within the detection chamber that
exceeds a pre-set rate causes the rate compensation
circuit to increase the intensity of the light source, which
increases detector sensitivity. If the smoke continues to
build at this rate, an amplifier circuit is triggered and the
unit generates an alarm. If not, the detector reverts to
normal sensitivity.
PHOTOVOLTAIC
SENSOR CELL
LENS
IRED
LIGHT
SOURCE
ALARM
LED
LENS
SMOKE CHAMBER
B1178
Figure 1—Cross Section of Sensing Chamber Assembly
