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Duct smoke sensor
controller
Fastener
(2X)
Controller cover
Conduit nuts
(supplied by installer)
Conduit support plate
Cover gasket
(ordering option)
Conduit couplings
(supplied by installer)
Terminal block cover
Controller housing
and electronics
Alarm
Power
Te s t / r e s e t
switch
Trouble
C08208
Fig. 58 -- Controller Assembly
Duct smoke sensor
See
Detail A
Exhaust tube
Plug
Sampling tube
(ordered separately)
Intake
gasket
Cover gasket
(ordering option)
TSD-CO2
(ordering option)
Sensor housing
and electronics
Exhaust gasket
Coupling
Sensor cover
Detail A
Magnetic
test/reset
switch
Alarm
Trouble
Power
Dirty
C08209
Fig. 59 -- Smoke Detector Sensor
Air is introduced to the duct smoke detector sensor’s
sensing chamber through a sampling tube that extends into
the HVAC duct and is directed back into the ventilation
system through a (shorter) exhaust tube. The difference in
air pressure between the two tubes pulls the sampled air
through the sensing chamber. When a sufficient amount of
smoke is detected in the sensing chamber, the sensor
signals an alarm state and the controller automatically
takes the appropriate action to shut down fans and
blowers, change over air handling systems, notify the fire
alarm control panel, etc.
The sensor uses a process called differential sensing to
prevent gradual environmental changes from triggering false
alarms. A rapid change in environmental conditions, such as
smoke from a fire, causes the sensor to signal an alarm state
but dust and debris accumulated over time does not.
For installations using two sensors, the duct smoke
detector does not differentiate which sensor signals an
alarm or trouble condition.
Smoke Detector Locations
Supply Air —
The Supply Air smoke detector sensor is located to the left
of the unit’s indoor (supply) fan. See Fig. 60. Access is
through the fan access panel. There is no sampling tube used
at this location. The sampling tube inlet extends through the
side plate of the fan housing (into a high pressure area). The
controller is located on a bracket to the right of the return
filter, accessed through the lift--off filter panel.
Smoke Detector Sensor
C08245
Fig. 60 -- Typical Supply Air Smoke Detector Sensor
Location
Return Air without Economizer —
The sampling tube is located across the return air opening
on the unit basepan. See Fig. 61. The holes in the
sampling tube face downward, into the return air stream.
The sampling tube is connected via tubing to the return air
sensor that is mounted on a bracket high on the partition
between return filter and controller location. (This sensor
is shipped in a flat--mounting location. Installation
requires that this sensor be relocated to its operating
50HCQA