34
terminal for connecting to the controller. Each sensor has
four LEDs (for Power, Trouble, Alarm and Dirt y) and a
manua l test/reset button (on the left--side of the housing).
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
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 am ount of
smoke is detected in the sensing chamber, the sensor
signals an alarm state and the controller automatically
take s 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 gra dual 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
dete ctor does not differentiate which sensor signal s an
alarm or t rouble condition.
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
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. 6 0 -- Typical Supply Air Sm oke 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
50TCQA
