26
Fig. 29 — Controller Assembly
Sensor
The sensor includes a plastic housing, a printed circuit board, a
clear plastic cover, a sampling tube inlet and an exhaust tube. See
Fig. 30. The sampling tube, when used, and exhaust tube are at-
tached during installation. The sampling tube varies in length de-
pending on the size of the rooftop unit. The clear plastic cover per-
mits visual inspections without having to disassemble the sensor.
The cover attaches to the sensor housing using four captive screws
and forms an airtight chamber around the sensing electronics.
Each sensor includes a harness with an RJ45 terminal for connect-
ing to the controller. Each sensor has four LEDs: Power, Trouble,
Alarm and Dirty. A manual test/reset button is located on the left-
side of the housing.
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 suffi-
cient amount of smoke is detected in the sensing chamber, the sen-
sor 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 photoelectric (light scattering principle) process
called differential sensing preventing gradual environmental
changes from triggering false alarms. A rapid change in environ-
mental conditions, such as smoke from a fire, causes the sensor to
signal an alarm state, but dust and debris accumulated over time
does not.
Fig. 30 — Smoke Detector Sensor
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. 31. Access is through the fan ac-
cess panel. There is no sampling tube used at this location. The
sampling tube inlet extends through the side plate of the fan hous-
ing into a high pressure area. The control module is mounted in
the left side of the control box, accessed by opening the control
box access door.
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
Test/reset
switch
Trouble
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
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