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Controller Housing
and Electronics
Conduit Couplings
(supplied by installer)
Fastener
(2X)
Cover Gasket
(ordering option)
Alarm
Fig. 29 — Controller Assembly
Sensor
The sensor (see Fig. 30) includes a plastic housing, a printed cir-
cuit board, a clear plastic cover, a sampling tube inlet and an ex-
haust tube. 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
permits visual inspections without having to disassemble the sen-
sor. The cover attaches to the sensor housing using four captive
screws and forms an airtight chamber around the sensing electron-
ics. Each sensor includes a harness with an RJ45 terminal for con-
necting to the controller. Each sensor has four LEDs: Power, Trou-
ble, 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 to prevent 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.
For installations using two sensors, the duct smoke detector
does not differentiate which sensor signals an alarm or trouble
condition.
Duct Smoke Sensor
Controller
Conduit Nuts
(supplied by installer)
Conduit Support Plate
Terminal Block Cover
Controller Cover
Trouble
Power
Test/Reset
Switch
Exhaust Tube
See Detail A
Intake
Gasket
TSD-CO2
(ordering option)
Plug
Sampling Tube
(ordered separately)
Coupling
Detail A
Magnetic
Test/Reset
Switch
Fig. 30 — 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. 31. 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 hous-
ing (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.
SUPPLY AIR
SMOKE
DETECTOR
SENSOR
Fig. 31 — Typical Supply-Air Smoke Detector
Sensor Location
26
Duct Smoke Sensor
Exhaust Gasket
Sensor Housing
and Electronics
Cover Gasket
(ordering option)
Alarm
Power
Trouble
Dirty
Sensor Cover
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Table of Contents
Troubleshooting
