16
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.
Fig. 20 — 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. 21. 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.
Fig. 21 — 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. 22. The holes in the sampling tube face
downward, into the return air stream. The sampling tube is con-
nected 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. In-
stallation requires that this sensor be relocated to its operating lo-
cation and the tubing to the sampling tube be connected. See in-
stallation steps.)
Fig. 22 — Typical Return Air Detector Location
RETURN AIR WITH ECONOMIZER
The sampling tube is inserted through the side plates of the econo-
mizer housing, placing it across the return air opening on the unit
basepan. See Fig. 23. The holes in the sampling tube face down-
ward, 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 location and the tubing
to the sampling tube be connected. See installation steps.)
Fig. 23 — Return Air Sampling Tube Location
Completing Installation of Return Air Smoke
Sensor
1. Unscrew the two screws holding the return air sensor detector
plate. See Fig. 24. Save the screws.
2. Remove the return air sensor and its detector plate.
3. Rotate the detector plate so the sensor is facing outwards and
the sampling tube connection is on the bottom. See Fig. 25.
SEE DETAIL A
DETAIL
A
PLUG
SAMPLING TUBE
(ORDERED SEPARATELY)
COUPLING
MAGNETIC
TEST/RESET
SWITCH
ALARM
TROUBLE
POWER
DIRTY
SENSOR
COVER
COVER GASKET
(ORDERING OPTION)
SENSOR HOUSING
AND ELECTRONICS
EXHAUST GASKET
EXHAUST TUBE
DUCT SMOKE SENSOR
INTAKE
GASKET
TSD-CO2
(ORDERING OPTION)
SUPPLY AIR
SMOKE DETECTOR
*RA detector must be moved from shipping
position to operating position by installer.
RETURN AIR DETECTOR
SAMPLING TUBE
RETURN AIR
DETECTOR MODULE
(Shipping position
shown)*
CONTROLLER
MODULE
RETURN AIR
SAMPLING TUBE
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