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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. 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 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. 31 -- 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. 32. 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 location and the tubing
to the sampling tube be connected. See “Completing
Installation of Return Air Smoke Sensor:” for details.)
Return Air Detector Sampling Tube
Controller module
Return Air Detector module
(shipping position shown)*
*RA detector must be moved from shipping position to operating position by installer
C07307
Fig. 32 -- Typical Return Air Detector Location
Return Air with Economizer — The sampling tube is
inserted through the side plates of the economizer
housing, placing it across the return air opening on the
unit basepan. See Fig. 33. 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 location and the tubing
to the sampling tube be connected. See the following
installation procedure.)
Return Air
Sampling Tube
C08129
Fig. 33 -- Return Air Sampling Tube Location
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