50HCQA
Duct smoke sensor
| controller |
| Conduit nuts |
| (supplied by installer) |
| Conduit support plate |
| Terminal block cover |
Controller housing | Cover gasket |
and electronics | (ordering option) |
Conduit couplings | Controller cover |
| |
(supplied by installer) |
|
| Fastener |
| (2X) |
| Trouble |
Alarm | Power |
| Test/reset |
| switch |
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 amount of smoke is detected in the sensing chamber, the sensor 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 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. 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
Duct smoke sensor
Exhaust tube
Exhaust gasket
See
Detail A
Intake 
gasket
Plug
Sampling tube
(ordered separately)
Coupling
Detail A
Magnetic test/reset switch
Sensor housing and electronics
Cover gasket
(ordering option)
Sensor cover
Smoke Detector Sensor
C08245
Fig. 60 - 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. 61. The holes in the sampling tube face downward, into the return air stream.
Alarm | Power |
Trouble | Dirty |
C08209
Fig. 59 - Smoke Detector Sensor
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
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