P/N 315-049708FA-4
2
APPLICATION
The 8741, 8742 and 8743 duct smoke detectors provide early
detection of smoke and products of combustion present in
air moving through an HVAC duct supply, return, or both.
These devices are designed to prevent the recirculation of
smoke in areas by the air handling system’s fans and blow-
ers. Complete systems may be shut down in the event of
smoke detection.
For the correct installation of a duct smoke unit please refer
to NFPA 72 (National Fire Alarm Code), NFPA 90A (Standard
for Installation of Air Conditioning and Ventilation Systems),
NFPA 70 (National Electrical Code) and NFPA 92A (Recom-
mended Practice for Smoke Control Systems).
OPERATION
When the Models 8741, 8742 and 8743 are operating, a
sample of air is drawn from the duct and passed through the
sampling chamber by means of the input sampling tube. The
air sample passes through the smoke detector mounted in
the duct housing and is exhausted back into the duct
through the outlet tube.
This detector is equipped with cover removal switch (SW1) that
instantly provides a trouble condition upon removal of the clear
cover. For all testing and inspection with the cover removed, the
cover removal switch (designated as SW1 on PCB) must be
manually depressed to simulate normal operation.
LED Indicator
The 8741, 8742 and 8743 contain an LED indicator (located on
the smoke detector) capable of flashing either one of three
distinct colors: green, yellow, or red. During each flash interval,
the microprocessor based detector checks the following:
•
for smoke in its sensing chamber
•
that its critical smoke sensing electronics are operating.
Based on the results of these checks, the LED indicator
flashes as follows:
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