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3-2.5.2.4.9
Application
In-duct
DH-2000
August 2013
How to Change a Photoelectric Detector's Pre-Alarm and Alarm
Thresholds
Purpose: To change the pre-alarm and alarm thresholds of one or more
photoelectric detectors. The photoelectric detector is UL Listed and FM
Approved for alarm reporting anywhere within the obscuration range
of 0.5 to 3.5 percent per foot when used for an open-area application.
Alarm thresholds can be set in 0.1 percent-per-foot increments. A pre-
alarm threshold can also be set anywhere within the obscuration range
of 0.2 to 3.4 percent per foot, but must be less than the detector's
alarm threshold. Two additional alarm-reporting ranges are defined for
special applications. The in-duct range refers to detector placement in
an air duct. The DH-2000 range refers to detector placement in a DH-
2000 Duct Housing with associated sampling tubes to monitor the air
in either a supply- or return-air duct. The alarm ranges for these
special applications are as follows:
Pre-Alm Range (%/ft.)
0.2 - 1.9
0.2 - 1.9
Photoelectric detectors can be automatically programmed to
change alarm thresholds by time of day if they are configured for
day/night operation. The night alarm thresholds must be less than
the corresponding day thresholds.
3-38
Alm Range (%/ft.)
0.5 - 2.0
0.5 - 2.0
P/N 06-236530-001
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