Chapter 3: Operating instructions
P/N 3101890-EN • REV 006 • ISS 21JUN18 49
Switching the smoke detector alarm sensitivity thresholds
Intelligent addressable smoke detectors are configured with two alarm sensitivity thresholds: primary and
alternate. The alarm sensitivity setting, configured in the VM-CU, sets the threshold at which the smoke detector
activates an alarm event. This allows you to increase or reduce an individual detector’s sensitivity at various times
of the day, dependent upon, environmental conditions, occupancy, manufacturing processes, etc.
A time control is commonly used to automatically switch alarm sensitivity thresholds. However, you can manually
switch alarm sensitivity thresholds by using command menus.
Primary alarm sensitivity threshold
Typically, the primary alarm sensitivity threshold is set to a lower threshold. This threshold is commonly used for a
daytime operation to reduce the occurrence of nuisance alarms when a facility is occupied, or when
environmental conditions may create prealarm conditions.
Alternate alarm sensitivity threshold
The alternate alarm sensitivity threshold sets the secondary threshold at which the smoke detector activates an
alarm event. Typically, the alternate threshold is set to a higher sensitivity threshold. This threshold is commonly
used for a nighttime or weekend operation, when the facility is unoccupied.
Alarm sensitivity settings
Alarm sensitivity settings are expressed in percent of smoke obscuration per foot. The setting defines the
threshold at which the detector will change to the alarm state when the smoke in its sensing chamber exceeds the
obscuration per foot threshold.
The alarm sensitivity setting can be set to one of five sensitivity levels.
• Most: Activates an alarm event when the smoke level reaches approximately 1.0 %/ft obscuration (0.7 %/ft for
ionization detectors)
• More: Activates an alarm event when the smoke level reaches approximately 2.0 %/ft obscuration (1.0 %/ft for
ionization detectors)
• Normal: Activates an alarm event when the smoke level reaches approximately 2.5 %/ft obscuration (1.2 %/ft
for ionization detectors)
• Less: Activates an alarm event when the smoke level reaches approximately 3.0 %/ft obscuration (1.4 %/ft for
ionization detectors)
• Least: Activates an alarm event when the smoke level reaches approximately 3.5 %/ft obscuration (1.6 %/ft
for ionization detectors, 2.46 %/ft for a SIGA-SD Duct Smoke Detector)
Note: When smoke detectors having both ionization and photoelectric elements are used, the sensitivity setting
applies to both elements.
Switching the sensitivity threshold
To activate the alternate alarm sensitivity settings:
1. Access the Main Menu, and then select Activate.
2. Select Alt Sensitivity.
3. Enter the access level password.
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