Bosch D296 Series, Installation Manual

10

en | Installation considerations

Long-range beam smoke detectors

2017.03 | 7.0 | F.01U.068.899

Installation manual

Bosch Security Systems, Inc.

Always select surfaces that are not subject to building movement. The automatic
compensation circuits eliminate most problems created by normal building expansions and
contractions. Sometimes the walls and support structure might be subject to more significant
movement. This can be caused by heavy equipment operation, such as cranes anchored to the
top of the walls.
When you are uncertain about mounting surface stability, measure the detector’s signal
voltage. This voltage must be between 3.8 VDC and 4.2 VDC. Beam misalignment can cause
this voltage to increase or decrease. The detector indicates a trouble condition when, over a
long period, the voltage:
–

increases to greater than ~4.8 VDC or

–

decreases to less than ~2 VDC

A trouble condition also occurs when voltage decreases to ~0.4 VDC for more than 20 sec. For
how to take a voltage reading, see Reference voltage adjustment, page 27

.

To prevent movement if you expect the mounting surface to move:
–

relocate the detector to a stable surface or

–

add supports to the mounting surface

Mounting the detector to a 4-inch square or octagonal electrical mounting box can bow the
mounting plate. Bowing occurs because the mounting box screw tabs are below flush with the
top edges of the mounting box. Over tightening the mounting screws bows the mounting plate
inward at the bottom, causing the optics to aim low. Irregularities in the flatness of the
mounting box edge surfaces or at the screw tabs worsens this condition. Only use mounting
boxes with flat, regular surfaces and properly formed screw tabs. Minimize misalignment
caused by mounting plate bowing by tightening the mounting screws to secure the mounting
plate to:
–

2 in. (5 cm) or

–

2 lb (0.9 k) torque

3.5

Plan for the effects of stratification in cold environments

Air stratification might prevent smoke from reaching detectors mounted close to the ceiling.
Stratification occurs when smoke, rising because it is warmer than the surrounding air,
reaches a level where it is the same temperature as the surrounding air and does not rise to
the ceiling. In extremely cold environments such as unheated warehouses, smoke cools very
quickly and is less likely to rise to the ceiling. Add more detectors at lower mounting heights
to compensate.

3.6

Design for the expected fire load

When designing a fire alarm system, set detector sensitivity to:
–

respond to the proper smoke obscuration and

–

reduce the chance of a false activation within the application

As illustrated in the following figure, the total obscuration of the infrared beam depends on
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the density of the smoke and

–

width of the smoke cloud along the beam path