4.4 Provide a stable mounting surface | 4.6 Consider the expected Fire load |
Beam smoke detectors depend on the measurement of the projected beam to sense smoke. Therefore, shifts in the alignment of the beam due to movement of the transmitter/receiver can cause trouble or alarm conditions.
•Always select a stable mounting surface.
•Never mount the unit to a suspended support such as a pipe or length of wood supported at only one end.
This type of mounting can create a “pendulum effect” which greatly multiplies even very small movements at one end of the support. For example, a 2 in. (5.1 cm) movement translates into a beam misalignment of over 20 ft at 350 ft (6 m at 107 m).
Mounting surfaces should be supported at opposite corners to reduce the pendulum effect.
• Always select surfaces not subject to building movement.
The automatic compensation circuits of the DS240 and DS241 will eliminate most problems created by normal building expansions and contractions. In some unusual circumstances, the walls and support structure may be subject to more significant movement due to the operation of heavy equipment, such as cranes, anchored to the top of the walls.
When in doubt about mounting surface stability, measure the signal voltage of the detector. This voltage should be 4.0 VDC. Misalignment of the beam can cause this voltage to increase or decrease. The detector will indicate a trouble condition when the voltage increases to more than 4.8 VDC, or when it decreases to less than 2.0 VDC over a long period of time or to 0.4 VDC greater than 20 sec. For more information on reading this voltage, see Section 8.3 Reference Voltage Calibration on page 6).
If movement of the mounting surface is suspected, relocate the detector to a surface that does not move or add supports to the mounting surface to prohibit movement.
•DO NOT
When the detector is mounted to an electrical mounting box [4 in. (10 cm) square or octagonal], the mounting plate may bow as a result of the mounting box screw tabs being below flush with the top edges of the mounting box.
Irregularities in the flatness of the mounting box edge surfaces or screw tabs will worsen this condition. Using only mounting boxes with flat, regular surfaces and properly formed screw tabs, and tightening the mounting screws to secure the mounting plate to 2 in./lb torque will minimize any misalignment caused by bowing of the mounting plate.
4.5 Consider the effects of stratification in cold environments
In very cold environments such as unheated warehouses, smoke may cool very quickly and is less likely to rise to the ceiling. Consider additional units at lower mounting heights to help compensate for this situation.
When designing a fire alarm system, consider the expected fire load within the application.
For instance, fires caused by the ignition of flammable petroleum- based liquids usually result in a rapid buildup of heavy smoke. When these types of fires are probable, use sensitivity settings 0 or 1 which provide a response time of 5 sec.
5.0Mounting
NOTE: This product is not designed for use in outdoor applications.
Install a 4 in. (10 cm) square or octagonal electrical box (not supplied) to a rigid surface that will not be subject to movement or vibrations.
NOTE: If not mounting to an electrical box, be sure the surface will not be subject to movement or vibrations. For example: do not mount directly to a suspended ceiling without extra support.
•Remove the receiver's access door (1 screw), then remove the cover (4 screws). See Figure 4.
COVER MOUNTING
SCREWS (4)
ACCESS DOOR
Figure 4 - Access Door and Cover
•Remove the receiver’s backplate by removing the single mounting screw from the top of the circuit board carrier plate then separating the two plates (see Figure 5).
REMOVE TO
EXPOSE BACKPLATE
MOUNTING
SLOTS (4)
DO NOT
REMOVE
WIRING
ENTRANCE
Figure 5 - Removing the Backplate
• Bring wiring from the electrical box through the wire entrance.
NOTE: All wiring should be unpowered.
•Securely mount the backplate to the electrical box.
•Return the circuit carrier plate to the backplate. Secure it in place with the single mounting screw.
•Repeat this mounting procedure for the transmitter.
DS240/DS241 Installation Instructions | © 2004 Bosch | P/N: 22066P Page 3 |
