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 type, fit, and aesthetics. The position of a surface-mounted BMS is
relatively easy to adjust during final installation to accommodate variances
in door type and fit, whereas recessed models are relatively difficult to
adjust. There may be a cost-effectiveness limit on door type selection and
fit adjustment that may dictate BMS type selection. For new construction
contracts, doors and frames for recessed BMS should be specified to be
procured with the appropriate recesses already in the doors and frames.
e) Applying a BMS where not required, as a "nice to have" feature,
should be avoided. Overapplication of any sensor, despite its reliability,
increases maintenance requirements and the likelihood of false or nuisance
alarms. On the other hand, not applying a BMS where required may produce an
unnecessary vulnerability into the security system design. The system
designer must keep in mind that a BMS detects movement of a portal but does
not detect movement within a space.
f) A BMS which is not securely mounted can have sensitivity loss
or cause nuisance alarms after repeated portal opening and closing. Good
mounting hardware and proper installation techniques will minimize such
problems. Assuring correct polarity alignment is particularly important for
a recessed BMS.
g) If multiple BMSs are required for a particular application,
they must be installed carefully to avoid an improper connection, which may
result in two leads having a "jump" between them, rendering the sensor(s)
inoperative.
h) Glass encapsulated reed BMSs must be handled with care to
preclude inadvertent damage. These are particularly suitable for highly
corrosive environments.
i) Some models of BMSs have a minimum separation as well as a
maximum separation required between switch and magnet housings. To maximize
performance, installation requires use of an ohm meter. The meter is
attached to the switch leads. Moving the magnet housing toward and away
from the switch will, by marking the two positions where the meter indicates
the switch has activated (0 ohms for a switch closure), indicate the maximum
adjustment range possible so that sensitivity can be properly adjusted by
correct positioning of the housings.
j) Performance testing of BMS should be conducted with other
sensors in the protected space deactivated so that, for example, faulty BMS
performance is not masked by a volumetric motion sensor sensing a portal
opening.
4.1.1.2 Glass Breakage Detectors These sensors are used to detect breakage
of glass by an intruder who is attempting to enter a portal by bypassing
security hardware (e.g., lock) or IDS devices such as the BMS.
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