UFC 4-021-02NF
27 September 2006
change 1, 23 October 2006
Figure 5-2. Separate ACS and IDS CPUs
5-3.2
Interior Point Sensors
5-3.2.1 Balanced Magnetic Switch(s) (BMS). BMS use a magnetic field or
mechanical contact to determine if an alarm signal is initiated (for example, if an access
portal such as a door, window, or roof hatch is been opened). BMS differ from standard
magnetic status switches in that BMS incorporate two aligned magnets with an
associated reed switch. If an external magnet is applied to the switch area, it upsets the
balanced magnetic field such that an alarm signal is received. Standard magnetic
switches can be defeated by holding a magnet near the switch. Mechanical contacts
can be defeated by holding the contact in the closed closed position with a piece of
metal or taping them closed. Balanced magnetic switches are not susceptible to
external magnetic fields and will generate an alarm if tampering occurs. Therefore, only
specify balanced magnetic switches for access portal sensors. Figures 5-3, 5-4, and 5-5
show some typical applications of BMS.
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