Rev. A.2, 6/00
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of the proximity switch array should allow
considerable door movement prior to the delay
starting. The benefit of this large movement (approximately 1”) is the
avoidance of false
initiation
through (for example) the door being rattled from the outside or moved by the wind.
The movement stroke can be reduced by loosening the screws that hold the proximity switch
array to the sub-plate and sliding the array farther from the door. Securitron recommends that
this be done only in special situations. Examples would be if the door will not physically move
far enough to reliably initiate delay without reducing the stroke because the door is thicker than
1 3/4” and you have not added a spacer to the MXD sex bolt (see Section 2.3.1) or if you
deliberately want to mechanically limit the amount of door movement because of high security
concerns for that door (you wish to avoid the possible insertion of a crowbar).
5. REDUNDANT OPERATION AND TAMPER PROOFING
The proximity switch array contains three proximity switches for the following reasons. Two are
wired such that if
either
switch de-energizes as the permanent magnet is separated from the
switch array, the delay initiate signal will be given. This provides redundant reliability of safe
egress operation as single component failure will not stop the MXD from allowing egress.
The third proximity protects against a certain type of
tampering
. It is wired such that if another
permanent magnet is brought near to it, it will initiate the delay. It is positioned so that it never
gets close enough to the permanent magnet pack on the door to trigger. A building guard
however may wish to defeat the function of the MXD in letting people go out, either because he
imagines that he is doing a useful thing by increasing security (at the expense of life safety) or
because he wishes to avoid having to respond to door alarms. If the guard comes to
understand that a permanent magnet is mounted behind the strike and that separation of this
magnet pack from the lock housing initiates the delay signal, he may try to defeat this function
by placing an external magnet around the housing. This will generally result in the delay
initiating from the third “tamper” proximity unit. The MXD therefore includes a strong defense
against tampering with its safety function. This function should nevertheless be
periodically
tested by building management
as maintenance of life safety should be the paramount
concern.
