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 communication is inexpensive and relatively speedy. The advantage of this
type of installation exists where leased telephone line pair or proprietary
wire connections are impractical due to unavailability, extreme distances,
or high cost. The disadvantage is in the limited (less than 10) number of
reporting zones per system and the vulnerability of the telephone line used
for reporting. The principal applications of the digital reporting scheme
is residence and retail establishment usage in the central station or police
connect terminations.
8.4.1.3 Simple Multiplexed Alarm Reporting Systems. Multiplex alarm
reporting is a relatively new technique capable of having several
simultaneous reports use the same circuit. Differentiations in time or
frequency separate the individual reports to avoid interference or clashing
which would result in incomprehensible messages. The system requires the
signal to be separated (demultiplexed) at the receiving end in order to
display and record the event reports. Multiplex wiring advantages are
apparent where multiple reports on the same circuits are required, such as
in large systems where one pathway could be used or multiple reporting
premises have large reporting needs (up to 256 sensor zones per subscriber).
The same is true where very high point-to-point wiring expense is evident
and line supervision polling techniques are required for security. The
disadvantage is the vulnerability of reports beyond any fault in the line
and costs of telephone facilities, engineering, and receiving equipment.
8.4.1.4 Microprocessor-Based Alarm Reporting Systems. The equipment for
this system requires point-to-point wiring, and the display is initiated on
an "IF - THEN" scheme. Audible, visual, and language annunciation can be
used in local or remote centralized reporting. The transmission techniques
can be individual dedicated wire pairs for each display terminal or digital,
multiplexed communications. The most popular method of transmission is via
modem because of the vast amount of information available through this
system and the ability to provide control to, in addition to monitoring
from, a remote site. The local reports of events and alarms must be changed
into a transmittable form and translated at the central control. The
modulation/demodulation technique is used commonly for the transfer of
computer-to-computer information over existing telephone line facilities.
The benefit of microprocessors with cathode ray tube (CRT) displays over
other annunciation devices is the method of information display regarding
the alarm or event reporting. When an alarm occurs, the device identifies
the specific location (usually in English) of the occurrence and provides
information regarding the proper course of action to follow. Decisions of
"what to do next" are removed from the discretion and interpretation of the
responding personnel by the previously determined directions associated with
each event report. Figure 52 illustrates a microprocessor-based reporting
and control system which incorporates multiplexed data path scheme. This
system is appropriate for both exterior perimeter and individual facility
applications and is in use at many Navy facilities.
8.4.2 Status Control. The status indications of the display system are
divided into the annunciation of particular event reports. The need to
clearly differentiate the indicators is apparent when the system size is
13.02-123
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