FUNCTIONING OF EQUIPMENT
This chapter contains a circuit description for each of
open, the voltage at the tamper alarm output will drop to
the equipment operation modes. Explanations are
less than 1 volt and the remotely located Control Unit
will be activated. The internal tamper (door) switch is
Figure 4-1 Audible alarm block diagram (Located
held closed when the front access door is closed and the
back of manual)
external tamper (pry-off) switch is held closed when the
Primary Power Supply and Battery
audible alarm is installed.
This circuit is used to monitor the resistance between
Primary power (115 Vac) is routed into the audible alarm
the inner and outer enclosures, as well as the 5.0 0.5 V
from the Control Unit through a 3-terminal group L1, a
toggle switch (S3, POWER ON-OFF) and a 0.5 ampere
dc from the tamper switches, and the output of the
analog switch. Its output is normally 5.0 V dc, 0.5 V
fuse into the ac power supply, dc battery trickle charger,
the audio ramp generator, and the amplifier package.
dc. If the resistance between the enclosures should
Ac power into the primary power supply is rectified,
drop below 10K ohms, or if one of the tamper switches
regulated and filtered to 27.5 to 28V dc and in then
opens, or if the analog switch is activated, the
applied to the power supply-charger.
impedance monitor will indicate an alarm at its output.
The power supply-charger serves a dual purpose: it
During an alarm condition, the monitor output is less
provides the circuitry of the audible alarm with regulated
than 1 volt.
27.5 to 28V dc and monitors the battery potential,
applying charging pulses to the battery whenever the
The level detector is activated by a change in level, or
potential falls below 27V dc.
alarm indication, from the remotely located Control Unit.
Secondary or Emergency Power
When a Control Unit alarm is not present, the input to
Secondary power is supplied by a 24-volt, gel cell
the level detector is 5.0 0.5 V dc. During an alarm,
electrolyte battery whenever the ac power to the primary
the level drops to less than 1 volt. The level detector
power supply fails.
controls the analog switch.
If for any reason the Audible Alarm is
When the level detector is activated (during an alarm
deactivated for a period that may
from the Control Unit), its output turns on the analog
exceed six months, the battery should
switch. Therefore, the analog switch applies regulated
be removed, and placed in storage.
+27.5 to 28V dc to the ramp generator, VCO, and driver
Batteries in storage should be
amplifier (buffer), as well as activating the impedance
recharged every six months. Charging
supply shall be a constant voltage
source. Set between 30 31 volts, with a
The ramp generator produces a sawtooth wave which
charging current not to exceed 300
causes the VCO output to sweep upward in frequency.
milliamps per 2.5 AMP-HR battery for a
The ramp is directly coupled to the voltage controlled a
24 hour charging rate.
stable oscillator (VCO). The linearly increasing voltage
5-Volt Series Regulator
level of the ramp will sweep the VCO from
Operating off the 27-volt power supply output, the series
approximately 500 Hz to 2000 Hz in one second and
regulator supplies 5V dc to the impedance monitor
then repeat. This signal is then coupled to the driver
through the tamper switches. (Whenever the 5-volts is
circuit for amplification before passing to the power
interrupted by the opening of one or both switches, the
amplifier. The ramp generator is activated by the
impedance monitor produces an alarm output).
Internal and External Tamper
4-10. Voltage Controlled Oscillator (VCO)
Internal Tamper (Door) and External (Pry-off) switches
The voltage controlled
are connected in series with the +5V dc regulator and
oscillator generates the signal that is reproduced by the
the tamper alarm output of the impedance monitor. The
speaker driver as an audible alarm. It is caused to
voltage at the tamper alarm output will normally be 4.5
change the frequency of its output by the ramp
to 5.5 V dc during the non-alarm condition, with the
switches closed. If either of the tamper switches is
Change 1 4-1