FUNCTIONING OF EQUIPMENT
Section I. FUNCTIONAL SYSTEM OPERATION
a. The Magnetic Weapon Sensor (MWS) is a subsystem of the Joint-Service Interior Intrusion Detection System (J-
SIIDS) The MWS functions in conjunction with the J-SIIDS Control Unit to protect military arms rooms
b. The MWS employs a loop sensor to detect the magnetic field disturbance caused by the removal of a weapon from its
rack. The loop sensor is installed on a weapons rack in a military arms room, and is connected to the MWS Signal
Processor Unit ((SPU) The presence of the weapons in the rack distorts the earth's magnetic field, which is coupled
through the loop sensor wire. When a weapon is removed from the rack, the resulting changes in the magnetic field
generates a minute, low frequency, alternating current in the loop sensor wire. This acts as a functional input signal to
the SPU. The SPU processes that signal and outputs an operational alarm.
c. The SPU also will output a tamper alarm: (1) if the loop sensor wire is cut or shorted; or, (2) if the SPU cover is
moved a fraction of an inch from the SPU chassis In addition, the SPU will output both operational and tamper alarms, if
20 vdc power from the J-SIIDS Control Unit is lost.
d. Function of the MWS are explained in the following two paragraphs with reference to figure 5-1 (functional block
5-2. Operational Alarm Function
Low frequency signals induced in the loop sensor wire by movement of the weapon are fed into the SPU through an EMI
shielded input and filter assembly. From the input and filter assembly, the input signals pass through a signal injection
transformer to the primary of a step-up transformer.
From the secondary of the step up transformer, the signals are buffered and amplified by a low-noise bandpass
preamplifier. From the output of the preamplifier, the signals are low-pass filtered, buffered, and amplified by a
bandpass postamplifier. At the output. of the postamplifier, the signals are sensed by a bipolar level detector. The
threshold of the bipolar level detector is adjusted to the proper level during installation checkout. Refer to paragraph 210.
Outputs of the bipolar level detector are OR'd to trigger an operational alarm output one-shot. The output of the one-shot
switches on the operational alarm relay drivers, which actuates (opens) the alarm output relay. Actuation of the
5-3. Tamper Alarm Functions
a. Loop Sensor Anti-Tamper Function.ntegrity of the MWS loop sensor wire is monitored automatically by a signal
generated in the SPU. A square-wave oscillator generates a 1 KHz line monitoring signal. This signal is applied to the
primary of the signal injection transformer through a buffer network. When the loop sensor wire is intact and operational,
a balanced condition is maintained by a reference load in the SPU and the EOL Module. This balanced condition results
in a minimum output from the differentially connected secondary windings of the signal injection transformer. If the loop
sensor wire is cut or shorted, the signal injection transformer becomes unbalanced. This causes an input to the tamper
detector. .The output from the tamper detector turns on the tamper alarm relay drivers. This operates (opens) the
tamper output relay. Openings of the tamper alarm output relay changes the impedance across the output terminals.
b. SPU Enclosure Anti-Tamper Function Power from the JSIIDS Control Unit energizes (closes) both operational
and tamper alarm output relays through SPU tamper switch contacts (normally closed) Movement of the cover beyond
specified limits actuates (opens) the tamper switch. This de-energizes both operational and tamper alarm output relays,
and produces both operational and tamper alarm outputs. Disruption of power from the Control Unit to the SPU produces
the same effect as opening the tamper switch.