LR3/Disco 3
The volumetric sensor is installed in its own housing on the roof, just in front of the row 2 interior lamp housing, and
monitors for intrusion into the passenger compartment when the anti-theft alarm system is armed.
The volumetric sensor consists of a microcontroller, two acoustic transmitters and two acoustic receivers. One transmitter
and receiver pair faces forwards and one transmitter and receiver pair faces rearwards, to ensure complete coverage of
the passenger compartment. The front transmitter and receiver pair are in a rubber mounting attached to the
microcontroller housing. The rear transmitter and receiver pair are in a remote rubber mounting and connected to the
microcontroller housing by a four wire lead.
The volumetric sensor is powered by a feed from the CJB. The CJB activates and de-activates the volumetric sensor
when it arms and disarms the anti-theft alarm system in the volumetric mode. When the volumetric sensor is active it
outputs ultrasonic pulses from the transmitters and checks the echoes picked up by the receivers for changes to the
passenger compartment profile. If it detects a change of profile, indicating movement in the passenger compartment, the
volumetric sensor reports the alarm to the CJB.
Each time the volumetric sensor is armed, it performs a self test. If there are no faults the volumetric sensor sends an
acknowledgment signal to the CJB. If the CJB does not receive the acknowledgment signal it de-activates the volumetric
sensor.
SYSTEM OPERATION
General
The CJB automatically arms and disarms the anti-theft alarm system when it operates the central locking system. For
additional information, refer to
Handles, Locks, Latches and Entry Systems
(501-14 Handles, Locks, Latches and Entry
Systems)
Arming
On vehicles without the volumetric sensor and the tilt sensor, the anti-theft alarm system is armed in the perimeter mode
when the vehicle is either locked or superlocked.
On vehicles with the volumetric sensor, the anti-theft alarm system is armed in one of two modes:
Perimeter mode, where only the hinged panels are monitored, is employed when the vehicle is locked with the
remote handset or the door key lock.
Volumetric mode, where the hinged panels, the vehicle interior and, if the tilt sensor is incorporated, the vehicle
attitude, are monitored. Volumetric mode is employed when the vehicle is superlocked with the remote handset or
the door key lock.
The CJB arms the anti-theft alarm system when it locks or superlocks the vehicle, provided the following conditions
coexist:
The driver door is shut.
A valid key is not in the ignition switch.
The anti-theft alarm system is not in panic alarm mode.
The anti-theft alarm system is enabled.
The CJB is not in transit mode.
Mislock
If the driver door is open when a lock or superlock request is received, the anti-theft alarm system remains disarmed and
the CJB generates a mislock sound with a 100 milliseconds 'chirp' on the horns.
When the CJB arms the anti-theft alarm system, it enters the perimeter mode by beginning to monitor the status of the
hinged panels and, where applicable, sending an arming signal to the BBUS. On a vehicle with a volumetric sensor
installed, the CJB then transitions into the volumetric mode by sending arming signals to the volumetric sensor and the tilt
sensor. The CJB ignores alarm signals from the volumetric sensor for 30 seconds after sending the arming signal, to
2
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Rear transmitter/receiver pair
