User's Manual

GlobalTrak ™ GT Lite Operation and Maintenance Manual
2.1 GT Lite Detailed Hardware Description
Functional and Electrical Systems
This section details the general functional and electrical systems of the GT Lite, including the
higher-level application functions, sensor response and GPS.
System Design
GT Lite is designed with low power usage in mind. To keep to that design, two processors are
used: A main processor and a low power controller.
Main Processor
The main processor controls all higher level processes. Some examples of these are GPS
control, creating and sending of messages, configuration control. To keep power usage down,
this processor is normally in a state of sleep, waking only for periodic transmissions or when
woken by the low power controller.
Low Power Controller
The low power controller handles all sensor and external inputs to the device. All sensors are
interfaced through the low power controller, allowing the main processor to sleep while
sensors are monitored. When a sensor enters an alarm condition as determined by the low
power controller, it wakes the main processor to take appropriate action.
Wireless sensors are also interfaced through the low power controller which also contains the
ZigBee stack and radio. Wireless sensor alarms are generated from the wireless devices
themselves. If a wireless device alarms, the low power controller wakes the main processor
upon receipt of the alarm message.
Sensors
Optic Sensor
The sensor has a spectral response wavelength range from 320 to 840 nm λ, with sensitivity
greater than 0.3 A/W across the range.
The sensor output is be sampled by the low power controller at a rate of 1 reading per
second, even when the GT Lite is in its lowest power state. The measured value is to be
compared against a stored threshold, and when exceeded, a message is immediately
generated and sent to the IMB. The value returned to the IMB in each message is the peak
of the sensor output over the previous interval. The sensor is re-armed after the sensor level
returns from the alarm state. At the point where the sensor level crosses the threshold back
to a typical level the sensor alarm is once again active.
The threshold is user programmable, changeable over-the-air through the GSM network or
locally. Also the threshold can be disabled, such that no event message is generated.
The optic sensor is mounted interior to the enclosure, with exterior light presented to the
optic sensor through a light pipe or optical window, to preserve the enclosure environmental
seal.
Prepared: R. Straz Date: July 25, 2007 Page 16 of
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