BACKGROUND INFORMATION
STU Operation
The STU is designed to be outside on a trailer, railcar or locomotive in a vertical orientation
either on the end of the asset or horizontal on the top. The STU has an internal GPS antenna
that must have a clear view of the sky. Both the GPS and data communications antennas are
in the apex of the enclosure and must be positioned to optimize the signal outward away
from the asset and have access to as much sky as possible.
The unit gets its power to operate from the sun. Solar power is used to keep the internal
batteries and power system charged. The ideal position is one that optimizes the chance of
getting direct sunlight sometime during the day. Indirect sunlight provides enough power to
run the unit, but does not significantly charge the batteries.
Once the unit is installed (or put outside in the sun) it should start reporting within an hour
or two. It will report up to every 10 minutes while moving (Moving Timed) and every 2
hours while stopped (Timed). The Moving Timed reports are over the air programmable but
can never be set lower than every 10 minutes while moving. The Timed Reports are in
intervals of 2 hours. This means that it will start reporting every 2 hours from the
hour/minute that it wakes up. If the unit can not get out a message, then the unit will store
the message and try to send it out at the next report time. The two possible reasons that a
message will not be sent immediately are:
1.
The unit can not communicate with a cell tower
2.
The power of the unit has dropped below its normal operation threshold
Communication requires sufficient proximity to a cell tower for adequate signal strength and
the ability of the unit to reach the Lat-Lon web-site (via the internet) for validation that the
message was received.
STU Power
During shipping, the STU internal battery rapidly drains because the unit tries to get a GPS
fix and cannot, and tries to establish cellular communications and cannot. Therefore, the
STU will most likely have a depleted battery when you receive it. To initialize the unit’s
power, place the unit outdoors where it can get a GPS fix with a good sky view. Placing the
STU where direct sun is hitting the solar panels is the quickest way to charge the internal
battery.
The power level of the STU is reported in each message as bus voltage. The user can see
how much power the STU has as it operates from day to day by building a voltage history
report or by adding the bus voltage field to other reports. Some critical voltages are listed in
the table below:
Minimum voltage to power GPS (to build a message)
6.8V
Minimum voltage to power the GSM radio to transmit a report
7.0V
Max voltage – charging batteries with 100mA
12.5V
Charging batteries with at least 60mA
12.0V
Minimal battery charging
10.0V
