4.23. UNIT’S TAIP REFERENCE
4.23.20
(TD) Time and Distance signals configuration
Qualifiers
:
Q
,
S
,
R
The
Time and Distance
signals are set by its corresponding
Time and
Distance
counter which is a counter that follows a
Time and Distance
criteria. This criteria allows to create a counter that does not follow
a time or distance criteria independantely from each other, instead,
combines these two variables to generate an intelligent trigger to be
used for a more efficient vehicle tracking.
These signals are imme-
diately reset by the processor after being evaluated in order to allow
future triggers
.
Time and Distance criteria
The main purpose of this counter is to control the reporting frequency
according to the vehicle’s displacement. So that the unit increases the
report frequency when the vehicle is moving (accumulating traveled
distance) and decreases it when the vehicle is not moving. This is
more efficient than having the unit report by a
time-only
criteria
were almost all of the reports triggered when the vehicle is not mov-
ing are not relevant.
The counter can also be configured to follow a
time-only
criteria.
To do so, set the
Distance Threshold
parameter to
0
and the unit
will only use the
Minimum Report Time
as trigger.
Note:
How does this criteria works ?
First, the signal has to be triggered by a distance threshold that
tells the activate its associated TD signal whenever the accumulated
distance exceeds this value. This
distance-only
scheme has two prob-
lems:
1. What if the vehicle goes too fast and/or the distance threshold
is low ?. It will set the signal too frequent.
2. What if the vehicle moves too slow and/or the distance thresh-
old is large?. Or worse, what if it does not move at all?. It will
activate the signal very few times or may never activate it.
To solve this problem the
distance-only
trigger is improved with a
Time and Distance
trigger that adds
two
controlling parameters
for the
Distance threshold
. These parameters are the
Minimum Time
and the
Maximum Time
.
The
Maximum Time
takes control of the signal when the unit has not
exceeded the
Distance Threshold
for a long time. So this value ensures
a minimum triggering frecuency. One way to see this parameter, is
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