6.25. (TD) TIME AND DISTANCE SIGNALS CONFIGURATION
6.25
(TD) Time and Distance signals configuration
Qualifiers
:
Q
,
S
,
R
The
Time and Distance
signals are set by its corresponding
Time and Dis-
tance
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 dis-
tance 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 immediately 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 ac-
cording 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 moving 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 problems:
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 threshold 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
Dis-
tance threshold
. These parameters are the
Minimum Time
and the
Maxi-
mum Time
.
The
Maximum Time
takes control of the signal when the unit has not ex-
ceeded the
Distance Threshold
for a long time. So this value ensures a
minimum triggering frecuency. One way to see this parameter, is that this
time will be the signal activation period when the vehicle is stationary.
The
Minimum Time
takes control of the signal when the unit exceeds the
Distance threshold
. Assuring that even when the unit is exceeding the
Dis-
tance threshold
it will not activate the signal too frequently, no more frequent
than the configured minimum time value. One way of seeing this parameter
is that this time will be the report period when the vehicle is moving too
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