Wavetronix SmartSensor HD (101-0415) - User Guide - Manual (Page 68)

CHAPTER 7 • DATA 67
memory fills up faster and must be downloaded from more often. See the Storage section of
this chapter for more information on how to figure out how many days’ worth of memory
your sensor has based on its current settings.
Interval
Interval data refers to the data collected about all the vehicles that pass the sensor in a set
amount of time. This interval of time should be carefully chosen because the length of it
affects how long the sensor can store data onboard. A shorter interval means the sensor
records data more often, which means that the sensor’s onboard memory fills up faster. A
longer interval means you can leave the sensor alone for longer periods of time. Ultimately
the interval size should be selected to meet the requirements of your application. For ex-
ample, in real-time applications, onboard storage capacity may not be a concern at all and
the data may need to be aggregated over short periods of time (20 seconds) to reduce re-
porting latency. To set the interval, click anywhere inside the Interval field and use the up/
down arrows to change the interval (see Figure 7.2). See the Storage section in this chapter
for more information.
Once you download the interval data, you will have the following information for each lane
or approach:
˽ Name – Displays the name of each lane or approach. To change the name, go to the
Lane Configuration screen or the Approaches screen.
˽ Volume – Shows the number of vehicles detected during the interval.
˽ Occupancy – Gives the percentage of time during the interval that the detection zone
was occupied.
Occupancy is calculated by summing the durations of all vehicles in the interval and di-
viding that quantity by the length of the interval. For example, if the interval length is five
minutes and 100 vehicles pass the sensor during the interval with a duration of 0.09 seconds
each (sum of the durations is 9 seconds), then the occupancy for that interval would be
calculated by dividing 9 seconds by 300 seconds, which is 3%.
Rather than using the uncalibrated detection duration, or the time that a vehicle is in the ra-
dar beam, in the occupancy calculation, a more accurate occupancy measurement is made
by first calculating the vehicle length and then converting that to a duration by adding the
simulated loop size and dividing by the speed. Occupancy based on vehicle length is more
accurate than occupancy based on uncalibrated detection duration because the vehicle
length calculation removes the effect of the antenna beam widening as it gets farther from
the sensor. The occupancy calculation is shown in the following equation:
1
Interval Size All Vehicles in
the Interval
Vehicle Speed
Vehicle Length + Loop Size
∑
*
Calibrated Duration