700-SDI-RADAR-300WL-Man Rev 2 11 Apr Mar 2022
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Part# 21371
INSTALLATION
3.1
SITE SELECTION AND FEATURES
When determining where to mount the 300WL a
direct, unobstructed line to the water surface is
available for both the surface velocity sensor and the level sensor. Any close object in the vicinity of
the sensor can reduce accuracy and introduce offsets in measurements. The best practice is to have
a 1m zone around both sensors clear of obstructions.
The height of the instrument above the water surface and the inclination determine the area on the
surface that is covered by the radar beam (see Section 3.2). This measurement area should be clear
of any obstacles. There should be no vegetation between the radar and the measurement area
because it could affect measurement accuracy.
Additionally, for the level meter, the water surface directly below the unit should be calm, clean of
vegetation, rocks, sand deposition or other obstacles that could affect measurement. The surface
velocity radar should be pointed upstream (water flowing towards the radar).
The structure holding the instrument (pole, bridge fence, etc.) must be solid and without vibrations.
Vibrations of the mounting structure can affect the sensor’s ability to eliminate detected obstacles
resulting in inaccurate measurements. Vibrations should be avoided or reduced by any applicable
means. If mounting at a site that has periodic vibrations (i.e. train bridge) be aware of the
measurement quality indicator during a vibration period in order to determine the reliability of the
data. Details can be found in Section 2.1.
Installations where pedestrians, cars or other objects are moving in front of the flow sensor closer
than 75 m should be avoided to prevent reflected power from those objects being received by the
radar and significantly affecting measurement accuracy (refer to in Section 2.6 and Figure 2-1 for a
detailed explanation).
3.2
DETERMINING RADAR FOOTPRINT
The radars’ paths and footprints are calculated based on 3 dB signal drop (half signal power) due to
the antenna pattern. Most of the return energy is reflected from the inside of the calculated
footprints (ellipse for the surface velocity sensor and circle for the level sensor – see Figure 3-1), but
some energy could be also received from objects outside of the footprint. Although the sensors
have an internal signal processing algorithm to filter such reflections, large objects close to the
footprint perimeter can cause some measurement inaccuracies. Therefore, it is recommended to
keep the zone around the target shape of the radars as clear as possible for the best measurement
accuracy.
