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2150EX Area Velocity Flow Module
Section 2 Preparation and Installation
2-27
2.7.1 Positioning the AV
Sensor
Sensor installation is discussed in Section 2.8 of this manual.
Consult your Isco Mounting Rings instruction manual for
detailed hardware information. This section explains how to
position the AV Sensor in flow streams.
Several factors concerning the AV Sensor’s installation may
affect your system’s performance. Review the following to under-
stand how to obtain the best results:
Uniform flow - The AV Sensor provides the best results in flow
streams with uniform flow. An example of uniform flow is shown
in the margin.
Avoid poor channel conditions - Poor channel conditions may
cause incorrect or erratic readings. Areas to avoid are:
• outfalls or channel intersections
• flow streams at very low levels with high flow rates
• turbulence
• channel sections that are apt to collect debris or silt
• depths that consistently run below 2.54 cm (1 inch).
Install the AV Sensor in streams where the liquid covers the
sensor. The AV Sensor can detect levels above approximately
1.0 cm (0.4 inch) and typically can measure velocities in streams
as low as 2.54 cm (1 inch). Streams that run consistently below
2.54 cm are not a good application for the 2150EX.
The example in the margin shows an illustration of these poor
conditions. The outfall is drawing down the liquid level and the
AV Sensor is disturbing the flow. In this example, the AV Sensor
should be moved forward to avoid the drawdown near the outfall.
Offsets - You can install the AV Sensor above the bottom of the
flow stream or along the side of the channel, as long as it will be
continually submerged. The 2150EX can be adjusted to measure
level with the AV Sensor at nearly any depth. The AV Sensor
cannot, of course, measure a liquid level that falls below its
position in the flow stream.
Installing the AV Sensor above the bottom has advantages:
• It avoids heavy concentrations of silt, sand, or other solids.
• It aids installation in narrow or hard-to-reach locations.
• It maximizes level resolution over a specific level range.
• It can avoid obstructions in the flow stream.
When the AV Sensor is installed above the bottom of the channel,
a Zero Level Offset must be entered in the program settings (see
Section 3.3.2).
Liquid properties - Velocity measurements depend on the
presence of some particles in the stream such as suspended
solids or air bubbles. If the stream lacks particles it may be nec-
essary to aerate the water upstream from the sensor.
Ideal Conditions - Uniform Flow
Poor Conditions