Hach US9001 Manuel D'utilisation page 9

When the installation is above a narrow channel, do not install the sensor too high because the beam
may be wider than the channel. This can cause false echoes from the tops of the channel walls
rather than from the water surface. To prevent false echoes, find the applicable sensor height so that
the entire beam falls within the channel and does not hit any obstructions.
Select the applicable sensor height:
1. Take the measurements. Refer to Figure 6.
2. Calculate the angle from the axis, Θ = arc tan × (D2/D1) ≈ 80.5 × (D2/D1).
3. To avoid interference from outside obstructions, make sure that the calculated angle from the axis
is less than the half beam angle (6 ° typical) of the sensor.
Figure 6 Sensor height selection
Install the sensor
Install the ultrasonic sensor so that it is over the center of the flow stream and the sensor face is
parallel with the flow. The sensor face should be parallel with the flow, so that the signal is
perpendicular to the flow and the signal echo does not bounce off the channel walls. The signal
bouncing off the wall may cause erratic readings or a complete echo loss.
The ultrasonic sensor has several mounting hardware options. Refer to Figure 7 and Figure 8. Refer
to the instructions supplied with the mounting hardware for installation information.
English 9