Hach US9001 Manuel D'utilisation page 7

Guideline
Do not hang the sensor by the sensor cable.
Prevent the sun from shining directly on the sensor.
For the US9001 (downlooking) sensor, make sure
that the lowest mounting nut is more than 6.4 mm
(0.25 in.) from the sensor face. Refer to
Prevent strong winds and air currents from blowing
directly under the sensor.
Install the sensor so that the ultrasonic signal does
not hit the sides of a small pipe or narrow
flumes/channels.
Install the sensor sufficiently high above the surface
of the water so that it does not go under the water
when the level increases.
Figure 3 US9001 (downlooking) sensor
1 Hex nut
Table 2 Site installation guidelines
Details
The sensor cable may stretch and cause measurement
errors.
Intense, direct sunlight on the sensor will increase the
temperature of the sensor housing higher than the ambient
air temperature. This can cause inaccurate measurements.
If the mounting nut is near the sensor face, level spikes
can occur at extreme temperatures.
Figure 3.
Hand tighten the hex nut, then tighten ½ turn. Do not
overtighten the hex nut or the isolation gasket will not
decrease vibrations.
The strength of the ultrasonic signal is decreased by the
wind.
The ultrasonic signal emits a half beam angle of 6 °. Refer
to Figure 4
distance for the measurement target to prevent false
echoes and incorrect level measurements. Refer to the
FSDATA Desktop documentation to change the application
settings.
The speed of sound in water is much faster than in air. A
sensor that is under the water will give unusual values.
2 Gasket, vibration isolation
and Figure 5. Set the minimum and maximum
English 7