YSI IFL 700 IQ - Manual (Page 13)

IFL 70x IQ Commissioning
3 - 3 ba76129e01 10/2012
Sensor installation The following conditions should always be met:

Vertical
 Sufficient distance from the basin wall (minimum distance, see for-
mula in Fig. 3-1).
If the distance to the wall of the basin is small, the wall should be
rather smooth.
 Immersion depth (0.05 m ... 3 m)
 Minimum distance between the sensor bottom and sludge blanket =
0.4 m ("dead zone").
Ideally, at the installation location the ultrasonic cone is free of barriers
that move the sensor from its position or cross the measuring cone and
thus cause interfering echoes.
Additional measures are required in order to minimize negative impacts
(see section 3.3.5).
3.3.3 Influence of permanently installed fixtures
Permanently installed fixtures in the vicinity of the measuring cone
reflect the ultrasonic waves transmitted and thus cause interfering
echoes.
If there are permanently installed fixtures in the expectation range of
the sludge blanket level, it is not possible to clearly assign an echo to a
sludge level. In this case, a different installation location must be
selected (e.g. with a greater distance from the wall). Alternatively, the
evaluation range can be adjusted.
3.3.4 Influence of gas bubbles and suspended particles
Gas bubbles and suspended particles reduce the propagation of ultra-
sonic waves. A high concentration of gas bubbles and suspended par-
ticles can in extreme cases lower the range of the sensor.
If there are range problems, the sensor must be immersed deeper
(note the dead zone and maximum depth of immersion).
With the IFL 700 IQ sensor, the mechanical wiper removes
gas bubbles and dirt from the surface of the ultrasonic
transducer.