12
Installation and Operating Manual
IP227, Rev DA
Mobrey MCU200 Series
February 2020
blanket sensors, the gain-adjustment changes the density of sludge at which the system will
switch, increased gain giving increased solids levels.
The particular procedures outlined below for gain adjustments give the mid point gain settings,
which may need to be adjusted to meet specific site/sensor future requirements as indicated
above.
4.2
Interface detection
Suspended Solids blanket sludge discharge detection
The Mobrey MCU200 Series control unit can be used with a Mobrey 433SD sensor to provide
sludge-blanket level detection in a settling tank, and assist with the control of an automatic
de-sludging process. The Mobrey 433SD sensor is normally suspended in the settling tank.
Similarly, the control unit can be used with a Mobrey sludge pipe and a pair of 488S sensors to
control the end of a de-sludge cycle when thin solids are discharged.
Figure 7
shows the operation of a Mobrey 433SD sensor. In a clear liquid, the ultrasonic signal is
carried across the gap and the sensor “oscillates”. In a dirty liquid - one containing high levels of
suspended solids - the signal cannot cross the gap and the oscillation ceases.
Note
The same attenuation occurs when the sensor is in air.
Figure 7. Type 433 sensor for suspended solids blanket alarm
An alternative sensor type is the Mobrey sludge pipe, which is installed on the sludge discharge
line from the settling tank. In this application, it is essential to install the pipe section below the
bottom of the tank and close to the tank discharge (
Figure 8
).
Clear liquid signal
transmitted
.
Solids attenuate
the signal
.
