14
Installation and Operating Manual
IP227, Rev DA
Mobrey MCU200 Series
February 2020
– Check the setting in practice by taking a sludge sample at the switching point, and adjust
as necessary. Increasing the gain makes the switching point occur at a higher percentage
of suspended solids.
For different ID (Internal Diameter) pipelines or sensor gaps, of dimensions ‘D’ mm, each
division on the potentiometer represents approximately (180, D) %solids.
In a 3.7 MHz system, on a 150mm gap sensor each division on the potentiometer
represents 0.25% solids: for sensor gaps D mm the divisions are (38¸D) %solids typically.
Overflow alarm or fine solids detection
Set the operating frequency on the control unit to 3.7 MHz if the sensor is suitable.
This will improve the sensitivity.
Reduce the time delay setting and use the potentiometer gain to locate the position for
the switching point of 0% solids.
Assume the potentiometer gain adjustment is (90¸ D) %solids per division increase to set
initial switch point.
Interface detection between two dissimilar liquids
Viscous liquids, emulsions and liquids containing solid particles have a greater ultrasonic
attenuation than clear liquids. This technique is used to detect which liquid is present at the
sensor e.g. the separation of oil and water. For this application, Mobrey 402SD or 433SD sensors
operating at 3.7 MHz are used to produce the maximum ultrasonic difference between two
liquids monitored. An alternative technique for pipelines is the use of a Mobrey sludge pipe
section with Mobrey 448SD type sensors.
The gain potentiometer on the PCB of the control unit is adjustable for the sensor to oscillate
only in the liquid with a lower ultrasonic attenuation. This liquid in the example of
Figure 9
is
usually clear, e.g. water.
Note
The signal when oil is present in the sensor gap will be the same as that for air in the gap, and
that emulsion layers give a very high attenuation.
Reduce the gain (potentiometer) with the sensor immersed in one of the liquids until a
“false dry” indication is obtained. Note the position of the potentiometer.
Repeat for the sensor immersed in the other liquid.
Set the potentiometer half-way between these two values. Correct performance requires
a total difference between the two set points of at least 3 divisions.