Filter
Top Products
12
Service Manual
Third edition, June 1997
1.1 Radar Principle
The radar transmitter on top of the tank emits microwaves
directed by an antenna towards the surface of the tank con-
tent. The echo from the surface is picked up by the antenna
again, and the difference in frequency between the transmit-
ted and the reflected signal is directly proportional to the
measured distance, i.e. the ullage indication.
The radar waves are not affected by the atmosphere inside
the tank - aggressive chemicals, thick, sticky liquids or any
other tank media can be measured without restrictions.
The ideal condition for ullage measurement is a stable cargo
surface perpendicular to the radar beam.
Trim or list, foam and waves on the cargo surface and bottom
sludge weakens the radar echo. However, the radar echo is
usually strong enough for reliable measurements.
But in exceptional cases the radar echo can be lost during
turbulent loading/discharging, or with strong trim/list
angles, or when measuring close to the tank bottom.
Figure 1-4. An inclined cargo
level weakens the radar echo.
Trim/list angles of more than +
3
°
can lead to error in the
ullage measurement.
Figure 1-5. Waves on the
surface give a scattered and
weakened echo signal. Turbu-
lent loading and discharging,
especially close to empty tank,
can lead to error in the ullage
measurement.