Emerson Rosemount 3100 Series, Reference Manual, Page: 20 / 144

Reference Manual
00809-0100-4840, Rev. BA
July 2008
Rosemount 3100 Series
3-4
Figure 3-1. Min and max
distances from vessel wall
Liquid Surface
Conditions
Guidelines:
a) Foaming liquids can reduce the size of the returned echo because foam is
a poor ultrasonic reflector. Mount an ultrasonic transmitter over an area of
clear liquid, such as near the inlet to a tank or well. In extreme conditions,
or where this is not possible, the transmitter may be mounted in a vented
stilling tube provided that the inside measurement of the stilling tube is at
least 4 in. (100 mm) and is smooth and free from joints or protrusions. It is
important that the bottom of the stilling tube stays covered to prevent the
ingress of foams.
b) Avoid mounting the transmitter directly over any inlet stream.
c) Liquid surface turbulence is not normally a problem unless it is excessive.
The effects of turbulence are minor, but excessive turbulence can be dealt
with by fine-tuning the transmitter on site, if necessary.
In-tank Effects
Guidelines:
a) Stirrers or agitators can cause a vortex. Mount the transmitter off-center of
any vortex to maximize the return echo.
b) If stirrer blades become uncovered, they create echoes as they pass
through the ultrasonic beam. The transmitter can learn to ignore these
false echoes (see “Learn About Echoes From False Targets (The
3102/3105)“ on page 5-12.
c) In non-linear tanks with rounded or conical bottoms, mount the transmitter
off-center. If needed, a perforated reflector plate can be installed on the
tank bottom directly under the transmitter center line to ensure a
satisfactory return echo.
d) Avoid mounting the transmitter directly above pumps because the
transmitter will detect the pump casing as the liquid falls away. If this is not
possible, fine-tuning of the transmitter on site may be required.
Max. 3°
C
Use non-metallic
fitting / flange
C = 0.11m/m (1.3”/ft)
C Min. = 0.3m (12”)
Beam angle
6° max.