11
Reference Manual
00809-0200-4841, Rev BA
December 2014
Section 3: Installation
3.3.1
Consider liquid surface conditions
Guidelines
1.
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.
2.
Avoid mounting the transmitter directly over any inlet stream.
3.
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.
3.3.2
Consider in-tank effects
Guidelines
1.
Stirrers or agitators can cause a vortex. Mount the transmitter off-center of any vortex
to maximize the return echo.
2.
If stirrer blades become uncovered, they create echoes as they pass through the
ultrasonic beam. The transmitter can learn to ignore false echoes (see
3.
In 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.
4.
Avoid detecting pump casings, as the liquid falls away, by not mounting the transmitter
directly above pumps. If this is not possible, fine-tuning of the transmitter on-site may
be required.
3.3.3
Mounting the transmitter above the liquid surface
A 1-in. thread is provided to mount the transmitter. The thread form is either
BSPP (G1)
or
NPT
,
and is
marked
below the mounting thread.
To help installation, flange accessories and bracket kits are available from Emerson Process
Management. The accessory flanges supplied are manufactured from PVC and are a full face
design. Care must be taken when installing to raised face mating flanges on the tank or vessel to
prevent distortion of the PVC flange by over-tightening the bolts. See
for ordering information.
Note
Never suspend the transmitter by the cable.
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