51-638 Echotel Model 338 Two-Wire Ultrasonic Transmitter
2
1.2.4 Obstructions
Ensure that no obstacles (e.g. fill pipes, ladders, bracing
members, thermometers, etc) protrude into the ultrasonic
beam. Even though one fixed object in the tank can be
blocked out by appropriate programming, it is advised to
avoid these obstructions.
1.2.5 Standpipes
In applications where the material level may come into the
dead zone, the transducer must be mounted in a stand-
pipe. Refer to
Section 1.6.1, Measurement Configuration
Parameters, P05: Dead Zone
for dead zone value. The inner
rim of the standpipe must be smooth and free of burrs.
The minimum diameter for a given length of standpipe is
shown at left.
1.2.6 Foam
Foaming of the liquid surface may render ultrasonic level
measurement impossible. If possible, a mounting location
should be found where foaming is at a minimum. Another
alternative is to install the transducer in a stilling well that
extends below the lowest level to be measured in the tank.
1.2.7 Vapors
Closed tanks that contain chemicals or other liquids that
create vapors may severely reduce the maximum measuring
range. Refer to the
Section 2.4, Measurement Range
Calculations
for more information.
1.2.8 Wind
Intensive moving of the air in the vicinity of the ultrasonic
beam is to be avoided. A strong wind may not allow the
return echo to be received by the ultrasonic transducer.
1.2.9 Open channel flow measurement
For the best accuracy, install the transducer as close as pos-
sible above the expected maximum water level in the flume
or weir.
Install the Model 338 upstream of the flume throat or weir
crest in the location defined by the manufacturer of the
primary measuring device. The unit should also be aligned
with the longitudinal axis of the flume or weir.
Diameter
Length
Standpipe Length
Minimum Diameter
6" (150 mm)
3" (75 mm)
8" (200 mm)
3" (75 mm)
10" (250 mm)
4" (100 mm)
12" (300 mm)
4" (100 mm)
14" (350 mm)
5" (125 mm)
