51-638 Echotel Model 338 Two-Wire Ultrasonic Transmitter
36
2.4
Measurement Range Calculations
Ultrasonic non-contact transmitters are typically rated for
a maximum range in ideal conditions. Experience has
shown that maximum range must be reduced for certain
factors. Although the maximum range rating is somewhat
conservative, each application must be evaluated for specific
conditions in the tank.
Several application parameters that affect ultrasonic
performance are shown in the tank at the left. Each of
these parameters is assigned a Performance Multiplier in
the chart below. Multiply the maximum potential range
(20 feet or 6 meters) of the Model 338 by each of the
applicable Performance Multipliers to calculate the maxi-
mum allowable range for the application.
Beam spread
interference
Beam spread
interference
Vapors
Foam
Surface
agitation
EXAMPLE:
A slightly agitated 12' tank with no condensation, no interference, and a light froth on the surface.
Maximum allowable range: 20'
×
0.9
×
1.0
×
1.0
×
0.8 = 14.4 feet
Since the maximum allowable range is 14.4 feet, the 338 is suitable for this 12 foot tank.
Performance
Operating parameter
Condition
multiplier
SURFACE AGITATION:
Surface agitation or waves can degrade the
Smooth, glass-like surface . . . . . . . . . . . . . . . . . . . . .1.0
performance. Moderate agitation results in only slight degradation of
Slight agitation, choppiness . . . . . . . . . . . . . . . . . . .0.9
performance. The worst case is when the surface is a good reflector, but
Heavy agitation . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.8
in the wrong direction.
Slight vortex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.7
VAPORS AND STEAM:
Vapors can cause problems when the liquid
No condensation . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0
process temperature is well above the temperature of the airspace. The
Little condensation . . . . . . . . . . . . . . . . . . . . . . . . . .0.9
greater the difference, the more expected vapor problems. The problems
Much condensation / foggy appearance . . . . . . . . . .0.8
result from condensation or layering in the sound path, both of which
attenuate the sound signal, and degrade performance. If a vent is used,
be sure that it is well away from the transducer.
BEAM SPREAD INTERFERENCE:
It is recommended that no
No interference within 2.5° half beam angle . . . . . .1.0
obstructions, such as ladder rungs, fill pipes, support struts, etc., be
Agitator at speed less than 60 RPM . . . . . . . . . . . . .1.0
allowed within the 5° ultrasonic beam. If an obstruction is unavoidable,
Interference outside 2°, . . . . . . . . . . . . . . . . . . . . . .0.8
make it as far away as possible from the transducer. Interference from
far from transducer (in bottom third of range)
agitator blades is only an intermittent interference that usually has little
Interference outside 2°, . . . . . . . . . . . . . . . . . . . . . .0.5
effect on performance. A special software algorithm can also help
near to transducer (in top third of range)
suppress false echoes from agitator blades that are within the beam angle.
Agitator at speed greater than 60 RPM . . . . . . . .C/F
FOAM:
Foam can attenuate the ultrasound and render the system
No foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0
inoperative. If possible, moving the transducer to an area in the tank
Light froth, less than 0.25" thick . . . . . . . . . . . . . . .0.8
where there is less foam will improve the performance. Thick,
Light foam, less than 0.5" thick . . . . . . . . . . . . . . . .0.5
heavy-density foams can sometimes produce a reflection from the top
Light foam, more than 1" thick . . . . . . . . . . . . . . . .0.1
of the foam.
NOTE
:
The multipliers shown above are general guidelines.
For further assistance consult the factory.
