Figure 11. Ultrasonic Level Meter.
Advantage
The ultrasonic sensor is considered to be highly accurate (1-2% error) and only
specialists in the integration of GLONASS satellite monitoring systems are
engaged in its installation.
Disadvantage
In real life, ultrasonic technology has not proved to be the best because of
problems with installation, the quality of which is influenced by many points
that appear during installation:
-Fixing.
The sensor is attached to the fuel tank with special glue or fixed with a metal
tape wrapped around the tank. Thus, it is necessary to achieve a perfect fit of the
device to the surface. If the contact is not very tight, the ultrasound waves are
distorted, which leads to the transfer of incorrect data.
- Partitions.
If there are partitions in the tank, it is possible that they will become a real
obstacle to transmitting the signal from the FLS to the GPS terminal, and, as a
result, to obtain accurate indicators.
- Rough tank surface.
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Inside the tank is far from always smooth and even, which leads to distortion
and scattering of the ultrasound signal.
- Foreign objects in the tank.
Often, dirt and water accumulate at the bottom of the tank, and ice in the winter.
When floating, they interfere with the ultrasonic signal, which deceptively
indicates constant fluctuations in fuel level.
In the simplest and most common case, when the ultrasonic sensor 0 is
located at the upper point of the tank, the medium level is calculated as the
difference between the height of the tank and the distance between the sensor
and the surface of the medium (in the general case, a correction should be made
that takes into account the difference between the actual height of the sensor and
the height of the tank) . This distance is calculated from the measured time it
takes for the ultrasonic pulse to travel from the sensor to the surface of the
controlled medium and vice versa.
Here Vs is the propagation velocity of the ultrasonic signal in a given
medium.
The chemical and physical properties of the medium do not affect the
measurement result obtained by the ultrasonic testing method, therefore, the
level of aggressive, abrasive, viscous and adhesive substances can be measured
without problems. However, it must be remembered that the speed of ultrasound
is influenced by the temperature of the air in the environment of its propagation.
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In addition, being highly temperature dependent, the speed of ultrasound
depends on air pressure: it increases with increasing pressure. Relative changes
in the speed of sound associated with changes in pressure in a normal
atmosphere are approximately 5%. The speed of ultrasound also depends on the
composition of the air, for example, on the percentage of CO2 and humidity.
The influence of relative humidity on the speed of ultrasound is less than the
effect exerted by temperature and pressure: the additional difference in speed in
dry and moisture-saturated air is about 2%.
The main advantages of the ultrasonic testing method:
non-contact;
applicable to contaminated liquids;
the implementation of the method does not impose high requirements on the
wear resistance and strength of the equipment;
independence of the density of the controlled environment.
Disadvantages:
large divergence of the radiation cone;
reflections from non-stationary obstacles (for example, agitators) can cause
measurement errors;
applicable only in tanks with normal atmospheric pressure;
the signal is influenced by dust, steam, gas mixtures and foam.
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