NOTES
Warning
These devices are not designed for critical safety or emergency shut-down purposes. Therefore they
should never be used in an application, where a malfunction of the device could cause personal injury.
Environmental Influences
Ultrasonic sensors are made for the use in atmospheric air. Environmental Influences like rain, snow, dust
or smoke have no influence on the accuracy of the measurement. However, measurements under
pressure (higher that the atmospheric pressure) are not possible with ultrasound sensors.
Strong wind or air turbulences may lead to instability in measurement values. A flow speed up to a few
m/s is unproblematic and will have no influence on the sensor's accuracy.
Target Influences
Liquids
are excellently detectable with ultra sound. A classic application for ultrasonic sensors is level
measurement. The sound beam axis however must have a maximum deviation of 3° vertically to the
liquid level (no strong waves), otherwise the reflected sound will miss the sensor.
Hot Targets
with high temperatures cause a thermal convection in the surrounding air. For this reason the sound
beam may be strongly diverted vertically to it's axis, so that the echo is weakened, or can no longer be
received at all.
For convex (cylindrical and spherical) surfaces,
every area element has a different angle to the sound cone’s axis. The reflected cone thus diverges and
the portion of the sound energy reflected to the receiver is reduced correspondingly. The maximum range
decreases with the decreasing size of the cylinder (ball).
The roughness and surface structures of the object
to be detected also determine the scanning capacities of the ultrasonic sensors. Surface structures that
are larger than the ultrasound wavelength, as well as coarse-grained bulk materials, reflect ultrasound in
a scattered manner, and are not detected optimally by the sensor under these conditions.
Hard material
reflects almost all of the impulse energy from ultrasound applications in a way that makes them very easy
to detect with ultrasound.
Soft material,
on the other hand, absorbs almost all of the impulse energy. It is thus harder to detect with ultrasound.
These materials include felt, cotton, coarse meshes, foam, etc.
Thin-walled foils
behave like soft materials. To be able to use ultrasound, the foil thickness should be at least 0.01 mm.
